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Minted Token Asset Id

Icon LinkMinted Token Asset ID

The asset ID of a token on the Fuel network is determined by two factors:

  • The ID of the contract that minted the token,
  • A sub-identifier (Sub ID)
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Both of which are bits256 strings.

The process involves applying a SHA-256 hash algorithm to the combination of the Contract ID and the Sub ID, to derive an Asset ID - as explained here Icon Link.

Consider the following simplified token contract: 

contract;
 
use std::asset::{burn, mint, transfer};
 
abi Token {
    fn transfer_to_address(target: Address, asset_id: AssetId, coins: u64);
    fn transfer_to_contract(recipient: ContractId, asset_id: AssetId, coins: u64);
    fn mint_coins(sub_id: b256, mint_amount: u64);
    fn burn_coins(sub_id: b256, burn_amount: u64);
}
 
impl Token for Contract {
    fn transfer_to_address(recipient: Address, asset_id: AssetId, amount: u64) {
        transfer(Identity::Address(recipient), asset_id, amount);
    }
 
    fn transfer_to_contract(target: ContractId, asset_id: AssetId, amount: u64) {
        transfer(Identity::ContractId(target), asset_id, amount);
    }
    fn mint_coins(sub_id: b256, mint_amount: u64) {
        mint(sub_id, mint_amount);
    }
 
    fn burn_coins(sub_id: b256, burn_amount: u64) {
        burn(sub_id, burn_amount);
    }
}

Imagine that this contract is already deployed and we are about to mint some coins: 

import { bn, getMintedAssetId, Provider, Wallet } from 'fuels';
 
import { LOCAL_NETWORK_URL, WALLET_PVT_KEY } from '../../../../env';
import { TokenFactory } from '../../../../typegend';
 
const provider = await Provider.create(LOCAL_NETWORK_URL);
const deployer = Wallet.fromPrivateKey(WALLET_PVT_KEY, provider);
 
const deployContract = await TokenFactory.deploy(deployer);
const { contract } = await deployContract.waitForResult();
 
// Any valid bits256 string can be used as a sub ID
const subID =
  '0xc7fd1d987ada439fc085cfa3c49416cf2b504ac50151e3c2335d60595cb90745';
const mintAmount = bn(1000);
 
const { waitForResult } = await contract.functions
  .mint_coins(subID, mintAmount)
  .call();
await waitForResult();
 
// Get the minted
const mintedAssetId = getMintedAssetId(contract.id.toB256(), subID);

Icon LinkObtaining the Asset ID

Since the asset ID depends on the contract ID, which is always dynamic (unlike the sub ID, which can be set to a fixed value), the helper getMintedAssetId can be used to easily obtain the asset ID for a given contract ID and sub ID.

Icon LinkCreate Asset Id

The SDK provides a helper named createAssetId which takes the contract ID and sub ID as parameters. This helper internally calls getMintedAssetId and returns the Sway native parameter AssetId Icon Link, ready to be used in a Sway program invocation: 

import type { AssetId, B256Address } from 'fuels';
import { createAssetId } from 'fuels';
 
const contractId: B256Address =
  '0x67eb6a384151a30e162c26d2f3e81ca2023dfa1041000210caed42ead32d63c0';
const subID: B256Address =
  '0xc7fd1d987ada439fc085cfa3c49416cf2b504ac50151e3c2335d60595cb90745';
 
const assetId: AssetId = createAssetId(contractId, subID);
// {
//   bits: '0x16c1cb95e999d0c74806f97643af158e821a0063a0c8ea61183bad2497b57478'
// }