Implement EIP-4906 (MetadataUpdated event)

contracts/GuildPin.sol

@@ -141,7 +141,7 @@ contract GuildPin is IGuildPin, Initializable, OwnableUpgradeable, UUPSUpgradeab
 
         cids[tokenId] = newCid;
 
-        emit TokenURIUpdated(tokenId);
+        emit MetadataUpdate(tokenId);
     }
 
     function setPinStrings(GuildAction guildAction, PinStrings memory pinStrings) public onlyOwner {

contracts/interfaces/IERC4906.sol

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import { IERC721Upgradeable } from "@openzeppelin/contracts-upgradeable/token/ERC721/IERC721Upgradeable.sol";
+import { IERC165Upgradeable } from "@openzeppelin/contracts-upgradeable/utils/introspection/IERC165Upgradeable.sol";
+
+/// @title EIP-721 Metadata Update Extension
+interface IERC4906 is IERC165Upgradeable, IERC721Upgradeable {
+    /// @dev This event emits when the metadata of a token is changed.
+    /// So that the third-party platforms such as NFT market could
+    /// timely update the images and related attributes of the NFT.
+    event MetadataUpdate(uint256 _tokenId);
+
+    /// @dev This event emits when the metadata of a range of tokens is changed.
+    /// So that the third-party platforms such as NFT market could
+    /// timely update the images and related attributes of the NFTs.
+    event BatchMetadataUpdate(uint256 _fromTokenId, uint256 _toTokenId);
+}

contracts/interfaces/IGuildPin.sol

@@ -106,10 +106,6 @@ interface IGuildPin {
     /// @param guildAction The action whose strings were set.
     event PinStringsSet(GuildAction guildAction);
 
-    /// @notice Event emitted whenever a token's cid is updated.
-    /// @param tokenId The id of the updated token.
-    event TokenURIUpdated(uint256 tokenId);
-
     /// @notice Event emitted when the validSigner is changed.
     /// @param newValidSigner The new address of validSigner.
     event ValidSignerChanged(address newValidSigner);

contracts/token/SoulboundERC721.sol

@@ -3,16 +3,18 @@ pragma solidity 0.8.19;
 
 /* solhint-disable max-line-length */
 
+import { IERC4906 } from "../interfaces/IERC4906.sol";
 import { ERC721Upgradeable } from "@openzeppelin/contracts-upgradeable/token/ERC721/ERC721Upgradeable.sol";
 import { IERC721Upgradeable } from "@openzeppelin/contracts-upgradeable/token/ERC721/IERC721Upgradeable.sol";
 import { ERC721EnumerableUpgradeable } from "@openzeppelin/contracts-upgradeable/token/ERC721/extensions/ERC721EnumerableUpgradeable.sol";
 import { IERC721EnumerableUpgradeable } from "@openzeppelin/contracts-upgradeable/token/ERC721/extensions/IERC721EnumerableUpgradeable.sol";
+import { IERC165Upgradeable } from "@openzeppelin/contracts-upgradeable/utils/introspection/IERC165Upgradeable.sol";
 
 /* solhint-enable max-line-length */
 
 /// @title An enumerable soulbound ERC721.
 /// @notice Allowance and transfer-related functions are disabled.
-contract SoulboundERC721 is ERC721Upgradeable, ERC721EnumerableUpgradeable {
+contract SoulboundERC721 is ERC721Upgradeable, ERC721EnumerableUpgradeable, IERC4906 {
     /// @notice Empty space reserved for future updates.
     uint256[50] private __gap;
 
@@ -28,8 +30,11 @@ contract SoulboundERC721 is ERC721Upgradeable, ERC721EnumerableUpgradeable {
     /// @inheritdoc ERC721EnumerableUpgradeable
     function supportsInterface(
         bytes4 interfaceId
-    ) public view virtual override(ERC721EnumerableUpgradeable, ERC721Upgradeable) returns (bool) {
-        return interfaceId == type(IERC721EnumerableUpgradeable).interfaceId || super.supportsInterface(interfaceId);
+    ) public view virtual override(ERC721EnumerableUpgradeable, ERC721Upgradeable, IERC165Upgradeable) returns (bool) {
+        return
+            interfaceId == 0x49064906 || // ERC4906
+            interfaceId == type(IERC721EnumerableUpgradeable).interfaceId ||
+            super.supportsInterface(interfaceId);
     }
 
     function approve(

docs/contracts/interfaces/IERC4906.md

@@ -0,0 +1,43 @@
+# IERC4906
+
+EIP-721 Metadata Update Extension
+
+## Events
+
+### MetadataUpdate
+
+```solidity
+event MetadataUpdate(
+    uint256 _tokenId
+)
+```
+
+This event emits when the metadata of a token is changed.
+So that the third-party platforms such as NFT market could
+timely update the images and related attributes of the NFT.
+
+#### Parameters
+
+| Name | Type | Description |
+| :--- | :--- | :---------- |
+| `_tokenId` | uint256 |  |
+### BatchMetadataUpdate
+
+```solidity
+event BatchMetadataUpdate(
+    uint256 _fromTokenId,
+    uint256 _toTokenId
+)
+```
+
+This event emits when the metadata of a range of tokens is changed.
+So that the third-party platforms such as NFT market could
+timely update the images and related attributes of the NFTs.
+
+#### Parameters
+
+| Name | Type | Description |
+| :--- | :--- | :---------- |
+| `_fromTokenId` | uint256 |  |
+| `_toTokenId` | uint256 |  |
+

docs/contracts/interfaces/IGuildPin.md

@@ -177,21 +177,6 @@ Event emitted when pretty strings are set for a GuildAction.
 | Name | Type | Description |
 | :--- | :--- | :---------- |
 | `guildAction` | enum IGuildPin.GuildAction | The action whose strings were set. |
-### TokenURIUpdated
-
-```solidity
-event TokenURIUpdated(
-    uint256 tokenId
-)
-```
-
-Event emitted whenever a token's cid is updated.
-
-#### Parameters
-
-| Name | Type | Description |
-| :--- | :--- | :---------- |
-| `tokenId` | uint256 | The id of the updated token. |
 ### ValidSignerChanged
 
 ```solidity

test/GuildPin.spec.ts

@@ -705,9 +705,9 @@ describe("GuildPin", () => {
         expect(decodeTokenURI(newTokenURI)).to.contain(cids[1]);
       });
 
-      it("should emit TokenURIUpdated event", async () => {
+      it("should emit MetadataUpdate event", async () => {
         await expect(pin.updateImageURI(samplePinData, timestamp, cids[0], signature))
-          .to.emit(pin, "TokenURIUpdated")
+          .to.emit(pin, "MetadataUpdate")
           .withArgs(1);
       });
     });