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Fetch multiple prices

Overview​

Follow this tutorial to implement a more advanced example of handling HTTP requests with x/async.

You'll create a contract that fetches prices of multiple cryptocurrencies from the CoinGecko API and extracts price values from the JSON response using the JSON precompile.

1. Create a contract​

Create a new file MultiCoinPrices.sol:

warden-http-examples/src/MultiCoinPrices.sol
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.25;

import "./interfaces/IAsync.sol";
import "./interfaces/Http.sol";
import "./interfaces/IJson.sol";

contract MultiCoinPrices {
    uint64 public lastTaskId;

    int256 public bitcoinPrice;
    int256 public tetherPrice;
    int256 public uniswapPrice;

    bytes public responseBody;

    // Fetch different prices from the CoinGecko API: 
    function run() public returns (Http.Request memory request) {
        request.url = "https://api.coingecko.com/api/v3/simple/price?ids=bitcoin,tether,uniswap&vs_currencies=usd";
        request.method = "GET";
        request.body = "";

        lastTaskId = IASYNC_CONTRACT.addTask("http", abi.encode(request), address(this));

        bitcoinPrice = 0;
        tetherPrice = 0;
        uniswapPrice = 0;
    }

    // A callback function: the Warden node calls it automatically
    function cb() external {
        TaskByIdResponse memory task = IASYNC_CONTRACT.taskById(lastTaskId);
        if (task.taskResponse.result.id == 0) {
            revert("Not ready yet");
        }

        Http.Response memory response = abi.decode(task.taskResponse.result.output, (Http.Response));

        require(response.status == 200, "HTTP request failed");

        responseBody = response.body;

        // Extract prices using the JSON precompile
        IJson.ReadKeyValue[] memory keyValuePairs = new IJson.ReadKeyValue[](3);
        keyValuePairs[0] = IJson.ReadKeyValue("bitcoin.usd", "float", 2);
        keyValuePairs[1] = IJson.ReadKeyValue("tether.usd", "float", 2);
        keyValuePairs[2] = IJson.ReadKeyValue("uniswap.usd", "float", 2);
        
        bytes[] memory readResult = IJSON_CONTRACT.read(responseBody, keyValuePairs);

        bitcoinPrice = abi.decode(readResult[0], (int256));
        tetherPrice = abi.decode(readResult[1], (int256));
        uniswapPrice = abi.decode(readResult[2], (int256));
    }
}

2. Deploy​

  1. Deploy the contract:

    forge create --rpc-url $RPC_URL --private-key $PRIVATE_KEY \
      src/MultiCoinPrices.sol:MultiCoinPrices --broadcast

  2. Note down the value returned as Deployed to and set it as an environment variable:

    export CONTRACT_ADDRESS=my-contract-address

3. Make an HTTP request​

  1. Make an HTTP request by calling the run() function:

    cast send $CONTRACT_ADDRESS "run()" \
      --private-key $PRIVATE_KEY \
      --rpc-url $RPC_URL

  2. Wait a few seconds, then use the cb() function to process the result:

    cast send $CONTRACT_ADDRESS "cb()" \
      --private-key $PRIVATE_KEY \
      --rpc-url $RPC_URL

  3. Check the prices:

    cast call $CONTRACT_ADDRESS "bitcoinPrice()(int256)" --rpc-url $RPC_URL
    cast call $CONTRACT_ADDRESS "tetherPrice()(int256)" --rpc-url $RPC_URL
    cast call $CONTRACT_ADDRESS "uniswapPrice()(int256)" --rpc-url $RPC_URL

    In the output, you'll see the price of each cryptocurrency displayed with 2 decimal places of precision.

Next steps​

Learn how to use other Plugins: