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Merge pull request #476 from martriay/add-token-vesting

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Add token vesting
This commit is contained in:
Francisco Giordano
2017-10-05 18:44:39 -03:00
committed by GitHub
parent 5cf503673f ffd1090718
commit 5aba967db9
6 changed files with 210 additions and 484 deletions
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57
contracts/token/LimitedTransferToken.sol
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pragma solidity ^0.4.11;
import "./ERC20.sol";
/**
* @title LimitedTransferToken
* @dev LimitedTransferToken defines the generic interface and the implementation to limit token
* transferability for different events. It is intended to be used as a base class for other token
* contracts.
* LimitedTransferToken has been designed to allow for different limiting factors,
* this can be achieved by recursively calling super.transferableTokens() until the base class is
* hit. For example:
* function transferableTokens(address holder, uint64 time) constant public returns (uint256) {
* return min256(unlockedTokens, super.transferableTokens(holder, time));
* }
* A working example is VestedToken.sol:
* https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/token/VestedToken.sol
*/
contract LimitedTransferToken is ERC20 {
/**
* @dev Checks whether it can transfer or otherwise throws.
*/
modifier canTransfer(address _sender, uint256 _value) {
require(_value <= transferableTokens(_sender, uint64(now)));
_;
}
/**
* @dev Checks modifier and allows transfer if tokens are not locked.
* @param _to The address that will receive the tokens.
* @param _value The amount of tokens to be transferred.
*/
function transfer(address _to, uint256 _value) canTransfer(msg.sender, _value) public returns (bool) {
return super.transfer(_to, _value);
}
/**
* @dev Checks modifier and allows transfer if tokens are not locked.
* @param _from The address that will send the tokens.
* @param _to The address that will receive the tokens.
* @param _value The amount of tokens to be transferred.
*/
function transferFrom(address _from, address _to, uint256 _value) canTransfer(_from, _value) public returns (bool) {
return super.transferFrom(_from, _to, _value);
}
/**
* @dev Default transferable tokens function returns all tokens for a holder (no limit).
* @dev Overwriting transferableTokens(address holder, uint64 time) is the way to provide the
* specific logic for limiting token transferability for a holder over time.
*/
function transferableTokens(address holder, uint64 time) public constant returns (uint256) {
return balanceOf(holder);
}
}

103
contracts/token/TokenVesting.sol Normal file
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pragma solidity ^0.4.11;
import './ERC20Basic.sol';
import '../ownership/Ownable.sol';
import '../math/Math.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 {
using SafeMath for uint256;
event Released(uint256 amount);
event Revoked();
// beneficiary of tokens after they are released
address beneficiary;
uint256 cliff;
uint256 start;
uint256 duration;
bool revocable;
mapping (address => uint256) released;
/**
* @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 _cliff duration in seconds of the cliff in which tokens will begin to vest
* @param _duration duration in seconds of the period in which the tokens will vest
* @param _revocable whether the vesting is revocable or not
*/
function TokenVesting(address _beneficiary, uint256 _start, uint256 _cliff, uint256 _duration, bool _revocable) {
require(_beneficiary != 0x0);
require(_cliff <= _duration);
beneficiary = _beneficiary;
revocable = _revocable;
duration = _duration;
cliff = _start + _cliff;
start = _start;
}
/**
* @notice Transfers vested tokens to beneficiary.
* @param token ERC20 token which is being vested
*/
function release(ERC20Basic token) {
uint256 vested = vestedAmount(token);
require(vested > 0);
token.transfer(beneficiary, vested);
released[token] = released[token].add(vested);
Released(vested);
}
/**
* @notice Allows the owner to revoke the vesting. Tokens already vested remain in the contract.
* @param token ERC20 token which is being vested
*/
function revoke(ERC20Basic token) onlyOwner {
require(revocable);
uint256 balance = token.balanceOf(this);
uint256 vested = vestedAmount(token);
token.transfer(owner, balance - vested);
Revoked();
}
/**
* @dev Calculates the amount that has already vested but hasn't been released yet.
* @param token ERC20 token which is being vested
*/
function vestedAmount(ERC20Basic token) constant returns (uint256) {
if (now < cliff) {
return 0;
} else if (now >= start + duration) {
return token.balanceOf(this);
} else {
uint256 currentBalance = token.balanceOf(this);
uint256 totalBalance = currentBalance.add(released[token]);
uint256 vested = totalBalance.mul(now - start).div(duration);
uint256 unreleased = vested.sub(released[token]);
// currentBalance can be 0 in case of vesting being revoked earlier.
return Math.min256(currentBalance, unreleased);
}
}
}

241
contracts/token/VestedToken.sol
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pragma solidity ^0.4.11;
import "../math/Math.sol";
import "./StandardToken.sol";
import "./LimitedTransferToken.sol";
/**
* @title Vested token
* @dev Tokens that can be vested for a group of addresses.
*/
contract VestedToken is StandardToken, LimitedTransferToken {
uint256 MAX_GRANTS_PER_ADDRESS = 20;
struct TokenGrant {
address granter; // 20 bytes
uint256 value; // 32 bytes
uint64 cliff;
uint64 vesting;
uint64 start; // 3 * 8 = 24 bytes
bool revokable;
bool burnsOnRevoke; // 2 * 1 = 2 bits? or 2 bytes?
} // total 78 bytes = 3 sstore per operation (32 per sstore)
mapping (address => TokenGrant[]) public grants;
event NewTokenGrant(address indexed from, address indexed to, uint256 value, uint256 grantId);
/**
* @dev Grant tokens to a specified address
* @param _to address The address which the tokens will be granted to.
* @param _value uint256 The amount of tokens to be granted.
* @param _start uint64 Time of the beginning of the grant.
* @param _cliff uint64 Time of the cliff period.
* @param _vesting uint64 The vesting period.
*/
function grantVestedTokens(
address _to,
uint256 _value,
uint64 _start,
uint64 _cliff,
uint64 _vesting,
bool _revokable,
bool _burnsOnRevoke
) public {
// Check for date inconsistencies that may cause unexpected behavior
require(_cliff >= _start && _vesting >= _cliff);
require(tokenGrantsCount(_to) < MAX_GRANTS_PER_ADDRESS); // To prevent a user being spammed and have his balance locked (out of gas attack when calculating vesting).
uint256 count = grants[_to].push(
TokenGrant(
_revokable ? msg.sender : 0, // avoid storing an extra 20 bytes when it is non-revokable
_value,
_cliff,
_vesting,
_start,
_revokable,
_burnsOnRevoke
)
);
transfer(_to, _value);
NewTokenGrant(msg.sender, _to, _value, count - 1);
}
/**
* @dev Revoke the grant of tokens of a specifed address.
* @param _holder The address which will have its tokens revoked.
* @param _grantId The id of the token grant.
*/
function revokeTokenGrant(address _holder, uint256 _grantId) public {
TokenGrant storage grant = grants[_holder][_grantId];
require(grant.revokable);
require(grant.granter == msg.sender); // Only granter can revoke it
address receiver = grant.burnsOnRevoke ? 0xdead : msg.sender;
uint256 nonVested = nonVestedTokens(grant, uint64(now));
// remove grant from array
delete grants[_holder][_grantId];
grants[_holder][_grantId] = grants[_holder][grants[_holder].length.sub(1)];
grants[_holder].length -= 1;
balances[receiver] = balances[receiver].add(nonVested);
balances[_holder] = balances[_holder].sub(nonVested);
Transfer(_holder, receiver, nonVested);
}
/**
* @dev Calculate the total amount of transferable tokens of a holder at a given time
* @param holder address The address of the holder
* @param time uint64 The specific time.
* @return An uint256 representing a holder's total amount of transferable tokens.
*/
function transferableTokens(address holder, uint64 time) public constant returns (uint256) {
uint256 grantIndex = tokenGrantsCount(holder);
if (grantIndex == 0) return super.transferableTokens(holder, time); // shortcut for holder without grants
// Iterate through all the grants the holder has, and add all non-vested tokens
uint256 nonVested = 0;
for (uint256 i = 0; i < grantIndex; i++) {
nonVested = SafeMath.add(nonVested, nonVestedTokens(grants[holder][i], time));
}
// Balance - totalNonVested is the amount of tokens a holder can transfer at any given time
uint256 vestedTransferable = SafeMath.sub(balanceOf(holder), nonVested);
// Return the minimum of how many vested can transfer and other value
// in case there are other limiting transferability factors (default is balanceOf)
return Math.min256(vestedTransferable, super.transferableTokens(holder, time));
}
/**
* @dev Check the amount of grants that an address has.
* @param _holder The holder of the grants.
* @return A uint256 representing the total amount of grants.
*/
function tokenGrantsCount(address _holder) public constant returns (uint256 index) {
return grants[_holder].length;
}
/**
* @dev Calculate amount of vested tokens at a specific time
* @param tokens uint256 The amount of tokens granted
* @param time uint64 The time to be checked
* @param start uint64 The time representing the beginning of the grant
* @param cliff uint64 The cliff period, the period before nothing can be paid out
* @param vesting uint64 The vesting period
* @return An uint256 representing the amount of vested tokens of a specific grant
* transferableTokens
* | _/-------- vestedTokens rect
* | _/
* | _/
* | _/
* | _/
* | /
* | .|
* | . |
* | . |
* | . |
* | . |
* | . |
* +===+===========+---------+----------> time
* Start Cliff Vesting
*/
function calculateVestedTokens(
uint256 tokens,
uint256 time,
uint256 start,
uint256 cliff,
uint256 vesting) public constant returns (uint256)
{
// Shortcuts for before cliff and after vesting cases.
if (time < cliff) return 0;
if (time >= vesting) return tokens;
// Interpolate all vested tokens.
// As before cliff the shortcut returns 0, we can use just calculate a value
// in the vesting rect (as shown in above's figure)
// vestedTokens = (tokens * (time - start)) / (vesting - start)
uint256 vestedTokens = SafeMath.div(
SafeMath.mul(
tokens,
SafeMath.sub(time, start)
),
SafeMath.sub(vesting, start)
);
return vestedTokens;
}
/**
* @dev Get all information about a specific grant.
* @param _holder The address which will have its tokens revoked.
* @param _grantId The id of the token grant.
* @return Returns all the values that represent a TokenGrant(address, value, start, cliff,
* revokability, burnsOnRevoke, and vesting) plus the vested value at the current time.
*/
function tokenGrant(address _holder, uint256 _grantId) public constant returns (address granter, uint256 value, uint256 vested, uint64 start, uint64 cliff, uint64 vesting, bool revokable, bool burnsOnRevoke) {
TokenGrant storage grant = grants[_holder][_grantId];
granter = grant.granter;
value = grant.value;
start = grant.start;
cliff = grant.cliff;
vesting = grant.vesting;
revokable = grant.revokable;
burnsOnRevoke = grant.burnsOnRevoke;
vested = vestedTokens(grant, uint64(now));
}
/**
* @dev Get the amount of vested tokens at a specific time.
* @param grant TokenGrant The grant to be checked.
* @param time The time to be checked
* @return An uint256 representing the amount of vested tokens of a specific grant at a specific time.
*/
function vestedTokens(TokenGrant grant, uint64 time) private constant returns (uint256) {
return calculateVestedTokens(
grant.value,
uint256(time),
uint256(grant.start),
uint256(grant.cliff),
uint256(grant.vesting)
);
}
/**
* @dev Calculate the amount of non vested tokens at a specific time.
* @param grant TokenGrant The grant to be checked.
* @param time uint64 The time to be checked
* @return An uint256 representing the amount of non vested tokens of a specific grant on the
* passed time frame.
*/
function nonVestedTokens(TokenGrant grant, uint64 time) private constant returns (uint256) {
return grant.value.sub(vestedTokens(grant, time));
}
/**
* @dev Calculate the date when the holder can transfer all its tokens
* @param holder address The address of the holder
* @return An uint256 representing the date of the last transferable tokens.
*/
function lastTokenIsTransferableDate(address holder) public constant returns (uint64 date) {
date = uint64(now);
uint256 grantIndex = grants[holder].length;
for (uint256 i = 0; i < grantIndex; i++) {
date = Math.max64(grants[holder][i].vesting, date);
}
}
}

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test/TokenVesting.js Normal file
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const BigNumber = web3.BigNumber
require('chai')
.use(require('chai-as-promised'))
.use(require('chai-bignumber')(BigNumber))
.should();
import EVMThrow from './helpers/EVMThrow'
import latestTime from './helpers/latestTime';
import {increaseTimeTo, duration} from './helpers/increaseTime';
const MintableToken = artifacts.require('MintableToken');
const TokenVesting = artifacts.require('TokenVesting');
contract('TokenVesting', function ([_, owner, beneficiary]) {
const amount = new BigNumber(1000);
beforeEach(async function () {
this.token = await MintableToken.new({ from: owner });
this.start = latestTime() + duration.minutes(1); // +1 minute so it starts after contract instantiation
this.cliff = duration.years(1);
this.duration = duration.years(2);
this.vesting = await TokenVesting.new(beneficiary, this.start, this.cliff, this.duration, true, { from: owner });
await this.token.mint(this.vesting.address, amount, { from: owner });
});
it('cannot be released before cliff', async function () {
await this.vesting.release(this.token.address).should.be.rejectedWith(EVMThrow);
});
it('can be released after cliff', async function () {
await increaseTimeTo(this.start + this.cliff + duration.weeks(1));
await this.vesting.release(this.token.address).should.be.fulfilled;
});
it('should release proper amount after cliff', async function () {
await increaseTimeTo(this.start + this.cliff);
const { receipt } = await this.vesting.release(this.token.address);
const releaseTime = web3.eth.getBlock(receipt.blockNumber).timestamp;
const balance = await this.token.balanceOf(beneficiary);
balance.should.bignumber.equal(amount.mul(releaseTime - this.start).div(this.duration).floor());
});
it('should linearly release tokens during vesting period', async function () {
const vestingPeriod = this.duration - this.cliff;
const checkpoints = 4;
for (let i = 1; i <= checkpoints; i++) {
const now = this.start + this.cliff + i * (vestingPeriod / checkpoints);
await increaseTimeTo(now);
await this.vesting.release(this.token.address);
const balance = await this.token.balanceOf(beneficiary);
const expectedVesting = amount.mul(now - this.start).div(this.duration).floor();
balance.should.bignumber.equal(expectedVesting);
}
});
it('should have released all after end', async function () {
await increaseTimeTo(this.start + this.duration);
await this.vesting.release(this.token.address);
const balance = await this.token.balanceOf(beneficiary);
balance.should.bignumber.equal(amount);
});
it('should be revoked by owner if revocable is set', async function () {
await this.vesting.revoke(this.token.address, { from: owner }).should.be.fulfilled;
});
it('should fail to be revoked by owner if revocable not set', async function () {
const vesting = await TokenVesting.new(beneficiary, this.start, this.cliff, this.duration, false, { from: owner } );
await vesting.revoke(this.token.address, { from: owner }).should.be.rejectedWith(EVMThrow);
});
it('should return the non-vested tokens when revoked by owner', async function () {
await increaseTimeTo(this.start + this.cliff + duration.weeks(1));
await this.vesting.release(this.token.address);
const vested = await this.vesting.vestedAmount(this.token.address);
const balance = await this.token.balanceOf(this.vesting.address);
await this.vesting.revoke(this.token.address, { from: owner });
const ownerBalance = await this.token.balanceOf(owner);
ownerBalance.should.bignumber.equal(balance.sub(vested));
});
it('should keep the vested tokens when revoked by owner', async function () {
await increaseTimeTo(this.start + this.cliff + duration.weeks(1));
await this.vesting.release(this.token.address);
const vested = await this.vesting.vestedAmount(this.token.address);
await this.vesting.revoke(this.token.address, { from: owner });
const balance = await this.token.balanceOf(this.vesting.address);
balance.should.bignumber.equal(vested);
});
});

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test/VestedToken.js
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const assertJump = require('./helpers/assertJump');
const timer = require('./helpers/timer');
var VestedTokenMock = artifacts.require("./helpers/VestedTokenMock.sol");
contract('VestedToken', function(accounts) {
let token = null
let now = 0
const tokenAmount = 50
const granter = accounts[0]
const receiver = accounts[1]
beforeEach(async () => {
token = await VestedTokenMock.new(granter, 100);
now = web3.eth.getBlock(web3.eth.blockNumber).timestamp;
})
it('granter can grant tokens without vesting', async () => {
await token.transfer(receiver, tokenAmount, { from: granter })
assert.equal(await token.balanceOf(receiver), tokenAmount);
assert.equal(await token.transferableTokens(receiver, now), tokenAmount);
})
describe('getting a revokable/non-burnable token grant', async () => {
const cliff = 10000
const vesting = 20000 // seconds
beforeEach(async () => {
await token.grantVestedTokens(receiver, tokenAmount, now, now + cliff, now + vesting, true, false, { from: granter })
})
it('tokens are received', async () => {
assert.equal(await token.balanceOf(receiver), tokenAmount);
})
it('has 0 transferable tokens before cliff', async () => {
assert.equal(await token.transferableTokens(receiver, now), 0);
})
it('all tokens are transferable after vesting', async () => {
assert.equal(await token.transferableTokens(receiver, now + vesting), tokenAmount);
})
it('throws when trying to transfer non vested tokens', async () => {
try {
await token.transfer(accounts[7], 1, { from: receiver })
assert.fail('should have thrown before');
} catch(error) {
assertJump(error);
}
})
it('throws when trying to transfer from non vested tokens', async () => {
try {
await token.approve(accounts[7], 1, { from: receiver })
await token.transferFrom(receiver, accounts[7], tokenAmount, { from: accounts[7] })
assert.fail('should have thrown before');
} catch(error) {
assertJump(error);
}
})
it('can be revoked by granter', async () => {
await token.revokeTokenGrant(receiver, 0, { from: granter });
assert.equal(await token.balanceOf(receiver), 0);
assert.equal(await token.balanceOf(granter), 100);
})
it('cannot be revoked by non granter', async () => {
try {
await token.revokeTokenGrant(receiver, 0, { from: accounts[3] });
assert.fail('should have thrown before');
} catch(error) {
assertJump(error);
}
})
it('can be revoked by granter and non vested tokens are returned', async () => {
await timer(cliff);
await token.revokeTokenGrant(receiver, 0, { from: granter });
assert.equal(await token.balanceOf(receiver), tokenAmount * cliff / vesting);
})
it('can transfer all tokens after vesting ends', async () => {
await timer(vesting);
await token.transfer(accounts[7], tokenAmount, { from: receiver })
assert.equal(await token.balanceOf(accounts[7]), tokenAmount);
})
it('can approve and transferFrom all tokens after vesting ends', async () => {
await timer(vesting);
await token.approve(accounts[7], tokenAmount, { from: receiver })
await token.transferFrom(receiver, accounts[7], tokenAmount, { from: accounts[7] })
assert.equal(await token.balanceOf(accounts[7]), tokenAmount);
})
it('can handle composed vesting schedules', async () => {
await timer(cliff);
await token.transfer(accounts[7], 12, { from: receiver })
assert.equal(await token.balanceOf(accounts[7]), 12);
let newNow = web3.eth.getBlock(web3.eth.blockNumber).timestamp
await token.grantVestedTokens(receiver, tokenAmount, newNow, newNow + cliff, newNow + vesting, false, false, { from: granter })
await token.transfer(accounts[7], 13, { from: receiver })
assert.equal(await token.balanceOf(accounts[7]), tokenAmount / 2);
assert.equal(await token.balanceOf(receiver), 3 * tokenAmount / 2)
assert.equal(await token.transferableTokens(receiver, newNow), 0)
await timer(vesting);
await token.transfer(accounts[7], 3 * tokenAmount / 2, { from: receiver })
assert.equal(await token.balanceOf(accounts[7]), tokenAmount * 2)
})
})
describe('getting a non-revokable token grant', async () => {
const cliff = 10000
const vesting = 20000 // seconds
beforeEach(async () => {
await token.grantVestedTokens(receiver, tokenAmount, now, now + cliff, now + vesting, false, false, { from: granter })
})
it('tokens are received', async () => {
assert.equal(await token.balanceOf(receiver), tokenAmount);
})
it('throws when granter attempts to revoke', async () => {
try {
await token.revokeTokenGrant(receiver, 0, { from: granter });
assert.fail('should have thrown before');
} catch(error) {
assertJump(error);
}
})
})
describe('getting a revokable/burnable token grant', async () => {
const cliff = 100000
const vesting = 200000 // seconds
const burnAddress = '0x000000000000000000000000000000000000dead'
beforeEach(async () => {
await token.grantVestedTokens(receiver, tokenAmount, now, now + cliff, now + vesting, true, true, { from: granter })
})
it('tokens are received', async () => {
assert.equal(await token.balanceOf(receiver), tokenAmount);
})
it('can be revoked by granter and tokens are burned', async () => {
await token.revokeTokenGrant(receiver, 0, { from: granter });
assert.equal(await token.balanceOf(receiver), 0);
assert.equal(await token.balanceOf(burnAddress), tokenAmount);
})
it('cannot be revoked by non granter', async () => {
try {
await token.revokeTokenGrant(receiver, 0, { from: accounts[3] });
assert.fail('should have thrown before');
} catch(error) {
assertJump(error);
}
})
it('can be revoked by granter and non vested tokens are returned', async () => {
await timer(cliff);
await token.revokeTokenGrant(receiver, 0, { from: granter });
assert.equal(await token.balanceOf(burnAddress), tokenAmount * cliff / vesting);
})
})
});

11
test/helpers/VestedTokenMock.sol
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pragma solidity ^0.4.11;
import '../../contracts/token/VestedToken.sol';
// mock class using StandardToken
contract VestedTokenMock is VestedToken {
function VestedTokenMock(address initialAccount, uint256 initialBalance) {
balances[initialAccount] = initialBalance;
totalSupply = initialBalance;
}
}