Chainlink Functions Starter Kit

• Chainlink Functions Starter Kit
• Overview
• Quickstart
  • Requirements
  • Steps
• Command Glossary
  • Functions Commands
  • Functions Subscription Management Commands
• Request Configuration
  • JavaScript Code
    • Functions Library
  • Modifying Contracts
  • Simulating Requests
  • Off-chain Secrets
• Automation Integration

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.

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. Set the required environment variables.
   1. This can be done by copying the file .env.example to a new file named .env. (This renaming is important so that it won't be tracked by Git.) Then, change the following values:
      • PRIVATE_KEY for your development wallet
      • MUMBAI_RPC_URL or SEPOLIA_RPC_URL for the network that you intend to use
   2. If desired, the ETHERSCAN_API_KEY or POLYGONSCAN_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.
      
      
4. 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
     
     
5. Test an end-to-end request and fulfillment locally by simulating it using:
   npx hardhat functions-simulate
   
   
6. 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 ETHERSCAN_API_KEY or POLYGONSCAN_API_KEY are set if using --verify true, depending on which network is used.
   
   
7. 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.
   
   
8. 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

Command Glossary

Each of these 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 mumbai --contract 0x787Fe00416140b37B026f3605c6C72d096110Bb8

Functions Commands

Command	Description	Parameters
compile	Compiles all smart contracts
functions-simulate	Simulates an end-to-end fulfillment locally for the FunctionsConsumer contract	gaslimit (optional): Maximum amount of gas that can be used to call fulfillRequest in the client contract (defaults to 100,000 & must be less than 300,000)
functions-deploy-client	Deploys the FunctionsConsumer contract	network: Name of blockchain network, verify (optional): Set to true to verify the deployed FunctionsConsumer contract (defaults to false)
functions-request	Initiates a request from a FunctionsConsumer client contract using data from Functions-request-config.js	network: Name of blockchain network, contract: Address of the client contract to call, subid: Billing subscription ID used to pay for the request, gaslimit (optional): Maximum amount of gas that can be used to call fulfillRequest in the client contract (defaults to 100,000 & must be less than 300,000), requestgas (optional): Gas limit for calling the executeRequest function (defaults to 1,500,000), simulate (optional): Flag indicating if simulation should be run before making an on-chain request (defaults to true)
functions-read	Reads the latest response (or error) returned to a FunctionsConsumer or AutomatedFunctionsConsumer client contract	network: Name of blockchain network, contract: Address of the client contract to read
functions-deploy-auto-client	Deploys the AutomatedFunctionsConsumer contract and sets the Functions request using data from Functions-request-config.js	network: Name of blockchain network, subid: Billing subscription ID used to pay for Functions requests, gaslimit (optional): Maximum amount of gas that can be used to call fulfillRequest in the client contract (defaults to 250000), interval (optional): Update interval in seconds for Chainlink Automation to call performUpkeep (defaults to 300), verify (optional): Set to true to verify the deployed AutomatedFunctionsConsumer contract (defaults to false), simulate (optional): Flag indicating if simulation should be run before making an on-chain request (defaults to true)
functions-check-upkeep	Checks if checkUpkeep returns true for an Automation compatible contract	network: Name of blockchain network, contract: Address of the contract to check, data (optional): Hex string representing bytes that are passed to the checkUpkeep function (defaults to empty bytes)
functions-perform-upkeep	Manually call performUpkeep in an Automation compatible contract	network: Name of blockchain network, contract: Address of the contract to call, data (optional): Hex string representing bytes that are passed to the performUpkeep function (defaults to empty bytes)
functions-set-auto-request	Updates the Functions request in deployed AutomatedFunctionsConsumer contract using data from Functions-request-config.js	network: Name of blockchain network, contract: Address of the contract to update, subid: Billing subscription ID used to pay for Functions requests, interval (optional): Update interval in seconds for Chainlink Automation to call performUpkeep (defaults to 300), gaslimit (optional): Maximum amount of gas that can be used to call fulfillRequest in the client contract (defaults to 250,000)
functions-set-oracle-addr	Updates the oracle address for a client contract using the FunctionsOracle address from network-config.js	network: Name of blockchain network, contract: Address of the client contract to update
functions-build-request	Creates a JSON file with Functions request parameters including encrypted secrets, using data from Functions-request-config.js	network: Name of blockchain network, output (optional): Output JSON file name (defaults to Functions-request.json), simulate (optional): Flag indicating if simulation should be run before building the request JSON file (defaults to true)
functions-build-offchain-secrets	Builds an off-chain secrets object that can be uploaded and referenced via URL	network: Name of blockchain network, output (optional): Output JSON file name (defaults to offchain-secrets.json)

Functions Subscription Management Commands

Command	Description	Parameters
functions-sub-create	Creates a new Functions billing subscription for Functions client contracts	network: Name of blockchain network, amount (optional): Initial amount used to fund the subscription in LINK (decimals are accepted), contract (optional): Address of the client contract to add to the subscription
functions-sub-info	Gets the Functions billing subscription balance, owner, and list of authorized client contract addresses	network: Name of blockchain network, subid: Subscription ID
functions-sub-fund	Funds a Functions billing subscription with LINK	network: Name of blockchain network, subid: Subscription ID, amount: Amount to fund subscription in LINK (decimals are accepted)
functions-sub-cancel	Cancels a Functions billing subscription and refunds the unused balance. Cancellation is only possible if there are no pending requests.	network: Name of blockchain network, subid: Subscription ID, refundaddress (optional): Address where the remaining subscription balance is sent (defaults to caller's address)
functions-sub-add	Authorizes a client contract to use the Functions billing subscription	network: Name of blockchain network, subid: Subscription ID, contract: Address of the client contract to authorize for billing
functions-sub-remove	Removes a client contract from a Functions billing subscription	network: Name of blockchain network, subid: Subscription ID, contract: Address of the client contract to remove from billing subscription
functions-sub-transfer	Request ownership of a Functions subscription be transferred to a new address	network: Name of blockchain network, subid: Subscription ID, newowner: Address of the new owner
functions-sub-accept	Accepts ownership of a Functions subscription after a transfer is requested	network: Name of blockchain network, subid: Subscription ID
functions-timeout-requests	Times out expired requests	network: Name of blockchain network, requestids: 1 or more request IDs to timeout separated by commas

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.

Setting Name	Description
codeLocation	This specifies where the JavaScript code for a request is located. Currently, only the Location.Inline option is supported (represented by the value 0). This means the JavaScript string is provided directly in the on-chain request instead of being referenced via a URL.
secretsLocation	This specifies where the encrypted secrets for a request are located. Location.Inline (represented by the value 0) means encrypted secrets are provided directly on-chain, while Location.Remote (represented by 1) means secrets are referenced via encrypted URLs.
codeLanguage	This specifies the language of the source code which is executed in a request. Currently, only JavaScript is supported (represented by the value 0).
source	This is a string containing the source code which is executed in a request. This must be valid JavaScript code that returns a Buffer. See the JavaScript Code section for more details.
secrets	This is a JavaScript object which contains secret values that are injected into the JavaScript source code and can be accessed using the name secrets. This object will be automatically encrypted by the tooling using the DON public key before making an on-chain request. This object can only contain string values.
walletPrivateKey	This is the EVM private key. It is used to generate a signature for the encrypted secrets such that the secrets cannot be reused by an unauthorized 3rd party.
args	This is an array of strings which contains values that are injected into the JavaScript source code and can be accessed using the name args. This provides a convenient way to set modifiable parameters within a request.
expectedReturnType	This specifies the expected return type of a request. It has no on-chain impact, but is used by the CLI to decode the response bytes into the specified type. The options are uint256, int256, string, or Buffer.
secretsURLs	This is an array of URLs where encrypted off-chain secrets can be fetched when a request is executed if secretsLocation == Location.Remote. This array is converted into a space-separated string, encrypted using the DON public key, and used as the secrets parameter on-chain.
perNodeOffchainSecrets	This is an array of secrets objects that enables the optional ability to assign a separate set of secrets for each node in the DON if secretsLocation == Location.Remote. It is used by the functions-build-offchain-secret command. See the Off-chain Secrets section for more details.
globalOffchainSecrets	This is a default secrets object that can be used by DON members to process a request. It is used by the functions-build-offchain-secret command. See the Off-chain Secrets section for more details.

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 stored directly on the blockchain, encrypted secrets can also be hosted off-chain and be fetched by DON nodes via HTTP when a request is initiated.

Off-chain secrets also enable 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 perNodeOffchainSecrets in Functions-request-config.js before running the functions-build-offchain-secrets command. The number of objects in the array must correspond to the number of nodes in the DON. Default secrets can be entered into the globalOffchainSecrets 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, perNodeOffchainSecrets can be left empty and a single set of secrets can be entered for globalOffchainSecrets.

To generate the encrypted secrets JSON file, run 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 S3, Github, or another hosting service that allows the JSON file to be fetched via URL. Once the JSON file is uploaded, set secretsLocation to Location.Remote in Functions-request-config.js and 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 ETHERSCAN_API_KEY or POLYGONSCAN_API_KEY environment variables are set. API keys for these services are freely available to anyone who creates an EtherScan or PolygonScan 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.