Add address to string conversion (#3403)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

CHANGELOG.md

@@ -6,6 +6,7 @@
  * `TimelockController`: Migrate `_call` to `_execute` and allow inheritance and overriding similar to `Governor`. ([#3317](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3317))
  * `CrossChainEnabledPolygonChild`: replace the `require` statement with the custom error `NotCrossChainCall`. ([#3380](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3380))
  * `ERC20FlashMint`: Add customizable flash fee receiver. ([#3327](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3327))
+ * `Strings`: add a new overloaded function `toHexString` that converts an `address` with fixed length of 20 bytes to its not checksummed ASCII `string` hexadecimal representation. ([#3403](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3403))
 
 ## 4.6.0 (2022-04-26)
 

contracts/mocks/StringsMock.sol

@@ -16,4 +16,8 @@ contract StringsMock {
     function fromUint256HexFixed(uint256 value, uint256 length) public pure returns (string memory) {
         return Strings.toHexString(value, length);
     }
+
+    function fromAddressHexFixed(address addr) public pure returns (string memory) {
+        return Strings.toHexString(addr);
+    }
 }

contracts/utils/Strings.sol

@@ -8,6 +8,7 @@ pragma solidity ^0.8.0;
  */
 library Strings {
     bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";
+    uint8 private constant _ADDRESS_LENGTH = 20;
 
     /**
      * @dev Converts a `uint256` to its ASCII `string` decimal representation.
@@ -64,4 +65,11 @@ library Strings {
         require(value == 0, "Strings: hex length insufficient");
         return string(buffer);
     }
+
+    /**
+     * @dev Converts an `address` with fixed length of 20 bytes to its not checksummed ASCII `string` hexadecimal representation.
+     */
+    function toHexString(address addr) internal pure returns (string memory) {
+        return toHexString(uint256(uint160(addr)), _ADDRESS_LENGTH);
+    }
 }

test/utils/Strings.test.js

@@ -56,4 +56,16 @@ contract('Strings', function (accounts) {
         .to.equal(web3.utils.toHex(constants.MAX_UINT256));
     });
   });
+
+  describe('from address - fixed hex format', function () {
+    it('converts a random address', async function () {
+      const addr = '0xa9036907dccae6a1e0033479b12e837e5cf5a02f';
+      expect(await this.strings.fromAddressHexFixed(addr)).to.equal(addr);
+    });
+
+    it('converts an address with leading zeros', async function () {
+      const addr = '0x0000e0ca771e21bd00057f54a68c30d400000000';
+      expect(await this.strings.fromAddressHexFixed(addr)).to.equal(addr);
+    });
+  });
 });