Unique Cell

A unique cell can be created on the Nervos CKB through TypeID which makes sure the unique cell cannot be updated or destroyed.

The unique cell data can store any format data, such as Extensible UDT (xUDT) token information and the contract will not check the content and format of the cell data.

When minting xUDT assets, a unique cell can be created at the same time to store xUDT information, but for the same xUDT, only the first unique cell that appears will be accepted.

Unique Type Script

unique type script:
  code_hash: 
    unique_type
  args:
    type_id[0..20]

How to generate unique type script args

https://github.com/nervosnetwork/rfcs/blob/master/rfcs/0022-transaction-structure/0022-transaction-structure.md#type-id

There are two ways to create a new cell with a specific type id.

1. Create a transaction which uses any out point as tx.inputs[0] and has a output cell whose type script is Type ID. The output cell's type script args is the hash of tx.inputs[0] and its output index. Because any out point can only be used once as an input, tx.inputs[0] and thus the new type id must be different in each creation transaction.
2. Destroy an old cell with a specific type id and create a new cell with the same type id in the same transaction.

Implementation can be found in generator-example/src/index.ts and generator-example/src/lumos.ts

xUDT Information

The following is the info data format recommended by xUDT：

# general

# The number of decimals the XUDT token uses - e.g. 8, means to divide the token amount by 100000000 to get its user representation. 
# 0xF0-0xFF reserved
decimal: uint8  

# The length of the name in bytes
name_len: uint8

# The name of the XUDT token - e.g. USDT, means to convert 'Tether USDT' to hex form '0x5465746865722055534454'
name: variable max 255

# The length of the symbol in bytes
symbol_len: uint8

# The symbol of the XUDT token - e.g. USDT, means to convert 'USDT' to hex form '0x55534454'
symbol: variable max 255

# optional
# tag0 | data_len0 | data0 | tag1 | data_len1 | data1 | tag2 | data_len2 | data2
total_supply: tag(4bytes) | data_length(4bytes) | data
...

Notice: The xUDT information format is NOT a key-value structure.

You can find the code about how to construct the xUDT information data in metadata/examples/index.ts

The @utxostack/metadata SDK should be installed first.

npm i @utxostack/metadata
# or
yarn add @utxostack/metadata
# or
pnpm add @utxostack/metadata

import { TokenInfo, encodeTokenInfo, Metadata, encodeMetadata } from '@utxostack/metadata'
const token: TokenInfo = {
  decimal: 8,
  name: 'Bitcoin',
  symbol: 'BTC',
  totalSupply: `0x${(BigInt(2100_0000) * BigInt(10 ** 8)).toString(16)}`,
}
const data = encodeTokenInfo(token)
console.log('encoded token info:', data)

const metadata: Metadata = {
  issuer: '0xa8efe3e8d534fbad88251c1f82cf2428f87637a27cfbf28b6365e9b74d895d18',
  circulatingSupply: `0x${(BigInt(1600_0000) * BigInt(10 ** 8)).toString(16)}`,
  tokenInfoCellTypeHash: '0x0f251aec82b7d329bfe94ac8456fd96c463248aec5551b18fd215ca5dcb94be7',
};
const hexData = encodeMetadata(metadata)
console.log('encoded metadata:', hexData)

Development

Build contracts:

make build

Run tests:

make test