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Encode request data offchain

This tutorial shows you how make multiple API calls from your smart contract to a Decentralized Oracle Network. After OCR completes offchain computation and aggregation, the DON returns the asset price to your smart contract. This example returns the BTC/USD price.

This guide assumes that you know how to build HTTP requests and how to use secrets. Read the API query parameters and API use secrets guides before you follow the example in this document. To build a decentralized asset price, send a request to the DON to fetch the price from many different API providers. Then, calculate the median price. The API providers in this example are:

Read the Call Multiple Data Sources tutorial before you follow the steps in this example. This tutorial uses the same example but with a slightly different process:

  • Instead of sending the request data (source code, encrypted secrets reference, and arguments) in the request, you will first encode it offchain and then send the encoded request. Encoding the request offchain from your front end or a server rather than onchain from your smart contract. This helps save gas.

Prerequisites

Set up your environment

You must provide the private key from a testnet wallet to run the examples in this documentation. Install a Web3 wallet, configure Node.js, clone the smartcontractkit/smart-contract-examples repository, and configure a .env.enc file with the required environment variables.

Install and configure your Web3 wallet for Polygon Mumbai:

  1. Install Deno so you can compile and simulate your Functions source code on your local machine.

  2. Install the MetaMask wallet or other Ethereum Web3 wallet.

  3. Set the network for your wallet to the Polygon Mumbai testnet. If you need to add Mumbai to your wallet, you can find the chain ID and the LINK token contract address on the LINK Token Contracts page.

  4. Request testnet MATIC from the Polygon Faucet.

  5. Request testnet LINK from faucets.chain.link/mumbai.

Install the required frameworks and dependencies:

  1. Install the latest release of Node.js 20. Optionally, you can use the nvm package to switch between Node.js versions with nvm use 20.

    Note: To ensure you are running the correct version in a terminal, type node -v.

    node -v
    $ node -v
v20.9.0

  2. In a terminal, clone the smart-contract examples repository and change directories. This example repository imports the Chainlink Functions Toolkit NPM package. You can import this package to your own projects to enable them to work with Chainlink Functions.

    git clone https://github.com/smartcontractkit/smart-contract-examples.git && \
cd ./smart-contract-examples/functions-examples/

  3. Run npm install to install the dependencies.

    npm install

  4. For higher security, the examples repository encrypts your environment variables at rest.

    1. Set an encryption password for your environment variables.

      npx env-enc set-pw

    2. Run npx env-enc set to configure a .env.enc file with the basic variables that you need to send your requests to the Polygon Mumbai network.

      • POLYGON_MUMBAI_RPC_URL: Set a URL for the Polygon Mumbai testnet. You can sign up for a personal endpoint from Alchemy, Infura, or another node provider service.

      • PRIVATE_KEY: Find the private key for your testnet wallet. If you use MetaMask, follow the instructions to Export a Private Key. Note: Your private key is needed to sign any transactions you make such as making requests.

      npx env-enc set

Configure your onchain resources

After you configure your local environment, configure some onchain resources to process your requests, receive the responses, and pay for the work done by the DON.

Deploy a Functions consumer contract on Polygon Mumbai

  1. Open the FunctionsConsumerExample.sol contract in Remix.

    Open in Remix What is Remix?

  2. Compile the contract.

  3. Open MetaMask and select the Polygon Mumbai network.

  4. In Remix under the Deploy & Run Transactions tab, select Injected Provider - MetaMask in the Environment list. Remix will use the MetaMask wallet to communicate with Polygon Mumbai.

  5. Under the Deploy section, fill in the router address for your specific blockchain. You can find both of these addresses on the Supported Networks page. For Polygon Mumbai, the router address is 0x6E2dc0F9DB014aE19888F539E59285D2Ea04244C.

  6. Click the Deploy button to deploy the contract. MetaMask prompts you to confirm the transaction. Check the transaction details to make sure you are deploying the contract to Polygon Mumbai.

  7. After you confirm the transaction, the contract address appears in the Deployed Contracts list. Copy the contract address.

Create a subscription

Follow the Managing Functions Subscriptions guide to accept the Chainlink Functions Terms of Service (ToS), create a subscription, fund it, then add your consumer contract address to it.

You can find the Chainlink Functions Subscription Manager at functions.chain.link.

Tutorial

This tutorial is configured to get the median BTC/USD price from multiple data sources. For a detailed explanation of the code example, read the Examine the code section.

You can locate the scripts used in this tutorial in the examples/9-send-cbor directory.

  1. Make sure your subscription has enough LINK to pay for your requests. Also, you must maintain a minimum balance to upload encrypted secrets to the DON (Read the minimum balance for uploading encrypted secrets section to learn more). You can check your subscription details (including the balance in LINK) in the Chainlink Functions Subscription Manager. If your subscription runs out of LINK, follow the Fund a Subscription guide. This guide recommends maintaining at least 2 LINK within your subscription.

  2. Get a free API key from CoinMarketCap and note your API key.

  3. Run npx env-enc set to add an encrypted COINMARKETCAP_API_KEY to your .env.enc file.

    npx env-enc set

To run the example:

  1. Open the file request.js, which is located in the 9-send-cbor folder.

  2. Replace the consumer contract address and the subscription ID with your own values.

    const consumerAddress = "0x8dFf78B7EE3128D00E90611FBeD20A71397064D9" // REPLACE this with your Functions consumer address
const subscriptionId = 3 // REPLACE this with your subscription ID

  3. Make a request:

    node examples/9-send-cbor/request.js

    The script runs your function in a sandbox environment before making an onchain transaction:

    $ node examples/9-send-cbor/request.js
secp256k1 unavailable, reverting to browser version
Start simulation...
Performing simulation with the following versions:
deno 1.36.3 (release, aarch64-apple-darwin)
v8 11.6.189.12
typescript 5.1.6


Simulation result {
capturedTerminalOutput: 'Median Bitcoin price: 25713.36\n',
responseBytesHexstring: '0x0000000000000000000000000000000000000000000000000000000000273c48'
}
✅ Decoded response to uint256:  2571336n

Estimate request costs...
Duplicate definition of Transfer (Transfer(address,address,uint256,bytes), Transfer(address,address,uint256))
Fulfillment cost estimated to 0.000000000000215 LINK

Make request...
Upload encrypted secret to gateways https://01.functions-gateway.testnet.chain.link/user. StorageSlotId 0. Expiration in minutes: 15

✅ Secrets uploaded properly to gateways https://01.functions-gateway.testnet.chain.link/user! Gateways response:  { version: 1693899379, success: true }

✅ Functions request sent! Transaction hash 0x310c93ba1c9515a8e1dc4308e198c36f5f915410fc67c13f80ffb29a43dcbe60. Waiting for a response...
See your request in the explorer https://mumbai.polygonscan.com/tx/0x310c93ba1c9515a8e1dc4308e198c36f5f915410fc67c13f80ffb29a43dcbe60

✅ Request 0x74b5b88db49dad155d1cd9b0da47cb140caf1f824cf09a88bc46132c21d41d20 fulfilled with code: 0. Cost is 0.000039224977086446 LINK. Complete response:  {
requestId: '0x74b5b88db49dad155d1cd9b0da47cb140caf1f824cf09a88bc46132c21d41d20',
subscriptionId: 3,
totalCostInJuels: 39224977086446n,
responseBytesHexstring: '0x0000000000000000000000000000000000000000000000000000000000273c48',
errorString: '',
returnDataBytesHexstring: '0x',
fulfillmentCode: 0
}

✅ Decoded response to uint256:  2571336n

    The output of the example gives you the following information:

    • Your request is first run on a sandbox environment to ensure it is correctly configured.

    • The fulfillment costs are estimated before making the request.

    • The encrypted secrets were uploaded to the secrets endpoint https://01.functions-gateway.testnet.chain.link/user.

    • Your request was successfully sent to Chainlink Functions. The transaction in this example is 0x310c93ba1c9515a8e1dc4308e198c36f5f915410fc67c13f80ffb29a43dcbe60 and the request ID is 0x74b5b88db49dad155d1cd9b0da47cb140caf1f824cf09a88bc46132c21d41d20.

    • The DON successfully fulfilled your request. The total cost was: 0.000039224977086446 LINK.

    • The consumer contract received a response in bytes with a value of 0x0000000000000000000000000000000000000000000000000000000000273c48. Decoding it offchain to uint256 gives you a result: 2571336. The median BTC price is 25713.36 USD.

Examine the code

FunctionsConsumerExample.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.19;

import {FunctionsClient} from "@chainlink/contracts/src/v0.8/functions/dev/v1_0_0/FunctionsClient.sol";
import {ConfirmedOwner} from "@chainlink/contracts/src/v0.8/shared/access/ConfirmedOwner.sol";
import {FunctionsRequest} from "@chainlink/contracts/src/v0.8/functions/dev/v1_0_0/libraries/FunctionsRequest.sol";

/**
 * THIS IS AN EXAMPLE CONTRACT THAT USES HARDCODED VALUES FOR CLARITY.
 * THIS IS AN EXAMPLE CONTRACT THAT USES UN-AUDITED CODE.
 * DO NOT USE THIS CODE IN PRODUCTION.
 */
contract FunctionsConsumerExample is FunctionsClient, ConfirmedOwner {
    using FunctionsRequest for FunctionsRequest.Request;

    bytes32 public s_lastRequestId;
    bytes public s_lastResponse;
    bytes public s_lastError;

    error UnexpectedRequestID(bytes32 requestId);

    event Response(bytes32 indexed requestId, bytes response, bytes err);

    constructor(
        address router
    ) FunctionsClient(router) ConfirmedOwner(msg.sender) {}

    /**
     * @notice Send a simple request
     * @param source JavaScript source code
     * @param encryptedSecretsUrls Encrypted URLs where to fetch user secrets
     * @param donHostedSecretsSlotID Don hosted secrets slotId
     * @param donHostedSecretsVersion Don hosted secrets version
     * @param args List of arguments accessible from within the source code
     * @param bytesArgs Array of bytes arguments, represented as hex strings
     * @param subscriptionId Billing ID
     */
    function sendRequest(
        string memory source,
        bytes memory encryptedSecretsUrls,
        uint8 donHostedSecretsSlotID,
        uint64 donHostedSecretsVersion,
        string[] memory args,
        bytes[] memory bytesArgs,
        uint64 subscriptionId,
        uint32 gasLimit,
        bytes32 donID
    ) external onlyOwner returns (bytes32 requestId) {
        FunctionsRequest.Request memory req;
        req.initializeRequestForInlineJavaScript(source);
        if (encryptedSecretsUrls.length > 0)
            req.addSecretsReference(encryptedSecretsUrls);
        else if (donHostedSecretsVersion > 0) {
            req.addDONHostedSecrets(
                donHostedSecretsSlotID,
                donHostedSecretsVersion
            );
        }
        if (args.length > 0) req.setArgs(args);
        if (bytesArgs.length > 0) req.setBytesArgs(bytesArgs);
        s_lastRequestId = _sendRequest(
            req.encodeCBOR(),
            subscriptionId,
            gasLimit,
            donID
        );
        return s_lastRequestId;
    }

    /**
     * @notice Send a pre-encoded CBOR request
     * @param request CBOR-encoded request data
     * @param subscriptionId Billing ID
     * @param gasLimit The maximum amount of gas the request can consume
     * @param donID ID of the job to be invoked
     * @return requestId The ID of the sent request
     */
    function sendRequestCBOR(
        bytes memory request,
        uint64 subscriptionId,
        uint32 gasLimit,
        bytes32 donID
    ) external onlyOwner returns (bytes32 requestId) {
        s_lastRequestId = _sendRequest(
            request,
            subscriptionId,
            gasLimit,
            donID
        );
        return s_lastRequestId;
    }

    /**
     * @notice Store latest result/error
     * @param requestId The request ID, returned by sendRequest()
     * @param response Aggregated response from the user code
     * @param err Aggregated error from the user code or from the execution pipeline
     * Either response or error parameter will be set, but never both
     */
    function fulfillRequest(
        bytes32 requestId,
        bytes memory response,
        bytes memory err
    ) internal override {
        if (s_lastRequestId != requestId) {
            revert UnexpectedRequestID(requestId);
        }
        s_lastResponse = response;
        s_lastError = err;
        emit Response(requestId, s_lastResponse, s_lastError);
    }
}
Open in Remix What is Remix?

  • To write a Chainlink Functions consumer contract, your contract must import FunctionsClient.sol and FunctionsRequest.sol. You can read the API references: FunctionsClient and FunctionsRequest.

    These contracts are available in an NPM package, so you can import them from within your project.

    import {FunctionsClient} from "@chainlink/contracts/src/v0.8/functions/dev/v1_0_0/FunctionsClient.sol";
import {FunctionsRequest} from "@chainlink/contracts/src/v0.8/functions/dev/v1_0_0/libraries/FunctionsRequest.sol";

  • Use the FunctionsRequest.sol library to get all the functions needed for building a Chainlink Functions request.

    using FunctionsRequest for FunctionsRequest.Request;

  • The latest request id, latest received response, and latest received error (if any) are defined as state variables:

    bytes32 public s_lastRequestId;
bytes public s_lastResponse;
bytes public s_lastError;

  • We define the Response event that your smart contract will emit during the callback

    event Response(bytes32 indexed requestId, bytes response, bytes err);

  • Pass the router address for your network when you deploy the contract:

    constructor(address router) FunctionsClient(router)

  • The three remaining functions are:

    • sendRequest for sending a request. It receives the JavaScript source code, encrypted secretsUrls (in case the encrypted secrets are hosted by the user), DON hosted secrets slot id and version (in case the encrypted secrets are hosted by the DON), list of arguments to pass to the source code, subscription id, and callback gas limit as parameters. Then:

      • It uses the FunctionsRequestlibrary to initialize the request and add any passed encrypted secrets reference or arguments. You can read the API Reference for Initializing a request, adding user hosted secrets, adding DON hosted secrets, adding arguments, and adding bytes arguments.

        FunctionsRequest.Request memory req;
req.initializeRequestForInlineJavaScript(source);
if (encryptedSecretsUrls.length > 0)
    req.addSecretsReference(encryptedSecretsUrls);
else if (donHostedSecretsVersion > 0) {
    req.addDONHostedSecrets(
        donHostedSecretsSlotID,
        donHostedSecretsVersion
    );
}
if (args.length > 0) req.setArgs(args);
if (bytesArgs.length > 0) req.setBytesArgs(bytesArgs);

      • It sends the request to the router by calling the FunctionsClient sendRequest function. You can read the API reference for sending a request. Finally, it stores the request id in s_lastRequestId then return it.

        s_lastRequestId = _sendRequest(
    req.encodeCBOR(),
    subscriptionId,
    gasLimit,
    jobId
);
return s_lastRequestId;

        Note: _sendRequest accepts requests encoded in bytes. Therefore, you must encode it using encodeCBOR.

    • sendRequestCBOR for sending a request already encoded in bytes. It receives the request object encoded in bytes, subscription id, and callback gas limit as parameters. Then, it sends the request to the router by calling the FunctionsClient sendRequest function. Note: This function is helpful if you want to encode a request offchain before sending it, saving gas when submitting the request.

  • fulfillRequest to be invoked during the callback. This function is defined in FunctionsClient as virtual (read fulfillRequest API reference). So, your smart contract must override the function to implement the callback. The implementation of the callback is straightforward: the contract stores the latest response and error in s_lastResponse and s_lastError before emitting the Response event.

    s_lastResponse = response;
s_lastError = err;
emit Response(requestId, s_lastResponse, s_lastError);

JavaScript example

source.js

The JavaScript code is similar to the Call Multiple Data Sources tutorial.

request.js

This explanation focuses on the request.js script and shows how to use the Chainlink Functions NPM package in your own JavaScript/TypeScript project to send requests to a DON. The code is self-explanatory and has comments to help you understand all the steps.

The script imports:

  • path and fs : Used to read the source file.
  • ethers: Ethers.js library, enables the script to interact with the blockchain.
  • @chainlink/functions-toolkit: Chainlink Functions NPM package. All its utilities are documented in the NPM README.
  • @chainlink/env-enc: A tool for loading and storing encrypted environment variables. Read the official documentation to learn more.
  • ../abi/functionsClient.json: The abi of the contract your script will interact with. Note: The script was tested with this FunctionsConsumerExample contract.

The script has two hardcoded values that you have to change using your own Functions consumer contract and subscription ID:

const consumerAddress = "0x8dFf78B7EE3128D00E90611FBeD20A71397064D9" // REPLACE this with your Functions consumer address
const subscriptionId = 3 // REPLACE this with your subscription ID

The primary function that the script executes is makeRequestMumbai. This function can be broken into seven main parts:

  1. Definition of necessary identifiers:

    • routerAddress: Chainlink Functions router address on Polygon Mumbai.
    • donId: Identifier of the DON that will fulfill your requests on Polygon Mumbai.
    • gatewayUrls: The secrets endpoint URL to which you will upload the encrypted secrets.
    • explorerUrl: Block explorer url of Polygon Mumbai.
    • source: The source code must be a string object. That's why we use fs.readFileSync to read source.js and then call toString() to get the content as a string object.
    • args: During the execution of your function, These arguments are passed to the source code. The args value is ["1", "bitcoin", "btc-bitcoin"]. These arguments are BTC IDs at CoinMarketCap, CoinGecko, and Coinpaprika. You can adapt args to fetch other asset prices.
    • secrets: The secrets object that will be encrypted.
    • slotIdNumber: Slot ID at the DON where to upload the encrypted secrets.
    • expirationTimeMinutes: Expiration time in minutes of the encrypted secrets.
    • gasLimit: Maximum gas that Chainlink Functions can use when transmitting the response to your contract.
    • Initialization of ethers signer and provider objects. The signer is used to make transactions on the blockchain, and the provider reads data from the blockchain.

  2. Simulating your request in a local sandbox environment:

    • Use simulateScript from the Chainlink Functions NPM package.
    • Read the response of the simulation. If successful, use the Functions NPM package decodeResult function and ReturnType enum to decode the response to the expected returned type (ReturnType.uint256 in this example).

  3. Estimating the costs:

    • Initialize a SubscriptionManager from the Functions NPM package, then call the estimateFunctionsRequestCost function.
    • The response is returned in Juels (1 LINK = 10**18 Juels). Use the ethers.utils.formatEther utility function to convert the output to LINK.

  4. Encrypt the secrets, upload the encrypted secrets to the DON, and then encode the reference to the DON-hosted encrypted secrets. This is done in three steps:

    • Initialize a SecretsManager instance from the Functions NPM package, then call the encryptSecrets function.
    • Call the uploadEncryptedSecretsToDON function of the SecretsManager instance. This function returns an object containing a success boolean as long as version, the secret version on the DON storage.
    • Call the buildDONHostedEncryptedSecretsReference function of the SecretsManager instance and use the slot ID and version to encode the DON-hosted encrypted secrets reference.

  5. Encode the request data offchain using the buildRequestCBOR function from the Functions NPM package.

  6. Making a Chainlink Functions request:

    • Initialize your functions consumer contract using the contract address, abi, and ethers signer.
    • Make a static call to the sendRequestCBOR function of your consumer contract to return the request ID that Chainlink Functions will generate.
    • Call the sendRequestCBOR function of your consumer contract. Note: The encoded data that was generated by buildRequestCBOR is passed in the request.

  7. Waiting for the response:

    • Initialize a ResponseListener from the Functions NPM package and then call the listenForResponseFromTransaction function to wait for a response. By default, this function waits for five minutes.
    • Upon reception of the response, use the Functions NPM package decodeResult function and ReturnType enum to decode the response to the expected returned type (ReturnType.uint256 in this example).

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