How to Use Real-Time Data in Fuel Contracts

This guide explains how to use real-time Pyth data in Fuel contracts.

Install the Pyth SDK

Use the following dependency in your Forc.toml file to use the latest Pyth Fuel package:

[dependencies]
pyth_interface = { git = "https://github.com/pyth-network/pyth-crosschain", tag = "pyth-fuel-contract-v0.5.0" }

Pyth also provides a javascript SDK to interact with the Pyth contract on Fuel. You can install it using the following command:

bash copy npm install --save @pythnetwork/pyth-fuel-js

bash copy yarn add @pythnetwork/pyth-fuel-js

Write Contract Code

The code snippet below provides an example module fetching the ETH/USD price from Pyth price feeds:

contract;

use pyth_interface::{data_structures::price::{Price, PriceFeedId}, PythCore};

use std::bytes::Bytes;

abi UpdatePrice {
    fn valid_time_period() -> u64;
    fn get_price(price_feed_id: PriceFeedId) -> Price;
    fn get_price_unsafe(price_feed_id: PriceFeedId) -> Price;
    fn update_fee(update_data: Vec<Bytes>) -> u64;
    #[payable]
    fn update_price_feeds(update_fee: u64, update_data: Vec<Bytes>);
}

const PYTH_MAINNET_CONTRACT_ID = 0x1c86fdd9e0e7bc0d2ae1bf6817ef4834ffa7247655701ee1b031b52a24c523da; // Mainnet Contract
const PYTH_TESTNET_CONTRACT_ID = 0x25146735b29d4216639f7f8b1d7b921ff87a1d3051de62d6cceaacabeb33b8e7; // Testnet Contract
const FUEL_ETH_BASE_ASSET_ID = 0xf8f8b6283d7fa5b672b530cbb84fcccb4ff8dc40f8176ef4544ddb1f1952ad07;

impl UpdatePrice for Contract {
    fn valid_time_period() -> u64 {
        let pyth_contract = abi(PythCore, PYTH_MAINNET_CONTRACT_ID);
        let period = pyth_contract.valid_time_period();
        period
    }
    fn get_price(price_feed_id: PriceFeedId) -> Price {
        let pyth_contract = abi(PythCore, PYTH_MAINNET_CONTRACT_ID);
        let price = pyth_contract.price(price_feed_id);
        price
    }
    fn get_price_unsafe(price_feed_id: PriceFeedId) -> Price {
        let pyth_contract = abi(PythCore, PYTH_MAINNET_CONTRACT_ID);
        let price = pyth_contract.price_unsafe(price_feed_id);
        price
    }
    fn update_fee(update_data: Vec<Bytes>) -> u64 {
        let pyth_contract = abi(PythCore, PYTH_MAINNET_CONTRACT_ID);
        let fee = pyth_contract.update_fee(update_data);
        fee
    }
    #[payable]
    fn update_price_feeds(update_fee: u64, update_data: Vec<Bytes>) {
        let pyth_contract = abi(PythCore, PYTH_MAINNET_CONTRACT_ID);
        pyth_contract
            .update_price_feeds {
                asset_id: FUEL_ETH_BASE_ASSET_ID,
                coins: update_fee,
            }(update_data);
    }
}

The update_data argument contains verified prices from Pyth. Calling pyth_contract.update_price_feeds with this value updates the on-chain Pyth price and ensures your application has recent price data. The update_data can be fetched from Hermes; Consult Fetch Price Updates for more information on how to fetch the update_data.

Regarding the Pyth contract on Fuel, the caller must pay the fee in the base asset for functions like update_price_feeds. The fee is currently set to the minimum possible value (1 wei).

The code snippet above does the following things:

Defines an UpdatePrice ABI with functions to interact with the Pyth contract.
Implements the UpdatePrice ABI for the contract, providing the following functionality:
- valid_time_period(): Retrieves the valid time period from the Pyth contract.
- get_price(price_feed_id): Gets the price for a given price feed ID.
- get_price_unsafe(price_feed_id): Gets the price for a given price feed ID without staleness checks.
- update_fee(update_data): Calculates the fee required to update the price feeds.
- update_price_feeds(update_fee, update_data): Updates the price feeds with the provided data and fee.
Uses the PYTH_MAINNET_CONTRACT_ID constant to interact with the Pyth contract on testnet.
Uses the FUEL_ETH_BASE_ASSET_ID constant as the asset ID for paying update fees.

To use this contract, you would typically:

Call update_fee() to get the required fee for updating price feeds.
Call update_price_feeds() with the fee and update data to refresh the price feeds.
Use get_price() or get_price_unsafe() to read the updated prices.

Write Client Code

The code snippet below provides an example of how to fetch price updates using NextJS, a full example can be found here.

import { TestContractAbi__factory } from "@/sway-api";
import PYTH_CONTRACT_ABI from "../abi/pyth-contract-abi.json";
import { arrayify, Contract, hexlify } from "fuels";
import { HermesClient } from "@pythnetwork/hermes-client";

const HERMES_ENDPOINT = "https://hermes.pyth.network/";
const FUEL_ETH_BASE_ASSET_ID =
  "0xf8f8b6283d7fa5b672b530cbb84fcccb4ff8dc40f8176ef4544ddb1f1952ad07";
const ETH_USD_PRICE_FEED_ID =
  "0xff61491a931112ddf1bd8147cd1b641375f79f5825126d665480874634fd0ace"; // ETH/USD

const contractId =
  CURRENT_ENVIRONMENT === "local"
    ? contractIds.testContract
    : (process.env.NEXT_PUBLIC_TESTNET_CONTRACT_ID as string); // Testnet Contract ID
const pythContractId = process.env
  .NEXT_PUBLIC_PYTH_TESTNET_CONTRACT_ID as string; // Testnet Contract ID

async function updateAndGetPrice() {
  const fetchPriceUpdateData = async () => {
    const connection = new HermesClient(HERMES_ENDPOINT);

    // Latest price updates
    const priceUpdates = await connection.getLatestPriceUpdates([
      ETH_USD_PRICE_FEED_ID,
    ]);

    const buffer = Buffer.from(priceUpdates.binary.data[0], "hex");
    return buffer;
  };

  const updateData = await fetchPriceUpdateData();

  const { waitForResult: waitForResultFee } = await contract.functions
    .update_fee([arrayify(updateData)])
    .addContracts([pythContract])
    .call();
  const { value: fee } = await waitForResultFee();

  await contract.functions
    .update_price_feeds(fee, [arrayify(updateData)])
    .addContracts([pythContract])
    .callParams({
      forward: [fee, hexlify(FUEL_ETH_BASE_ASSET_ID)],
    })
    .call();

  const { value: price } = await contract.functions
    .get_price(hexlify(ETH_USD_PRICE_FEED_ID))
    .addContracts([pythContract])
    .get();

  console.log("Latest ETH/USD price after update:", price);
  return price;
}

updateAndGetPrice().catch(console.error);

fetch-and-update-btc-price, which fetches the latest price update from Hermes and updates the Pyth price feeds on Fuel.

How to Use Real-Time Data in Fuel Contracts

Install the Pyth SDK

Write Contract Code

Write Client Code

Additional Resources

Interface

Example Applications

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