ERC1155: Add a simple catch-all implementation of the metadata URI interface

contracts/mocks/ERC1155MetadataURICatchAllMock.sol

@@ -0,0 +1,22 @@
+pragma solidity ^0.6.0;
+
+import "../token/ERC1155/ERC1155MetadataURICatchAll.sol";
+
+/**
+ * @title ERC1155MetadataURICatchAllMock
+ * This mock just publicizes internal functions for testing purposes
+ * (mint is not specific to the tested contract but required by shouldBehaveLikeERC1155)
+ */
+contract ERC1155MetadataURICatchAllMock is ERC1155MetadataURICatchAll {
+    constructor (string memory uri) public ERC1155MetadataURICatchAll(uri) {
+        // solhint-disable-previous-line no-empty-blocks
+    }
+
+    function mint(address to, uint256 id, uint256 value, bytes memory data) public {
+        _mint(to, id, value, data);
+    }
+
+    function setURI(string memory newuri) public {
+        _setURI(newuri);
+    }
+}

contracts/token/ERC1155/ERC1155MetadataURICatchAll.sol

@@ -0,0 +1,46 @@
+pragma solidity ^0.6.0;
+
+import "./ERC1155.sol";
+import "./IERC1155MetadataURI.sol";
+import "../../introspection/ERC165.sol";
+
+contract ERC1155MetadataURICatchAll is ERC165, ERC1155, IERC1155MetadataURI {
+    // Catch-all URI with placeholders, e.g. https://example.com/{locale}/{id}.json
+    string private _uri;
+
+     /*
+     *     bytes4(keccak256('uri(uint256)')) == 0x0e89341c
+     */
+    bytes4 private constant _INTERFACE_ID_ERC1155_METADATA_URI = 0x0e89341c;
+
+    /**
+     * @dev Constructor function
+     */
+    constructor (string memory uri) public {
+        _setURI(uri);
+
+        // register the supported interfaces to conform to ERC1155 via ERC165
+        _registerInterface(_INTERFACE_ID_ERC1155_METADATA_URI);
+    }
+
+    /**
+     * @notice A distinct Uniform Resource Identifier (URI) for a given token.
+     * @dev URIs are defined in RFC 3986.
+     * The URI MUST point to a JSON file that conforms to the "ERC-1155 Metadata URI JSON Schema".
+     * param id uint256 ID of the token to query (ignored in this particular implementation,
+     * as an {id} parameter in the string is expected)
+     * @return URI string
+    */
+    function uri(uint256 /*id*/) external view override returns (string memory) {
+        return _uri;
+    }
+
+    /**
+     * @dev Internal function to set a new URI
+     * @param newuri New URI to be set
+     */
+    function _setURI(string memory newuri) internal virtual {
+        _uri = newuri;
+        emit URI(_uri, 0);
+    }
+}

contracts/token/ERC1155/IERC1155MetadataURI.sol

@@ -0,0 +1,11 @@
+pragma solidity ^0.6.0;
+
+import "./IERC1155.sol";
+
+/**
+ * @title ERC-1155 Multi Token Standard basic interface, optional metadata URI extension
+ * @dev See https://eips.ethereum.org/EIPS/eip-1155
+ */
+abstract contract IERC1155MetadataURI is IERC1155 {
+    function uri(uint256 id) external view virtual returns (string memory);
+}

contracts/token/ERC1155/README.md

@@ -4,9 +4,15 @@ sections:
     contracts:
       - IERC1155
       - ERC1155
+      - IERC1155MetadataURI
+      - ERC1155MetadataURICatchAll
       - IERC1155Receiver
+      - ERC1155Holder
 ---
 
 This set of interfaces and contracts are all related to the [ERC1155 Multi Token Standard](https://eips.ethereum.org/EIPS/eip-1155).
 
-The EIP consists of two interfaces which fulfill different roles, found here as `IERC1155`  and `IERC1155Receiver`. Only `IERC1155` is required for a contract to be ERC1155 compliant. The basic functionality is implemented in `ERC1155`.
+The EIP consists of three interfaces which fulfill different roles, found here as `IERC1155`, `IERC1155MetadataURI` and `IERC1155Receiver`. Only `IERC1155` is required for a contract to be ERC1155 compliant. The basic functionality is implemented in `ERC1155`.
+
+Additionally, `ERC1155MetadataURICatchAll` implements functionality for setting and querying a simple catch-all URI (i.e. one URI for all tokens, with the ID as a parameter) for metadata via the `IERC1155MetadataURI` interface.
+`ERC1155Holder` implements the `IERC1155Receiver` interface for contracts that can receive (and hold) ERC1155 tokens.

test/token/ERC1155/ERC1155MetadataURICatchAll.test.js

@@ -0,0 +1,60 @@
+const { accounts, contract } = require('@openzeppelin/test-environment');
+const { BN, expectEvent } = require('@openzeppelin/test-helpers');
+
+const { expect } = require('chai');
+
+const { shouldBehaveLikeERC1155 } = require('./ERC1155.behavior');
+const ERC1155MetadataURICatchAllMock = contract.fromArtifact('ERC1155MetadataURICatchAllMock');
+
+describe('ERC1155MetadataURICatchAll', function () {
+  const [creator, ...otherAccounts] = accounts;
+
+  const uriInit = 'https://example.com/{id}.json';
+  const tokenId = new BN(0); // catch-all always uses id 0 in event
+
+  beforeEach(async function () {
+    this.token = await ERC1155MetadataURICatchAllMock.new(uriInit, { from: creator });
+  });
+
+  it('emits a URI event in constructor', async function () {
+    await expectEvent.inConstruction(this.token, 'URI', {
+      value: uriInit,
+      id: tokenId,
+    });
+  });
+
+  shouldBehaveLikeERC1155(otherAccounts);
+
+  it('has a uri', async function () {
+    expect(await this.token.uri(
+      tokenId
+    )).to.be.equal(uriInit);
+  });
+
+  describe('internal functions', function () {
+    const uriNew = 'https://example.com/{locale}/{id}.json';
+
+    describe('_setURI(string memory newuri)', function () {
+      let receipt;
+      beforeEach(async function () {
+        receipt = await this.token.setURI(
+          uriNew,
+          { from: creator }
+        );
+      });
+
+      it('emits a URI event', function () {
+        expectEvent(receipt, 'URI', {
+          value: uriNew,
+          id: tokenId,
+        });
+      });
+
+      it('has correct URI set', async function () {
+        expect(await this.token.uri(
+          tokenId
+        )).to.be.equal(uriNew);
+      });
+    });
+  });
+});