ERC-721 Metadata Facet

ERC-721 token metadata retrieval for diamonds

Key Features

• Exposes external view functions for metadata retrieval.
• Accesses shared diamond storage for name, symbol, and base URI.
• Functions are routed through the diamond proxy.
• Compatible with ERC-2535 diamond standard.

Overview

This facet provides external view functions for retrieving ERC-721 token metadata, such as name, symbol, and token URIs, within a Compose diamond. It accesses shared diamond storage to ensure consistency across facets. Developers integrate this facet to expose token metadata directly through the diamond proxy.

Storage

ERC721MetadataStorage

Definition

struct ERC721MetadataStorage {
  string name;
  string symbol;
  string baseURI;
}

---

ERC721Storage

Definition

struct ERC721Storage {
  mapping(uint256 tokenId => address owner) ownerOf;
  mapping(address owner => uint256 balance) balanceOf;
  mapping(address owner => mapping(address operator => bool approved)) isApprovedForAll;
  mapping(uint256 tokenId => address approved) approved;
}

State Variables

Property	Type	Description
STORAGE_POSITION	bytes32	Diamond storage slot position for this module (Value: keccak256("erc721.metadata"))
ERC721_STORAGE_POSITION	bytes32	Diamond storage slot position for this module (Value: keccak256("erc721"))

Functions

name

Returns the token collection name.

function name() external view returns (string memory);

Returns:

Property	Type	Description
-	string	The name of the token collection.

---

symbol

Returns the token collection symbol.

function symbol() external view returns (string memory);

Returns:

Property	Type	Description
-	string	The symbol of the token collection.

---

tokenURI

Provide the metadata URI for a given token ID.

function tokenURI(uint256 _tokenId) external view returns (string memory);

Parameters:

Property	Type	Description
_tokenId	uint256	tokenID of the NFT to query the metadata from

Returns:

Property	Type	Description
-	string	the URI providing the detailed metadata of the specified tokenID

---

exportSelectors

Exports the function selectors of the ERC721MetadataFacet This function is use as a selector discovery mechanism for diamonds

function exportSelectors() external pure returns (bytes memory);

Returns:

Property	Type	Description
-	bytes	selectors The exported function selectors of the ERC721MetadataFacet

Errors

Signature:

error ERC721NonexistentToken(uint256 _tokenId);

Signature:

error ERC721InvalidOwner(address _owner);

Best Practices

Best Practice

• Ensure the ERC721MetadataFacet is added to the diamond with the correct selectors.
• Call name(), symbol(), and tokenURI() through the diamond proxy address.
• Verify storage slot compatibility if upgrading or adding facets that interact with ERC-721 storage.

Security Considerations

Security

The tokenURI function reverts with ERC721NonexistentToken if the provided _tokenId does not exist within the diamond's state. Input validation for _tokenId is crucial. Access to metadata is read-only and does not pose reentrancy risks. Follow standard Solidity security practices for diamond interactions.

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Last updated:March 13, 2026