feat: add baseTokenURI to ERC721Metadata

contracts/mocks/ERC721FullMock.sol

@@ -26,4 +26,12 @@ contract ERC721FullMock is ERC721Full, ERC721Mintable, ERC721MetadataMintable, E
     function setTokenURI(uint256 tokenId, string memory uri) public {
         _setTokenURI(tokenId, uri);
     }
+
+    function setBaseTokenURI(string memory baseURI) public {
+        _setBaseTokenURI(baseURI);
+    }
+
+    function baseTokenURI() public view returns (string memory) {
+        return _baseTokenURI();
+    }
 }

contracts/token/ERC721/ERC721Metadata.sol

@@ -12,6 +12,9 @@ contract ERC721Metadata is Context, ERC165, ERC721, IERC721Metadata {
     // Token symbol
     string private _symbol;
 
+    // Base URI
+    string private _baseURI;
+
     // Optional mapping for token URIs
     mapping(uint256 => string) private _tokenURIs;
 
@@ -56,7 +59,16 @@ contract ERC721Metadata is Context, ERC165, ERC721, IERC721Metadata {
      * Throws if the token ID does not exist. May return an empty string.
      * @param tokenId uint256 ID of the token to query
      */
-    function tokenURI(uint256 tokenId) external view returns (string memory) {
+    function tokenURI(uint256 tokenId) public view returns (string memory) {
+        return string(abi.encodePacked(_baseTokenURI(), _tokenURI(tokenId)));
+    }
+
+    /**
+     * @dev Internal returns an URI for a given token ID.
+     * Throws if the token ID does not exist. May return an empty string.
+     * @param tokenId uint256 ID of the token to query
+     */
+    function _tokenURI(uint256 tokenId) internal view returns (string memory) {
         require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");
         return _tokenURIs[tokenId];
     }
@@ -72,6 +84,22 @@ contract ERC721Metadata is Context, ERC165, ERC721, IERC721Metadata {
         _tokenURIs[tokenId] = uri;
     }
 
+    /**
+     * @dev Internal function to get the base token URI.
+     * @return string representing the base token URI
+     */
+    function _baseTokenURI() internal view returns (string memory) {
+        return _baseURI;
+    }
+
+    /**
+     * @dev Internal function to set the base token URI.
+     * @param uri string base URI to assign
+     */
+    function _setBaseTokenURI(string memory uri) internal {
+        _baseURI = uri;
+    }
+
     /**
      * @dev Internal function to burn a specific token.
      * Reverts if the token does not exist.

test/token/ERC721/ERC721Full.test.js

@@ -72,8 +72,8 @@ contract('ERC721Full', function ([
     });
 
     describe('metadata', function () {
+      const baseURI = 'https://api.com/v1/';
       const sampleUri = 'mock://mytoken';
-
       it('has a name', async function () {
         expect(await this.token.name()).to.be.equal(name);
       });
@@ -82,11 +82,32 @@ contract('ERC721Full', function ([
         expect(await this.token.symbol()).to.be.equal(symbol);
       });
 
+      it('sets and returns the base token URI', async function () {
+        await this.token.setBaseTokenURI(baseURI);
+        expect(await this.token.baseTokenURI()).to.be.equal(baseURI);
+      });
+
       it('sets and returns metadata for a token id', async function () {
         await this.token.setTokenURI(firstTokenId, sampleUri);
         expect(await this.token.tokenURI(firstTokenId)).to.be.equal(sampleUri);
       });
 
+      it('sets and returns metadata for a token id with base token URI set', async function () {
+        await this.token.setBaseTokenURI(baseURI);
+        await this.token.setTokenURI(firstTokenId, sampleUri);
+        expect(await this.token.tokenURI(firstTokenId)).to.be.equal(baseURI + sampleUri);
+      });
+
+      it('changes base token URI set', async function () {
+        await this.token.setBaseTokenURI(baseURI);
+        await this.token.setTokenURI(firstTokenId, sampleUri);
+        expect(await this.token.tokenURI(firstTokenId)).to.be.equal(baseURI + sampleUri);
+
+        const newBaseURI = 'https://api.com/v2/';
+        await this.token.setBaseTokenURI(newBaseURI);
+        expect(await this.token.tokenURI(firstTokenId)).to.be.equal(newBaseURI + sampleUri);
+      });
+
       it('reverts when setting metadata for non existent token id', async function () {
         await expectRevert(
           this.token.setTokenURI(nonExistentTokenId, sampleUri), 'ERC721Metadata: URI set of nonexistent token'