ERC-1155 Metadata Facet

ERC-1155 token metadata and URI management

Key Features

• Exposes external uri function for token metadata retrieval.
• Reads from and writes to shared diamond storage for URI management.
• Compatible with ERC-2535 diamond standard for upgradeability.
• Exports its selectors for diamond discovery.

Overview

This facet provides external functions for managing and retrieving ERC-1155 token metadata URIs within a diamond. It accesses shared diamond storage to store and retrieve base URIs and token-specific URIs. Developers integrate this facet to expose ERC-1155 metadata functionality while maintaining diamond upgradeability.

Storage

ERC1155MetadataStorage

Definition

struct ERC1155MetadataStorage {
  string uri;
  string baseURI;
  mapping(uint256 tokenId => string) tokenURIs;
}

State Variables

Property	Type	Description
STORAGE_POSITION	bytes32	Diamond storage slot position for this module (Value: keccak256("erc1155.metadata"))

Functions

uri

Returns the URI for token type _id. If a token-specific URI is set in tokenURIs[_id], returns the concatenation of baseURI and tokenURIs[_id]. Note that baseURI is empty by default and must be set explicitly if concatenation is desired. If no token-specific URI is set, returns the default URI which applies to all token types. The default URI may contain the substring {id} which clients should replace with the actual token ID.

function uri(uint256 _id) external view returns (string memory);

Parameters:

Property	Type	Description
_id	uint256	The token ID to query.

Returns:

Property	Type	Description
-	string	The URI for the token type.

---

exportSelectors

Exports the function selectors of the ERC1155MetadataFacet 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 ERC1155MetadataFacet

Events

Emitted when the URI for token type _id changes to _value.

Signature:

event URI(string _value, uint256 indexed _id);

Parameters:

Property	Type	Description
_value	string	The new URI for the token type.
_id	uint256	The token type whose URI changed.

Best Practices

Best Practice

• Ensure the ERC1155MetadataFacet is correctly added to the diamond during initialization.
• Access URIs using the uri(uint256 _id) function through the diamond proxy.
• If using the baseURI concatenation feature, ensure baseURI is set via an appropriate admin facet.

Security Considerations

Security

The uri function is a read-only operation and does not pose reentrancy risks. Input validation for _id is handled by the caller or other facets interacting with this facet. Ensure that any facet responsible for setting URIs enforces appropriate access control to prevent unauthorized modifications.

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Last updated:March 13, 2026