Cosmos Non-Fungible Token

x/nft is an implementation of a Cosmos SDK module, per ADR 43open in new window, that allows you to create nft classification, create nft, transfer nft, update nft, and support various queries by integrating the module. It is fully compatible with the ERC721 specification.

Concepts

Class

x/nft module defines a struct Class to describe the common characteristics of a class of nft, under this class, you can create a variety of nft, which is equivalent to an erc721 contract for Ethereum. The design is defined in the ADR 043open in new window.

NFT

The full name of NFT is Non-Fungible Tokens. Because of the irreplaceable nature of NFT, it means that it can be used to represent unique things. The nft implemented by this module is fully compatible with Ethereum ERC721 standard.

State

Class

Class is mainly composed of id, name, symbol, description, uri, uri_hash,data where id is the unique identifier of the class, similar to the Ethereum ERC721 contract address, the others are optional.

  • Class: 0x01 | classID | -> ProtocolBuffer(Class)

NFT

NFT is mainly composed of class_id, id, uri, uri_hash and data. Among them, class_id and id are two-tuples that identify the uniqueness of nft, uri and uri_hash is optional, which identifies the off-chain storage location of the nft, and data is an Any type. Use Any chain of x/nft modules can be customized by extending this field

  • NFT: 0x02 | classID | 0x00 | nftID |-> ProtocolBuffer(NFT)

NFTOfClassByOwner

NFTOfClassByOwner is mainly to realize the function of querying all nfts using classID and owner, without other redundant functions.

  • NFTOfClassByOwner: 0x03 | owner | 0x00 | classID | 0x00 | nftID |-> 0x01

Owner

Since there is no extra field in NFT to indicate the owner of nft, an additional key-value pair is used to save the ownership of nft. With the transfer of nft, the key-value pair is updated synchronously.

  • OwnerKey: 0x04 | classID | 0x00 | nftID |-> owner

TotalSupply

TotalSupply is responsible for tracking the number of all nfts under a certain class. Mint operation is performed under the changed class, supply increases by one, burn operation, and supply decreases by one.

  • OwnerKey: 0x05 | classID |-> totalSupply

Messages

In this section we describe the processing of messages for the nft module.

MsgSend

You can use the MsgSend message to transfer the ownership of nft. This is a function provided by the x/nft module. Of course, you can use the Transfer method to implement your own transfer logic, but you need to pay extra attention to the transfer permissions.

The message handling should fail if:

  • provided ClassID does not exist.
  • provided Id does not exist.
  • provided Sender does not the owner of nft.

Events

The nft module emits proto events defined in the Protobuf referenceopen in new window.

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