Add ERC721URIStorage extension (#2555)

(cherry picked from commit 1705067e650a62e7f3f74909236511c1e1d472b8)

CHANGELOG.md

@@ -17,6 +17,7 @@
  * `ERC20Capped`: optimize gas usage of by enforcing te check directly in `_mint`. ([#2524](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2524))
  * Rename `UpgradeableProxy` to `ERC1967Proxy`. ([#2547](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2547))
  * `ERC777`: Optimize the gas costs of the constructor. ([#2551](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2551))
+ * `ERC721TokenUri`: Add a new extension ERC721TokenUri that implements the tokenURI behavior as it was available in 3.4.0. ([#2555](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2555))
 
 ### How to upgrade from 3.x
 

contracts/mocks/ERC721BurnableMock.sol

@@ -7,7 +7,19 @@ import "../token/ERC721/extensions/ERC721Burnable.sol";
 contract ERC721BurnableMock is ERC721Burnable {
     constructor(string memory name, string memory symbol) ERC721(name, symbol) { }
 
+    function exists(uint256 tokenId) public view returns (bool) {
+        return _exists(tokenId);
+    }
+
     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);
+    }
 }

contracts/mocks/ERC721EnumerableMock.sol

@@ -25,6 +25,10 @@ contract ERC721EnumerableMock is ERC721Enumerable {
         return _baseURI();
     }
 
+    function exists(uint256 tokenId) public view returns (bool) {
+        return _exists(tokenId);
+    }
+
     function mint(address to, uint256 tokenId) public {
         _mint(to, tokenId);
     }

contracts/mocks/ERC721PausableMock.sol

@@ -11,23 +11,31 @@ import "../token/ERC721/extensions/ERC721Pausable.sol";
 contract ERC721PausableMock is ERC721Pausable {
     constructor (string memory name, string memory symbol) ERC721(name, symbol) { }
 
-    function mint(address to, uint256 tokenId) public {
-        super._mint(to, tokenId);
+    function pause() external {
+        _pause();
     }
 
-    function burn(uint256 tokenId) public {
-        super._burn(tokenId);
+    function unpause() external {
+        _unpause();
     }
 
     function exists(uint256 tokenId) public view returns (bool) {
-        return super._exists(tokenId);
+        return _exists(tokenId);
     }
 
-    function pause() external {
-        _pause();
+    function mint(address to, uint256 tokenId) public {
+        _mint(to, tokenId);
     }
 
-    function unpause() external {
-        _unpause();
+    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);
     }
 }

contracts/mocks/ERC721URIStorageMock.sol

@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../token/ERC721/extensions/ERC721URIStorage.sol";
+
+/**
+ * @title ERC721Mock
+ * This mock just provides a public safeMint, mint, and burn functions for testing purposes
+ */
+contract ERC721URIStorageMock is ERC721URIStorage {
+    string private _baseTokenURI;
+
+    constructor (string memory name, string memory symbol) ERC721(name, symbol) { }
+
+    function _baseURI() internal view virtual override returns (string memory) {
+        return _baseTokenURI;
+    }
+
+    function setBaseURI(string calldata newBaseTokenURI) public {
+        _baseTokenURI = newBaseTokenURI;
+    }
+
+    function baseURI() public view returns (string memory) {
+        return _baseURI();
+    }
+
+    function setTokenURI(uint256 tokenId, string memory _tokenURI) public {
+        _setTokenURI(tokenId, _tokenURI);
+    }
+
+    function exists(uint256 tokenId) public view returns (bool) {
+        return _exists(tokenId);
+    }
+
+    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);
+    }
+}

contracts/token/ERC721/README.adoc

@@ -39,6 +39,8 @@ NOTE: This core set of contracts is designed to be unopinionated, allowing devel
 
 {{ERC721Burnable}}
 
+{{ERC721TokenUri}}
+
 == Presets
 
 These contracts are preconfigured combinations of the above features. They can be used through inheritance or as models to copy and paste their source code.

contracts/token/ERC721/extensions/ERC721URIStorage.sol

@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../ERC721.sol";
+
+/**
+ * @dev ERC721 token with storage based token uri management.
+ */
+abstract contract ERC721URIStorage is ERC721 {
+    using Strings for uint256;
+
+    // Optional mapping for token URIs
+    mapping (uint256 => string) private _tokenURIs;
+
+    /**
+     * @dev See {IERC721Metadata-tokenURI}.
+     */
+    function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
+        require(_exists(tokenId), "ERC721URIStorage: URI query for nonexistent token");
+
+        string memory _tokenURI = _tokenURIs[tokenId];
+        string memory base = _baseURI();
+
+        // If there is no base URI, return the token URI.
+        if (bytes(base).length == 0) {
+            return _tokenURI;
+        }
+        // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
+        if (bytes(_tokenURI).length > 0) {
+            return string(abi.encodePacked(base, _tokenURI));
+        }
+
+        return super.tokenURI(tokenId);
+    }
+
+    /**
+     * @dev Sets `_tokenURI` as the tokenURI of `tokenId`.
+     *
+     * Requirements:
+     *
+     * - `tokenId` must exist.
+     */
+    function _setTokenURI(uint256 tokenId, string memory _tokenURI) internal virtual {
+        require(_exists(tokenId), "ERC721URIStorage: URI set of nonexistent token");
+        _tokenURIs[tokenId] = _tokenURI;
+    }
+
+    /**
+     * @dev Destroys `tokenId`.
+     * The approval is cleared when the token is burned.
+     *
+     * Requirements:
+     *
+     * - `tokenId` must exist.
+     *
+     * Emits a {Transfer} event.
+     */
+    function _burn(uint256 tokenId) internal virtual override {
+        super._burn(tokenId);
+
+        if (bytes(_tokenURIs[tokenId]).length != 0) {
+            delete _tokenURIs[tokenId];
+        }
+    }
+}

test/token/ERC721/extensions/ERC721URIStorage.test.js

@@ -0,0 +1,87 @@
+const { BN, expectRevert } = require('@openzeppelin/test-helpers');
+
+const { expect } = require('chai');
+
+const ERC721URIStorageMock = artifacts.require('ERC721URIStorageMock');
+
+contract('ERC721URIStorage', function (accounts) {
+  const [ owner ] = accounts;
+
+  const name = 'Non Fungible Token';
+  const symbol = 'NFT';
+
+  const firstTokenId = new BN('5042');
+  const nonExistentTokenId = new BN('13');
+
+  beforeEach(async function () {
+    this.token = await ERC721URIStorageMock.new(name, symbol);
+  });
+
+  describe('token URI', function () {
+    beforeEach(async function () {
+      await this.token.mint(owner, firstTokenId);
+    });
+
+    const baseURI = 'https://api.com/v1/';
+    const sampleUri = 'mock://mytoken';
+
+    it('it is empty by default', async function () {
+      expect(await this.token.tokenURI(firstTokenId)).to.be.equal('');
+    });
+
+    it('reverts when queried for non existent token id', async function () {
+      await expectRevert(
+        this.token.tokenURI(nonExistentTokenId), 'ERC721URIStorage: URI query for nonexistent token',
+      );
+    });
+
+    it('can be set for a token id', async function () {
+      await this.token.setTokenURI(firstTokenId, sampleUri);
+      expect(await this.token.tokenURI(firstTokenId)).to.be.equal(sampleUri);
+    });
+
+    it('reverts when setting for non existent token id', async function () {
+      await expectRevert(
+        this.token.setTokenURI(nonExistentTokenId, sampleUri), 'ERC721URIStorage: URI set of nonexistent token',
+      );
+    });
+
+    it('base URI can be set', async function () {
+      await this.token.setBaseURI(baseURI);
+      expect(await this.token.baseURI()).to.equal(baseURI);
+    });
+
+    it('base URI is added as a prefix to the token URI', async function () {
+      await this.token.setBaseURI(baseURI);
+      await this.token.setTokenURI(firstTokenId, sampleUri);
+
+      expect(await this.token.tokenURI(firstTokenId)).to.be.equal(baseURI + sampleUri);
+    });
+
+    it('token URI can be changed by changing the base URI', async function () {
+      await this.token.setBaseURI(baseURI);
+      await this.token.setTokenURI(firstTokenId, sampleUri);
+
+      const newBaseURI = 'https://api.com/v2/';
+      await this.token.setBaseURI(newBaseURI);
+      expect(await this.token.tokenURI(firstTokenId)).to.be.equal(newBaseURI + sampleUri);
+    });
+
+    it('tokenId is appended to base URI for tokens with no URI', async function () {
+      await this.token.setBaseURI(baseURI);
+
+      expect(await this.token.tokenURI(firstTokenId)).to.be.equal(baseURI + firstTokenId);
+    });
+
+    it('tokens with URI can be burnt ', async function () {
+      await this.token.setTokenURI(firstTokenId, sampleUri);
+
+      await this.token.burn(firstTokenId, { from: owner });
+
+      expect(await this.token.exists(firstTokenId)).to.equal(false);
+      await expectRevert(
+        this.token.tokenURI(firstTokenId), 'ERC721URIStorage: URI query for nonexistent token',
+      );
+    });
+  });
+});