3.0.0-rc.1

* Add ERC20DeployReady

* Add ERC721DeployReady

* Improve docs

* Fix linter errors

* Rename DeployReady contracts to MinterPauser, add docs

* Fix deploy ready docs

* Minor doc adjustment

.babelrc

@@ -1,3 +0,0 @@
-{
-  "presets": ["es2015", "stage-2", "stage-3"]
-}

.circleci/config.yml

@@ -0,0 +1,84 @@
+version: 2
+# 2.1 does not yet support local run
+# unless with workaround. For simplicity just use it.
+# https://github.com/CircleCI-Public/circleci-cli/issues/79
+
+aliases:
+  - &defaults
+    docker:
+      - image: circleci/node:10
+
+  - &cache_key_node_modules
+    key: v1-node_modules-{{ checksum "package-lock.json" }}
+
+jobs:
+  dependencies:
+    <<: *defaults
+    steps:
+      - checkout
+      - restore_cache:
+          <<: *cache_key_node_modules
+      - run:
+          name: Install npm dependencies and prepare
+          command: |
+            if [ ! -d node_modules ]; then
+              npm ci
+            else
+              npm run prepare
+            fi
+      - persist_to_workspace:
+          root: .
+          paths:
+            - node_modules
+            - build
+      - save_cache:
+          paths:
+            - node_modules
+          <<: *cache_key_node_modules
+
+  lint:
+    <<: *defaults
+    steps:
+      - checkout
+      - attach_workspace:
+          at: .
+      - run:
+          name: Linter
+          command: npm run lint
+  test:
+    <<: *defaults
+    steps:
+      - checkout
+      - attach_workspace:
+          at: .
+      - run:
+          name: Unit tests
+          command: npm run test
+
+  coverage:
+    <<: *defaults
+    steps:
+      - checkout
+      - attach_workspace:
+          at: .
+      - run:
+          name: Unit tests with coverage report
+          command: npm run coverage
+
+      # TODO(xinbenlv, #1839): run SOLC_NIGHTLY to be run but allow it to fail.
+
+workflows:
+  version: 2
+  everything:
+    jobs:
+      - dependencies
+      - lint:
+          requires:
+            - dependencies
+      - test:
+          requires:
+            - dependencies
+      - coverage:
+          requires:
+            - dependencies
+

.codecov.yml

@@ -0,0 +1,3 @@
+comment: off
+coverage:
+  range: "100...100"

.dependabot/config.yml

@@ -0,0 +1,7 @@
+version: 1
+
+update_configs:
+  - package_manager: "javascript"
+    directory: "/"
+    update_schedule: "weekly"
+    version_requirement_updates: "increase_versions"

.editorconfig

@@ -0,0 +1,17 @@
+# EditorConfig is awesome: https://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_style = space
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.sol]
+indent_size = 4
+
+[*.js]
+indent_size = 2

.eslintrc

@@ -0,0 +1,62 @@
+{
+  "extends" : [
+    "standard",
+    "plugin:promise/recommended",
+  ],
+  "plugins": [
+    "mocha-no-only",
+    "promise",
+  ],
+  "env": {
+    "browser" : true,
+    "node"    : true,
+    "mocha"   : true,
+    "jest"    : true,
+  },
+  "globals" : {
+    "artifacts": false,
+    "contract": false,
+    "assert": false,
+    "web3": false,
+  },
+  "rules": {
+
+    // Strict mode
+    "strict": ["error", "global"],
+
+    // Code style
+    "array-bracket-spacing": ["off"],
+    "camelcase": ["error", {"properties": "always"}],
+    "comma-dangle": ["error", "always-multiline"],
+    "comma-spacing": ["error", {"before": false, "after": true}],
+    "dot-notation": ["error", {"allowKeywords": true, "allowPattern": ""}],
+    "eol-last": ["error", "always"],
+    "eqeqeq": ["error", "smart"],
+    "generator-star-spacing": ["error", "before"],
+    "indent": ["error", 2],
+    "linebreak-style": ["error", "unix"],
+    "max-len": ["error", 120, 2],
+    "no-debugger": "off",
+    "no-dupe-args": "error",
+    "no-dupe-keys": "error",
+    "no-mixed-spaces-and-tabs": ["error", "smart-tabs"],
+    "no-redeclare": ["error", {"builtinGlobals": true}],
+    "no-trailing-spaces": ["error", { "skipBlankLines": false }],
+    "no-undef": "error",
+    "no-use-before-define": "off",
+    "no-var": "error",
+    "object-curly-spacing": ["error", "always"],
+    "prefer-const": "error",
+    "quotes": ["error", "single"],
+    "semi": ["error", "always"],
+    "space-before-function-paren": ["error", "always"],
+
+    "mocha-no-only/mocha-no-only": ["error"],
+
+    "promise/always-return": "off",
+    "promise/avoid-new": "off",
+  },
+  "parserOptions": {
+    "ecmaVersion": 2018
+  }
+}

.gitattributes

@@ -0,0 +1 @@
+*.sol linguist-language=Solidity

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,21 @@
+---
+name: Bug report
+about: Report a bug in OpenZeppelin Contracts
+
+---
+
+<!-- Briefly describe the issue you're experiencing. Tell us what you were trying to do and what happened instead. -->
+
+<!-- Remember, this is not a place to ask for help debugging code. For that, we welcome you in the OpenZeppelin Community Forum: https://forum.openzeppelin.com/. -->
+
+**💻 Environment**
+
+<!-- Tell us what version of OpenZeppelin Contracts you're using, and how you're using it: Truffle, Remix, etc. -->
+
+**📝 Details**
+
+<!-- Describe the problem you have been experiencing in more detail. Include as much information as you think is relevant. Keep in mind that transactions can fail for many reasons; context is key here. -->
+
+**🔢 Code to reproduce bug**
+
+<!-- We will be able to better help if you provide a minimal example that triggers the bug. -->

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,4 @@
+contact_links:
+  - name: Support request
+    url: https://forum.openzeppelin.com/c/support/contracts/18
+    about: Ask the community in the Community Forum

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,14 @@
+---
+name: Feature request
+about: Suggest an idea for OpenZeppelin Contracts
+
+---
+
+**🧐 Motivation**
+<!-- Is your feature request related to a specific problem? Is it just a crazy idea? Tell us about it! -->
+
+**📝 Details**
+<!-- Please describe your feature request in detail. -->
+
+<!-- Make sure that you have reviewed the OpenZeppelin Contributor Guidelines. -->
+<!-- https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/CONTRIBUTING.md -->

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,22 @@
+<!-- 0. 🎉 Thank you for submitting a PR! -->
+
+<!-- 1. Does this close any open issues? Please list them below. -->
+
+<!-- Keep in mind that new features have a better chance of being merged fast if
+they were first discussed and designed with the maintainers. If there is no
+corresponding issue, please consider opening one for discussion first! -->
+
+Fixes #
+
+<!-- 2. Describe the changes introduced in this pull request. -->
+<!--    Include any context necessary for understanding the PR's purpose. -->
+
+<!-- 3. Before submitting, please make sure that you have:
+  - reviewed the OpenZeppelin Contributor Guidelines
+    (https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/CONTRIBUTING.md),
+  - added tests where applicable to test new functionality,
+  - made sure that your contracts are well-documented,
+  - run the Solidity linter (`npm run lint:sol`) and fixed any issues,
+  - run the JS linter and fixed any issues (`npm run lint:fix`), and
+  - updated the changelog, if applicable.
+-->

.github/stale.yml

@@ -0,0 +1,67 @@
+# Configuration for probot-stale - https://github.com/probot/stale
+
+# Number of days of inactivity before an Issue or Pull Request becomes stale
+daysUntilStale: 15
+
+# Number of days of inactivity before an Issue or Pull Request with the stale label is closed.
+# Set to false to disable. If disabled, issues still need to be closed manually, but will remain marked as stale.
+daysUntilClose: 15
+
+# Issues or Pull Requests with these labels will never be considered stale. Set to `[]` to disable
+exemptLabels:
+  - on hold
+  - meta
+
+# Set to true to ignore issues in a project (defaults to false)
+exemptProjects: false
+
+# Set to true to ignore issues in a milestone (defaults to false)
+exemptMilestones: false
+
+# Set to true to ignore issues with an assignee (defaults to false)
+exemptAssignees: false
+
+# Label to use when marking as stale
+staleLabel: stale
+
+# Comment to post when marking as stale. Set to `false` to disable
+markComment: >
+  Hi all!
+
+  This Pull Request has not had any recent activity, is it still relevant? If so, what is blocking it?
+  Is there anything we can do to help move it forward?
+
+  Thanks!
+
+
+# Comment to post when removing the stale label.
+# unmarkComment: >
+#   Your comment here.
+
+# Comment to post when closing a stale Issue or Pull Request.
+closeComment: >
+  Hi folks!
+
+  This Pull Request is being closed as there was no response to the previous prompt.
+  However, please leave a comment whenever you're ready to resume, so it can be reopened.
+
+  Thanks again!
+
+
+# Limit the number of actions per hour, from 1-30. Default is 30
+limitPerRun: 30
+
+# Limit to only `issues` or `pulls`
+only: pulls
+
+# Optionally, specify configuration settings that are specific to just 'issues' or 'pulls':
+# pulls:
+#   daysUntilStale: 30
+#   markComment: >
+#     This pull request has been automatically marked as stale because it has not had
+#     recent activity. It will be closed if no further activity occurs. Thank you
+#     for your contributions.
+
+# issues:
+#   exemptLabels:
+#     - confirmed

.gitignore

@@ -1,5 +1,52 @@
 *.swp
 *.swo
-node_modules/
+
+# Logs
+logs
+*.log
+
+# Runtime data
+pids
+*.pid
+*.seed
+allFiredEvents
+scTopics
+
+# Coverage directory used by tools like istanbul
+coverage
+coverage.json
+coverageEnv
+
+# node-waf configuration
+.lock-wscript
+
+# Dependency directory
+node_modules
+
+# Debug log from npm
+npm-debug.log
+
+# local env variables
+.env
+
+# truffle build directory
 build/
-.DS_Store/
+
+# macOS
+.DS_Store
+
+# truffle
+.node-xmlhttprequest-*
+
+# IntelliJ IDE
+.idea
+
+# docs artifacts
+docs/modules/api
+
+# only used to package @openzeppelin/contracts
+contracts/build/
+contracts/README.md
+
+# temporary artifact from solidity-coverage
+allFiredEvents

.solcover.js

@@ -0,0 +1,8 @@
+module.exports = {
+    norpc: true,
+    testCommand: 'npm test',
+    compileCommand: 'npm run compile',
+    skipFiles: [
+        'mocks',
+    ]
+}

.solhint.json

@@ -0,0 +1,10 @@
+{
+  "extends": "solhint:recommended",
+  "rules": {
+    "func-order": "off",
+    "mark-callable-contracts": "off",
+    "no-empty-blocks": "off",
+    "compiler-version": ["error", "^0.6.0"],
+    "private-vars-leading-underscore": "error"
+  }
+}

.travis.yml

@@ -1,12 +0,0 @@
-dist: trusty
-sudo: false
-group: beta
-language: node_js
-node_js:
-  - "6"
-before_install:
-  - npm i -g ethereumjs-testrpc
-  - npm i -g truffle
-script:
-  - testrpc&
-  - npm test

CHANGELOG.md

@@ -0,0 +1,175 @@
+# Changelog
+
+## 3.0.0 (unreleased)
+
+### New features
+ * `AccessControl`: new contract for managing permissions in a system, replacement for `Ownable` and `Roles`. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
+ * `SafeCast`: new functions to convert to and from signed and unsigned values: `toUint256` and `toInt256`. ([#2123](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2123))
+ * `EnumerableMap`: a new data structure for key-value pairs (like `mapping`) that can be iterated over. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+
+### Breaking changes
+ * `ERC721`: `burn(owner, tokenId)` was removed, use `burn(tokenId)` instead. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+ * `ERC721`: `_checkOnERC721Received` was removed. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+ * `ERC721`: `_transferFrom` and `_safeTransferFrom` were renamed to `_transfer` and `_safeTransfer`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+ * `Ownable`: removed `_transferOwnership`. ([#2162](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2162))
+ * `PullPayment`, `Escrow`: `withdrawWithGas` was removed. The old `withdraw` function now forwards all gas. ([#2125](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2125))
+ * `Roles` was removed, use `AccessControl` as a replacement. ([#2112](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2112))
+ * `ECDSA`: when receiving an invalid signature, `recover` now reverts instead of returning the zero address. ([#2114](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2114))
+ * `Create2`: added an `amount` argument to `deploy` for contracts with `payable` constructors. ([#2117](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2117))
+ * `Pausable`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `Strings`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `Counters`: moved to the `utils` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `SignedSafeMath`: moved to the `math` directory. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `ERC20Snapshot`: moved to the `token/ERC20` directory. `snapshot` was changed into an `internal` function. ([#2122](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2122))
+ * `Ownable`: moved to the `access` directory. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `Ownable`: removed `isOwner`. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `Secondary`: removed from the library, use `Ownable` instead. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `Escrow`, `ConditionalEscrow`, `RefundEscrow`: these now use `Ownable` instead of `Secondary`, their external API changed accordingly. ([#2120](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2120))
+ * `ERC20`: removed `_burnFrom`. ([#2119](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2119))
+ * `Address`: removed `toPayable`, use `payable(address)` instead. ([#2133](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2133))
+ * `ERC777`: `_send`, `_mint` and `_burn` now use the caller as the operator. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+ * `ERC777`: removed `_callsTokensToSend` and `_callTokensReceived`. ([#2134](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2134))
+ * `EnumerableSet`: renamed `get` to `at`. ([#2151](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2151))
+ * `ERC165Checker`: functions no longer have a leading underscore. ([#2150](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2150))
+ * `ERC721Metadata`, `ERC721Enumerable`: these contracts were removed, and their functionality merged into `ERC721`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+ * `ERC721`: added a constructor for `name` and `symbol`. ([#2160](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2160))
+ * `ERC20Detailed`: this contract was removed and its functionality merged into `ERC20`. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
+ * `ERC20`: added a constructor for `name` and `symbol`. `decimals` now defaults to 18. ([#2161](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2161))
+
+## 2.5.0 (2020-02-04)
+
+### New features
+ * `SafeCast.toUintXX`: new library for integer downcasting, which allows for safe operation on smaller types (e.g. `uint32`) when combined with `SafeMath`. ([#1926](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1926))
+ * `ERC721Metadata`: added `baseURI`, which can be used for dramatic gas savings when all token URIs share a prefix (e.g. `http://api.myapp.com/tokens/<id>`). ([#1970](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1970))
+ * `EnumerableSet`: new library for storing enumerable sets of values. Only `AddressSet` is supported in this release. ([#2061](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/2061))
+ * `Create2`: simple library to make usage of the `CREATE2` opcode easier. ([#1744](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1744))
+
+### Improvements
+ * `ERC777`: `_burn` is now internal, providing more flexibility and making it easier to create tokens that deflate. ([#1908](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1908))
+ * `ReentrancyGuard`: greatly improved gas efficiency by using the net gas metering mechanism introduced in the Istanbul hardfork. ([#1992](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1992), [#1996](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1996))
+ * `ERC777`: improve extensibility by making `_send` and related functions `internal`. ([#2027](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2027))
+ * `ERC721`: improved revert reason when transferring tokens to a non-recipient contract. ([#2018](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2018))
+
+### Breaking changes
+ * `ERC165Checker` now requires a minimum Solidity compiler version of 0.5.10. ([#1829](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1829))
+
+## 2.4.0 (2019-10-29)
+
+### New features
+ * `Address.toPayable`: added a helper to convert between address types without having to resort to low-level casting. ([#1773](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1773))
+ * Facilities to make metatransaction-enabled contracts through the Gas Station Network. ([#1844](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1844))
+ * `Address.sendValue`: added a replacement to Solidity's `transfer`, removing the fixed gas stipend. ([#1962](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1962))
+ * Added replacement for functions that don't forward all gas (which have been deprecated): ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))
+   * `PullPayment.withdrawPaymentsWithGas(address payable payee)`
+   * `Escrow.withdrawWithGas(address payable payee)`
+ * `SafeMath`: added support for custom error messages to `sub`, `div` and `mod` functions. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+
+### Improvements
+ * `Address.isContract`: switched from `extcodesize` to `extcodehash` for less gas usage. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
+ * `ERC20` and `ERC777` updated to throw custom errors on subtraction overflows. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+
+### Deprecations
+ * Deprecated functions that don't forward all gas: ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))
+   * `PullPayment.withdrawPayments(address payable payee)`
+   * `Escrow.withdraw(address payable payee)`
+
+### Breaking changes
+ * `Address` now requires a minimum Solidity compiler version of 0.5.5. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
+ * `SignatureBouncer` has been removed from drafts, both to avoid confusions with the GSN and `GSNRecipientSignature` (previously called `GSNBouncerSignature`) and because the API was not very clear. ([#1879](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1879))
+
+### How to upgrade from 2.4.0-beta
+
+The final 2.4.0 release includes a refactor of the GSN contracts that will be a breaking change for 2.4.0-beta users.
+
+ * The default empty implementations of `_preRelayedCall` and `_postRelayedCall` were removed and must now be explicitly implemented always in custom recipients. If your custom recipient didn't include an implementation, you can provide an empty one.
+ * `GSNRecipient`, `GSNBouncerBase`, and `GSNContext` were all merged into `GSNRecipient`.
+ * `GSNBouncerSignature` and `GSNBouncerERC20Fee` were renamed to `GSNRecipientSignature` and `GSNRecipientERC20Fee`.
+ * It is no longer necessary to inherit from `GSNRecipient` when using `GSNRecipientSignature` and `GSNRecipientERC20Fee`.
+
+For example, a contract using `GSNBouncerSignature` would have to be changed in the following way.
+
+```diff
+-contract MyDapp is GSNRecipient, GSNBouncerSignature {
++contract MyDapp is GSNRecipientSignature {
+```
+
+Refer to the table below to adjust your inheritance list.
+
+| 2.4.0-beta                         | 2.4.0                        |
+| ---------------------------------- | ---------------------------- |
+| `GSNRecipient, GSNBouncerSignature`| `GSNRecipientSignature`      |
+| `GSNRecipient, GSNBouncerERC20Fee` | `GSNRecipientERC20Fee`       |
+| `GSNBouncerBase`                   | `GSNRecipient`               |
+
+## 2.3.0 (2019-05-27)
+
+### New features
+ * `ERC1820`: added support for interacting with the [ERC1820](https://eips.ethereum.org/EIPS/eip-1820) registry contract (`IERC1820Registry`), as well as base contracts that can be registered as implementers there. ([#1677](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1677))
+ * `ERC777`: support for the [ERC777 token](https://eips.ethereum.org/EIPS/eip-777), which has multiple improvements over `ERC20` (but is backwards compatible with it) such as built-in burning, a more  straightforward permission system, and optional sender and receiver hooks on transfer (mandatory for contracts!). ([#1684](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1684))
+ * All contracts now have revert reason strings, which give insight into error conditions, and help debug failing transactions. ([#1704](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1704))
+
+### Improvements
+ * Reverted the Solidity version bump done in v2.2.0, setting the minimum compiler version to v0.5.0, to prevent unexpected build breakage. Users are encouraged however to stay on top of new compiler releases, which usually include bugfixes. ([#1729](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1729))
+
+### Bugfixes
+ * `PostDeliveryCrowdsale`: some validations where skipped when paired with other crowdsale flavors, such as `AllowanceCrowdsale`, or `MintableCrowdsale` and `ERC20Capped`, which could cause buyers to not be able to claim their purchased tokens. ([#1721](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1721))
+ * `ERC20._transfer`: the `from` argument was allowed to be the zero address, so it was possible to internally trigger a transfer of 0 tokens from the zero address. This address is not a valid destinatary of transfers, nor can it give or receive allowance, so this behavior was inconsistent. It now reverts. ([#1752](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1752))
+
+## 2.2.0 (2019-03-14)
+
+### New features
+ * `ERC20Snapshot`: create snapshots on demand of the token balances and total supply, to later retrieve and e.g. calculate dividends at a past time. ([#1617](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1617))
+ * `SafeERC20`: `ERC20` contracts with no return value (i.e. that revert on failure) are now supported. ([#1655](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1655))
+ * `ERC20`: added internal `_approve(address owner, address spender, uint256 value)`, allowing derived contracts to set the allowance of arbitrary accounts. ([#1609](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1609))
+ * `ERC20Metadata`: added internal `_setTokenURI(string memory tokenURI)`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+ * `TimedCrowdsale`: added internal `_extendTime(uint256 newClosingTime)` as well as `TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime)` event allowing to extend the crowdsale, as long as it hasn't already closed.
+
+### Improvements
+ * Upgraded the minimum compiler version to v0.5.2: this removes many Solidity warnings that were false positives. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
+ * `ECDSA`: `recover` no longer accepts malleable signatures (those using upper-range values for `s`, or 0/1 for `v`). ([#1622](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1622))
+ * `ERC721`'s transfers are now more gas efficient due to removal of unnecessary `SafeMath` calls. ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+ * Fixed variable shadowing issues. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
+
+### Bugfixes
+ * (minor) `SafeERC20`: `safeApprove` wasn't properly checking for a zero allowance when attempting to set a non-zero allowance. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
+
+### Breaking changes in drafts
+ * `TokenMetadata` has been renamed to `ERC20Metadata`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+ * The library `Counter` has been renamed to `Counters` and its API has been improved. See an example in `ERC721`, lines [17](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L17) and [204](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/3cb4a00fce1da76196ac0ac3a0ae9702b99642b5/contracts/token/ERC721/ERC721.sol#L204). ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+
+## 2.1.3 (2019-02-26)
+ * Backported `SafeERC20.safeApprove` bugfix. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
+
+## 2.1.2 (2019-01-17)
+ * Removed most of the test suite from the npm package, except `PublicRole.behavior.js`, which may be useful to users testing their own `Roles`.
+
+## 2.1.1 (2019-01-04)
+ * Version bump to avoid conflict in the npm registry.
+
+## 2.1.0 (2019-01-04)
+
+### New features
+ * Now targeting the 0.5.x line of Solidity compilers. For 0.4.24 support, use version 2.0 of OpenZeppelin.
+ * `WhitelistCrowdsale`: a crowdsale where only whitelisted accounts (`WhitelistedRole`) can purchase tokens. Adding or removing accounts from the whitelist is done by whitelist admins (`WhitelistAdminRole`). Similar to the pre-2.0 `WhitelistedCrowdsale`. ([#1525](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1525), [#1589](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1589))
+ * `RefundablePostDeliveryCrowdsale`: replacement for `RefundableCrowdsale` (deprecated, see below) where tokens are only granted once the crowdsale ends (if it meets its goal). ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))
+ * `PausableCrowdsale`: allows for pausers (`PauserRole`) to pause token purchases. Other crowdsale operations (e.g. withdrawals and refunds, if applicable) are not affected. ([#832](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/832))
+ * `ERC20`: `transferFrom` and `_burnFrom ` now emit `Approval` events, to represent the token's state comprehensively through events. ([#1524](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1524))
+ * `ERC721`: added `_burn(uint256 tokenId)`, replacing the similar deprecated function (see below). ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
+ * `ERC721`: added `_tokensOfOwner(address owner)`, allowing to internally retrieve the array of an account's owned tokens. ([#1522](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1522))
+ * Crowdsales: all constructors are now `public`, meaning it is not necessary to extend these contracts in order to deploy them. The exception is `FinalizableCrowdsale`, since it is meaningless unless extended. ([#1564](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1564))
+ * `SignedSafeMath`: added overflow-safe operations for signed integers (`int256`). ([#1559](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1559), [#1588](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1588))
+
+### Improvements
+ * The compiler version required by `Array` was behind the rest of the libray so it was updated to `v0.4.24`. ([#1553](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1553))
+ * Now conforming to a 4-space indentation code style. ([1508](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1508))
+ * `ERC20`: more gas efficient due to removed redundant `require`s. ([#1409](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1409))
+ * `ERC721`: fixed a bug that prevented internal data structures from being properly cleaned, missing potential gas refunds. ([#1539](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1539) and [#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
+ * `ERC721`: general gas savings on `transferFrom`, `_mint` and `_burn`, due to redudant `require`s and `SSTORE`s. ([#1549](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1549))
+
+### Bugfixes
+
+### Breaking changes
+
+### Deprecations
+ * `ERC721._burn(address owner, uint256 tokenId)`: due to the `owner` parameter being unnecessary. ([#1550](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1550))
+ * `RefundableCrowdsale`: due to trading abuse potential on crowdsales that miss their goal. ([#1543](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1543))

CODE_OF_CONDUCT.md

@@ -0,0 +1,73 @@
+# Contributor Covenant Code of Conduct
+
+## Our Pledge
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of age, body
+size, disability, ethnicity, sex characteristics, gender identity and expression,
+level of experience, education, socio-economic status, nationality, personal
+appearance, race, religion, or sexual identity and orientation.
+
+## Our Standards
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+* Using welcoming and inclusive language
+* Being respectful of differing viewpoints and experiences
+* Gracefully accepting constructive criticism
+* Focusing on what is best for the community
+* Showing empathy towards other community members
+
+Examples of unacceptable behavior by participants include:
+
+* The use of sexualized language or imagery and unwelcome sexual attention or
+  advances
+* Trolling, insulting/derogatory comments, and personal or political attacks
+* Public or private harassment
+* Publishing others' private information, such as a physical or electronic
+  address, without explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+  professional setting
+
+## Our Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit, or
+reject comments, commits, code, wiki edits, issues, and other contributions
+that are not aligned to this Code of Conduct, or to ban temporarily or
+permanently any contributor for other behaviors that they deem inappropriate,
+threatening, offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project e-mail
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+further defined and clarified by project maintainers.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported by contacting the project team at maintainers@openzeppelin.org. All
+complaints will be reviewed and investigated and will result in a response that
+is deemed necessary and appropriate to the circumstances. The project team is
+obligated to maintain confidentiality with regard to the reporter of an incident.
+Further details of specific enforcement policies may be posted separately.
+
+Project maintainers who do not follow or enforce the Code of Conduct in good
+faith may face temporary or permanent repercussions as determined by other
+members of the project's leadership.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4,
+available at https://www.contributor-covenant.org/version/1/4/code-of-conduct.html
+
+[homepage]: https://www.contributor-covenant.org

CODE_STYLE.md

@@ -0,0 +1,69 @@
+# Code Style
+
+We value clean code and consistency, and those are prerequisites for us to
+include new code in the repository. Before proposing a change, please read this
+document and take some time to familiarize yourself with the style of the
+existing codebase.
+
+## Solidity code
+
+In order to be consistent with all the other Solidity projects, we follow the
+[official recommendations documented in the Solidity style guide](http://solidity.readthedocs.io/en/latest/style-guide.html).
+
+Any exception or additions specific to our project are documented below.
+
+### Naming
+
+* Try to avoid acronyms and abbreviations.
+
+* All state variables should be private.
+
+* Private state variables should have an underscore prefix.
+
+    ```
+    contract TestContract {
+      uint256 private _privateVar;
+      uint256 internal _internalVar;
+    }
+    ```
+
+* Parameters must not be prefixed with an underscore.
+
+    ```
+    function test(uint256 testParameter1, uint256 testParameter2) {
+    ...
+    }
+    ```
+
+* Internal and private functions should have an underscore prefix.
+
+    ```
+    function _testInternal() internal {
+      ...
+    }
+    ```
+
+    ```
+    function _testPrivate() private {
+      ...
+    }
+    ```
+
+* Events should be emitted immediately after the state change that they
+  represent, and consequently they should be named in past tense.
+
+    ```
+    function _burn(address _who, uint256 _value) internal {
+      super._burn(_who, _value);
+      emit TokensBurned(_who, _value);
+    }
+    ```
+
+  Some standards (e.g. ERC20) use present tense, and in those cases the
+  standard specification prevails.
+  
+* Interface names should have a capital I prefix.
+
+    ```
+    interface IERC777 {
+    ```

CONTRIBUTING.md

@@ -1,105 +1,71 @@
-Contributing to Zeppelin
+Contributing to OpenZeppelin Contracts
 =======
 
-## Design Guidelines
+We really appreciate and value contributions to OpenZeppelin Contracts. Please take 5' to review the items listed below to make sure that your contributions are merged as soon as possible.
 
-These are some global design goals in Zeppelin.
+## Contribution guidelines
 
-### D0 - Security in Depth
-We strive to provide secure, tested, audited code. To achieve this, we need to match intention with function. Thus, documentation, code clarity, community review and security discussions are fundamental.
+Smart contracts manage value and are highly vulnerable to errors and attacks. We have very strict [guidelines], please make sure to review them!
 
-### D1 - Simple and Modular
-Simpler code means easier audits, and better understanding of what each component does. We look for small files, small contracts, and small functions. If you can separate a contract into two independent functionalities you should probably do it.
+## Creating Pull Requests (PRs)
 
-### D2 - Naming Matters
+As a contributor, you are expected to fork this repository, work on your own fork and then submit pull requests. The pull requests will be reviewed and eventually merged into the main repo. See ["Fork-a-Repo"](https://help.github.com/articles/fork-a-repo/) for how this works.
 
-We take our time with picking names. Code is going to be written once, and read hundreds of times. Renaming for clarity is encouraged.
+## A typical workflow
 
-### D3 - Tests
+1) Make sure your fork is up to date with the main repository:
 
-Write tests for all your code. We encourage Test Driven Development so we know when our code is right. Even though not all code in the repository is tested at the moment, we aim to test every line of code in the future.
+```
+cd openzeppelin-contracts
+git remote add upstream https://github.com/OpenZeppelin/openzeppelin-contracts.git
+git fetch upstream
+git pull --rebase upstream master
+```
+NOTE: The directory `openzeppelin-contracts` represents your fork's local copy.
 
-### D4 - Check preconditions and post-conditions
-
-A very important way to prevent vulnerabilities is to catch a contract’s inconsistent state as early as possible. This is why we want functions to check pre- and post-conditions for executing its logic. When writing code, ask yourself what you are expecting to be true before and after the function runs, and express it in code.
-
-### D5 - Code Consistency
-
-Consistency on the way classes are used is paramount to an easier understanding of the library. The codebase should be as unified as possible. Read existing code and get inspired before you write your own. Follow the style guidelines. Don’t hesitate to ask for help on how to best write a specific piece of code.
-
-### D6 - Regular Audits
-Following good programming practices is a way to reduce the risk of vulnerabilities, but professional code audits are still needed. We will perform regular code audits on major releases, and hire security professionals to provide independent review.
-
-## Style Guidelines
-
-The design guidelines have quite a high abstraction level. These style guidelines are more concrete and easier to apply, and also more opinionated.
-
-### General
-
-#### G0 - Default to Solidity's official style guide.
-
-Follow the official Solidity style guide: http://solidity.readthedocs.io/en/latest/style-guide.html
-
-#### G1 - No Magic Constants
-
-Avoid constants in the code as much as possible. Magic strings are also magic constants.
-
-#### G2 - Code that Fails Early
-
-We ask our code to fail as soon as possible when an unexpected input was provided or unexpected state was found.
-
-#### G3 - Internal Amounts Must be Signed Integers and Represent the Smallest Units.
-
-Avoid representation errors by always dealing with weis when handling ether. GUIs can convert to more human-friendly representations. Use Signed Integers (int) to prevent underflow problems.
-
-
-### Testing
-
-#### T1 - Tests Must be Written Elegantly
-
-Style guidelines are not relaxed for tests. Tests are a good way to show how to use the library, and maintaining them is extremely necessary.
-
-Don't write long tests, write helper functions to make them be as short and concise as possible (they should take just a few lines each), and use good variable names.
-
-#### T2 - Tests Must not be Random
-
-Inputs for tests should not be generated randomly. Accounts used to create test contracts are an exception, those can be random. Also, the type and structure of outputs should be checked.
-
-
-### Documentation
-
-TODO
-
-## Pull Request Workflow
-
-Our workflow is based on GitHub's pull requests. We use feature branches, prepended with: `test`, `feature`, `fix`, `refactor`, or `remove` according to the change the branch introduces. Some examples for such branches are:
-```sh
-git checkout -b test/some-module
-git checkout -b feature/some-new-stuff
-git checkout -b fix/some-bug
-git checkout -b remove/some-file
+2) Branch out from `master` into `fix/some-bug-#123`:
+(Postfixing #123 will associate your PR with the issue #123 and make everyone's life easier =D)
+```
+git checkout -b fix/some-bug-#123
 ```
 
-We expect pull requests to be rebased to the master branch before merging:
-```sh
-git remote add zep git@github.com:OpenZeppelin/zeppelin-solidity.git
-git pull --rebase zep master
+3) Make your changes, add your files, commit, and push to your fork.
+
+```
+git add SomeFile.js
+git commit "Fix some bug #123"
+git push origin fix/some-bug-#123
 ```
 
-Note that we require rebasing your branch instead of merging it, for commit readability reasons.
+4) Run tests, linter, etc. This can be done by running local continuous integration and make sure it passes.
 
-After that, you can push the changes to your fork, by doing:
-```sh
-git push origin your_branch_name
-git push origin feature/some-new-stuff
-git push origin fix/some-bug
+```bash
+npm test
+npm run lint
 ```
 
-Finally go to [github.com/OpenZeppelin/zeppelin-solidity](https://github.com/OpenZeppelin/zeppelin-solidity) in your web browser and issue a new pull request.
+or you can simply run CircleCI locally
+```bash
+circleci local execute --job build
+circleci local execute --job test
+```
+*Note*: requires installing CircleCI and docker locally on your machine.
 
-Main contributors will review your code and possibly ask for changes before your code is pulled in to the main repository.  We'll check that all tests pass, review the coding style, and check for general code correctness. If everything is OK, we'll merge your pull request and your code will be part of Zeppelin.
+5) Go to [github.com/OpenZeppelin/openzeppelin-contracts](https://github.com/OpenZeppelin/openzeppelin-contracts) in your web browser and issue a new pull request.
 
-If you have any questions feel free to post them to
-[github.com/OpenZeppelin/zeppelin-solidity/issues](https://github.com/OpenZeppelin/zeppelin-solidity/issues).
+*IMPORTANT* Read the PR template very carefully and make sure to follow all the instructions. These instructions
+refer to some very important conditions that your PR must meet in order to be accepted, such as making sure that all tests pass, JS linting tests pass, Solidity linting tests pass, etc.
+
+6) Maintainers will review your code and possibly ask for changes before your code is pulled in to the main repository. We'll check that all tests pass, review the coding style, and check for general code correctness. If everything is OK, we'll merge your pull request and your code will be part of OpenZeppelin.
+
+*IMPORTANT* Please pay attention to the maintainer's feedback, since its a necessary step to keep up with the standards OpenZeppelin attains to.
+
+## All set!
+
+If you have any questions, feel free to post them to github.com/OpenZeppelin/openzeppelin-contracts/issues.
+
+Finally, if you're looking to collaborate and want to find easy tasks to start, look at the issues we marked as ["Good first issue"](https://github.com/OpenZeppelin/openzeppelin-contracts/labels/good%20first%20issue).
 
 Thanks for your time and code!
+
+[guidelines]: GUIDELINES.md

DOCUMENTATION.md

@@ -0,0 +1,16 @@
+Documentation is hosted at https://docs.openzeppelin.com/contracts.
+
+All of the content for the site is in this repository. The guides are in the
+[docs](/docs) directory, and the API Reference is extracted from comments in
+the source code. If you want to help improve the content, this is the
+repository you should be contributing to.
+
+[`solidity-docgen`](https://github.com/OpenZeppelin/solidity-docgen) is the
+program that extracts the API Reference from source code.
+
+The [`docs.openzeppelin.com`](https://github.com/OpenZeppelin/docs.openzeppelin.com)
+repository hosts the configuration for the entire site, which includes
+documetation for all of the OpenZeppelin projects.
+
+To run the docs locally you should run `npm run docs start` on this
+repository.

GUIDELINES.md

@@ -0,0 +1,64 @@
+Design Guidelines
+=======
+
+These are some global design goals in OpenZeppelin.
+
+#### D0 - Security in Depth
+We strive to provide secure, tested, audited code. To achieve this, we need to match intention with function. Thus, documentation, code clarity, community review and security discussions are fundamental.
+
+#### D1 - Simple and Modular
+Simpler code means easier audits, and better understanding of what each component does. We look for small files, small contracts, and small functions. If you can separate a contract into two independent functionalities you should probably do it.
+
+#### D2 - Naming Matters
+
+We take our time with picking names. Code is going to be written once, and read hundreds of times. Renaming for clarity is encouraged.
+
+#### D3 - Tests
+
+Write tests for all your code. We encourage Test Driven Development so we know when our code is right. Even though not all code in the repository is tested at the moment, we aim to test every line of code in the future.
+
+#### D4 - Check preconditions and post-conditions
+
+A very important way to prevent vulnerabilities is to catch a contract’s inconsistent state as early as possible. This is why we want functions to check pre- and post-conditions for executing its logic. When writing code, ask yourself what you are expecting to be true before and after the function runs, and express it in code.
+
+#### D5 - Code Consistency
+
+Consistency on the way classes are used is paramount to an easier understanding of the library. The codebase should be as unified as possible. Read existing code and get inspired before you write your own. Follow the style guidelines. Don’t hesitate to ask for help on how to best write a specific piece of code.
+
+#### D6 - Regular Audits
+Following good programming practices is a way to reduce the risk of vulnerabilities, but professional code audits are still needed. We will perform regular code audits on major releases, and hire security professionals to provide independent review.
+
+## Style Guidelines
+
+The design guidelines have quite a high abstraction level. These style guidelines are more concrete and easier to apply, and also more opinionated.
+
+### General
+
+#### G0 - Default to Solidity's official style guide.
+
+Follow the official Solidity style guide: https://solidity.readthedocs.io/en/latest/style-guide.html
+
+#### G1 - No Magic Constants
+
+Avoid constants in the code as much as possible. Magic strings are also magic constants.
+
+#### G2 - Code that Fails Early
+
+We ask our code to fail as soon as possible when an unexpected input was provided or unexpected state was found.
+
+#### G3 - Internal Amounts Must be Signed Integers and Represent the Smallest Units.
+
+Avoid representation errors by always dealing with weis when handling ether. GUIs can convert to more human-friendly representations. Use Signed Integers (int) to prevent underflow problems.
+
+
+### Testing
+
+#### T1 - Tests Must be Written Elegantly
+
+Style guidelines are not relaxed for tests. Tests are a good way to show how to use the library, and maintaining them is extremely necessary.
+
+Don't write long tests, write helper functions to make them be as short and concise as possible (they should take just a few lines each), and use good variable names.
+
+#### T2 - Tests Must not be Random
+
+Inputs for tests should not be generated randomly. Accounts used to create test contracts are an exception, those can be random. Also, the type and structure of outputs should be checked.

LICENSE

@@ -1,22 +1,22 @@
 The MIT License (MIT)
 
-Copyright (c) 2016 Smart Contract Solutions, Inc.
+Copyright (c) 2016-2019 zOS Global Limited
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
 "Software"), to deal in the Software without restriction, including
-without limitation the rights to use, copy, modify, merge, publish, 
+without limitation the rights to use, copy, modify, merge, publish,
 distribute, sublicense, and/or sell copies of the Software, and to
-permit persons to whom the Software is furnished to do so, subject to 
+permit persons to whom the Software is furnished to do so, subject to
 the following conditions:
 
 The above copyright notice and this permission notice shall be included
 in all copies or substantial portions of the Software.
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS 
-OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 
-MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
-IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY 
-CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
-TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE 
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

@@ -1,89 +1,78 @@
-# Zeppelin Solidity
-[![NPM Package](https://img.shields.io/npm/v/zeppelin-solidity.svg?style=flat-square)](https://www.npmjs.org/package/zeppelin-solidity)
-[![Build Status](https://img.shields.io/travis/OpenZeppelin/zeppelin-solidity.svg?branch=master&style=flat-square)](https://travis-ci.org/OpenZeppelin/zeppelin-solidity)
+# <img src="logo.png" alt="OpenZeppelin" height="40px">
 
-Zeppelin is a library for writing secure [Smart Contracts](https://en.wikipedia.org/wiki/Smart_contract) on Ethereum.
+[![NPM Package](https://img.shields.io/npm/v/@openzeppelin/contracts.svg)](https://www.npmjs.org/package/@openzeppelin/contracts)
+[![Build Status](https://circleci.com/gh/OpenZeppelin/openzeppelin-contracts.svg?style=shield)](https://circleci.com/gh/OpenZeppelin/openzeppelin-contracts)
+[![Coverage Status](https://codecov.io/gh/OpenZeppelin/openzeppelin-contracts/graph/badge.svg)](https://codecov.io/gh/OpenZeppelin/openzeppelin-contracts)
 
-With Zeppelin, you can build distributed applications, protocols and organizations:
-- using common contract security patterns (See [Onward with Ethereum Smart Contract Security](https://medium.com/bitcorps-blog/onward-with-ethereum-smart-contract-security-97a827e47702#.y3kvdetbz))
-- in the [Solidity language](http://solidity.readthedocs.io/en/develop/).
+**A library for secure smart contract development.** Build on a solid foundation of community-vetted code.
 
-> NOTE: New to smart contract development? Check our [introductory guide](https://medium.com/zeppelin-blog/the-hitchhikers-guide-to-smart-contracts-in-ethereum-848f08001f05#.cox40d2ut).
+ * Implementations of standards like [ERC20](https://docs.openzeppelin.com/contracts/erc20) and [ERC721](https://docs.openzeppelin.com/contracts/erc721).
+ * Flexible [role-based permissioning](https://docs.openzeppelin.com/contracts/access-control) scheme.
+ * Reusable [Solidity components](https://docs.openzeppelin.com/contracts/utilities) to build custom contracts and complex decentralized systems.
+ * First-class integration with the [Gas Station Network](https://docs.openzeppelin.com/contracts/gsn) for systems with no gas fees!
+ * Audited by leading security firms.
 
-## Getting Started
+## Overview
 
-Zeppelin integrates with [Truffle](https://github.com/ConsenSys/truffle), an Ethereum development environment. Please install Truffle and initialize your project with `truffle init`.
-```sh
-npm install -g truffle
-mkdir myproject && cd myproject
-truffle init
+### Installation
+
+```console
+$ npm install @openzeppelin/contracts
 ```
 
-To install the Zeppelin library, run:
-```sh
-npm i zeppelin-solidity
-```
+OpenZeppelin Contracts features a [stable API](https://docs.openzeppelin.com/contracts/releases-stability#api-stability), which means your contracts won't break unexpectedly when upgrading to a newer minor version.
 
-After that, you'll get all the library's contracts in the `contracts/zeppelin` folder. You can use the contracts in the library like so:
+### Usage
 
-```js
-import "./zeppelin/Ownable.sol";
+Once installed, you can use the contracts in the library by importing them:
 
-contract MyContract is Ownable {
-  ...
+```solidity
+pragma solidity ^0.5.0;
+
+import "@openzeppelin/contracts/token/ERC721/ERC721Full.sol";
+import "@openzeppelin/contracts/token/ERC721/ERC721Mintable.sol";
+
+contract MyNFT is ERC721Full, ERC721Mintable {
+    constructor() ERC721Full("MyNFT", "MNFT") public {
+    }
 }
 ```
 
-> NOTE: The current distribution channel is npm, which is not ideal. [We're looking into providing a better tool for code distribution](https://github.com/OpenZeppelin/zeppelin-solidity/issues/13), and ideas are welcome.
+_If you're new to smart contract development, head to [Developing Smart Contracts](https://docs.openzeppelin.com/learn/developing-smart-contracts) to learn about creating a new project and compiling your contracts._
 
-#### Truffle Beta Support
-We also support Truffle Beta npm integration. If you're using Truffle Beta, the contracts in `node_modules` will be enough, so feel free to delete the copies at your `contracts` folder. If you're using Truffle Beta, you can use Zeppelin contracts like so:
+To keep your system secure, you should **always** use the installed code as-is, and neither copy-paste it from online sources, nor modify it yourself. The library is designed so that only the contracts and functions you use are deployed, so you don't need to worry about it needlessly increasing gas costs.
 
-```js
-import "zeppelin-solidity/contracts/Ownable.sol";
+## Learn More
 
-contract MyContract is Ownable {
-  ...
-}
-```
+The guides in the sidebar will teach about different concepts, and how to use the related contracts that OpenZeppelin Contracts provides:
 
-For more info see [the Truffle Beta package management tutorial](http://truffleframework.com/tutorials/package-management).
+* [Access Control](https://docs.openzeppelin.com/contracts/access-control): decide who can perform each of the actions on your system.
+* [Tokens](https://docs.openzeppelin.com/contracts/tokens): create tradeable assets or collectives, and distribute them via [Crowdsales](https://docs.openzeppelin.com/contracts/crowdsales).
+* [Gas Station Network](https://docs.openzeppelin.com/contracts/gsn): let your users interact with your contracts without having to pay for gas themselves.
+* [Utilities](https://docs.openzeppelin.com/contracts/utilities): generic useful tools, including non-overflowing math, signature verification, and trustless paying systems.
 
+The [full API](https://docs.openzeppelin.com/contracts/api/token/ERC20) is also thoroughly documented, and serves as a great reference when developing your smart contract application. You can also ask for help or follow Contracts's development in the [community forum](https://forum.openzeppelin.com).
+
+Finally, you may want to take a look at the [guides on our blog](https://blog.openzeppelin.com/guides), which cover several common use cases and good practices.. The following articles provide great background reading, though please note, some of the referenced tools have changed as the tooling in the ecosystem continues to rapidly evolve.
+
+* [The Hitchhiker’s Guide to Smart Contracts in Ethereum](https://blog.openzeppelin.com/the-hitchhikers-guide-to-smart-contracts-in-ethereum-848f08001f05) will help you get an overview of the various tools available for smart contract development, and help you set up your environment.
+* [A Gentle Introduction to Ethereum Programming, Part 1](https://blog.openzeppelin.com/a-gentle-introduction-to-ethereum-programming-part-1-783cc7796094) provides very useful information on an introductory level, including many basic concepts from the Ethereum platform.
+* For a more in-depth dive, you may read the guide [Designing the Architecture for Your Ethereum Application](https://blog.openzeppelin.com/designing-the-architecture-for-your-ethereum-application-9cec086f8317), which discusses how to better structure your application and its relationship to the real world.
 
 ## Security
-Zeppelin is meant to provide secure, tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problem you might experience.
 
-If you find a security issue, please email [security@openzeppelin.org](mailto:security@openzeppelin.org).
+This project is maintained by [OpenZeppelin](https://openzeppelin.com), and developed following our high standards for code quality and security. OpenZeppelin is meant to provide tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problems you might experience.
 
-## Developer Resources
+The core development principles and strategies that OpenZeppelin is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.
 
-Building a distributed application, protocol or organization with Zeppelin?
+The latest audit was done on October 2018 on version 2.0.0.
 
-- Read documentation: http://zeppelin-solidity.readthedocs.io/en/latest/
+Please report any security issues you find to security@openzeppelin.org.
 
-- Ask for help and follow progress at: https://zeppelin-slackin.herokuapp.com/
-
-Interested in contributing to Zeppelin?
-
-- Framework proposal and roadmap: https://medium.com/zeppelin-blog/zeppelin-framework-proposal-and-development-roadmap-fdfa9a3a32ab#.iain47pak
-- Issue tracker: https://github.com/OpenZeppelin/zeppelin-solidity/issues
-- Contribution guidelines: https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/CONTRIBUTING.md
-
-## Collaborating organizations and audits by Zeppelin
-- [Golem](https://golem.network/)
-- [Mediachain](https://golem.network/)
-- [Truffle](http://truffleframework.com/)
-- [Firstblood](http://firstblood.io/)
-- [Rootstock](http://www.rsk.co/)
-- [Consensys](https://consensys.net/)
-- [DigixGlobal](https://www.dgx.io/)
-- [Coinfund](https://coinfund.io/)
-- [DemocracyEarth](http://democracy.earth/)
-- [Signatura](https://signatura.co/)
-- [Ether.camp](http://www.ether.camp/)
-
-among others...
+## Contribute
 
+OpenZeppelin exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the [contribution guide](CONTRIBUTING.md)!
 
 ## License
-Code released under the [MIT License](https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/LICENSE).
+
+OpenZeppelin is released under the [MIT License](LICENSE).

RELEASING.md

@@ -0,0 +1,99 @@
+# Releasing
+
+This document describes our release process, and contains the steps to be followed by an OpenZeppelin maintainer at the several stages of a release.
+
+We release a new version of OpenZeppelin monthly. Release cycles are tracked in the [issue milestones](https://github.com/OpenZeppelin/openzeppelin-contracts/milestones).
+
+Each release has at least one release candidate published first, intended for community review and any critical fixes that may come out of it. At the moment we leave 1 week between the first release candidate and the final release.
+
+Before starting make sure to verify the following items.
+* Your local `master` branch is in sync with your `upstream` remote (it may have another name depending on your setup).
+* Your repo is clean, particularly with no untracked files in the contracts and tests directories. Verify with `git clean -n`.
+
+
+## Creating the release branch
+
+We'll refer to a release `vX.Y.Z`.
+
+```
+git checkout master
+git checkout -b release-vX.Y.Z
+```
+
+## Creating a release candidate
+
+Once in the release branch, change the version string in `package.json`, `package-lock.json` and `ethpm.json` to `X.Y.Z-rc.R`. (This will be `X.Y.Z-rc.1` for the first release candidate.) Commit these changes and tag the commit as `vX.Y.Z-rc.R`.
+
+```
+git add package.json package-lock.json ethpm.json
+git commit -m "Release candidate vX.Y.Z-rc.R"
+git tag -a vX.Y.Z-rc.R
+git push upstream release-vX.Y.Z
+git push upstream vX.Y.Z-rc.R
+```
+
+Draft the release notes in our [GitHub releases](https://github.com/OpenZeppelin/openzeppelin-contracts/releases). Make sure to mark it as a pre-release! Try to be consistent with our previous release notes in the title and format of the text. Release candidates don't need a detailed changelog, but make sure to include a link to GitHub's compare page.
+
+Once the CI run for the new tag is green, publish on npm under the `next` tag. You should see the contracts compile automatically.
+
+```
+npm publish --tag next
+```
+
+Publish the release notes on GitHub and the forum, and ask our community manager to announce the release candidate on at least Twitter.
+
+## Creating the final release
+
+Make sure to have the latest changes from `upstream` in your local release branch.
+
+```
+git checkout release-vX.Y.Z
+git pull upstream
+```
+
+Before starting the release process, make one final commit to CHANGELOG.md, including the date of the release.
+
+Change the version string in `package.json`, `package-lock.json` and `ethpm.json` removing the "-rc.R" suffix. Commit these changes and tag the commit as `vX.Y.Z`.
+
+```
+git add package.json package-lock.json ethpm.json
+git commit -m "Release vX.Y.Z"
+git tag -a vX.Y.Z
+git push upstream release-vX.Y.Z
+git push upstream vX.Y.Z
+```
+
+Draft the release notes in GitHub releases. Try to be consistent with our previous release notes in the title and format of the text. Make sure to include a detailed changelog.
+
+Once the CI run for the new tag is green, publish on npm. You should see the contracts compile automatically.
+
+```
+npm publish
+```
+
+Publish the release notes on GitHub and ask our community manager to announce the release!
+
+Delete the `next` tag in the npm package as there is no longer a release candidate.
+
+```
+npm dist-tag rm --otp $2FA_CODE @openzeppelin/contracts next
+```
+
+## Merging the release branch
+
+After the final release, the release branch should be merged back into `master`. This merge must not be squashed because it would lose the tagged release commit. Since the GitHub repo is set up to only allow squashed merges, the merge should be done locally and pushed.
+
+Make sure to have the latest changes from `upstream` in your local release branch.
+
+```
+git checkout release-vX.Y.Z
+git pull upstream
+```
+
+```
+git checkout master
+git merge --no-ff release-vX.Y.Z
+git push upstream master
+```
+
+The release branch can then be deleted on GitHub.

audit/2017-03.md

@@ -0,0 +1,290 @@
+# OpenZeppelin Audit
+
+March, 2017
+Authored by Dennis Peterson and Peter Vessenes
+
+# Introduction
+
+Zeppelin requested that New Alchemy perform an audit of the contracts in their OpenZeppelin library. The OpenZeppelin contracts are a set of contracts intended to be a safe building block for a variety of uses by parties that may not be as sophisticated as the OpenZeppelin team. It is a design goal that the contracts be deployable safely and "as-is".
+
+The contracts are hosted at:
+
+https://github.com/OpenZeppelin/zeppelin-solidity
+
+All the contracts in the "contracts" folder are in scope.
+
+The git commit hash we evaluated is:
+9c5975a706b076b7000e8179f8101e0c61024c87
+
+# Disclaimer
+
+The audit makes no statements or warrantees about utility of the code, safety of the code, suitability of the business model, regulatory regime for the business model, or any other statements about fitness of the contracts to purpose, or their bugfree status. The audit documentation is for discussion purposes only.
+
+# Executive Summary
+
+Overall the OpenZeppelin codebase is of reasonably high quality -- it is clean, modular and follows best practices throughout.
+
+It is still in flux as a codebase, and needs better documentation per file as to expected behavior and future plans. It probably needs more comprehensive and aggressive tests written by people less nice than the current OpenZeppelin team.
+
+We identified two critical errors and one moderate issue, and would not recommend this commit hash for public use until these bugs are remedied.
+
+The repository includes a set of Truffle unit tests, a requirement and best practice for smart contracts like these; we recommend these be bulked up.
+
+# Discussion
+
+## Big Picture: Is This A Worthwhile Project?
+
+As soon as a developer touches OpenZeppelin contracts, they will modify something, leaving them in an un-audited state. We do not recommend developers deploy any unaudited code to the Blockchain if it will handle money, information or other things of value.
+
+> "In accordance with Unix philosophy, Perl gives you enough rope to hang yourself"
+> --Larry Wall
+
+We think this is an incredibly worthwhile project -- aided by the high code quality. Creating a framework that can be easily extended helps increase the average code quality on the Blockchain by charting a course for developers and encouraging containment of modifications to certain sections.
+
+> "Rust: The language that makes you take the safety off before shooting yourself in the foot"
+> -- (@mbrubeck)
+
+We think much more could be done here, and recommend the OpenZeppelin team keep at this and keep focusing on the design goal of removing rope and adding safety.
+
+## Solidity Version Updates Recommended
+
+Most of the code uses Solidity 0.4.11, but some files under `Ownership` are marked 0.4.0. These should be updated.
+
+Solidity 0.4.10 will add several features which could be useful in these contracts:
+
+- `assert(condition)`, which throws if the condition is false
+
+- `revert()`, which rolls back without consuming all remaining gas.
+
+- `address.transfer(value)`, which is like `send` but automatically propagates exceptions, and supports `.gas()`. See https://github.com/ethereum/solidity/issues/610 for more on this.
+
+## Error Handling: Throw vs Return False
+Solidity standards allow two ways to handle an error -- either calling `throw` or returning `false`. Both have benefits. In particular, a `throw` guarantees a complete wipe of the call stack (up to the preceding external call), whereas `false` allows a function to continue.
+
+In general we prefer `throw` in our code audits, because it is simpler -- it's less for an engineer to keep track of. Returning `false` and using logic to check results can quickly become a poorly-tracked state machine, and this sort of complexity can cause errors.
+
+In the OpenZeppelin contracts, both styles are used in different parts of the codebase. `SimpleToken` transfers throw upon failure, while the full ERC20 token returns `false`. Some modifiers `throw`, others just wrap the function body in a conditional, effectively allowing the function to return false if the condition is not met.
+
+We don't love this, and would usually recommend you stick with one style or the other throughout the codebase.
+
+In at least one case, these different techniques are combined cleverly (see the Multisig comments, line 65). As a set of contracts intended for general use, we recommend you either strive for more consistency or document explicit design criteria that govern which techniques are used where.
+
+Note that it may be impossible to use either one in all situations. For example, SafeMath functions pretty much have to throw upon failure, but ERC20 specifies returning booleans. Therefore we make no particular recommendations, but simply point out inconsistencies to consider.
+
+# Critical Issues
+
+## Stuck Ether in Crowdsale contract
+CrowdsaleToken.sol has no provision for withdrawing the raised ether. We *strongly* recommend a standard `withdraw` function be added. There is no scenario in which someone should deploy this contract as is, whether for testing or live.
+
+## Recursive Call in MultisigWallet
+Line 45 of `MultisigWallet.sol` checks if the amount being sent by `execute` is under a daily limit.
+
+This function can only be called by the "Owner". As a first angle of attack, it's worth asking what will happen if the multisig wallet owners reset the daily limit by approving a call to `resetSpentToday`.
+
+If a chain of calls can be constructed in which the owner confirms the `resetSpentToday` function and then withdraws through `execute` in a recursive call, the contract can be drained. In fact, this could be done without a recursive call, just through repeated `execute` calls alternating with the `confirm` calls.
+
+We are still working through the confirmation protocol in `Shareable.sol`, but we are not convinced that this is impossible, in fact it looks possible. The flexibility any shared owner has in being able to revoke confirmation later is another worrisome angle of approach even if some simple patches are included.
+
+This bug has a number of causes that need to be addressed:
+
+1. `resetSpentToday` and `confirm` together do not limit the days on which the function can be called or (it appears) the number of times it can be called.
+1. Once a call has been confirmed and `execute`d it appears that it can be re-executed. This is not good.
+3. `confirmandCheck` doesn't seem to have logic about whether or not the function in question has been called.
+4. Even if it did, `revoke` would need updates and logic to deal with revocation requests after a function call had been completed.
+
+We do not recommend using the MultisigWallet until these issues are fixed.
+
+# Moderate to Minor Issues
+
+## PullPayment
+PullPayment.sol needs some work. It has no explicit provision for cancelling a payment. This would be desirable in a number of scenarios; consider a payee losing their wallet, or giving a griefing address, or just an address that requires more than the default gas offered by `send`.
+
+`asyncSend` has no overflow checking. This is a bad plan. We recommend overflow and underflow checking at the layer closest to the data manipulation.
+
+`asyncSend` allows more balance to be queued up for sending than the contract holds. This is probably a bad idea, or at the very least should be called something different. If the intent is to allow this, it should have provisions for dealing with race conditions between competing `withdrawPayments` calls.
+
+It would be nice to see how many payments are pending. This would imply a bit of a rewrite; we recommend this contract get some design time, and that developers don't rely on it in its current state.
+
+## Shareable Contract
+
+We do not believe the `Shareable.sol` contract is ready for primetime. It is missing functions, and as written may be vulnerable to a reordering attack -- an attack in which a miner or other party "racing" with a smart contract participant inserts their own information into a list or mapping.
+
+The confirmation and revocation code needs to be looked over with a very careful eye imagining extraordinarily bad behavior by shared owners before this contract can be called safe.
+
+No sanity checks on the initial constructor's `required` argument are worrisome as well.
+
+# Line by Line Comments
+
+## Lifecycle
+
+### Killable
+
+Very simple, allows owner to call selfdestruct, sending funds to owner. No issues. However, note that `selfdestruct` should typically not be used; it is common that a developer may want to access data in a former contract, and they may not understand that `selfdestruct` limits access to the contract. We recommend better documentation about this dynamic, and an alternate function name for `kill` like `completelyDestroy` while `kill` would perhaps merely send funds to the owner.
+
+Also note that a killable function allows the owner to take funds regardless of other logic. This may be desirable or undesirable depending on the circumstances. Perhaps `Killable` should have a different name as well.
+
+### Migrations
+
+I presume that the goal of this contract is to allow and annotate a migration to a new smart contract address. We are not clear here how this would be accomplished by the code; we'd like to review with the OpenZeppelin team.
+
+### Pausable
+
+We like these pauses! Note that these allow significant griefing potential by owners, and that this might not be obvious to participants in smart contracts using the OpenZeppelin framework. We would recommend that additional sample logic be added to for instance the TokenContract showing safer use of the pause and resume functions. In particular, we would recommend a timelock after which anyone could unpause the contract.
+
+The modifers use the pattern `if(bool){_;}`. This is fine for functions that return false upon failure, but could be problematic for functions expected to throw upon failure. See our comments above on standardizing on `throw` or `return(false)`.
+
+## Ownership
+
+### Ownable
+
+Line 19: Modifier throws if doesn't meet condition, in contrast to some other inheritable modifiers (e.g. in Pausable) that use `if(bool){_;}`.
+
+### Claimable
+
+Inherits from Ownable but the existing owner sets a pendingOwner who has to claim ownership.
+
+Line 17: Another modifier that throws.
+
+### DelayedClaimable
+
+Is there any reason to descend from Ownable directly, instead of just Claimable, which descends from Ownable? If not, descending from both just adds confusion.
+
+### Contactable
+
+Allows owner to set a public string of contract information. No issues.
+
+### Shareable
+
+This needs some work. Doesn't check if `_required <= len(_owners)` for instance, that would be a bummer. What if _required were like `MAX - 1`?
+
+I have a general concern about the difference between `owners`, `_owners`, and `owner` in `Ownable.sol`. I recommend "Owners" be renamed. In general we do not recomment single character differences in variable names, although a preceding underscore is not uncommon in Solidity code.
+
+Line 34: "this contract only has six types of events"...actually only two.
+
+Line 61: Why is `ownerIndex` keyed by addresses hashed to `uint`s? Why not use the addresses directly, so `ownerIndex` is less obscure, and so there's stronger typing?
+
+Line 62: Do not love `++i) ... owners[2+ i]`. Makes me do math, which is not what I want to do. I want to not have to do math.
+
+There should probably be a function for adding a new operation, so the developer doesn't have to work directly with the internal data. (This would make the multisig contract even shorter.)
+
+There's a `revoke` function but not a `propose` function that we can see.
+
+Beware reordering. If `propose` allows the user to choose a bytes string for their proposal, bad things(TM) will happen as currently written.
+
+
+### Multisig
+
+Just an interface. Note it allows changing an owner address, but not changing the number of owners. This is somewhat limiting but also simplifies implementation.
+
+## Payment
+
+### PullPayment
+
+Safe from reentrance attack since ether send is at the end, plus it uses `.send()` rather than `.call.value()`.
+
+There's an argument to be made that `.call.value()` is a better option *if* you're sure that it will be done after all state updates, since `.send` will fail if the recipient has an expensive fallback function. However, in the context of a function meant to be embedded in other contracts, it's probably better to use `.send`. One possible compromise is to add a function which allows only the owner to send ether via `.call.value`.
+
+If you don't use `call.value` you should implement a `cancel` function in case some value is pending here.
+
+Line 14:
+Doesn't use safeAdd. Although it appears that payout amounts can only be increased, in fact the payer could lower the payout as much as desired via overflow. Also, the payer could add a large non-overflowing amount, causing the payment to exceed the contract balance and therefore fail when withdraw is attempted.
+
+Recommendation: track the sum of non-withdrawn asyncSends, and don't allow a new one which exceeds the leftover balance. If it's ever desirable to make payments revocable, it should be done explicitly.
+
+## Tokens
+
+### ERC20
+
+Standard ERC20 interface only.
+
+There's a security hole in the standard, reported at Edcon: `approve` does not protect against race conditions and simply replaces the current value. An approved spender could wait for the owner to call `approve` again, then attempt to spend the old limit before the new limit is applied. If successful, this attacker could successfully spend the sum of both limits.
+
+This could be fixed by either (1) including the old limit as a parameter, so the update will fail if some gets spent, or (2) using the value parameter as a delta instead of replacement value.
+
+This is not fixable while adhering to the current full ERC20 standard, though it would be possible to add a "secureApprove" function. The impact isn't extreme since at least you can only be attacked by addresses you approved. Also, users could mitigate this by always setting spending limits to zero and checking for spends, before setting the new limit.
+
+Edcon slides:
+https://drive.google.com/file/d/0ByMtMw2hul0EN3NCaVFHSFdxRzA/view
+
+### ERC20Basic
+
+Simpler interface skipping the Approve function. Note this departs from ERC20 in another way: transfer throws instead of returning false.
+
+### BasicToken
+
+Uses `SafeSub` and `SafeMath`, so transfer `throw`s instead of returning false. This complies with ERC20Basic but not the actual ERC20 standard.
+
+### StandardToken
+
+Implementation of full ERC20 token.
+
+Transfer() and transferFrom() use SafeMath functions, which will cause them to throw instead of returning false. Not a security issue but departs from standard.
+
+### SimpleToken
+
+Sample instantiation of StandardToken. Note that in this sample, decimals is 18 and supply only 10,000, so the supply is a small fraction of a single nominal token.
+
+### CrowdsaleToken
+
+StandardToken which mints tokens at a fixed price when sent ether.
+
+There's no provision for owner withdrawing the ether. As a sample for crowdsales it should be Ownable and allow the owner to withdraw ether, rather than stranding the ether in the contract.
+
+Note: an alternative pattern is a mint() function which is only callable from a separate crowdsale contract, so any sort of rules can be added without modifying the token itself.
+
+### VestedToken
+
+Lines 23, 27:
+Functions `transfer()` and `transferFrom()` have a modifier canTransfer which throws if not enough tokens are available. However, transfer() returns a boolean success. Inconsistent treatment of failure conditions may cause problems for other contracts using the token. (Note that transferableTokens() relies on safeSub(), so will also throw if there's insufficient balance.)
+
+Line 64:
+Delete not actually necessary since the value is overwritten in the next line anyway.
+
+## Root level
+
+### Bounty
+
+Avoids potential race condition by having each researcher deploy a separate contract for attack; if a research manages to break his associated contract, other researchers can't immediately claim the reward, they have to reproduce the attack in their own contracts.
+
+A developer could subvert this intent by implementing `deployContract()` to always return the same address. However, this would break the `researchers` mapping, updating the researcher address associated with the contract. This could be prevented by blocking rewrites in `researchers`.
+
+### DayLimit
+
+The modifier `limitedDaily` calls `underLimit`, which both checks that the spend is below the daily limit, and adds the input value to the daily spend. This is fine if all functions throw upon failure. However, not all OpenZeppelin functions do this; there are functions that returns false, and modifiers that wrap the function body in `if (bool) {_;}`. In these cases, `_value` will be added to `spentToday`, but ether may not actually be sent because other preconditions were not met. (However in the OpenZeppelin multisig this is not a problem.)
+
+Lines 4, 11:
+Comment claims that `DayLimit` is multiowned, and Shareable is imported, but DayLimit does not actually inherit from Shareable. The intent may be for child contracts to inherit from Shareable (as Multisig does); in this case the import should be removed and the comment altered.
+
+Line 46:
+Manual overflow check instead of using safeAdd. Since this is called from a function that throws upon failure anyway, there's no real downside to using safeAdd.
+
+### LimitBalance
+
+No issues.
+
+### MultisigWallet
+
+Lines 28, 76, 80:
+`kill`, `setDailyLimit`, and `resetSpentToday` only happen with multisig approval, and hashes for these actions are logged by Shareable. However, they should probably post their own events for easy reading.
+
+Line 45:
+This call to underLimit will reduce the daily limit, and then either throw or return 0. So in this case there's no danger that the limit will be reduced without the operation going through.
+
+Line 65:
+Shareable's onlyManyOwners will take the user's confirmation, and execute the function body if and only if enough users have confirmed. Whole thing throws if the send fails, which will roll back the confirmation. Confirm returns false if not enough have confirmed yet, true if the whole thing succeeds, and throws only in the exceptional circumstance that the designated transaction unexpectedly fails. Elegant design.
+
+Line 68:
+Throw here is good but note this function can fail either by returning false or by throwing.
+
+Line 92:
+A bit odd to split `clearPending()` between this contract and Shareable. However this does allow contracts inheriting from Shareable to use custom structs for pending transactions.
+
+
+### SafeMath
+
+Another interesting comment from the same Edcon presentation was that the overflow behavior of Solidity is undocumented, so in theory, source code that relies on it could break with a future revision.
+
+However, compiled code should be fine, and in the unlikely event that the compiler is revised in this way, there should be plenty of warning. (But this is an argument for keeping overflow checks isolated in SafeMath.)
+
+Aside from that small caveat, these are fine.
+

contracts/Bounty.sol

@@ -1,58 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import './PullPayment.sol';
-import './Killable.sol';
-
-
-/*
- * Bounty
- * 
- * This bounty will pay out to a researcher if they break invariant logic of the contract.
- */
-contract Bounty is PullPayment, Killable {
-  Target target;
-  bool public claimed;
-  mapping(address => address) public researchers;
-
-  event TargetCreated(address createdAddress);
-
-  function() payable {
-    if (claimed) throw;
-  }
-
-  function createTarget() returns(Target) {
-    target = Target(deployContract());
-    researchers[target] = msg.sender;
-    TargetCreated(target);
-    return target;
-  }
-
-  function deployContract() internal returns(address);
-
-  function checkInvariant() returns(bool){
-    return target.checkInvariant();
-  }
-
-  function claim(Target target) {
-    address researcher = researchers[target];
-    if (researcher == 0) throw;
-    // Check Target contract invariants
-    if (target.checkInvariant()) {
-      throw;
-    }
-    asyncSend(researcher, this.balance);
-    claimed = true;
-  }
-
-}
-
-/*
- * Target
- * 
- * Your main contract should inherit from this class and implement the checkInvariant method. This is a function that should check everything your contract assumes to be true all the time. If this function returns false, it means your contract was broken in some way and is in an inconsistent state. This is what security researchers will try to acomplish when trying to get the bounty.
- */
-contract Target {
-  function checkInvariant() returns(bool);
-}
-

contracts/Claimable.sol

@@ -1,29 +0,0 @@
-pragma solidity ^0.4.0;
-
-
-import './Ownable.sol';
-
-
-/*
- * Claimable
- *
- * Extension for the Ownable contract, where the ownership needs to be claimed. This allows the new owner to accept the transfer.
- */
-contract Claimable is Ownable {
-  address public pendingOwner;
-
-  modifier onlyPendingOwner() {
-    if (msg.sender == pendingOwner)
-      _;
-  }
-
-  function transferOwnership(address newOwner) onlyOwner {
-    pendingOwner = newOwner;
-  }
-
-  function claimOwnership() onlyPendingOwner {
-    owner = pendingOwner;
-    pendingOwner = 0x0;
-  }
-
-}

contracts/DayLimit.sol

@@ -1,75 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import './Shareable.sol';
-
-
-/*
- * DayLimit
- *
- * inheritable "property" contract that enables methods to be protected by placing a linear limit (specifiable)
- * on a particular resource per calendar day. is multiowned to allow the limit to be altered. resource that method
- * uses is specified in the modifier.
- */
-contract DayLimit {
-  // FIELDS
-
-  uint public dailyLimit;
-  uint public spentToday;
-  uint public lastDay;
-
-
-  // MODIFIERS
-
-  // simple modifier for daily limit.
-  modifier limitedDaily(uint _value) {
-    if (underLimit(_value))
-      _;
-  }
-
-
-  // CONSTRUCTOR
-  // stores initial daily limit and records the present day's index.
-  function DayLimit(uint _limit) {
-    dailyLimit = _limit;
-    lastDay = today();
-  }
-
-
-  // METHODS
-
-  // (re)sets the daily limit. doesn't alter the amount already spent today.
-  function _setDailyLimit(uint _newLimit) internal {
-    dailyLimit = _newLimit;
-  }
-
-  // resets the amount already spent today.
-  function _resetSpentToday() internal {
-    spentToday = 0;
-  }
-
-
-  // INTERNAL METHODS
-
-  // checks to see if there is at least `_value` left from the daily limit today. if there is, subtracts it and
-  // returns true. otherwise just returns false.
-  function underLimit(uint _value) internal returns (bool) {
-    // reset the spend limit if we're on a different day to last time.
-    if (today() > lastDay) {
-      spentToday = 0;
-      lastDay = today();
-    }
-    // check to see if there's enough left - if so, subtract and return true.
-    // overflow protection                    // dailyLimit check
-    if (spentToday + _value >= spentToday && spentToday + _value <= dailyLimit) {
-      spentToday += _value;
-      return true;
-    }
-    return false;
-  }
-
-  // determines today's index.
-  function today() private constant returns (uint) {
-    return now / 1 days;
-  }
-}

contracts/DelayedClaimable.sol

@@ -1,30 +0,0 @@
-pragma solidity ^0.4.4;
-import './Ownable.sol';
-import './Claimable.sol';
-
-/*
- * DelayedClaimable
- * Extension for the Claimable contract, where the ownership needs to be claimed before/after certain block number
- */
-
-contract DelayedClaimable is Ownable, Claimable {
-
-  uint public claimBeforeBlock;
-  uint public claimAfterBlock;
-
-  function setClaimBlocks(uint _claimBeforeBlock, uint _claimAfterBlock) onlyOwner {
-    if (_claimAfterBlock > claimBeforeBlock)
-        throw;
-    claimBeforeBlock = _claimBeforeBlock;
-    claimAfterBlock = _claimAfterBlock;
-  }
-
-  function claimOwnership() onlyPendingOwner {
-    if ((block.number > claimBeforeBlock) || (block.number < claimAfterBlock))
-        throw;
-    owner = pendingOwner;
-    pendingOwner = 0x0;
-    claimBeforeBlock = 0;
-  }
-
-}

contracts/GSN/Context.sol

@@ -0,0 +1,26 @@
+pragma solidity ^0.6.0;
+
+/*
+ * @dev Provides information about the current execution context, including the
+ * sender of the transaction and its data. While these are generally available
+ * via msg.sender and msg.data, they should not be accessed in such a direct
+ * manner, since when dealing with GSN meta-transactions the account sending and
+ * paying for execution may not be the actual sender (as far as an application
+ * is concerned).
+ *
+ * This contract is only required for intermediate, library-like contracts.
+ */
+contract Context {
+    // Empty internal constructor, to prevent people from mistakenly deploying
+    // an instance of this contract, which should be used via inheritance.
+    constructor () internal { }
+
+    function _msgSender() internal view virtual returns (address payable) {
+        return msg.sender;
+    }
+
+    function _msgData() internal view virtual returns (bytes memory) {
+        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
+        return msg.data;
+    }
+}

contracts/GSN/GSNRecipient.sol

@@ -0,0 +1,228 @@
+pragma solidity ^0.6.0;
+
+import "./IRelayRecipient.sol";
+import "./IRelayHub.sol";
+import "./Context.sol";
+
+/**
+ * @dev Base GSN recipient contract: includes the {IRelayRecipient} interface
+ * and enables GSN support on all contracts in the inheritance tree.
+ *
+ * TIP: This contract is abstract. The functions {IRelayRecipient-acceptRelayedCall},
+ *  {_preRelayedCall}, and {_postRelayedCall} are not implemented and must be
+ * provided by derived contracts. See the
+ * xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategies] for more
+ * information on how to use the pre-built {GSNRecipientSignature} and
+ * {GSNRecipientERC20Fee}, or how to write your own.
+ */
+abstract contract GSNRecipient is IRelayRecipient, Context {
+    // Default RelayHub address, deployed on mainnet and all testnets at the same address
+    address private _relayHub = 0xD216153c06E857cD7f72665E0aF1d7D82172F494;
+
+    uint256 constant private _RELAYED_CALL_ACCEPTED = 0;
+    uint256 constant private _RELAYED_CALL_REJECTED = 11;
+
+    // How much gas is forwarded to postRelayedCall
+    uint256 constant internal _POST_RELAYED_CALL_MAX_GAS = 100000;
+
+    /**
+     * @dev Emitted when a contract changes its {IRelayHub} contract to a new one.
+     */
+    event RelayHubChanged(address indexed oldRelayHub, address indexed newRelayHub);
+
+    /**
+     * @dev Returns the address of the {IRelayHub} contract for this recipient.
+     */
+    function getHubAddr() public view override returns (address) {
+        return _relayHub;
+    }
+
+    /**
+     * @dev Switches to a new {IRelayHub} instance. This method is added for future-proofing: there's no reason to not
+     * use the default instance.
+     *
+     * IMPORTANT: After upgrading, the {GSNRecipient} will no longer be able to receive relayed calls from the old
+     * {IRelayHub} instance. Additionally, all funds should be previously withdrawn via {_withdrawDeposits}.
+     */
+    function _upgradeRelayHub(address newRelayHub) internal virtual {
+        address currentRelayHub = _relayHub;
+        require(newRelayHub != address(0), "GSNRecipient: new RelayHub is the zero address");
+        require(newRelayHub != currentRelayHub, "GSNRecipient: new RelayHub is the current one");
+
+        emit RelayHubChanged(currentRelayHub, newRelayHub);
+
+        _relayHub = newRelayHub;
+    }
+
+    /**
+     * @dev Returns the version string of the {IRelayHub} for which this recipient implementation was built. If
+     * {_upgradeRelayHub} is used, the new {IRelayHub} instance should be compatible with this version.
+     */
+    // This function is view for future-proofing, it may require reading from
+    // storage in the future.
+    function relayHubVersion() public view returns (string memory) {
+        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
+        return "1.0.0";
+    }
+
+    /**
+     * @dev Withdraws the recipient's deposits in `RelayHub`.
+     *
+     * Derived contracts should expose this in an external interface with proper access control.
+     */
+    function _withdrawDeposits(uint256 amount, address payable payee) internal virtual {
+        IRelayHub(_relayHub).withdraw(amount, payee);
+    }
+
+    // Overrides for Context's functions: when called from RelayHub, sender and
+    // data require some pre-processing: the actual sender is stored at the end
+    // of the call data, which in turns means it needs to be removed from it
+    // when handling said data.
+
+    /**
+     * @dev Replacement for msg.sender. Returns the actual sender of a transaction: msg.sender for regular transactions,
+     * and the end-user for GSN relayed calls (where msg.sender is actually `RelayHub`).
+     *
+     * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.sender`, and use {_msgSender} instead.
+     */
+    function _msgSender() internal view virtual override returns (address payable) {
+        if (msg.sender != _relayHub) {
+            return msg.sender;
+        } else {
+            return _getRelayedCallSender();
+        }
+    }
+
+    /**
+     * @dev Replacement for msg.data. Returns the actual calldata of a transaction: msg.data for regular transactions,
+     * and a reduced version for GSN relayed calls (where msg.data contains additional information).
+     *
+     * IMPORTANT: Contracts derived from {GSNRecipient} should never use `msg.data`, and use {_msgData} instead.
+     */
+    function _msgData() internal view virtual override returns (bytes memory) {
+        if (msg.sender != _relayHub) {
+            return msg.data;
+        } else {
+            return _getRelayedCallData();
+        }
+    }
+
+    // Base implementations for pre and post relayedCall: only RelayHub can invoke them, and data is forwarded to the
+    // internal hook.
+
+    /**
+     * @dev See `IRelayRecipient.preRelayedCall`.
+     *
+     * This function should not be overriden directly, use `_preRelayedCall` instead.
+     *
+     * * Requirements:
+     *
+     * - the caller must be the `RelayHub` contract.
+     */
+    function preRelayedCall(bytes memory context) public virtual override returns (bytes32) {
+        require(msg.sender == getHubAddr(), "GSNRecipient: caller is not RelayHub");
+        return _preRelayedCall(context);
+    }
+
+    /**
+     * @dev See `IRelayRecipient.preRelayedCall`.
+     *
+     * Called by `GSNRecipient.preRelayedCall`, which asserts the caller is the `RelayHub` contract. Derived contracts
+     * must implement this function with any relayed-call preprocessing they may wish to do.
+     *
+     */
+    function _preRelayedCall(bytes memory context) internal virtual returns (bytes32);
+
+    /**
+     * @dev See `IRelayRecipient.postRelayedCall`.
+     *
+     * This function should not be overriden directly, use `_postRelayedCall` instead.
+     *
+     * * Requirements:
+     *
+     * - the caller must be the `RelayHub` contract.
+     */
+    function postRelayedCall(bytes memory context, bool success, uint256 actualCharge, bytes32 preRetVal) public virtual override {
+        require(msg.sender == getHubAddr(), "GSNRecipient: caller is not RelayHub");
+        _postRelayedCall(context, success, actualCharge, preRetVal);
+    }
+
+    /**
+     * @dev See `IRelayRecipient.postRelayedCall`.
+     *
+     * Called by `GSNRecipient.postRelayedCall`, which asserts the caller is the `RelayHub` contract. Derived contracts
+     * must implement this function with any relayed-call postprocessing they may wish to do.
+     *
+     */
+    function _postRelayedCall(bytes memory context, bool success, uint256 actualCharge, bytes32 preRetVal) internal virtual;
+
+    /**
+     * @dev Return this in acceptRelayedCall to proceed with the execution of a relayed call. Note that this contract
+     * will be charged a fee by RelayHub
+     */
+    function _approveRelayedCall() internal pure returns (uint256, bytes memory) {
+        return _approveRelayedCall("");
+    }
+
+    /**
+     * @dev See `GSNRecipient._approveRelayedCall`.
+     *
+     * This overload forwards `context` to _preRelayedCall and _postRelayedCall.
+     */
+    function _approveRelayedCall(bytes memory context) internal pure returns (uint256, bytes memory) {
+        return (_RELAYED_CALL_ACCEPTED, context);
+    }
+
+    /**
+     * @dev Return this in acceptRelayedCall to impede execution of a relayed call. No fees will be charged.
+     */
+    function _rejectRelayedCall(uint256 errorCode) internal pure returns (uint256, bytes memory) {
+        return (_RELAYED_CALL_REJECTED + errorCode, "");
+    }
+
+    /*
+     * @dev Calculates how much RelayHub will charge a recipient for using `gas` at a `gasPrice`, given a relayer's
+     * `serviceFee`.
+     */
+    function _computeCharge(uint256 gas, uint256 gasPrice, uint256 serviceFee) internal pure returns (uint256) {
+        // The fee is expressed as a percentage. E.g. a value of 40 stands for a 40% fee, so the recipient will be
+        // charged for 1.4 times the spent amount.
+        return (gas * gasPrice * (100 + serviceFee)) / 100;
+    }
+
+    function _getRelayedCallSender() private pure returns (address payable result) {
+        // We need to read 20 bytes (an address) located at array index msg.data.length - 20. In memory, the array
+        // is prefixed with a 32-byte length value, so we first add 32 to get the memory read index. However, doing
+        // so would leave the address in the upper 20 bytes of the 32-byte word, which is inconvenient and would
+        // require bit shifting. We therefore subtract 12 from the read index so the address lands on the lower 20
+        // bytes. This can always be done due to the 32-byte prefix.
+
+        // The final memory read index is msg.data.length - 20 + 32 - 12 = msg.data.length. Using inline assembly is the
+        // easiest/most-efficient way to perform this operation.
+
+        // These fields are not accessible from assembly
+        bytes memory array = msg.data;
+        uint256 index = msg.data.length;
+
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            // Load the 32 bytes word from memory with the address on the lower 20 bytes, and mask those.
+            result := and(mload(add(array, index)), 0xffffffffffffffffffffffffffffffffffffffff)
+        }
+        return result;
+    }
+
+    function _getRelayedCallData() private pure returns (bytes memory) {
+        // RelayHub appends the sender address at the end of the calldata, so in order to retrieve the actual msg.data,
+        // we must strip the last 20 bytes (length of an address type) from it.
+
+        uint256 actualDataLength = msg.data.length - 20;
+        bytes memory actualData = new bytes(actualDataLength);
+
+        for (uint256 i = 0; i < actualDataLength; ++i) {
+            actualData[i] = msg.data[i];
+        }
+
+        return actualData;
+    }
+}

contracts/GSN/GSNRecipientERC20Fee.sol

@@ -0,0 +1,150 @@
+pragma solidity ^0.6.0;
+
+import "./GSNRecipient.sol";
+import "../math/SafeMath.sol";
+import "../access/Ownable.sol";
+import "../token/ERC20/SafeERC20.sol";
+import "../token/ERC20/ERC20.sol";
+
+/**
+ * @dev A xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategy] that charges transaction fees in a special purpose ERC20
+ * token, which we refer to as the gas payment token. The amount charged is exactly the amount of Ether charged to the
+ * recipient. This means that the token is essentially pegged to the value of Ether.
+ *
+ * The distribution strategy of the gas payment token to users is not defined by this contract. It's a mintable token
+ * whose only minter is the recipient, so the strategy must be implemented in a derived contract, making use of the
+ * internal {_mint} function.
+ */
+contract GSNRecipientERC20Fee is GSNRecipient {
+    using SafeERC20 for __unstable__ERC20Owned;
+    using SafeMath for uint256;
+
+    enum GSNRecipientERC20FeeErrorCodes {
+        INSUFFICIENT_BALANCE
+    }
+
+    __unstable__ERC20Owned private _token;
+
+    /**
+     * @dev The arguments to the constructor are the details that the gas payment token will have: `name` and `symbol`. `decimals` is hard-coded to 18.
+     */
+    constructor(string memory name, string memory symbol) public {
+        _token = new __unstable__ERC20Owned(name, symbol);
+    }
+
+    /**
+     * @dev Returns the gas payment token.
+     */
+    function token() public view returns (IERC20) {
+        return IERC20(_token);
+    }
+
+    /**
+     * @dev Internal function that mints the gas payment token. Derived contracts should expose this function in their public API, with proper access control mechanisms.
+     */
+    function _mint(address account, uint256 amount) internal virtual {
+        _token.mint(account, amount);
+    }
+
+    /**
+     * @dev Ensures that only users with enough gas payment token balance can have transactions relayed through the GSN.
+     */
+    function acceptRelayedCall(
+        address,
+        address from,
+        bytes memory,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256,
+        uint256,
+        bytes memory,
+        uint256 maxPossibleCharge
+    )
+        public
+        view
+        virtual
+        override
+        returns (uint256, bytes memory)
+    {
+        if (_token.balanceOf(from) < maxPossibleCharge) {
+            return _rejectRelayedCall(uint256(GSNRecipientERC20FeeErrorCodes.INSUFFICIENT_BALANCE));
+        }
+
+        return _approveRelayedCall(abi.encode(from, maxPossibleCharge, transactionFee, gasPrice));
+    }
+
+    /**
+     * @dev Implements the precharge to the user. The maximum possible charge (depending on gas limit, gas price, and
+     * fee) will be deducted from the user balance of gas payment token. Note that this is an overestimation of the
+     * actual charge, necessary because we cannot predict how much gas the execution will actually need. The remainder
+     * is returned to the user in {_postRelayedCall}.
+     */
+    function _preRelayedCall(bytes memory context) internal virtual override returns (bytes32) {
+        (address from, uint256 maxPossibleCharge) = abi.decode(context, (address, uint256));
+
+        // The maximum token charge is pre-charged from the user
+        _token.safeTransferFrom(from, address(this), maxPossibleCharge);
+    }
+
+    /**
+     * @dev Returns to the user the extra amount that was previously charged, once the actual execution cost is known.
+     */
+    function _postRelayedCall(bytes memory context, bool, uint256 actualCharge, bytes32) internal virtual override {
+        (address from, uint256 maxPossibleCharge, uint256 transactionFee, uint256 gasPrice) =
+            abi.decode(context, (address, uint256, uint256, uint256));
+
+        // actualCharge is an _estimated_ charge, which assumes postRelayedCall will use all available gas.
+        // This implementation's gas cost can be roughly estimated as 10k gas, for the two SSTORE operations in an
+        // ERC20 transfer.
+        uint256 overestimation = _computeCharge(_POST_RELAYED_CALL_MAX_GAS.sub(10000), gasPrice, transactionFee);
+        actualCharge = actualCharge.sub(overestimation);
+
+        // After the relayed call has been executed and the actual charge estimated, the excess pre-charge is returned
+        _token.safeTransfer(from, maxPossibleCharge.sub(actualCharge));
+    }
+}
+
+/**
+ * @title __unstable__ERC20Owned
+ * @dev An ERC20 token owned by another contract, which has minting permissions and can use transferFrom to receive
+ * anyone's tokens. This contract is an internal helper for GSNRecipientERC20Fee, and should not be used
+ * outside of this context.
+ */
+// solhint-disable-next-line contract-name-camelcase
+contract __unstable__ERC20Owned is ERC20, Ownable {
+    uint256 private constant _UINT256_MAX = 2**256 - 1;
+
+    constructor(string memory name, string memory symbol) public ERC20(name, symbol) { }
+
+    // The owner (GSNRecipientERC20Fee) can mint tokens
+    function mint(address account, uint256 amount) public onlyOwner {
+        _mint(account, amount);
+    }
+
+    // The owner has 'infinite' allowance for all token holders
+    function allowance(address tokenOwner, address spender) public view override returns (uint256) {
+        if (spender == owner()) {
+            return _UINT256_MAX;
+        } else {
+            return super.allowance(tokenOwner, spender);
+        }
+    }
+
+    // Allowance for the owner cannot be changed (it is always 'infinite')
+    function _approve(address tokenOwner, address spender, uint256 value) internal override {
+        if (spender == owner()) {
+            return;
+        } else {
+            super._approve(tokenOwner, spender, value);
+        }
+    }
+
+    function transferFrom(address sender, address recipient, uint256 amount) public override returns (bool) {
+        if (recipient == owner()) {
+            _transfer(sender, recipient, amount);
+            return true;
+        } else {
+            return super.transferFrom(sender, recipient, amount);
+        }
+    }
+}

contracts/GSN/GSNRecipientSignature.sol

@@ -0,0 +1,70 @@
+pragma solidity ^0.6.0;
+
+import "./GSNRecipient.sol";
+import "../cryptography/ECDSA.sol";
+
+/**
+ * @dev A xref:ROOT:gsn-strategies.adoc#gsn-strategies[GSN strategy] that allows relayed transactions through when they are
+ * accompanied by the signature of a trusted signer. The intent is for this signature to be generated by a server that
+ * performs validations off-chain. Note that nothing is charged to the user in this scheme. Thus, the server should make
+ * sure to account for this in their economic and threat model.
+ */
+contract GSNRecipientSignature is GSNRecipient {
+    using ECDSA for bytes32;
+
+    address private _trustedSigner;
+
+    enum GSNRecipientSignatureErrorCodes {
+        INVALID_SIGNER
+    }
+
+    /**
+     * @dev Sets the trusted signer that is going to be producing signatures to approve relayed calls.
+     */
+    constructor(address trustedSigner) public {
+        require(trustedSigner != address(0), "GSNRecipientSignature: trusted signer is the zero address");
+        _trustedSigner = trustedSigner;
+    }
+
+    /**
+     * @dev Ensures that only transactions with a trusted signature can be relayed through the GSN.
+     */
+    function acceptRelayedCall(
+        address relay,
+        address from,
+        bytes memory encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes memory approvalData,
+        uint256
+    )
+        public
+        view
+        virtual
+        override
+        returns (uint256, bytes memory)
+    {
+        bytes memory blob = abi.encodePacked(
+            relay,
+            from,
+            encodedFunction,
+            transactionFee,
+            gasPrice,
+            gasLimit,
+            nonce, // Prevents replays on RelayHub
+            getHubAddr(), // Prevents replays in multiple RelayHubs
+            address(this) // Prevents replays in multiple recipients
+        );
+        if (keccak256(blob).toEthSignedMessageHash().recover(approvalData) == _trustedSigner) {
+            return _approveRelayedCall();
+        } else {
+            return _rejectRelayedCall(uint256(GSNRecipientSignatureErrorCodes.INVALID_SIGNER));
+        }
+    }
+
+    function _preRelayedCall(bytes memory) internal virtual override returns (bytes32) { }
+
+    function _postRelayedCall(bytes memory, bool, uint256, bytes32) internal virtual override { }
+}

contracts/GSN/IRelayHub.sol

@@ -0,0 +1,267 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Interface for `RelayHub`, the core contract of the GSN. Users should not need to interact with this contract
+ * directly.
+ *
+ * See the https://github.com/OpenZeppelin/openzeppelin-gsn-helpers[OpenZeppelin GSN helpers] for more information on
+ * how to deploy an instance of `RelayHub` on your local test network.
+ */
+interface IRelayHub {
+    // Relay management
+
+    /**
+     * @dev Adds stake to a relay and sets its `unstakeDelay`. If the relay does not exist, it is created, and the caller
+     * of this function becomes its owner. If the relay already exists, only the owner can call this function. A relay
+     * cannot be its own owner.
+     *
+     * All Ether in this function call will be added to the relay's stake.
+     * Its unstake delay will be assigned to `unstakeDelay`, but the new value must be greater or equal to the current one.
+     *
+     * Emits a {Staked} event.
+     */
+    function stake(address relayaddr, uint256 unstakeDelay) external payable;
+
+    /**
+     * @dev Emitted when a relay's stake or unstakeDelay are increased
+     */
+    event Staked(address indexed relay, uint256 stake, uint256 unstakeDelay);
+
+    /**
+     * @dev Registers the caller as a relay.
+     * The relay must be staked for, and not be a contract (i.e. this function must be called directly from an EOA).
+     *
+     * This function can be called multiple times, emitting new {RelayAdded} events. Note that the received
+     * `transactionFee` is not enforced by {relayCall}.
+     *
+     * Emits a {RelayAdded} event.
+     */
+    function registerRelay(uint256 transactionFee, string calldata url) external;
+
+    /**
+     * @dev Emitted when a relay is registered or re-registerd. Looking at these events (and filtering out
+     * {RelayRemoved} events) lets a client discover the list of available relays.
+     */
+    event RelayAdded(address indexed relay, address indexed owner, uint256 transactionFee, uint256 stake, uint256 unstakeDelay, string url);
+
+    /**
+     * @dev Removes (deregisters) a relay. Unregistered (but staked for) relays can also be removed.
+     *
+     * Can only be called by the owner of the relay. After the relay's `unstakeDelay` has elapsed, {unstake} will be
+     * callable.
+     *
+     * Emits a {RelayRemoved} event.
+     */
+    function removeRelayByOwner(address relay) external;
+
+    /**
+     * @dev Emitted when a relay is removed (deregistered). `unstakeTime` is the time when unstake will be callable.
+     */
+    event RelayRemoved(address indexed relay, uint256 unstakeTime);
+
+    /** Deletes the relay from the system, and gives back its stake to the owner.
+     *
+     * Can only be called by the relay owner, after `unstakeDelay` has elapsed since {removeRelayByOwner} was called.
+     *
+     * Emits an {Unstaked} event.
+     */
+    function unstake(address relay) external;
+
+    /**
+     * @dev Emitted when a relay is unstaked for, including the returned stake.
+     */
+    event Unstaked(address indexed relay, uint256 stake);
+
+    // States a relay can be in
+    enum RelayState {
+        Unknown, // The relay is unknown to the system: it has never been staked for
+        Staked, // The relay has been staked for, but it is not yet active
+        Registered, // The relay has registered itself, and is active (can relay calls)
+        Removed    // The relay has been removed by its owner and can no longer relay calls. It must wait for its unstakeDelay to elapse before it can unstake
+    }
+
+    /**
+     * @dev Returns a relay's status. Note that relays can be deleted when unstaked or penalized, causing this function
+     * to return an empty entry.
+     */
+    function getRelay(address relay) external view returns (uint256 totalStake, uint256 unstakeDelay, uint256 unstakeTime, address payable owner, RelayState state);
+
+    // Balance management
+
+    /**
+     * @dev Deposits Ether for a contract, so that it can receive (and pay for) relayed transactions.
+     *
+     * Unused balance can only be withdrawn by the contract itself, by calling {withdraw}.
+     *
+     * Emits a {Deposited} event.
+     */
+    function depositFor(address target) external payable;
+
+    /**
+     * @dev Emitted when {depositFor} is called, including the amount and account that was funded.
+     */
+    event Deposited(address indexed recipient, address indexed from, uint256 amount);
+
+    /**
+     * @dev Returns an account's deposits. These can be either a contracts's funds, or a relay owner's revenue.
+     */
+    function balanceOf(address target) external view returns (uint256);
+
+    /**
+     * Withdraws from an account's balance, sending it back to it. Relay owners call this to retrieve their revenue, and
+     * contracts can use it to reduce their funding.
+     *
+     * Emits a {Withdrawn} event.
+     */
+    function withdraw(uint256 amount, address payable dest) external;
+
+    /**
+     * @dev Emitted when an account withdraws funds from `RelayHub`.
+     */
+    event Withdrawn(address indexed account, address indexed dest, uint256 amount);
+
+    // Relaying
+
+    /**
+     * @dev Checks if the `RelayHub` will accept a relayed operation.
+     * Multiple things must be true for this to happen:
+     *  - all arguments must be signed for by the sender (`from`)
+     *  - the sender's nonce must be the current one
+     *  - the recipient must accept this transaction (via {acceptRelayedCall})
+     *
+     * Returns a `PreconditionCheck` value (`OK` when the transaction can be relayed), or a recipient-specific error
+     * code if it returns one in {acceptRelayedCall}.
+     */
+    function canRelay(
+        address relay,
+        address from,
+        address to,
+        bytes calldata encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes calldata signature,
+        bytes calldata approvalData
+    ) external view returns (uint256 status, bytes memory recipientContext);
+
+    // Preconditions for relaying, checked by canRelay and returned as the corresponding numeric values.
+    enum PreconditionCheck {
+        OK,                         // All checks passed, the call can be relayed
+        WrongSignature,             // The transaction to relay is not signed by requested sender
+        WrongNonce,                 // The provided nonce has already been used by the sender
+        AcceptRelayedCallReverted,  // The recipient rejected this call via acceptRelayedCall
+        InvalidRecipientStatusCode  // The recipient returned an invalid (reserved) status code
+    }
+
+    /**
+     * @dev Relays a transaction.
+     *
+     * For this to succeed, multiple conditions must be met:
+     *  - {canRelay} must `return PreconditionCheck.OK`
+     *  - the sender must be a registered relay
+     *  - the transaction's gas price must be larger or equal to the one that was requested by the sender
+     *  - the transaction must have enough gas to not run out of gas if all internal transactions (calls to the
+     * recipient) use all gas available to them
+     *  - the recipient must have enough balance to pay the relay for the worst-case scenario (i.e. when all gas is
+     * spent)
+     *
+     * If all conditions are met, the call will be relayed and the recipient charged. {preRelayedCall}, the encoded
+     * function and {postRelayedCall} will be called in that order.
+     *
+     * Parameters:
+     *  - `from`: the client originating the request
+     *  - `to`: the target {IRelayRecipient} contract
+     *  - `encodedFunction`: the function call to relay, including data
+     *  - `transactionFee`: fee (%) the relay takes over actual gas cost
+     *  - `gasPrice`: gas price the client is willing to pay
+     *  - `gasLimit`: gas to forward when calling the encoded function
+     *  - `nonce`: client's nonce
+     *  - `signature`: client's signature over all previous params, plus the relay and RelayHub addresses
+     *  - `approvalData`: dapp-specific data forwared to {acceptRelayedCall}. This value is *not* verified by the
+     * `RelayHub`, but it still can be used for e.g. a signature.
+     *
+     * Emits a {TransactionRelayed} event.
+     */
+    function relayCall(
+        address from,
+        address to,
+        bytes calldata encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes calldata signature,
+        bytes calldata approvalData
+    ) external;
+
+    /**
+     * @dev Emitted when an attempt to relay a call failed.
+     *
+     * This can happen due to incorrect {relayCall} arguments, or the recipient not accepting the relayed call. The
+     * actual relayed call was not executed, and the recipient not charged.
+     *
+     * The `reason` parameter contains an error code: values 1-10 correspond to `PreconditionCheck` entries, and values
+     * over 10 are custom recipient error codes returned from {acceptRelayedCall}.
+     */
+    event CanRelayFailed(address indexed relay, address indexed from, address indexed to, bytes4 selector, uint256 reason);
+
+    /**
+     * @dev Emitted when a transaction is relayed.
+     * Useful when monitoring a relay's operation and relayed calls to a contract
+     *
+     * Note that the actual encoded function might be reverted: this is indicated in the `status` parameter.
+     *
+     * `charge` is the Ether value deducted from the recipient's balance, paid to the relay's owner.
+     */
+    event TransactionRelayed(address indexed relay, address indexed from, address indexed to, bytes4 selector, RelayCallStatus status, uint256 charge);
+
+    // Reason error codes for the TransactionRelayed event
+    enum RelayCallStatus {
+        OK,                      // The transaction was successfully relayed and execution successful - never included in the event
+        RelayedCallFailed,       // The transaction was relayed, but the relayed call failed
+        PreRelayedFailed,        // The transaction was not relayed due to preRelatedCall reverting
+        PostRelayedFailed,       // The transaction was relayed and reverted due to postRelatedCall reverting
+        RecipientBalanceChanged  // The transaction was relayed and reverted due to the recipient's balance changing
+    }
+
+    /**
+     * @dev Returns how much gas should be forwarded to a call to {relayCall}, in order to relay a transaction that will
+     * spend up to `relayedCallStipend` gas.
+     */
+    function requiredGas(uint256 relayedCallStipend) external view returns (uint256);
+
+    /**
+     * @dev Returns the maximum recipient charge, given the amount of gas forwarded, gas price and relay fee.
+     */
+    function maxPossibleCharge(uint256 relayedCallStipend, uint256 gasPrice, uint256 transactionFee) external view returns (uint256);
+
+     // Relay penalization.
+     // Any account can penalize relays, removing them from the system immediately, and rewarding the
+    // reporter with half of the relay's stake. The other half is burned so that, even if the relay penalizes itself, it
+    // still loses half of its stake.
+
+    /**
+     * @dev Penalize a relay that signed two transactions using the same nonce (making only the first one valid) and
+     * different data (gas price, gas limit, etc. may be different).
+     *
+     * The (unsigned) transaction data and signature for both transactions must be provided.
+     */
+    function penalizeRepeatedNonce(bytes calldata unsignedTx1, bytes calldata signature1, bytes calldata unsignedTx2, bytes calldata signature2) external;
+
+    /**
+     * @dev Penalize a relay that sent a transaction that didn't target `RelayHub`'s {registerRelay} or {relayCall}.
+     */
+    function penalizeIllegalTransaction(bytes calldata unsignedTx, bytes calldata signature) external;
+
+    /**
+     * @dev Emitted when a relay is penalized.
+     */
+    event Penalized(address indexed relay, address sender, uint256 amount);
+
+    /**
+     * @dev Returns an account's nonce in `RelayHub`.
+     */
+    function getNonce(address from) external view returns (uint256);
+}
+

contracts/GSN/IRelayRecipient.sol

@@ -0,0 +1,74 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Base interface for a contract that will be called via the GSN from {IRelayHub}.
+ *
+ * TIP: You don't need to write an implementation yourself! Inherit from {GSNRecipient} instead.
+ */
+interface IRelayRecipient {
+    /**
+     * @dev Returns the address of the {IRelayHub} instance this recipient interacts with.
+     */
+    function getHubAddr() external view returns (address);
+
+    /**
+     * @dev Called by {IRelayHub} to validate if this recipient accepts being charged for a relayed call. Note that the
+     * recipient will be charged regardless of the execution result of the relayed call (i.e. if it reverts or not).
+     *
+     * The relay request was originated by `from` and will be served by `relay`. `encodedFunction` is the relayed call
+     * calldata, so its first four bytes are the function selector. The relayed call will be forwarded `gasLimit` gas,
+     * and the transaction executed with a gas price of at least `gasPrice`. `relay`'s fee is `transactionFee`, and the
+     * recipient will be charged at most `maxPossibleCharge` (in wei). `nonce` is the sender's (`from`) nonce for
+     * replay attack protection in {IRelayHub}, and `approvalData` is a optional parameter that can be used to hold a signature
+     * over all or some of the previous values.
+     *
+     * Returns a tuple, where the first value is used to indicate approval (0) or rejection (custom non-zero error code,
+     * values 1 to 10 are reserved) and the second one is data to be passed to the other {IRelayRecipient} functions.
+     *
+     * {acceptRelayedCall} is called with 50k gas: if it runs out during execution, the request will be considered
+     * rejected. A regular revert will also trigger a rejection.
+     */
+    function acceptRelayedCall(
+        address relay,
+        address from,
+        bytes calldata encodedFunction,
+        uint256 transactionFee,
+        uint256 gasPrice,
+        uint256 gasLimit,
+        uint256 nonce,
+        bytes calldata approvalData,
+        uint256 maxPossibleCharge
+    )
+        external
+        view
+        returns (uint256, bytes memory);
+
+    /**
+     * @dev Called by {IRelayHub} on approved relay call requests, before the relayed call is executed. This allows to e.g.
+     * pre-charge the sender of the transaction.
+     *
+     * `context` is the second value returned in the tuple by {acceptRelayedCall}.
+     *
+     * Returns a value to be passed to {postRelayedCall}.
+     *
+     * {preRelayedCall} is called with 100k gas: if it runs out during exection or otherwise reverts, the relayed call
+     * will not be executed, but the recipient will still be charged for the transaction's cost.
+     */
+    function preRelayedCall(bytes calldata context) external returns (bytes32);
+
+    /**
+     * @dev Called by {IRelayHub} on approved relay call requests, after the relayed call is executed. This allows to e.g.
+     * charge the user for the relayed call costs, return any overcharges from {preRelayedCall}, or perform
+     * contract-specific bookkeeping.
+     *
+     * `context` is the second value returned in the tuple by {acceptRelayedCall}. `success` is the execution status of
+     * the relayed call. `actualCharge` is an estimate of how much the recipient will be charged for the transaction,
+     * not including any gas used by {postRelayedCall} itself. `preRetVal` is {preRelayedCall}'s return value.
+     *
+     *
+     * {postRelayedCall} is called with 100k gas: if it runs out during execution or otherwise reverts, the relayed call
+     * and the call to {preRelayedCall} will be reverted retroactively, but the recipient will still be charged for the
+     * transaction's cost.
+     */
+    function postRelayedCall(bytes calldata context, bool success, uint256 actualCharge, bytes32 preRetVal) external;
+}

contracts/GSN/README.adoc

@@ -0,0 +1,30 @@
+= Gas Station Network (GSN)
+
+_Available since v2.4.0._
+
+This set of contracts provide all the tools required to make a contract callable via the https://gsn.openzeppelin.com[Gas Station Network].
+
+TIP: If you're new to the GSN, head over to our xref:learn::sending-gasless-transactions.adoc[overview of the system] and basic guide to xref:ROOT:gsn.adoc[creating a GSN-capable contract].
+
+The core contract a recipient must inherit from is {GSNRecipient}: it includes all necessary interfaces, as well as some helper methods to make interacting with the GSN easier.
+
+Utilities to make writing xref:ROOT:gsn-strategies.adoc[GSN strategies] easy are available in {GSNRecipient}, or you can simply use one of our pre-made strategies:
+
+* {GSNRecipientERC20Fee} charges the end user for gas costs in an application-specific xref:ROOT:tokens.adoc#ERC20[ERC20 token]
+* {GSNRecipientSignature} accepts all relayed calls that have been signed by a trusted third party (e.g. a private key in a backend)
+
+You can also take a look at the two contract interfaces that make up the GSN protocol: {IRelayRecipient} and {IRelayHub}, but you won't need to use those directly.
+
+== Recipient
+
+{{GSNRecipient}}
+
+== Strategies
+
+{{GSNRecipientSignature}}
+{{GSNRecipientERC20Fee}}
+
+== Protocol
+
+{{IRelayRecipient}}
+{{IRelayHub}}

contracts/Killable.sol

@@ -1,15 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import "./Ownable.sol";
-
-
-/*
- * Killable
- * Base contract that can be killed by owner. All funds in contract will be sent to the owner.
- */
-contract Killable is Ownable {
-  function kill() onlyOwner {
-    selfdestruct(owner);
-  }
-}

contracts/LimitBalance.sol

@@ -1,27 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-/**
- * LimitBalance
- * Simple contract to limit the balance of child contract.
- * Note this doesn't prevent other contracts to send funds 
- * by using selfdestruct(address);
- * See: https://github.com/ConsenSys/smart-contract-best-practices#remember-that-ether-can-be-forcibly-sent-to-an-account
- */
-contract LimitBalance {
-
-  uint public limit;
-
-  function LimitBalance(uint _limit) {
-    limit = _limit;
-  }
-
-  modifier limitedPayable() { 
-    if (this.balance > limit) {
-      throw;
-    }
-    _;
-    
-  }
-
-}

contracts/Migrations.sol

@@ -1,18 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import './Ownable.sol';
-
-
-contract Migrations is Ownable {
-  uint public lastCompletedMigration;
-
-  function setCompleted(uint completed) onlyOwner {
-    lastCompletedMigration = completed;
-  }
-
-  function upgrade(address newAddress) onlyOwner {
-    Migrations upgraded = Migrations(newAddress);
-    upgraded.setCompleted(lastCompletedMigration);
-  }
-}

contracts/Multisig.sol

@@ -1,29 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-/*
- * Multisig
- * Interface contract for multisig proxy contracts; see below for docs.
- */
-contract Multisig {
-  // EVENTS
-
-  // logged events:
-  // Funds has arrived into the wallet (record how much).
-  event Deposit(address _from, uint value);
-  // Single transaction going out of the wallet (record who signed for it, how much, and to whom it's going).
-  event SingleTransact(address owner, uint value, address to, bytes data);
-  // Multi-sig transaction going out of the wallet (record who signed for it last, the operation hash, how much, and to whom it's going).
-  event MultiTransact(address owner, bytes32 operation, uint value, address to, bytes data);
-  // Confirmation still needed for a transaction.
-  event ConfirmationNeeded(bytes32 operation, address initiator, uint value, address to, bytes data);
-
-
-  // FUNCTIONS
-
-  // TODO: document
-  function changeOwner(address _from, address _to) external;
-  function execute(address _to, uint _value, bytes _data) external returns (bytes32);
-  function confirm(bytes32 _h) returns (bool);
-}
-

contracts/MultisigWallet.sol

@@ -1,110 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import "./Multisig.sol";
-import "./Shareable.sol";
-import "./DayLimit.sol";
-
-
-/*
- * MultisigWallet
- * usage:
- * bytes32 h = Wallet(w).from(oneOwner).execute(to, value, data);
- * Wallet(w).from(anotherOwner).confirm(h);
- */
-contract MultisigWallet is Multisig, Shareable, DayLimit {
-  // TYPES
-
-  // Transaction structure to remember details of transaction lest it need be saved for a later call.
-  struct Transaction {
-    address to;
-    uint value;
-    bytes data;
-  }
-
-
-  // CONSTRUCTOR
-
-  // just pass on the owner array to the multiowned and
-  // the limit to daylimit
-  function MultisigWallet(address[] _owners, uint _required, uint _daylimit)
-    Shareable(_owners, _required)
-    DayLimit(_daylimit) { }
-
-
-  // METHODS
-
-  // kills the contract sending everything to `_to`.
-  function kill(address _to) onlymanyowners(sha3(msg.data)) external {
-    suicide(_to);
-  }
-
-  // gets called when no other function matches
-  function() payable {
-    // just being sent some cash?
-    if (msg.value > 0)
-      Deposit(msg.sender, msg.value);
-  }
-
-  // Outside-visible transact entry point. Executes transaction immediately if below daily spend limit.
-  // If not, goes into multisig process. We provide a hash on return to allow the sender to provide
-  // shortcuts for the other confirmations (allowing them to avoid replicating the _to, _value
-  // and _data arguments). They still get the option of using them if they want, anyways.
-  function execute(address _to, uint _value, bytes _data) external onlyOwner returns (bytes32 _r) {
-    // first, take the opportunity to check that we're under the daily limit.
-    if (underLimit(_value)) {
-      SingleTransact(msg.sender, _value, _to, _data);
-      // yes - just execute the call.
-      if (!_to.call.value(_value)(_data)) {
-        throw;
-      }
-      return 0;
-    }
-    // determine our operation hash.
-    _r = sha3(msg.data, block.number);
-    if (!confirm(_r) && txs[_r].to == 0) {
-      txs[_r].to = _to;
-      txs[_r].value = _value;
-      txs[_r].data = _data;
-      ConfirmationNeeded(_r, msg.sender, _value, _to, _data);
-    }
-  }
-
-  // confirm a transaction through just the hash. we use the previous transactions map, txs, in order
-  // to determine the body of the transaction from the hash provided.
-  function confirm(bytes32 _h) onlymanyowners(_h) returns (bool) {
-    if (txs[_h].to != 0) {
-      if (!txs[_h].to.call.value(txs[_h].value)(txs[_h].data)) {
-        throw;
-      }
-      MultiTransact(msg.sender, _h, txs[_h].value, txs[_h].to, txs[_h].data);
-      delete txs[_h];
-      return true;
-    }
-  }
-
-  function setDailyLimit(uint _newLimit) onlymanyowners(sha3(msg.data)) external {
-    _setDailyLimit(_newLimit);
-  }
-
-  function resetSpentToday() onlymanyowners(sha3(msg.data)) external {
-    _resetSpentToday();
-  }
-
-
-  // INTERNAL METHODS
-
-  function clearPending() internal {
-    uint length = pendingsIndex.length;
-    for (uint i = 0; i < length; ++i) {
-      delete txs[pendingsIndex[i]];
-    }
-    super.clearPending();
-  }
-
-
-  // FIELDS
-
-  // pending transactions we have at present.
-  mapping (bytes32 => Transaction) txs;
-}

contracts/Ownable.sol

@@ -1,26 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-/*
- * Ownable
- *
- * Base contract with an owner.
- * Provides onlyOwner modifier, which prevents function from running if it is called by anyone other than the owner.
- */
-contract Ownable {
-  address public owner;
-
-  function Ownable() {
-    owner = msg.sender;
-  }
-
-  modifier onlyOwner() {
-    if (msg.sender == owner)
-      _;
-  }
-
-  function transferOwnership(address newOwner) onlyOwner {
-    if (newOwner != address(0)) owner = newOwner;
-  }
-
-}

contracts/PullPayment.sol

@@ -1,30 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-/*
- * PullPayment
- * Base contract supporting async send for pull payments.
- * Inherit from this contract and use asyncSend instead of send.
- */
-contract PullPayment {
-  mapping(address => uint) public payments;
-
-  // store sent amount as credit to be pulled, called by payer
-  function asyncSend(address dest, uint amount) internal {
-    payments[dest] += amount;
-  }
-
-  // withdraw accumulated balance, called by payee
-  function withdrawPayments() {
-    address payee = msg.sender;
-    uint payment = payments[payee];
-    
-    if (payment == 0) throw;
-    if (this.balance < payment) throw;
-
-    payments[payee] = 0;
-    if (!payee.send(payment)) {
-      throw;
-    }
-  }
-}

contracts/SafeMath.sol

@@ -1,29 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-/**
- * Math operations with safety checks
- */
-contract SafeMath {
-  function safeMul(uint a, uint b) internal returns (uint) {
-    uint c = a * b;
-    assert(a == 0 || c / a == b);
-    return c;
-  }
-
-  function safeSub(uint a, uint b) internal returns (uint) {
-    assert(b <= a);
-    return a - b;
-  }
-
-  function safeAdd(uint a, uint b) internal returns (uint) {
-    uint c = a + b;
-    assert(c>=a && c>=b);
-    return c;
-  }
-
-  function assert(bool assertion) internal {
-    if (!assertion) throw;
-  }
-}
-

contracts/Shareable.sol

@@ -1,164 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-/*
- * Shareable
- *
- * Based on https://github.com/ethereum/dapp-bin/blob/master/wallet/wallet.sol
- *
- * inheritable "property" contract that enables methods to be protected by requiring the acquiescence of either a single, or, crucially, each of a number of, designated owners.
- *
- * usage:
- * use modifiers onlyowner (just own owned) or onlymanyowners(hash), whereby the same hash must be provided by some number (specified in constructor) of the set of owners (specified in the constructor) before the interior is executed.
- */
-contract Shareable {
-  // TYPES
-
-  // struct for the status of a pending operation.
-  struct PendingState {
-    uint yetNeeded;
-    uint ownersDone;
-    uint index;
-  }
-
-
-  // FIELDS
-
-  // the number of owners that must confirm the same operation before it is run.
-  uint public required;
-
-  // list of owners
-  uint[256] owners;
-  uint constant c_maxOwners = 250;
-  // index on the list of owners to allow reverse lookup
-  mapping(uint => uint) ownerIndex;
-  // the ongoing operations.
-  mapping(bytes32 => PendingState) pendings;
-  bytes32[] pendingsIndex;
-
-
-  // EVENTS
-
-  // this contract only has six types of events: it can accept a confirmation, in which case
-  // we record owner and operation (hash) alongside it.
-  event Confirmation(address owner, bytes32 operation);
-  event Revoke(address owner, bytes32 operation);
-
-
-  // MODIFIERS
-
-  // simple single-sig function modifier.
-  modifier onlyOwner {
-    if (isOwner(msg.sender))
-      _;
-  }
-
-  // multi-sig function modifier: the operation must have an intrinsic hash in order
-  // that later attempts can be realised as the same underlying operation and
-  // thus count as confirmations.
-  modifier onlymanyowners(bytes32 _operation) {
-    if (confirmAndCheck(_operation))
-      _;
-  }
-
-
-  // CONSTRUCTOR
-
-  // constructor is given number of sigs required to do protected "onlymanyowners" transactions
-  // as well as the selection of addresses capable of confirming them.
-  function Shareable(address[] _owners, uint _required) {
-    owners[1] = uint(msg.sender);
-    ownerIndex[uint(msg.sender)] = 1;
-    for (uint i = 0; i < _owners.length; ++i) {
-      owners[2 + i] = uint(_owners[i]);
-      ownerIndex[uint(_owners[i])] = 2 + i;
-    }
-    required = _required;
-  }
-
-
-  // METHODS
-
-  // Revokes a prior confirmation of the given operation
-  function revoke(bytes32 _operation) external {
-    uint index = ownerIndex[uint(msg.sender)];
-    // make sure they're an owner
-    if (index == 0) return;
-    uint ownerIndexBit = 2**index;
-    var pending = pendings[_operation];
-    if (pending.ownersDone & ownerIndexBit > 0) {
-      pending.yetNeeded++;
-      pending.ownersDone -= ownerIndexBit;
-      Revoke(msg.sender, _operation);
-    }
-  }
-
-  // Gets an owner by 0-indexed position (using numOwners as the count)
-  function getOwner(uint ownerIndex) external constant returns (address) {
-    return address(owners[ownerIndex + 1]);
-  }
-
-  function isOwner(address _addr) constant returns (bool) {
-    return ownerIndex[uint(_addr)] > 0;
-  }
-
-  function hasConfirmed(bytes32 _operation, address _owner) constant returns (bool) {
-    var pending = pendings[_operation];
-    uint index = ownerIndex[uint(_owner)];
-
-    // make sure they're an owner
-    if (index == 0) return false;
-
-    // determine the bit to set for this owner.
-    uint ownerIndexBit = 2**index;
-    return !(pending.ownersDone & ownerIndexBit == 0);
-  }
-
-  // INTERNAL METHODS
-
-  function confirmAndCheck(bytes32 _operation) internal returns (bool) {
-    // determine what index the present sender is:
-    uint index = ownerIndex[uint(msg.sender)];
-    // make sure they're an owner
-    if (index == 0) return;
-
-    var pending = pendings[_operation];
-    // if we're not yet working on this operation, switch over and reset the confirmation status.
-    if (pending.yetNeeded == 0) {
-      // reset count of confirmations needed.
-      pending.yetNeeded = required;
-      // reset which owners have confirmed (none) - set our bitmap to 0.
-      pending.ownersDone = 0;
-      pending.index = pendingsIndex.length++;
-      pendingsIndex[pending.index] = _operation;
-    }
-    // determine the bit to set for this owner.
-    uint ownerIndexBit = 2**index;
-    // make sure we (the message sender) haven't confirmed this operation previously.
-    if (pending.ownersDone & ownerIndexBit == 0) {
-      Confirmation(msg.sender, _operation);
-      // ok - check if count is enough to go ahead.
-      if (pending.yetNeeded <= 1) {
-        // enough confirmations: reset and run interior.
-        delete pendingsIndex[pendings[_operation].index];
-        delete pendings[_operation];
-        return true;
-      }
-      else
-        {
-          // not enough: record that this owner in particular confirmed.
-          pending.yetNeeded--;
-          pending.ownersDone |= ownerIndexBit;
-        }
-    }
-  }
-
-  function clearPending() internal {
-    uint length = pendingsIndex.length;
-    for (uint i = 0; i < length; ++i)
-    if (pendingsIndex[i] != 0)
-      delete pendings[pendingsIndex[i]];
-    delete pendingsIndex;
-  }
-
-}

contracts/Stoppable.sol

@@ -1,28 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import "./Ownable.sol";
-
-
-/*
- * Stoppable
- * Abstract contract that allows children to implement an
- * emergency stop mechanism.
- */
-contract Stoppable is Ownable {
-  bool public stopped;
-
-  modifier stopInEmergency { if (!stopped) _; }
-  modifier onlyInEmergency { if (stopped) _; }
-
-  // called by the owner on emergency, triggers stopped state
-  function emergencyStop() external onlyOwner {
-    stopped = true;
-  }
-
-  // called by the owner on end of emergency, returns to normal state
-  function release() external onlyOwner onlyInEmergency {
-    stopped = false;
-  }
-
-}

contracts/access/AccessControl.sol

@@ -0,0 +1,194 @@
+pragma solidity ^0.6.0;
+
+import "../utils/EnumerableSet.sol";
+import "../utils/Address.sol";
+import "../GSN/Context.sol";
+
+/**
+ * @dev Contract module that allows children to implement role-based access
+ * control mechanisms.
+ *
+ * Roles are referred to by their `bytes32` identifier. These should be exposed
+ * in the external API and be unique. The best way to achieve this is by
+ * using `public constant` hash digests:
+ *
+ * ```
+ * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
+ * ```
+ *
+ * Roles can be used to represent a set of permissions. To restrict access to a
+ * function call, use {hasRole}:
+ *
+ * ```
+ * function foo() public {
+ *     require(hasRole(MY_ROLE, _msgSender()));
+ *     ...
+ * }
+ * ```
+ *
+ * Roles can be granted and revoked dynamically via the {grantRole} and
+ * {revokeRole} functions. Each role has an associated admin role, and only
+ * accounts that have a role's admin role can call {grantRole} and {revokeRoke}.
+ *
+ * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
+ * that only accounts with this role will be able to grant or revoke other
+ * roles. More complex role relationships can be created by using
+ * {_setRoleAdmin}.
+ */
+abstract contract AccessControl is Context {
+    using EnumerableSet for EnumerableSet.AddressSet;
+    using Address for address;
+
+    struct RoleData {
+        EnumerableSet.AddressSet members;
+        bytes32 adminRole;
+    }
+
+    mapping (bytes32 => RoleData) private _roles;
+
+    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;
+
+    /**
+     * @dev Emitted when `account` is granted `role`.
+     *
+     * `sender` is the account that originated the contract call, an admin role
+     * bearer except when using {_setupRole}.
+     */
+    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);
+
+    /**
+     * @dev Emitted when `account` is revoked `role`.
+     *
+     * `sender` is the account that originated the contract call:
+     *   - if using `revokeRole`, it is the admin role bearer
+     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
+     */
+    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);
+
+    /**
+     * @dev Returns `true` if `account` has been granted `role`.
+     */
+    function hasRole(bytes32 role, address account) public view returns (bool) {
+        return _roles[role].members.contains(account);
+    }
+
+    /**
+     * @dev Returns the number of accounts that have `role`. Can be used
+     * together with {getRoleMember} to enumerate all bearers of a role.
+     */
+    function getRoleMemberCount(bytes32 role) public view returns (uint256) {
+        return _roles[role].members.length();
+    }
+
+    /**
+     * @dev Returns one of the accounts that have `role`. `index` must be a
+     * value between 0 and {getRoleMemberCount}, non-inclusive.
+     *
+     * Role bearers are not sorted in any particular way, and their ordering may
+     * change at any point.
+     *
+     * WARNING: When using {getRoleMember} and {getRoleMemberCount}, make sure
+     * you perform all queries on the same block. See the following
+     * https://forum.openzeppelin.com/t/iterating-over-elements-on-enumerableset-in-openzeppelin-contracts/2296[forum post]
+     * for more information.
+     */
+    function getRoleMember(bytes32 role, uint256 index) public view returns (address) {
+        return _roles[role].members.at(index);
+    }
+
+    /**
+     * @dev Returns the admin role that controls `role`. See {grantRole} and
+     * {revokeRole}.
+     *
+     * To change a role's admin, use {_setRoleAdmin}.
+     */
+    function getRoleAdmin(bytes32 role) public view returns (bytes32) {
+        return _roles[role].adminRole;
+    }
+
+    /**
+     * @dev Grants `role` to `account`.
+     *
+     * If `account` had not been already granted `role`, emits a {RoleGranted}
+     * event.
+     *
+     * Requirements:
+     *
+     * - the caller must have `role`'s admin role.
+     */
+    function grantRole(bytes32 role, address account) public virtual {
+        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to grant");
+
+        _grantRole(role, account);
+    }
+
+    /**
+     * @dev Revokes `role` from `account`.
+     *
+     * If `account` had been granted `role`, emits a {RoleRevoked} event.
+     *
+     * Requirements:
+     *
+     * - the caller must have `role`'s admin role.
+     */
+    function revokeRole(bytes32 role, address account) public virtual {
+        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to revoke");
+
+        _revokeRole(role, account);
+    }
+
+    /**
+     * @dev Revokes `role` from the calling account.
+     *
+     * Roles are often managed via {grantRole} and {revokeRole}: this function's
+     * purpose is to provide a mechanism for accounts to lose their privileges
+     * if they are compromised (such as when a trusted device is misplaced).
+     *
+     * If the calling account had been granted `role`, emits a {RoleRevoked}
+     * event.
+     *
+     * Requirements:
+     *
+     * - the caller must be `account`.
+     */
+    function renounceRole(bytes32 role, address account) public virtual {
+        require(account == _msgSender(), "AccessControl: can only renounce roles for self");
+
+        _revokeRole(role, account);
+    }
+
+    /**
+     * @dev Grants `role` to `account`.
+     *
+     * If `account` had not been already granted `role`, emits a {RoleGranted}
+     * event. Note that unlike {grantRole}, this function doesn't perform any
+     * checks on the calling account.
+     *
+     * Requirements:
+     *
+     * - this function can only be called from a constructor.
+     */
+    function _setupRole(bytes32 role, address account) internal virtual {
+        require(!address(this).isContract(), "AccessControl: roles cannot be setup after construction");
+        _grantRole(role, account);
+    }
+
+    /**
+     * @dev Sets `adminRole` as `role`'s admin role.
+     */
+    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
+        _roles[role].adminRole = adminRole;
+    }
+
+    function _grantRole(bytes32 role, address account) private {
+        if (_roles[role].members.add(account)) {
+            emit RoleGranted(role, account, _msgSender());
+        }
+    }
+
+    function _revokeRole(bytes32 role, address account) private {
+        if (_roles[role].members.remove(account)) {
+            emit RoleRevoked(role, account, _msgSender());
+        }
+    }
+}

contracts/access/Ownable.sol

@@ -0,0 +1,66 @@
+pragma solidity ^0.6.0;
+
+import "../GSN/Context.sol";
+/**
+ * @dev Contract module which provides a basic access control mechanism, where
+ * there is an account (an owner) that can be granted exclusive access to
+ * specific functions.
+ *
+ * By default, the owner account will be the one that deploys the contract. This
+ * can later be changed with {transferOwnership}.
+ *
+ * This module is used through inheritance. It will make available the modifier
+ * `onlyOwner`, which can be applied to your functions to restrict their use to
+ * the owner.
+ */
+contract Ownable is Context {
+    address private _owner;
+
+    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
+
+    /**
+     * @dev Initializes the contract setting the deployer as the initial owner.
+     */
+    constructor () internal {
+        address msgSender = _msgSender();
+        _owner = msgSender;
+        emit OwnershipTransferred(address(0), msgSender);
+    }
+
+    /**
+     * @dev Returns the address of the current owner.
+     */
+    function owner() public view returns (address) {
+        return _owner;
+    }
+
+    /**
+     * @dev Throws if called by any account other than the owner.
+     */
+    modifier onlyOwner() {
+        require(_owner == _msgSender(), "Ownable: caller is not the owner");
+        _;
+    }
+
+    /**
+     * @dev Leaves the contract without owner. It will not be possible to call
+     * `onlyOwner` functions anymore. Can only be called by the current owner.
+     *
+     * NOTE: Renouncing ownership will leave the contract without an owner,
+     * thereby removing any functionality that is only available to the owner.
+     */
+    function renounceOwnership() public virtual onlyOwner {
+        emit OwnershipTransferred(_owner, address(0));
+        _owner = address(0);
+    }
+
+    /**
+     * @dev Transfers ownership of the contract to a new account (`newOwner`).
+     * Can only be called by the current owner.
+     */
+    function transferOwnership(address newOwner) public virtual onlyOwner {
+        require(newOwner != address(0), "Ownable: new owner is the zero address");
+        emit OwnershipTransferred(_owner, newOwner);
+        _owner = newOwner;
+    }
+}

contracts/access/README.adoc

@@ -0,0 +1,9 @@
+= Access
+
+Contract modules for authorization and access control mechanisms.
+
+== Contracts
+
+{{Ownable}}
+
+{{AccessControl}}

contracts/cryptography/ECDSA.sol

@@ -0,0 +1,81 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.
+ *
+ * These functions can be used to verify that a message was signed by the holder
+ * of the private keys of a given address.
+ */
+library ECDSA {
+    /**
+     * @dev Returns the address that signed a hashed message (`hash`) with
+     * `signature`. This address can then be used for verification purposes.
+     *
+     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:
+     * this function rejects them by requiring the `s` value to be in the lower
+     * half order, and the `v` value to be either 27 or 28.
+     *
+     * IMPORTANT: `hash` _must_ be the result of a hash operation for the
+     * verification to be secure: it is possible to craft signatures that
+     * recover to arbitrary addresses for non-hashed data. A safe way to ensure
+     * this is by receiving a hash of the original message (which may otherwise
+     * be too long), and then calling {toEthSignedMessageHash} on it.
+     */
+    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
+        // Check the signature length
+        if (signature.length != 65) {
+            revert("ECDSA: invalid signature length");
+        }
+
+        // Divide the signature in r, s and v variables
+        bytes32 r;
+        bytes32 s;
+        uint8 v;
+
+        // ecrecover takes the signature parameters, and the only way to get them
+        // currently is to use assembly.
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            r := mload(add(signature, 0x20))
+            s := mload(add(signature, 0x40))
+            v := byte(0, mload(add(signature, 0x60)))
+        }
+
+        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
+        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
+        // the valid range for s in (281): 0 < s < secp256k1n ÷ 2 + 1, and for v in (282): v ∈ {27, 28}. Most
+        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
+        //
+        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
+        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
+        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
+        // these malleable signatures as well.
+        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) {
+            revert("ECDSA: invalid signature 's' value");
+        }
+
+        if (v != 27 && v != 28) {
+            revert("ECDSA: invalid signature 'v' value");
+        }
+
+        // If the signature is valid (and not malleable), return the signer address
+        address signer = ecrecover(hash, v, r, s);
+        require(signer != address(0), "ECDSA: invalid signature");
+
+        return signer;
+    }
+
+    /**
+     * @dev Returns an Ethereum Signed Message, created from a `hash`. This
+     * replicates the behavior of the
+     * https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign[`eth_sign`]
+     * JSON-RPC method.
+     *
+     * See {recover}.
+     */
+    function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
+        // 32 is the length in bytes of hash,
+        // enforced by the type signature above
+        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
+    }
+}

contracts/cryptography/MerkleProof.sol

@@ -0,0 +1,31 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev These functions deal with verification of Merkle trees (hash trees),
+ */
+library MerkleProof {
+    /**
+     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
+     * defined by `root`. For this, a `proof` must be provided, containing
+     * sibling hashes on the branch from the leaf to the root of the tree. Each
+     * pair of leaves and each pair of pre-images are assumed to be sorted.
+     */
+    function verify(bytes32[] memory proof, bytes32 root, bytes32 leaf) internal pure returns (bool) {
+        bytes32 computedHash = leaf;
+
+        for (uint256 i = 0; i < proof.length; i++) {
+            bytes32 proofElement = proof[i];
+
+            if (computedHash <= proofElement) {
+                // Hash(current computed hash + current element of the proof)
+                computedHash = keccak256(abi.encodePacked(computedHash, proofElement));
+            } else {
+                // Hash(current element of the proof + current computed hash)
+                computedHash = keccak256(abi.encodePacked(proofElement, computedHash));
+            }
+        }
+
+        // Check if the computed hash (root) is equal to the provided root
+        return computedHash == root;
+    }
+}

contracts/cryptography/README.adoc

@@ -0,0 +1,9 @@
+= Cryptography
+
+This collection of libraries provides simple and safe ways to use different cryptographic primitives.
+
+== Libraries
+
+{{ECDSA}}
+
+{{MerkleProof}}

contracts/deploy-ready/ERC20MinterPauser.sol

@@ -0,0 +1,85 @@
+pragma solidity ^0.6.0;
+
+import "../access/AccessControl.sol";
+import "../GSN/Context.sol";
+import "../token/ERC20/ERC20.sol";
+import "../token/ERC20/ERC20Burnable.sol";
+import "../token/ERC20/ERC20Pausable.sol";
+
+/**
+ * @dev {ERC20} token, including:
+ *
+ *  - ability for holders to burn (destroy) their tokens
+ *  - a minter role that allows for token minting (creation)
+ *  - a pauser role that allows to stop all token transfers
+ *
+ * This contract uses {AccessControl} to lock permissioned functions using the
+ * different roles - head to its documentation for details.
+ *
+ * The account that deploys the contract will be granted the minter role, the
+ * pauser role, and the default admin role, meaning it will be able to grant
+ * both the minter and pauser roles.
+ */
+contract ERC20MinterPauser is Context, AccessControl, ERC20Burnable, ERC20Pausable {
+    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
+    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");
+
+    /**
+     * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE` and `PAUSER_ROLE` to the
+     * account that deploys the contract.
+     *
+     * See {ERC20-constructor}.
+     */
+    constructor(string memory name, string memory symbol) public ERC20(name, symbol) {
+        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
+
+        _setupRole(MINTER_ROLE, _msgSender());
+        _setupRole(PAUSER_ROLE, _msgSender());
+    }
+
+    /**
+     * @dev Creates `amount` new tokens for `to`.
+     *
+     * See {ERC20-_mint}.
+     *
+     * Requirements:
+     *
+     * - the caller must have the `MINTER_ROLE`.
+     */
+    function mint(address to, uint256 amount) public {
+        require(hasRole(MINTER_ROLE, _msgSender()), "ERC20MinterPauser: must have minter role to mint");
+        _mint(to, amount);
+    }
+
+    /**
+     * @dev Pauses all token transfers.
+     *
+     * See {ERC20Pausable} and {Pausable-_pause}.
+     *
+     * Requirements:
+     *
+     * - the caller must have the `PAUSER_ROLE`.
+     */
+    function pause() public {
+        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC20MinterPauser: must have pauser role to pause");
+        _pause();
+    }
+
+    /**
+     * @dev Unpauses all token transfers.
+     *
+     * See {ERC20Pausable} and {Pausable-_unpause}.
+     *
+     * Requirements:
+     *
+     * - the caller must have the `PAUSER_ROLE`.
+     */
+    function unpause() public {
+        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC20MinterPauser: must have pauser role to unpause");
+        _unpause();
+    }
+
+    function _beforeTokenTransfer(address from, address to, uint256 amount) internal override(ERC20, ERC20Pausable) {
+        super._beforeTokenTransfer(from, to, amount);
+    }
+}

contracts/deploy-ready/ERC721MinterPauser.sol

@@ -0,0 +1,85 @@
+pragma solidity ^0.6.0;
+
+import "../access/AccessControl.sol";
+import "../GSN/Context.sol";
+import "../token/ERC721/ERC721.sol";
+import "../token/ERC721/ERC721Burnable.sol";
+import "../token/ERC721/ERC721Pausable.sol";
+
+/**
+ * @dev {ERC721} token, including:
+ *
+ *  - ability for holders to burn (destroy) their tokens
+ *  - a minter role that allows for token minting (creation)
+ *  - a pauser role that allows to stop all token transfers
+ *
+ * This contract uses {AccessControl} to lock permissioned functions using the
+ * different roles - head to its documentation for details.
+ *
+ * The account that deploys the contract will be granted the minter role, the
+ * pauser role, and the default admin role, meaning it will be able to grant
+ * both the minter and pauser roles.
+ */
+contract ERC721MinterPauser is Context, AccessControl, ERC721Burnable, ERC721Pausable {
+    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
+    bytes32 public constant PAUSER_ROLE = keccak256("PAUSER_ROLE");
+
+    /**
+     * @dev Grants `DEFAULT_ADMIN_ROLE`, `MINTER_ROLE` and `PAUSER_ROLE` to the
+     * account that deploys the contract.
+     *
+     * See {ERC721-constructor}.
+     */
+    constructor(string memory name, string memory symbol) public ERC721(name, symbol) {
+        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
+
+        _setupRole(MINTER_ROLE, _msgSender());
+        _setupRole(PAUSER_ROLE, _msgSender());
+    }
+
+    /**
+     * @dev Creates the `tokenId` tokens for `to`.
+     *
+     * See {ERC721-_mint}.
+     *
+     * Requirements:
+     *
+     * - the caller must have the `MINTER_ROLE`.
+     */
+    function mint(address to, uint256 tokenId) public {
+        require(hasRole(MINTER_ROLE, _msgSender()), "ERC721MinterPauser: must have minter role to mint");
+        _mint(to, tokenId);
+    }
+
+    /**
+     * @dev Pauses all token transfers.
+     *
+     * See {ERC721Pausable} and {Pausable-_pause}.
+     *
+     * Requirements:
+     *
+     * - the caller must have the `PAUSER_ROLE`.
+     */
+    function pause() public {
+        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC721MinterPauser: must have pauser role to pause");
+        _pause();
+    }
+
+    /**
+     * @dev Unpauses all token transfers.
+     *
+     * See {ERC20Pausable} and {Pausable-_unpause}.
+     *
+     * Requirements:
+     *
+     * - the caller must have the `PAUSER_ROLE`.
+     */
+    function unpause() public {
+        require(hasRole(PAUSER_ROLE, _msgSender()), "ERC721MinterPauser: must have pauser role to unpause");
+        _unpause();
+    }
+
+    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal override(ERC721, ERC721Pausable) {
+        super._beforeTokenTransfer(from, to, tokenId);
+    }
+}

contracts/deploy-ready/README.adoc

@@ -0,0 +1,13 @@
+= Deploy Ready
+
+These contracts integrate different Ethereum standards (ERCs) with custom extensions and modules, showcasing common configurations that are ready to deploy **without having to write any Solidity code**.
+
+They can be used as-is for quick prototyping and testing, but are **also suitable for production environments**.
+
+TIP: Intermediate and advanced users can use these as starting points when writing their own contracts, extending them with custom functionality as they see fit.
+
+== Tokens
+
+{{ERC20MinterPauser}}
+
+{{ERC721MinterPauser}}

contracts/drafts/TokenVesting.sol

@@ -0,0 +1,174 @@
+pragma solidity ^0.6.0;
+
+import "../token/ERC20/SafeERC20.sol";
+import "../access/Ownable.sol";
+import "../math/SafeMath.sol";
+
+/**
+ * @title TokenVesting
+ * @dev A token holder contract that can release its token balance gradually like a
+ * typical vesting scheme, with a cliff and vesting period. Optionally revocable by the
+ * owner.
+ */
+contract TokenVesting is Ownable {
+    // The vesting schedule is time-based (i.e. using block timestamps as opposed to e.g. block numbers), and is
+    // therefore sensitive to timestamp manipulation (which is something miners can do, to a certain degree). Therefore,
+    // it is recommended to avoid using short time durations (less than a minute). Typical vesting schemes, with a
+    // cliff period of a year and a duration of four years, are safe to use.
+    // solhint-disable not-rely-on-time
+
+    using SafeMath for uint256;
+    using SafeERC20 for IERC20;
+
+    event TokensReleased(address token, uint256 amount);
+    event TokenVestingRevoked(address token);
+
+    // beneficiary of tokens after they are released
+    address private _beneficiary;
+
+    // Durations and timestamps are expressed in UNIX time, the same units as block.timestamp.
+    uint256 private _cliff;
+    uint256 private _start;
+    uint256 private _duration;
+
+    bool private _revocable;
+
+    mapping (address => uint256) private _released;
+    mapping (address => bool) private _revoked;
+
+    /**
+     * @dev Creates a vesting contract that vests its balance of any ERC20 token to the
+     * beneficiary, gradually in a linear fashion until start + duration. By then all
+     * of the balance will have vested.
+     * @param beneficiary address of the beneficiary to whom vested tokens are transferred
+     * @param cliffDuration duration in seconds of the cliff in which tokens will begin to vest
+     * @param start the time (as Unix time) at which point vesting starts
+     * @param duration duration in seconds of the period in which the tokens will vest
+     * @param revocable whether the vesting is revocable or not
+     */
+    constructor (address beneficiary, uint256 start, uint256 cliffDuration, uint256 duration, bool revocable) public {
+        require(beneficiary != address(0), "TokenVesting: beneficiary is the zero address");
+        // solhint-disable-next-line max-line-length
+        require(cliffDuration <= duration, "TokenVesting: cliff is longer than duration");
+        require(duration > 0, "TokenVesting: duration is 0");
+        // solhint-disable-next-line max-line-length
+        require(start.add(duration) > block.timestamp, "TokenVesting: final time is before current time");
+
+        _beneficiary = beneficiary;
+        _revocable = revocable;
+        _duration = duration;
+        _cliff = start.add(cliffDuration);
+        _start = start;
+    }
+
+    /**
+     * @return the beneficiary of the tokens.
+     */
+    function beneficiary() public view returns (address) {
+        return _beneficiary;
+    }
+
+    /**
+     * @return the cliff time of the token vesting.
+     */
+    function cliff() public view returns (uint256) {
+        return _cliff;
+    }
+
+    /**
+     * @return the start time of the token vesting.
+     */
+    function start() public view returns (uint256) {
+        return _start;
+    }
+
+    /**
+     * @return the duration of the token vesting.
+     */
+    function duration() public view returns (uint256) {
+        return _duration;
+    }
+
+    /**
+     * @return true if the vesting is revocable.
+     */
+    function revocable() public view returns (bool) {
+        return _revocable;
+    }
+
+    /**
+     * @return the amount of the token released.
+     */
+    function released(address token) public view returns (uint256) {
+        return _released[token];
+    }
+
+    /**
+     * @return true if the token is revoked.
+     */
+    function revoked(address token) public view returns (bool) {
+        return _revoked[token];
+    }
+
+    /**
+     * @notice Transfers vested tokens to beneficiary.
+     * @param token ERC20 token which is being vested
+     */
+    function release(IERC20 token) public {
+        uint256 unreleased = _releasableAmount(token);
+
+        require(unreleased > 0, "TokenVesting: no tokens are due");
+
+        _released[address(token)] = _released[address(token)].add(unreleased);
+
+        token.safeTransfer(_beneficiary, unreleased);
+
+        emit TokensReleased(address(token), unreleased);
+    }
+
+    /**
+     * @notice Allows the owner to revoke the vesting. Tokens already vested
+     * remain in the contract, the rest are returned to the owner.
+     * @param token ERC20 token which is being vested
+     */
+    function revoke(IERC20 token) public onlyOwner {
+        require(_revocable, "TokenVesting: cannot revoke");
+        require(!_revoked[address(token)], "TokenVesting: token already revoked");
+
+        uint256 balance = token.balanceOf(address(this));
+
+        uint256 unreleased = _releasableAmount(token);
+        uint256 refund = balance.sub(unreleased);
+
+        _revoked[address(token)] = true;
+
+        token.safeTransfer(owner(), refund);
+
+        emit TokenVestingRevoked(address(token));
+    }
+
+    /**
+     * @dev Calculates the amount that has already vested but hasn't been released yet.
+     * @param token ERC20 token which is being vested
+     */
+    function _releasableAmount(IERC20 token) private view returns (uint256) {
+        return _vestedAmount(token).sub(_released[address(token)]);
+    }
+
+    /**
+     * @dev Calculates the amount that has already vested.
+     * @param token ERC20 token which is being vested
+     */
+    function _vestedAmount(IERC20 token) private view returns (uint256) {
+        uint256 currentBalance = token.balanceOf(address(this));
+        uint256 totalBalance = currentBalance.add(_released[address(token)]);
+
+        if (block.timestamp < _cliff) {
+            return 0;
+        } else if (block.timestamp >= _start.add(_duration) || _revoked[address(token)]) {
+            return totalBalance;
+        } else {
+            return totalBalance.mul(block.timestamp.sub(_start)).div(_duration);
+        }
+    }
+}

contracts/examples/BadArrayUse.sol

@@ -1,23 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import '../PullPayment.sol';
-
-
-// UNSAFE CODE, DO NOT USE!
-contract BadArrayUse is PullPayment {
-  address[] employees;
-
-  function payBonus() {
-    for (var i = 0; i < employees.length; i++) {
-			address employee = employees[i];
-			uint bonus = calculateBonus(employee);
-    	asyncSend(employee, bonus);
-    }
-  }
-
-	function calculateBonus(address employee) returns (uint) {
-    // some expensive computation...
-  }
-
-}

contracts/examples/BadFailEarly.sol

@@ -1,17 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-// UNSAFE CODE, DO NOT USE!
-contract BadFailEarly {
-
-  uint constant DEFAULT_SALARY = 50000;
-  mapping(string => uint) nameToSalary;
-
-  function getSalary(string name) constant returns (uint) {
-    if (bytes(name).length != 0 && nameToSalary[name] != 0) {
-      return nameToSalary[name];
-    } else {
-      return DEFAULT_SALARY;
-    }
-  }
-}

contracts/examples/BadPushPayments.sol

@@ -1,23 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-// UNSAFE CODE, DO NOT USE!
-contract BadPushPayments {
-
-	address highestBidder;
-	uint highestBid;
-
-	function bid() payable {
-		if (msg.value < highestBid) throw;
-
-		if (highestBidder != 0) {
-      // return bid to previous winner
-			if (!highestBidder.send(highestBid)) {
-        throw;
-      }
-		}
-
-	  highestBidder = msg.sender;
-	  highestBid = msg.value;
-	}
-}

contracts/examples/GoodArrayUse.sol

@@ -1,25 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import '../PullPayment.sol';
-
-
-contract GoodArrayUse is PullPayment {
-  address[] employees;
-  mapping(address => uint) bonuses;
-
-  function payBonus() {
-    for (uint i = 0; i < employees.length; i++) {
-			address employee = employees[i];
-			uint bonus = bonuses[employee];
-    	asyncSend(employee, bonus);
-    }
-  }
-
-	function calculateBonus(address employee) returns (uint) {
-    uint bonus = 0;
-    // some expensive computation...
-    bonuses[employee] = bonus;
-  }
-
-}

contracts/examples/GoodFailEarly.sol

@@ -1,15 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-contract GoodFailEarly {
-
-  uint constant DEFAULT_SALARY = 50000;
-  mapping(string => uint) nameToSalary;
-
-  function getSalary(string name) constant returns (uint) {
-    if (bytes(name).length == 0) throw;
-    if (nameToSalary[name] == 0) throw;
-
-    return nameToSalary[name];
-  }
-}

contracts/examples/GoodPullPayments.sol

@@ -1,27 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-contract GoodPullPayments {
-  address highestBidder;
-  uint highestBid;
-  mapping(address => uint) refunds;
-
-  function bid() external payable {
-    if (msg.value < highestBid) throw;
-
-    if (highestBidder != 0) {
-      refunds[highestBidder] += highestBid;
-    }
-
-    highestBidder = msg.sender;
-    highestBid = msg.value;
-  }
-
-  function withdrawBid() external {
-    uint refund = refunds[msg.sender];
-    refunds[msg.sender] = 0;
-    if (!msg.sender.send(refund)) {
-      refunds[msg.sender] = refund;
-    }
-  }
-}

contracts/examples/ProofOfExistence.sol

@@ -1,38 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-/*
- * Proof of Existence example contract
- * see https://medium.com/zeppelin-blog/the-hitchhikers-guide-to-smart-contracts-in-ethereum-848f08001f05
- */
-contract ProofOfExistence {
-
-  mapping (bytes32 => bool) public proofs;
-
-  // store a proof of existence in the contract state
-  function storeProof(bytes32 proof) {
-    proofs[proof] = true;
-  }
-
-  // calculate and store the proof for a document
-  function notarize(string document) {
-    var proof = calculateProof(document);
-    storeProof(proof);
-  }
-
-  // helper function to get a document's sha256
-  function calculateProof(string document) constant returns (bytes32) {
-    return sha256(document);
-  }
-
-  // check if a document has been notarized
-  function checkDocument(string document) constant returns (bool) {
-    var proof = calculateProof(document);
-    return hasProof(proof);
-  }
-
-  // returns true if proof is stored
-  function hasProof(bytes32 proof) constant returns (bool) {
-    return proofs[proof];
-  }
-}

contracts/examples/PullPaymentBid.sol

@@ -1,20 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import '../PullPayment.sol';
-
-
-contract PullPaymentBid is PullPayment {
-  address public highestBidder;
-  uint public highestBid;
-  
-  function bid() external payable {
-    if (msg.value <= highestBid) throw;
-    
-    if (highestBidder != 0) {
-      asyncSend(highestBidder, highestBid);
-    }
-    highestBidder = msg.sender;
-    highestBid = msg.value;
-  }
-}

contracts/examples/StoppableBid.sol

@@ -1,26 +0,0 @@
-pragma solidity ^0.4.4;
-
-
-import '../PullPayment.sol';
-import '../Stoppable.sol';
-
-
-contract StoppableBid is Stoppable, PullPayment {
-  address public highestBidder;
-  uint public highestBid;
-
-  function bid() external payable stopInEmergency {
-    if (msg.value <= highestBid) throw;
-    
-    if (highestBidder != 0) {
-      asyncSend(highestBidder, highestBid);
-    }
-    highestBidder = msg.sender;
-    highestBid = msg.value;
-  }
-
-  function withdraw() onlyInEmergency {
-    selfdestruct(owner);
-  }
-
-}

contracts/introspection/ERC165.sol

@@ -0,0 +1,52 @@
+pragma solidity ^0.6.0;
+
+import "./IERC165.sol";
+
+/**
+ * @dev Implementation of the {IERC165} interface.
+ *
+ * Contracts may inherit from this and call {_registerInterface} to declare
+ * their support of an interface.
+ */
+contract ERC165 is IERC165 {
+    /*
+     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
+     */
+    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
+
+    /**
+     * @dev Mapping of interface ids to whether or not it's supported.
+     */
+    mapping(bytes4 => bool) private _supportedInterfaces;
+
+    constructor () internal {
+        // Derived contracts need only register support for their own interfaces,
+        // we register support for ERC165 itself here
+        _registerInterface(_INTERFACE_ID_ERC165);
+    }
+
+    /**
+     * @dev See {IERC165-supportsInterface}.
+     *
+     * Time complexity O(1), guaranteed to always use less than 30 000 gas.
+     */
+    function supportsInterface(bytes4 interfaceId) public view override returns (bool) {
+        return _supportedInterfaces[interfaceId];
+    }
+
+    /**
+     * @dev Registers the contract as an implementer of the interface defined by
+     * `interfaceId`. Support of the actual ERC165 interface is automatic and
+     * registering its interface id is not required.
+     *
+     * See {IERC165-supportsInterface}.
+     *
+     * Requirements:
+     *
+     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
+     */
+    function _registerInterface(bytes4 interfaceId) internal virtual {
+        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
+        _supportedInterfaces[interfaceId] = true;
+    }
+}

contracts/introspection/ERC165Checker.sol

@@ -0,0 +1,104 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Library used to query support of an interface declared via {IERC165}.
+ *
+ * Note that these functions return the actual result of the query: they do not
+ * `revert` if an interface is not supported. It is up to the caller to decide
+ * what to do in these cases.
+ */
+library ERC165Checker {
+    // As per the EIP-165 spec, no interface should ever match 0xffffffff
+    bytes4 private constant _INTERFACE_ID_INVALID = 0xffffffff;
+
+    /*
+     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
+     */
+    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
+
+    /**
+     * @dev Returns true if `account` supports the {IERC165} interface,
+     */
+    function supportsERC165(address account) internal view returns (bool) {
+        // Any contract that implements ERC165 must explicitly indicate support of
+        // InterfaceId_ERC165 and explicitly indicate non-support of InterfaceId_Invalid
+        return _supportsERC165Interface(account, _INTERFACE_ID_ERC165) &&
+            !_supportsERC165Interface(account, _INTERFACE_ID_INVALID);
+    }
+
+    /**
+     * @dev Returns true if `account` supports the interface defined by
+     * `interfaceId`. Support for {IERC165} itself is queried automatically.
+     *
+     * See {IERC165-supportsInterface}.
+     */
+    function supportsInterface(address account, bytes4 interfaceId) internal view returns (bool) {
+        // query support of both ERC165 as per the spec and support of _interfaceId
+        return supportsERC165(account) &&
+            _supportsERC165Interface(account, interfaceId);
+    }
+
+    /**
+     * @dev Returns true if `account` supports all the interfaces defined in
+     * `interfaceIds`. Support for {IERC165} itself is queried automatically.
+     *
+     * Batch-querying can lead to gas savings by skipping repeated checks for
+     * {IERC165} support.
+     *
+     * See {IERC165-supportsInterface}.
+     */
+    function supportsAllInterfaces(address account, bytes4[] memory interfaceIds) internal view returns (bool) {
+        // query support of ERC165 itself
+        if (!supportsERC165(account)) {
+            return false;
+        }
+
+        // query support of each interface in _interfaceIds
+        for (uint256 i = 0; i < interfaceIds.length; i++) {
+            if (!_supportsERC165Interface(account, interfaceIds[i])) {
+                return false;
+            }
+        }
+
+        // all interfaces supported
+        return true;
+    }
+
+    /**
+     * @notice Query if a contract implements an interface, does not check ERC165 support
+     * @param account The address of the contract to query for support of an interface
+     * @param interfaceId The interface identifier, as specified in ERC-165
+     * @return true if the contract at account indicates support of the interface with
+     * identifier interfaceId, false otherwise
+     * @dev Assumes that account contains a contract that supports ERC165, otherwise
+     * the behavior of this method is undefined. This precondition can be checked
+     * with {supportsERC165}.
+     * Interface identification is specified in ERC-165.
+     */
+    function _supportsERC165Interface(address account, bytes4 interfaceId) private view returns (bool) {
+        // success determines whether the staticcall succeeded and result determines
+        // whether the contract at account indicates support of _interfaceId
+        (bool success, bool result) = _callERC165SupportsInterface(account, interfaceId);
+
+        return (success && result);
+    }
+
+    /**
+     * @notice Calls the function with selector 0x01ffc9a7 (ERC165) and suppresses throw
+     * @param account The address of the contract to query for support of an interface
+     * @param interfaceId The interface identifier, as specified in ERC-165
+     * @return success true if the STATICCALL succeeded, false otherwise
+     * @return result true if the STATICCALL succeeded and the contract at account
+     * indicates support of the interface with identifier interfaceId, false otherwise
+     */
+    function _callERC165SupportsInterface(address account, bytes4 interfaceId)
+        private
+        view
+        returns (bool, bool)
+    {
+        bytes memory encodedParams = abi.encodeWithSelector(_INTERFACE_ID_ERC165, interfaceId);
+        (bool success, bytes memory result) = account.staticcall.gas(30000)(encodedParams);
+        if (result.length < 32) return (false, false);
+        return (success, abi.decode(result, (bool)));
+    }
+}

contracts/introspection/ERC1820Implementer.sol

@@ -0,0 +1,35 @@
+pragma solidity ^0.6.0;
+
+import "./IERC1820Implementer.sol";
+
+/**
+ * @dev Implementation of the {IERC1820Implementer} interface.
+ *
+ * Contracts may inherit from this and call {_registerInterfaceForAddress} to
+ * declare their willingness to be implementers.
+ * {IERC1820Registry-setInterfaceImplementer} should then be called for the
+ * registration to be complete.
+ */
+contract ERC1820Implementer is IERC1820Implementer {
+    bytes32 constant private _ERC1820_ACCEPT_MAGIC = keccak256(abi.encodePacked("ERC1820_ACCEPT_MAGIC"));
+
+    mapping(bytes32 => mapping(address => bool)) private _supportedInterfaces;
+
+    /**
+     * See {IERC1820Implementer-canImplementInterfaceForAddress}.
+     */
+    function canImplementInterfaceForAddress(bytes32 interfaceHash, address account) public view override returns (bytes32) {
+        return _supportedInterfaces[interfaceHash][account] ? _ERC1820_ACCEPT_MAGIC : bytes32(0x00);
+    }
+
+    /**
+     * @dev Declares the contract as willing to be an implementer of
+     * `interfaceHash` for `account`.
+     *
+     * See {IERC1820Registry-setInterfaceImplementer} and
+     * {IERC1820Registry-interfaceHash}.
+     */
+    function _registerInterfaceForAddress(bytes32 interfaceHash, address account) internal virtual {
+        _supportedInterfaces[interfaceHash][account] = true;
+    }
+}

contracts/introspection/IERC165.sol

@@ -0,0 +1,22 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Interface of the ERC165 standard, as defined in the
+ * https://eips.ethereum.org/EIPS/eip-165[EIP].
+ *
+ * Implementers can declare support of contract interfaces, which can then be
+ * queried by others ({ERC165Checker}).
+ *
+ * For an implementation, see {ERC165}.
+ */
+interface IERC165 {
+    /**
+     * @dev Returns true if this contract implements the interface defined by
+     * `interfaceId`. See the corresponding
+     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
+     * to learn more about how these ids are created.
+     *
+     * This function call must use less than 30 000 gas.
+     */
+    function supportsInterface(bytes4 interfaceId) external view returns (bool);
+}

contracts/introspection/IERC1820Implementer.sol

@@ -0,0 +1,17 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Interface for an ERC1820 implementer, as defined in the
+ * https://eips.ethereum.org/EIPS/eip-1820#interface-implementation-erc1820implementerinterface[EIP].
+ * Used by contracts that will be registered as implementers in the
+ * {IERC1820Registry}.
+ */
+interface IERC1820Implementer {
+    /**
+     * @dev Returns a special value (`ERC1820_ACCEPT_MAGIC`) if this contract
+     * implements `interfaceHash` for `account`.
+     *
+     * See {IERC1820Registry-setInterfaceImplementer}.
+     */
+    function canImplementInterfaceForAddress(bytes32 interfaceHash, address account) external view returns (bytes32);
+}

contracts/introspection/IERC1820Registry.sol

@@ -0,0 +1,109 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Interface of the global ERC1820 Registry, as defined in the
+ * https://eips.ethereum.org/EIPS/eip-1820[EIP]. Accounts may register
+ * implementers for interfaces in this registry, as well as query support.
+ *
+ * Implementers may be shared by multiple accounts, and can also implement more
+ * than a single interface for each account. Contracts can implement interfaces
+ * for themselves, but externally-owned accounts (EOA) must delegate this to a
+ * contract.
+ *
+ * {IERC165} interfaces can also be queried via the registry.
+ *
+ * For an in-depth explanation and source code analysis, see the EIP text.
+ */
+interface IERC1820Registry {
+    /**
+     * @dev Sets `newManager` as the manager for `account`. A manager of an
+     * account is able to set interface implementers for it.
+     *
+     * By default, each account is its own manager. Passing a value of `0x0` in
+     * `newManager` will reset the manager to this initial state.
+     *
+     * Emits a {ManagerChanged} event.
+     *
+     * Requirements:
+     *
+     * - the caller must be the current manager for `account`.
+     */
+    function setManager(address account, address newManager) external;
+
+    /**
+     * @dev Returns the manager for `account`.
+     *
+     * See {setManager}.
+     */
+    function getManager(address account) external view returns (address);
+
+    /**
+     * @dev Sets the `implementer` contract as `account`'s implementer for
+     * `interfaceHash`.
+     *
+     * `account` being the zero address is an alias for the caller's address.
+     * The zero address can also be used in `implementer` to remove an old one.
+     *
+     * See {interfaceHash} to learn how these are created.
+     *
+     * Emits an {InterfaceImplementerSet} event.
+     *
+     * Requirements:
+     *
+     * - the caller must be the current manager for `account`.
+     * - `interfaceHash` must not be an {IERC165} interface id (i.e. it must not
+     * end in 28 zeroes).
+     * - `implementer` must implement {IERC1820Implementer} and return true when
+     * queried for support, unless `implementer` is the caller. See
+     * {IERC1820Implementer-canImplementInterfaceForAddress}.
+     */
+    function setInterfaceImplementer(address account, bytes32 interfaceHash, address implementer) external;
+
+    /**
+     * @dev Returns the implementer of `interfaceHash` for `account`. If no such
+     * implementer is registered, returns the zero address.
+     *
+     * If `interfaceHash` is an {IERC165} interface id (i.e. it ends with 28
+     * zeroes), `account` will be queried for support of it.
+     *
+     * `account` being the zero address is an alias for the caller's address.
+     */
+    function getInterfaceImplementer(address account, bytes32 interfaceHash) external view returns (address);
+
+    /**
+     * @dev Returns the interface hash for an `interfaceName`, as defined in the
+     * corresponding
+     * https://eips.ethereum.org/EIPS/eip-1820#interface-name[section of the EIP].
+     */
+    function interfaceHash(string calldata interfaceName) external pure returns (bytes32);
+
+    /**
+     *  @notice Updates the cache with whether the contract implements an ERC165 interface or not.
+     *  @param account Address of the contract for which to update the cache.
+     *  @param interfaceId ERC165 interface for which to update the cache.
+     */
+    function updateERC165Cache(address account, bytes4 interfaceId) external;
+
+    /**
+     *  @notice Checks whether a contract implements an ERC165 interface or not.
+     *  If the result is not cached a direct lookup on the contract address is performed.
+     *  If the result is not cached or the cached value is out-of-date, the cache MUST be updated manually by calling
+     *  {updateERC165Cache} with the contract address.
+     *  @param account Address of the contract to check.
+     *  @param interfaceId ERC165 interface to check.
+     *  @return True if `account` implements `interfaceId`, false otherwise.
+     */
+    function implementsERC165Interface(address account, bytes4 interfaceId) external view returns (bool);
+
+    /**
+     *  @notice Checks whether a contract implements an ERC165 interface or not without using nor updating the cache.
+     *  @param account Address of the contract to check.
+     *  @param interfaceId ERC165 interface to check.
+     *  @return True if `account` implements `interfaceId`, false otherwise.
+     */
+    function implementsERC165InterfaceNoCache(address account, bytes4 interfaceId) external view returns (bool);
+
+    event InterfaceImplementerSet(address indexed account, bytes32 indexed interfaceHash, address indexed implementer);
+
+    event ManagerChanged(address indexed account, address indexed newManager);
+}

contracts/introspection/README.adoc

@@ -0,0 +1,28 @@
+= Introspection
+
+This set of interfaces and contracts deal with https://en.wikipedia.org/wiki/Type_introspection[type introspection] of contracts, that is, examining which functions can be called on them. This is usually referred to as a contract's _interface_.
+
+Ethereum contracts have no native concept of an interface, so applications must usually simply trust they are not making an incorrect call. For trusted setups this is a non-issue, but often unknown and untrusted third-party addresses need to be interacted with. There may even not be any direct calls to them! (e.g. `ERC20` tokens may be sent to a contract that lacks a way to transfer them out of it, locking them forever). In these cases, a contract _declaring_ its interface can be very helpful in preventing errors.
+
+There are two main ways to approach this.
+
+* Locally, where a contract implements `IERC165` and declares an interface, and a second one queries it directly via `ERC165Checker`.
+* Globally, where a global and unique registry (`IERC1820Registry`) is used to register implementers of a certain interface (`IERC1820Implementer`). It is then the registry that is queried, which allows for more complex setups, like contracts implementing interfaces for externally-owned accounts.
+
+Note that, in all cases, accounts simply _declare_ their interfaces, but they are not required to actually implement them. This mechanism can therefore be used to both prevent errors and allow for complex interactions (see `ERC777`), but it must not be relied on for security.
+
+== Local
+
+{{IERC165}}
+
+{{ERC165}}
+
+{{ERC165Checker}}
+
+== Global
+
+{{IERC1820Registry}}
+
+{{IERC1820Implementer}}
+
+{{ERC1820Implementer}}

contracts/math/Math.sol

@@ -0,0 +1,29 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Standard math utilities missing in the Solidity language.
+ */
+library Math {
+    /**
+     * @dev Returns the largest of two numbers.
+     */
+    function max(uint256 a, uint256 b) internal pure returns (uint256) {
+        return a >= b ? a : b;
+    }
+
+    /**
+     * @dev Returns the smallest of two numbers.
+     */
+    function min(uint256 a, uint256 b) internal pure returns (uint256) {
+        return a < b ? a : b;
+    }
+
+    /**
+     * @dev Returns the average of two numbers. The result is rounded towards
+     * zero.
+     */
+    function average(uint256 a, uint256 b) internal pure returns (uint256) {
+        // (a + b) / 2 can overflow, so we distribute
+        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
+    }
+}

contracts/math/README.adoc

@@ -0,0 +1,11 @@
+= Math
+
+These are math-related utilities.
+
+== Libraries
+
+{{SafeMath}}
+
+{{SignedSafeMath}}
+
+{{Math}}

contracts/math/SafeMath.sol

@@ -0,0 +1,150 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @dev Wrappers over Solidity's arithmetic operations with added overflow
+ * checks.
+ *
+ * Arithmetic operations in Solidity wrap on overflow. This can easily result
+ * in bugs, because programmers usually assume that an overflow raises an
+ * error, which is the standard behavior in high level programming languages.
+ * `SafeMath` restores this intuition by reverting the transaction when an
+ * operation overflows.
+ *
+ * Using this library instead of the unchecked operations eliminates an entire
+ * class of bugs, so it's recommended to use it always.
+ */
+library SafeMath {
+    /**
+     * @dev Returns the addition of two unsigned integers, reverting on
+     * overflow.
+     *
+     * Counterpart to Solidity's `+` operator.
+     *
+     * Requirements:
+     * - Addition cannot overflow.
+     */
+    function add(uint256 a, uint256 b) internal pure returns (uint256) {
+        uint256 c = a + b;
+        require(c >= a, "SafeMath: addition overflow");
+
+        return c;
+    }
+
+    /**
+     * @dev Returns the subtraction of two unsigned integers, reverting on
+     * overflow (when the result is negative).
+     *
+     * Counterpart to Solidity's `-` operator.
+     *
+     * Requirements:
+     * - Subtraction cannot overflow.
+     */
+    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
+        return sub(a, b, "SafeMath: subtraction overflow");
+    }
+
+    /**
+     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
+     * overflow (when the result is negative).
+     *
+     * Counterpart to Solidity's `-` operator.
+     *
+     * Requirements:
+     * - Subtraction cannot overflow.
+     */
+    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
+        require(b <= a, errorMessage);
+        uint256 c = a - b;
+
+        return c;
+    }
+
+    /**
+     * @dev Returns the multiplication of two unsigned integers, reverting on
+     * overflow.
+     *
+     * Counterpart to Solidity's `*` operator.
+     *
+     * Requirements:
+     * - Multiplication cannot overflow.
+     */
+    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
+        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
+        // benefit is lost if 'b' is also tested.
+        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
+        if (a == 0) {
+            return 0;
+        }
+
+        uint256 c = a * b;
+        require(c / a == b, "SafeMath: multiplication overflow");
+
+        return c;
+    }
+
+    /**
+     * @dev Returns the integer division of two unsigned integers. Reverts on
+     * division by zero. The result is rounded towards zero.
+     *
+     * Counterpart to Solidity's `/` operator. Note: this function uses a
+     * `revert` opcode (which leaves remaining gas untouched) while Solidity
+     * uses an invalid opcode to revert (consuming all remaining gas).
+     *
+     * Requirements:
+     * - The divisor cannot be zero.
+     */
+    function div(uint256 a, uint256 b) internal pure returns (uint256) {
+        return div(a, b, "SafeMath: division by zero");
+    }
+
+    /**
+     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
+     * division by zero. The result is rounded towards zero.
+     *
+     * Counterpart to Solidity's `/` operator. Note: this function uses a
+     * `revert` opcode (which leaves remaining gas untouched) while Solidity
+     * uses an invalid opcode to revert (consuming all remaining gas).
+     *
+     * Requirements:
+     * - The divisor cannot be zero.
+     */
+    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
+        // Solidity only automatically asserts when dividing by 0
+        require(b > 0, errorMessage);
+        uint256 c = a / b;
+        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
+
+        return c;
+    }
+
+    /**
+     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
+     * Reverts when dividing by zero.
+     *
+     * Counterpart to Solidity's `%` operator. This function uses a `revert`
+     * opcode (which leaves remaining gas untouched) while Solidity uses an
+     * invalid opcode to revert (consuming all remaining gas).
+     *
+     * Requirements:
+     * - The divisor cannot be zero.
+     */
+    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
+        return mod(a, b, "SafeMath: modulo by zero");
+    }
+
+    /**
+     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
+     * Reverts with custom message when dividing by zero.
+     *
+     * Counterpart to Solidity's `%` operator. This function uses a `revert`
+     * opcode (which leaves remaining gas untouched) while Solidity uses an
+     * invalid opcode to revert (consuming all remaining gas).
+     *
+     * Requirements:
+     * - The divisor cannot be zero.
+     */
+    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
+        require(b != 0, errorMessage);
+        return a % b;
+    }
+}

contracts/math/SignedSafeMath.sol

@@ -0,0 +1,60 @@
+pragma solidity ^0.6.0;
+
+/**
+ * @title SignedSafeMath
+ * @dev Signed math operations with safety checks that revert on error.
+ */
+library SignedSafeMath {
+    int256 constant private _INT256_MIN = -2**255;
+
+    /**
+     * @dev Multiplies two signed integers, reverts on overflow.
+     */
+    function mul(int256 a, int256 b) internal pure returns (int256) {
+        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
+        // benefit is lost if 'b' is also tested.
+        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
+        if (a == 0) {
+            return 0;
+        }
+
+        require(!(a == -1 && b == _INT256_MIN), "SignedSafeMath: multiplication overflow");
+
+        int256 c = a * b;
+        require(c / a == b, "SignedSafeMath: multiplication overflow");
+
+        return c;
+    }
+
+    /**
+     * @dev Integer division of two signed integers truncating the quotient, reverts on division by zero.
+     */
+    function div(int256 a, int256 b) internal pure returns (int256) {
+        require(b != 0, "SignedSafeMath: division by zero");
+        require(!(b == -1 && a == _INT256_MIN), "SignedSafeMath: division overflow");
+
+        int256 c = a / b;
+
+        return c;
+    }
+
+    /**
+     * @dev Subtracts two signed integers, reverts on overflow.
+     */
+    function sub(int256 a, int256 b) internal pure returns (int256) {
+        int256 c = a - b;
+        require((b >= 0 && c <= a) || (b < 0 && c > a), "SignedSafeMath: subtraction overflow");
+
+        return c;
+    }
+
+    /**
+     * @dev Adds two signed integers, reverts on overflow.
+     */
+    function add(int256 a, int256 b) internal pure returns (int256) {
+        int256 c = a + b;
+        require((b >= 0 && c >= a) || (b < 0 && c < a), "SignedSafeMath: addition overflow");
+
+        return c;
+    }
+}

contracts/mocks/AccessControlMock.sol

@@ -0,0 +1,17 @@
+pragma solidity ^0.6.0;
+
+import "../access/AccessControl.sol";
+
+contract AccessControlMock is AccessControl {
+    constructor() public {
+        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
+    }
+
+    function setRoleAdmin(bytes32 roleId, bytes32 adminRoleId) public {
+        _setRoleAdmin(roleId, adminRoleId);
+    }
+
+    function setupRole(bytes32 roleId, address account) public {
+        _setupRole(roleId, account);
+    }
+}

contracts/mocks/AddressImpl.sol

@@ -0,0 +1,16 @@
+pragma solidity ^0.6.0;
+
+import "../utils/Address.sol";
+
+contract AddressImpl {
+    function isContract(address account) external view returns (bool) {
+        return Address.isContract(account);
+    }
+
+    function sendValue(address payable receiver, uint256 amount) external {
+        Address.sendValue(receiver, amount);
+    }
+
+    // sendValue's tests require the contract to hold Ether
+    receive () external payable { }
+}

contracts/mocks/ArraysImpl.sol

@@ -0,0 +1,17 @@
+pragma solidity ^0.6.0;
+
+import "../utils/Arrays.sol";
+
+contract ArraysImpl {
+    using Arrays for uint256[];
+
+    uint256[] private _array;
+
+    constructor (uint256[] memory array) public {
+        _array = array;
+    }
+
+    function findUpperBound(uint256 element) external view returns (uint256) {
+        return _array.findUpperBound(element);
+    }
+}

contracts/mocks/ConditionalEscrowMock.sol

@@ -0,0 +1,16 @@
+pragma solidity ^0.6.0;
+
+import "../payment/escrow/ConditionalEscrow.sol";
+
+// mock class using ConditionalEscrow
+contract ConditionalEscrowMock is ConditionalEscrow {
+    mapping(address => bool) private _allowed;
+
+    function setAllowed(address payee, bool allowed) public {
+        _allowed[payee] = allowed;
+    }
+
+    function withdrawalAllowed(address payee) public view override returns (bool) {
+        return _allowed[payee];
+    }
+}

contracts/mocks/ContextMock.sol

@@ -0,0 +1,27 @@
+pragma solidity ^0.6.0;
+
+import "../GSN/Context.sol";
+
+contract ContextMock is Context {
+    event Sender(address sender);
+
+    function msgSender() public {
+        emit Sender(_msgSender());
+    }
+
+    event Data(bytes data, uint256 integerValue, string stringValue);
+
+    function msgData(uint256 integerValue, string memory stringValue) public {
+        emit Data(_msgData(), integerValue, stringValue);
+    }
+}
+
+contract ContextMockCaller {
+    function callSender(ContextMock context) public {
+        context.msgSender();
+    }
+
+    function callData(ContextMock context, uint256 integerValue, string memory stringValue) public {
+        context.msgData(integerValue, stringValue);
+    }
+}

contracts/mocks/CountersImpl.sol

@@ -0,0 +1,21 @@
+pragma solidity ^0.6.0;
+
+import "../utils/Counters.sol";
+
+contract CountersImpl {
+    using Counters for Counters.Counter;
+
+    Counters.Counter private _counter;
+
+    function current() public view returns (uint256) {
+        return _counter.current();
+    }
+
+    function increment() public {
+        _counter.increment();
+    }
+
+    function decrement() public {
+        _counter.decrement();
+    }
+}

contracts/mocks/Create2Impl.sol

@@ -0,0 +1,25 @@
+pragma solidity ^0.6.0;
+
+import "../utils/Create2.sol";
+import "../introspection/ERC1820Implementer.sol";
+
+contract Create2Impl {
+    function deploy(uint256 value, bytes32 salt, bytes memory code) public {
+        Create2.deploy(value, salt, code);
+    }
+
+    function deployERC1820Implementer(uint256 value, bytes32 salt) public {
+        // solhint-disable-next-line indent
+        Create2.deploy(value, salt, type(ERC1820Implementer).creationCode);
+    }
+
+    function computeAddress(bytes32 salt, bytes32 codeHash) public view returns (address) {
+        return Create2.computeAddress(salt, codeHash);
+    }
+
+    function computeAddressWithDeployer(bytes32 salt, bytes32 codeHash, address deployer) public pure returns (address) {
+        return Create2.computeAddress(salt, codeHash, deployer);
+    }
+
+    receive() payable external {}
+}

contracts/mocks/ECDSAMock.sol

@@ -0,0 +1,15 @@
+pragma solidity ^0.6.0;
+
+import "../cryptography/ECDSA.sol";
+
+contract ECDSAMock {
+    using ECDSA for bytes32;
+
+    function recover(bytes32 hash, bytes memory signature) public pure returns (address) {
+        return hash.recover(signature);
+    }
+
+    function toEthSignedMessageHash(bytes32 hash) public pure returns (bytes32) {
+        return hash.toEthSignedMessageHash();
+    }
+}

contracts/mocks/ERC165/ERC165InterfacesSupported.sol

@@ -0,0 +1,56 @@
+pragma solidity ^0.6.0;
+
+import "../../introspection/IERC165.sol";
+
+/**
+ * https://eips.ethereum.org/EIPS/eip-214#specification
+ * From the specification:
+ * > Any attempts to make state-changing operations inside an execution instance with STATIC set to true will instead
+ * throw an exception.
+ * > These operations include [...], LOG0, LOG1, LOG2, [...]
+ *
+ * therefore, because this contract is staticcall'd we need to not emit events (which is how solidity-coverage works)
+ * solidity-coverage ignores the /mocks folder, so we duplicate its implementation here to avoid instrumenting it
+ */
+contract SupportsInterfaceWithLookupMock is IERC165 {
+    /*
+     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
+     */
+    bytes4 public constant INTERFACE_ID_ERC165 = 0x01ffc9a7;
+
+    /**
+     * @dev A mapping of interface id to whether or not it's supported.
+     */
+    mapping(bytes4 => bool) private _supportedInterfaces;
+
+    /**
+     * @dev A contract implementing SupportsInterfaceWithLookup
+     * implement ERC165 itself.
+     */
+    constructor () public {
+        _registerInterface(INTERFACE_ID_ERC165);
+    }
+
+    /**
+     * @dev Implement supportsInterface(bytes4) using a lookup table.
+     */
+    function supportsInterface(bytes4 interfaceId) public view override returns (bool) {
+        return _supportedInterfaces[interfaceId];
+    }
+
+    /**
+     * @dev Private method for registering an interface.
+     */
+    function _registerInterface(bytes4 interfaceId) internal {
+        require(interfaceId != 0xffffffff, "ERC165InterfacesSupported: invalid interface id");
+        _supportedInterfaces[interfaceId] = true;
+    }
+}
+
+contract ERC165InterfacesSupported is SupportsInterfaceWithLookupMock {
+    constructor (bytes4[] memory interfaceIds) public {
+        for (uint256 i = 0; i < interfaceIds.length; i++) {
+            _registerInterface(interfaceIds[i]);
+        }
+    }
+}

contracts/mocks/ERC165/ERC165NotSupported.sol

@@ -0,0 +1,3 @@
+pragma solidity ^0.6.0;
+
+contract ERC165NotSupported { }

contracts/mocks/ERC165CheckerMock.sol

@@ -0,0 +1,19 @@
+pragma solidity ^0.6.0;
+
+import "../introspection/ERC165Checker.sol";
+
+contract ERC165CheckerMock {
+    using ERC165Checker for address;
+
+    function supportsERC165(address account) public view returns (bool) {
+        return account.supportsERC165();
+    }
+
+    function supportsInterface(address account, bytes4 interfaceId) public view returns (bool) {
+        return account.supportsInterface(interfaceId);
+    }
+
+    function supportsAllInterfaces(address account, bytes4[] memory interfaceIds) public view returns (bool) {
+        return account.supportsAllInterfaces(interfaceIds);
+    }
+}

contracts/mocks/ERC165Mock.sol

@@ -0,0 +1,9 @@
+pragma solidity ^0.6.0;
+
+import "../introspection/ERC165.sol";
+
+contract ERC165Mock is ERC165 {
+    function registerInterface(bytes4 interfaceId) public {
+        _registerInterface(interfaceId);
+    }
+}

contracts/mocks/ERC1820ImplementerMock.sol

@@ -0,0 +1,9 @@
+pragma solidity ^0.6.0;
+
+import "../introspection/ERC1820Implementer.sol";
+
+contract ERC1820ImplementerMock is ERC1820Implementer {
+    function registerInterfaceForAddress(bytes32 interfaceHash, address account) public {
+        _registerInterfaceForAddress(interfaceHash, account);
+    }
+}

contracts/mocks/ERC20BurnableMock.sol

@@ -0,0 +1,14 @@
+pragma solidity ^0.6.0;
+
+import "../token/ERC20/ERC20Burnable.sol";
+
+contract ERC20BurnableMock is ERC20Burnable {
+    constructor (
+        string memory name,
+        string memory symbol,
+        address initialAccount,
+        uint256 initialBalance
+    ) public ERC20(name, symbol) {
+        _mint(initialAccount, initialBalance);
+    }
+}

contracts/mocks/ERC20CappedMock.sol

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+pragma solidity ^0.6.0;
+
+import "../token/ERC20/ERC20Capped.sol";
+
+contract ERC20CappedMock is ERC20Capped {
+    constructor (string memory name, string memory symbol, uint256 cap)
+        public ERC20(name, symbol) ERC20Capped(cap)
+    { }
+
+    function mint(address to, uint256 tokenId) public {
+        _mint(to, tokenId);
+    }
+}

contracts/mocks/ERC20DecimalsMock.sol

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+pragma solidity ^0.6.0;
+
+import "../token/ERC20/ERC20.sol";
+
+contract ERC20DecimalsMock is ERC20 {
+    constructor (string memory name, string memory symbol, uint8 decimals) public ERC20(name, symbol) {
+        _setupDecimals(decimals);
+    }
+
+    function setupDecimals(uint8 decimals) public {
+        _setupDecimals(decimals);
+    }
+}

contracts/mocks/ERC20Mock.sol

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+pragma solidity ^0.6.0;
+
+import "../token/ERC20/ERC20.sol";
+
+// mock class using ERC20
+contract ERC20Mock is ERC20 {
+    constructor (
+        string memory name,
+        string memory symbol,
+        address initialAccount,
+        uint256 initialBalance
+    ) public payable ERC20(name, symbol) {
+        _mint(initialAccount, initialBalance);
+    }
+
+    function mint(address account, uint256 amount) public {
+        _mint(account, amount);
+    }
+
+    function burn(address account, uint256 amount) public {
+        _burn(account, amount);
+    }
+
+    function transferInternal(address from, address to, uint256 value) public {
+        _transfer(from, to, value);
+    }
+
+    function approveInternal(address owner, address spender, uint256 value) public {
+        _approve(owner, spender, value);
+    }
+}

contracts/mocks/ERC20PausableMock.sol

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+pragma solidity ^0.6.0;
+
+import "../token/ERC20/ERC20Pausable.sol";
+
+// mock class using ERC20Pausable
+contract ERC20PausableMock is ERC20Pausable {
+    constructor (
+        string memory name,
+        string memory symbol,
+        address initialAccount,
+        uint256 initialBalance
+    ) public ERC20(name, symbol) {
+        _mint(initialAccount, initialBalance);
+    }
+
+    function pause() external {
+        _pause();
+    }
+
+    function unpause() external {
+        _unpause();
+    }
+}

contracts/mocks/ERC20SnapshotMock.sol

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+pragma solidity ^0.6.0;
+
+import "../token/ERC20/ERC20Snapshot.sol";
+
+
+contract ERC20SnapshotMock is ERC20Snapshot {
+    constructor(
+        string memory name,
+        string memory symbol,
+        address initialAccount,
+        uint256 initialBalance
+    ) public ERC20(name, symbol) {
+        _mint(initialAccount, initialBalance);
+    }
+
+    function snapshot() public {
+        _snapshot();
+    }
+
+    function mint(address account, uint256 amount) public {
+        _mint(account, amount);
+    }
+
+    function burn(address account, uint256 amount) public {
+        _burn(account, amount);
+    }
+}

contracts/mocks/ERC721BurnableMock.sol

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+pragma solidity ^0.6.0;
+
+import "../token/ERC721/ERC721Burnable.sol";
+
+contract ERC721BurnableMock is ERC721Burnable {
+    constructor(string memory name, string memory symbol) public ERC721(name, symbol) { }
+
+    function mint(address to, uint256 tokenId) public {
+        _mint(to, tokenId);
+    }
+}

contracts/mocks/ERC721GSNRecipientMock.sol

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+pragma solidity ^0.6.0;
+
+import "../token/ERC721/ERC721.sol";
+import "../GSN/GSNRecipient.sol";
+import "../GSN/GSNRecipientSignature.sol";
+
+/**
+ * @title ERC721GSNRecipientMock
+ * A simple ERC721 mock that has GSN support enabled
+ */
+contract ERC721GSNRecipientMock is ERC721, GSNRecipient, GSNRecipientSignature {
+    constructor(string memory name, string memory symbol, address trustedSigner)
+        public
+        ERC721(name, symbol)
+        GSNRecipientSignature(trustedSigner)
+    { }
+
+    function mint(uint256 tokenId) public {
+        _mint(_msgSender(), tokenId);
+    }
+
+    function _msgSender() internal view override(Context, GSNRecipient) returns (address payable) {
+        return GSNRecipient._msgSender();
+    }
+
+    function _msgData() internal view override(Context, GSNRecipient) returns (bytes memory) {
+        return GSNRecipient._msgData();
+    }
+}

contracts/mocks/ERC721Mock.sol

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+pragma solidity ^0.6.0;
+
+import "../token/ERC721/ERC721.sol";
+
+/**
+ * @title ERC721Mock
+ * This mock just provides a public safeMint, mint, and burn functions for testing purposes
+ */
+contract ERC721Mock is ERC721 {
+    constructor (string memory name, string memory symbol) public ERC721(name, symbol) { }
+
+    function exists(uint256 tokenId) public view returns (bool) {
+        return _exists(tokenId);
+    }
+
+    function setTokenURI(uint256 tokenId, string memory uri) public {
+        _setTokenURI(tokenId, uri);
+    }
+
+    function setBaseURI(string memory baseURI) public {
+        _setBaseURI(baseURI);
+    }
+
+    function mint(address to, uint256 tokenId) public {
+        _mint(to, tokenId);
+    }
+
+    function safeMint(address to, uint256 tokenId) public {
+        _safeMint(to, tokenId);
+    }
+
+    function safeMint(address to, uint256 tokenId, bytes memory _data) public {
+        _safeMint(to, tokenId, _data);
+    }
+
+    function burn(uint256 tokenId) public {
+        _burn(tokenId);
+    }
+}