@retryable/request

@retryable/request - HTTP(s) request retry on recoverable errors.

When the connection fails with one of ECONNRESET, ENOTFOUND, ESOCKETTIMEDOUT, ETIMEDOUT, ECONNREFUSED, EHOSTUNREACH, EPIPE, EAI_AGAIN or when an HTTP 5xx or 429 error occurrs, the request will automatically be re-attempted as these are often recoverable errors and will go away on retry.

Installation

Install with npm.

npm install --save @retryable/request

Usage

@retryable/request is a drop-in replacement for request but adds two new options maxAttempts and retryDelay. It also adds one property to the response (or the error object, upon a network error), attempts. It supports callbacks or promises.

With callbacks

var request = require('@retryable/request');

request({
  url: 'https://api.domain.com/v1/a/b',
  json: true,

  // The below parameters are specific to @retryable/request
  maxAttempts: 5,   // (default) try 5 times
  retryDelay: 5000,  // (default) wait for 5s before trying again
  retryStrategy: request.RetryStrategies.HTTPOrNetworkError // (default) retry on 5xx or network errors
}, function(err, response, body){
  // this callback will only be called when the request succeeded or after maxAttempts or on error
  if (response) {
    console.log('The number of request attempts: ' + response.attempts);
  }
});

How to define your own retry strategy

A retry strategy let you specify when @retryable/request should retry a request

/**
 * @param  {Null | Object} err
 * @param  {Object} response
 * @param  {Object} body
 * @param  {Object} options copy 
 * @return {Boolean} true if the request should be retried
 */
function myRetryStrategy(err, response, body, options){
  // retry the request if we had an error or if the response was a 'Bad Gateway'
  return !!err || response.statusCode === 502;
}

/**
 * @param  {Null | Object} err
 * @param  {Object} response
 * @param  {Object} body
 * @param  {Object} options copy 
 * @return {Object} mustRetry: {Boolean} true if the request should be retried
 *                  options: {Object} new options for request
 */
function myRetryStrategy(err, response, body, options){
  options.url = 'new url'; //you can overwrite some attributes or create new object 
  return {
    mustRetry: !!err || response.statusCode === 502,
    options: options, //then it should be passed back, it will be used for new requests
  }
}

/**
 * With an asynchronous retry strategy
 * @param  {Null | Object} err
 * @param  {Object} response
 * @param  {Object} body
 * @param  {Object} options copy 
 * @return {Object} mustRetry: {Boolean} true if the request should be retried
 *                  options: {Object} new options for request
 */
async function myRetryStrategy(err, response, body, options){
  let token = await getNewApiAuthToken();
  options.headers = {'Authorization': `Bearer ${token}`}
  return {
    mustRetry: true,
    options: options, // retry with new auth token
  }
}

request({
  url: 'https://api.domain.com/v1/a/b'
  json:true,
  retryStrategy: myRetryStrategy
}, function(err, response, body){
  // this callback will only be called when the request succeeded or after maxAttempts or on error
});

How to define your own delay strategy

A delay strategy let you specify how long @retryable/request should wait before trying again the request

/**
 * @param  {Null | Object} err
 * @param  {Object} response
 * @param  {Object} body
 * @return {Number} number of milliseconds to wait before trying again the request
 */
function myDelayStrategy(err, response, body){
  // set delay of retry to a random number between 500 and 3500 ms
  return Math.floor(Math.random() * (3500 - 500 + 1) + 500);
}

request({
  url: 'https://api.domain.com/v1/a/b'
  json:true,
  delayStrategy: myDelayStrategy // delayStrategy is called 1 less times than the maxAttempts set
}, function(err, response, body){
  // this callback will only be called when the request succeeded or after maxAttempts or on error
});

Here is how to implement an exponential backoff strategy:

/**
 * @param   {Number} attempts The number of times that the request has been attempted.
 * @return  {Number} number of milliseconds to wait before retrying again the request.
 */
function getExponentialBackoff(attempts) {
  return (Math.pow(2, attempts) * 100) + Math.floor(Math.random() * 50);
}

function constructExponentialBackoffStrategy() {
  let attempts = 0;
  return () => {
    attempts += 1;
    return getExponentialBackoff(attempts);
  };
}

request({
  url: 'https://api.domain.com/v1/a/b'
  json:true,
  delayStrategy: constructExponentialBackoffStrategy() // need to invoke the function to return the closure.
}, function(err, response, body){
  // this callback will only be called when the request succeeded or after maxAttempts or on error
});

How to access the underlying request library

You can access to the underlying request library thanks to request.Request:

const request = require('@retryable/request');
console.log(request.Request); // original request library

Thus, if needed, it's possible to monkey-patch or extend the underlying Request library:

request.Request = class extends request.Request {
  constructor(url, options, f, retryConfig) {
    super(url, options, f, retryConfig);
    // this constructor will be called for every @retryable/request call,
    // and give you global logging
    console.log('Request', url, options, f, retryConfig);
  }
}

Modifying request options

You can use the defaults method to provide default options like so:

var request = require('@retryable/request').defaults({ json: true, retryStrategy: myRetryStrategy });

API surface

As with request, several helpers are provided for various HTTP methods and usage:

• request(options [, callback]).
• request(url [, callback]) - same as request(options [, callback]).
• request(url, options [, callback]) - same as request(options [, callback]).
• request.get(url [, callback]) - same as request(options [, callback]), defaults options.method to GET.
• request.get(url, options [, callback]) - same as request(options [, callback]), defaults options.method to GET.
• request.head(url) - same as request(options [, callback]), defaults options.method to HEAD.
• request.post(url) - same as request(options [, callback]), defaults options.method to POST.
• request.put(url) - same as request(options [, callback]), defaults options.method to PUT.
• request.patch(url) - same as request(options [, callback]), defaults options.method to PATCH.
• request.del(url) - same as request(options [, callback]), defaults options.method to DELETE.
• request.delete(url) - same as request(options [, callback]), defaults options.method to DELETE.

License

MIT