External Adapter Helper

This repo helps with creating Chainlink external adapters in NodeJS.

Adding to your project

yarn add external-adapter

Usage

const { Requester, Validator } = require('external-adapter')

Validator

Custom parameters can be given to the Validator in order to ensure that the requester supplied parameters which are expected by the endpoint.

const customParams = {
  // An array of strings can be used to indicate that one of
  // the following keys must be supplied by the requester
  base: ['base', 'from', 'coin'],
  quote: ['quote', 'to', 'market'],
  // Specific keys can be given a Boolean flag to indicate
  // whether or not the requester is required to provide
  // a value
  endpoint: false
}

Validator

The Validator relies on the data supplied in the customParams object to ensure that a requester supplied the expected parameters.

Arguments

• callback (Function): The callback function to execute if validation fails
• input (Object): The request payload from the Chainlink node
• customParams (Object): A customParams object as shown above

Validation of the requester's input parameters can be done by creating an instance of the Validator.

// The input data is validated upon instantiating the Validator
// If input validation fails, the callback is called with an error
const validator = new Validator(callback, input, customParams)

Validated params can be obtained from the validator.validated object.

// The jobRunID is always supplied by the Chainlink node, but in case
// it's not supplied upon invoking the external adapter, it will default
// to '1'
const jobRunID = validator.validated.id
// Since endpoint doesn't need to be supplied by the requester, we can
// assign a default value
const endpoint = validator.validated.data.endpoint || 'price'
// We specified that one of the values in the base array should be a
// parameter in use, that value is stored in the name of the key you
// specified for the array
const base = validator.validated.data.base
const quote = validator.validated.data.quote

Requester

The Requester is a wrapper around a retryable pattern for reaching out to an endpoint. It can be supplied with a customError object to describe the custom error cases which the adapter should retry fetching data even if the response was successful.

const customError = (data) => {
  // Error cases should return true
  if (Object.keys(data).length === 0) return true
  // If no error case is caught, return false
  return false
}

request

Arguments

• config (Object): An axios config object
• customError (Object): A customError object as shown above
• retries (Number): The number of retries the adapter should attempt to call the API
• delay (Number): The delay between retries (value in ms)

Call Requester.request to have the adapter retry failed connection attempts (along with any customError cases) for the given URL within the config.

Requester.request(config, customError, retries, delay)
  .then(response => {
    // Optionally store the desired result at data.result
    response.data.result = Requester.validateResultNumber(response.data,
                                                          ['eth', 'usd'])
    // Return the successful response back to the Chainlink node
    callback(response.statusCode, Requester.success(jobRunID, response))
  })
  .catch(error => {
    callback(500, Requester.errored(jobRunID, error))
  })

validateResultNumber

Arguments

• data (Object): The response's data object
• path (Array): An array of strings (or values of strings) or numbers for indicies to walk the JSON path

You can use validateResultNumber to obtain the value at the given path and receive a number. It takes the response data's object and an array representing the JSON path to return. If the value at the given path is undefined or 0, an error will be thrown.

const result = Requester.validateResultNumber(response.data, ['eth', 'usd'])

getResult

Arguments

• data (Object): The response's data object
• path (Array): An array of strings (or values of strings) or numbers for indicies to walk the JSON path

The getResult function is similar to validateResultNumber but if the value at the given path is not found, no error will be thrown.

const result = Requester.getResult(response.data, ['eth', 'usd'])

errored

Returns the error object formatted in a way which is expected by the Chainlink node.

Arguments

• jobRunID (String): The job's run ID
• error (Object): The error object

.catch(error => {
  callback(500, Requester.errored(jobRunID, error))
})

success

Returns the response object formatted in a way which is expected by the Chainlink node.

Arguments

• jobRunID (String): The job's run ID
• response (Object): The response object

.then(response => {
  callback(response.statusCode, Requester.success(jobRunID, response))
})