Chainlink Functions Starter Kit

• Chainlink Functions Starter Kit
• Overview
  • Supported Networks
    • Mainnets
    • Testnets
• For Beginners
  • Tutorials & examples
• Quickstart
  • Requirements
  • Steps
• Environment Variable Management
  • Environment Variable Management Commands
• Functions Command Glossary
  • Functions Commands
  • Functions Subscription Management Commands
• Request Configuration
  • JavaScript Code
    • Functions Library
  • Modifying Contracts
  • Simulating Requests
  • Off-chain Secrets
• Automation Integration
• Gas Spikes

Overview

This project is currently in a closed beta. Request access to send on-chain requests here https://functions.chain.link/

Chainlink Functions allows users to request data from almost any API and perform custom computation using JavaScript.

It works by using a decentralized oracle network (DON).
When a request is initiated, each node in the DON executes the user-provided JavaScript code simultaneously. Then, nodes use the Chainlink OCR protocol to come to consensus on the results. Finally, the median result is returned to the requesting contract via a callback function.

Chainlink Functions also enables users to share encrypted secrets with each node in the DON. This allows users to access APIs that require authentication, without exposing their API keys to the general public.

Supported Networks

Mainnets

• Not supported yet.

Testnets

• Ethereum Sepolia: ETHEREUM_SEPOLIA_RPC_URL, --network ethereumSepolia
• Polygon Mumbai: POLYGON_MUMBAI_RPC_URL, --network polygonMumbai
• Avalanche Fuji: AVALANCHE_FUJI_RPC_URL, --network avalancheFuji

For Beginners

If you're new to web3, it is recommended starting with the Functions - Getting Started before diving into the code.

The above document will help you:

• Set up a wallet
• Get funds
• Provides more detailed step-by-step instructions and further information

Tutorials & examples

For more detailed tutorials and examples, check out the Chainlink Functions Tutorials to get started.

Quickstart

Requirements

• Node.js version 18

Steps

1. Clone this repository to your local machine
   
   
2. Open this directory in your command line, then run npm install to install all dependencies.
   
   
3. Aquire a Github personal access token which allows reading and writing Gists.
   1. Visit https://github.com/settings/tokens?type=beta and click "Generate new token"
   2. Name the token and enable read & write access for Gists from the "Account permissions" drop-down menu. Do not enable any additional permissions.
   3. Click "Generate token" and copy the resulting personal access token for step 4.
      
      
4. Set the required environment variables.
   1. Set an encryption password for your environment variables to a secure password by running:
      npx env-enc set-pw
      
   2. Use the command npx env-enc set to set the required environment variables (see Environment Variable Management):
      • GITHUB_API_TOKEN for your Github token obtained from step 3
      • PRIVATE_KEY for your development wallet
      • POLYGON_MUMBAI_RPC_URL, ETHEREUM_SEPOLIA_RPC_URL, AVALANCHE_FUJI_RPC_URL for the network that you intend to use
   3. If desired, the <explorer>_API_KEY can be set in order to verify contracts, along with any values used in the secrets object in Functions-request-config.js such as COINMARKETCAP_API_KEY.
      
      
5. There are two files to notice that the default example will use:
   • contracts/FunctionsConsumer.sol contains the smart contract that will receive the data
   • calculation-example.js contains JavaScript code that will be executed by each node of the DON
     
     
6. Test an end-to-end request and fulfillment locally by simulating it using:
   npx hardhat functions-simulate
   
   
7. Deploy and verify the client contract to an actual blockchain network by running:
   npx hardhat functions-deploy-client --network network_name_here --verify true
   Note: Make sure <explorer>_API_KEY is set if using --verify true, depending on which network is used.
   
   
8. Create, fund & authorize a new Functions billing subscription by running:
   npx hardhat functions-sub-create --network network_name_here --amount LINK_funding_amount_here --contract 0xDeployed_client_contract_address_here
   Note: Ensure your wallet has a sufficient LINK balance before running this command. Testnet LINK can be obtained at faucets.chain.link.
   
   
9. Make an on-chain request by running:
   npx hardhat functions-request --network network_name_here --contract 0xDeployed_client_contract_address_here --subid subscription_id_number_here

Environment Variable Management

This repo uses the NPM package @chainlink/env-enc for keeping environment variables such as wallet private keys, RPC URLs, and other secrets encrypted at rest. This reduces the risk of credential exposure by ensuring credentials are not visible in plaintext.

By default, all encrypted environment variables will be stored in a file named .env.enc in the root directory of this repo.

First, set the encryption password by running the command npx env-enc set-pw. The password must be set at the beginning of each new session. If this password is lost, there will be no way to recover the encrypted environment variables.

Run the command npx env-enc set to set and save environment variables. These variables will be loaded into your environment when the config() method is called at the top of hardhat.config.js. Use npx env-enc view to view all currently saved environment variables. When pressing ENTER, the terminal will be cleared to prevent these values from remaining visible. Running npx env-enc remove VAR_NAME_HERE deletes the specified environment variable. The command npx env-enc remove-all deletes the entire saved environment variable file.

When running this command on a Windows machine, you may receive a security confirmation prompt. Enter r to proceed.

NOTE: When you finish each work session, close down your terminal to prevent your encryption password from becoming exposes if your machine is compromised.

Environment Variable Management Commands

The following commands accept an optional --path flag followed by a path to the desired encrypted environment variable file. If one does not exist, it will be created automatically by the npx env-enc set command.

The --path flag has no effect on the npx env-enc set-pw command as the password is stored as an ephemeral environment variable for the current terminal session.

Functions Command Glossary

The Functions and Functions subscription management commands commands can be executed in the following format: npx hardhat command_here --parameter1 parameter_1_value_here --parameter2 parameter_2_value_here

Example: npx hardhat functions-read --network polygonMumbai --contract 0x787Fe00416140b37B026f3605c6C72d096110Bb8

Functions Commands

Functions Subscription Management Commands

Request Configuration

Chainlink Functions requests can be configured by modifying values in the requestConfig object found in the Functions-request-config.js file located in the root of this repository.

JavaScript Code

The JavaScript source code for a Functions request can use vanilla Node.js features, but cannot use any require statements or imported modules other than the built-in modules buffer, crypto, querystring, string_decoder, url, and util.

It must return a JavaScript Buffer which represents the response bytes that are sent back to the requesting contract. Encoding functions are provided in the Functions library. Additionally, the script must return in less than 10 seconds or it will be terminated and send back an error to the requesting contract.

In order to make HTTP requests, the source code must use the Functions.makeHttpRequest function from the exposed Functions library. Asynchronous code with top-level await statements is supported, as shown in the file API-request-example.js.

Functions Library

The Functions library is injected into the JavaScript source code and can be accessed using the name Functions.

In order to make HTTP requests, only the Functions.makeHttpRequest function can be used. All other methods of accessing the Internet are restricted. The function takes an object with the following parameters.

{
  url: String with the URL to which the request is sent,
  method (optional): String specifying the HTTP method to use which can be either 'GET', 'POST', 'PUT', 'DELETE', 'PATCH', 'HEAD', or 'OPTIONS' (defaults to 'GET'),
  headers (optional): Object with headers to use in the request,
  params (optional): Object with URL query parameters,
  data (optional): Object which represents the body sent with the request,
  timeout (optional): Number with the maximum request duration in ms (defaults to 5000 ms),
  responseType (optional): String specifying the expected response type which can be either 'json', 'arraybuffer', 'document', 'text' or 'stream' (defaults to 'json'),
}

The function returns a promise that resolves to either a success response object or an error response object.

A success response object will have the following parameters.

{
  error: false,
  data: Response data sent by the server,
  status: Number representing the response status,
  statusText: String representing the response status,
  headers: Object with response headers sent by the server,
}

An error response object will have the following parameters.

{
  error: true,
  message (may be undefined): String containing error message,
  code (may be undefined): String containing an error code,
  response (may be undefined): Object containing response sent from the server,
}

This library also exposes functions for encoding JavaScript values into Buffers which represent the bytes that a returned on-chain.

• Functions.encodeUint256 takes a positive JavaScript integer number and returns a Buffer of 32 bytes representing a uint256 type in Solidity.
• Functions.encodeInt256 takes a JavaScript integer number and returns a Buffer of 32 bytes representing a int256 type in Solidity.
• Functions.encodeString takes a JavaScript string and returns a Buffer representing a string type in Solidity.

Remember, it is not required to use these encoding functions. The JavaScript code must only return a Buffer which represents the bytes array that is returned on-chain.

Modifying Contracts

Client contracts which initiate a request and receive a fulfillment can be modified for specific use cases. The only requirements are that the contract successfully calls sendRequest in the FunctionsOracle contract and correctly implements their own handleOracleFulfillment function. At this time, the maximum amount of gas that handleOracleFulfillment can use is 300,000. See FunctionsClient.sol for details.

Simulating Requests

An end-to-end request initiation and fulfillment can be simulated for the default FunctionsConsumer contract using the functions-simulate command. This command will report the total estimated gas use. If the FunctionsConsumer client contract is modified, this task must also be modified to accomodate the changes. See tasks/Functions-client/simulate for details.

Note: The actual gas use on-chain can vary, so it is recommended to set a higher fulfillment gas limit when making a request to account for any differences.

Off-chain Secrets

Instead of using encrypted secrets written directly on the blockchain, encrypted secrets are hosted off-chain and be fetched by DON nodes via HTTP when a request is initiated. This allows encrypted secrets to be deleted when they are no longer in use. By default, the tooling automatically uploads secrets to private Github Gists and deletes them once a request is fulfilled unless the secrets are being used for an AutomatedFunctionsConsumer.sol contract. If integrating with Chainlink Automation, it is recommended to delete the secrets Gist manually once it is not longer in use. Note that if there are URL(s) provided for the secretsURLs parameter in Functions_request_config.js, automatic Gist uploading will be disabled in favor of using the provided URL(s).

Additionally, per-node secrets allow a separate set of secrets to be assigned to each node in the DON. Each node will not be able to decrypt the set of secrets belonging to another node. Optionally, a set of default secrets encrypted with the DON public key can be used as a fallback by any DON member who does not have a set of secrets assigned to them. This handles the case where a new member is added to the DON, but the assigned secrets have not yet been updated.

To use per-node assigned secrets, enter a list of secrets objects into perNodeSecrets in Functions-request-config.js. The number of objects in the array must correspond to the number of nodes in the DON. Default secrets can be entered into the secrets parameter of Functions-request-config.js. Each secrets object must have the same set of entries, but the values for each entry can be different (ie: [ { apiKey: '123' }, { apiKey: '456' }, ... ]). If the per-node secrets feature is not desired, perNodeSecrets can be left empty and a single set of secrets can be entered for secrets.

If you prefer to host secrets elsewhere instead of having them automatically uploaded to a Github Gist, generate the encrypted secrets JSON file by running the command npx hardhat functions-build-offchain-secrets --network network_name_here. This will output the file offchain-secrets.json which can be uploaded to any other hosting service that allows the JSON file to be fetched via URL. Once the JSON file is uploaded, enter the URL(s) where the JSON file is hosted into secretsURLs. Multiple URLs can be entered as a fallback in case any of the URLs are offline. Each URL should host the exact same JSON file. The tooling will automatically pack the secrets URL(s) into a space-separated string and encrypt the string using the DON public key so no 3rd party can view the URLs. Finally, this encrypted string of URLs is used in the secrets parameter when making an on-chain request.

URLs which host secrets must be available every time a request is executed by DON nodes. For optimal security, it is recommended to expire the URLs when the off-chain secrets are no longer in use.

Automation Integration

Chainlink Functions can be used with Chainlink Automation in order to automatically trigger a Functions request.

1. Create & fund a new Functions billing subscription by running:
   npx hardhat functions-sub-create --network network_name_here --amount LINK_funding_amount_here
   Note: Ensure your wallet has a sufficient LINK balance before running this command.
   
   
2. Deploy the AutomationFunctionsConsumer client contract by running:
   npx hardhat functions-deploy-auto-client --network network_name_here --subid subscription_id_number_here --interval time_between_requests_here --verify true
   Note: Make sure <explorer>_API_KEY environment variable is set. API keys for these services are freely available to anyone who creates an EtherScan, PolygonScan or SnowTrace account.
   
   
3. Register the contract for upkeep via the Chainlink Automation web app here: https://automation.chain.link/
   • Be sure to set the Gas limit for the performUpkeep function to a high enough value. The recommended value is 1,000,000.
   • Find further documentation for working with Chainlink Automation here: https://docs.chain.link/chainlink-automation/introduction

Once the contract is registered for upkeep, check the latest response or error with the commands npx hardhat functions-read --network network_name_here --contract contract_address_here.

For debugging, use the command npx hardhat functions-check-upkeep --network network_name_here --contract contract_address_here to see if Automation needs to call performUpkeep. To manually trigger a request, use the command npx hardhat functions-perform-upkeep --network network_name_here --contract contract_address_here.

Gas Spikes

When on-chain traffic is high, transaction gas prices can spike unexpectedly. This may decrease the accuracy of the estimated requests costs or cause transactions to fail. In order to mitigate these problems, ensure your billing subscription balance has a sufficient buffer of two or more times the expected request cost in LINK. Additionally, you can manually set a hardcoded transaction gas price in the HardHat tooling by modifying the gasPrice parameter in the networks.js config file for a particular network.