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:
predicate;
configurable {
PIN: u64 = 1337,
}
fn main(pin: u64) -> bool {
return PIN == pin;
}
We can interact with the above and include it in a custom transaction like so:
// #import { Provider, ScriptTransactionRequest, TESTNET_NETWORK_URL, Wallet };
import { PredicateFactory } from 'path/to/typegen/outputs';
import type { PredicateInputs } from 'path/to/typegen/outputs';
import { SENDER_PVT_KEY, RECEIVER_ADDRESS } from 'path/to/my/env/file';
// Setup
const provider = await Provider.create(TESTNET_NETWORK_URL);
const sender = Wallet.fromPrivateKey(SENDER_PVT_KEY, provider);
const receiver = Wallet.fromAddress(RECEIVER_ADDRESS, 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: PredicateInputs = [1337];
const predicate = new PredicateFactory({ 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();