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Custom Transactions ​

Utilizing predicate logic unlocks a wide range of possibilities for your dApps when creating transactions. Therefore, pairing predicates with custom transactions can help you achieve more complex use cases. This can be achieved by instantiating a custom transaction, appending the predicate resources, and submitting the transaction via a successfully validated predicate.

Custom transactions can be shaped via a ScriptTransactionRequest instance. For more information on crafting custom transactions and the methods available to them, please refer to the Transaction Request guide.

However, this guide will demonstrate how to use a predicate in a custom transaction. Consider the following predicate, where a configurable pin must be used to validate the predicate and unlock the funds:

rust
predicate;

configurable {
    PIN: u64 = 1337,
}

fn main(pin: u64) -> bool {
    return PIN == pin;
}
See code in context

We can interact with the above and include it in a custom transaction like so:

ts
import { Provider, ScriptTransactionRequest, Wallet } from 'fuels';

import { LOCAL_NETWORK_URL, WALLET_PVT_KEY } from '../env';
import { ConfigurablePin } from '../typegend';
import type { ConfigurablePinInputs } from '../typegend/predicates/ConfigurablePin';

// Setup
const provider = await Provider.create(LOCAL_NETWORK_URL);
const sender = Wallet.fromPrivateKey(WALLET_PVT_KEY, provider);
const receiver = Wallet.generate({ provider });
const assetId = provider.getBaseAssetId();
const amountToFundPredicate = 300_000;
const amountToReceiver = 100_000;

// Instantiate the predicate using valid predicate data, aka the pin we need
// to send the funds to the receiver
const data: ConfigurablePinInputs = [1337];
const predicate = new ConfigurablePin({ provider, data });

// Fund the predicate, so that we can send these funds via predicate logic
// to the receiver
const fundPredicateTx = await sender.transfer(
  predicate.address,
  amountToFundPredicate,
  assetId
);
await fundPredicateTx.waitForResult();
const initialPredicateBalance = await predicate.getBalance(assetId);

// Instantiate the script request
const customRequest = new ScriptTransactionRequest();

// Get the predicate resources that we would like to transfer
const predicateResources = await predicate.getResourcesToSpend([
  { assetId, amount: amountToReceiver },
]);

// Add the resources for the transfer of the asset to the receiver. The resources
// adds the required inputs, and the output is for the transfer to the receiver address
customRequest.addResources(predicateResources);
customRequest.addCoinOutput(receiver.address, amountToReceiver, assetId);

// Estimate the transaction cost and fund accordingly
const txCost = await predicate.getTransactionCost(customRequest);
customRequest.gasLimit = txCost.gasUsed;
customRequest.maxFee = txCost.maxFee;
await predicate.fund(customRequest, txCost);

// Submit the transaction and await it's result
const predicateTx = await predicate.sendTransaction(customRequest);
await predicateTx.waitForResult();
See code in context