@hmcts/requestretry NPM

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

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Installation

Install with npm.

npm install --save requestretry

Usage

Request-retry 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('requestretry');

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

  // The below parameters are specific to request-retry
  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);
  }
});

With promises

When you're using promises, you can pass the two following options:

fullResponse (default true) - To resolve the promise with the full response or just the body
promiseFactory (default whenjs) - A function to allow the usage of a different promise implementation library

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

  fullResponse: true // (default) To resolve the promise with the full response or just the body
})
.then(function (response) {
  // response = The full response object or just the body
})
.catch(function(error) {
  // error = Any occurred error
})

Using promiseFactory option to use a different promise implementation library

// See the tests for different libraries usage examples

/**
 * @param  {Function} resolver The promise resolver function
 * @return {Object} The promise instance
 */
function customPromiseFactory(resolver) {
  // With when.js
  return require('when').promise(resolver);

  // With RSVP.js
  var Promise = require('rsvp').Promise;

  return new Promise(resolver);
}

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

  // Custom promise factory function
  promiseFactory: customPromiseFactory
})
.then(function (response) {
  // response = The full response object or just the body
})
.catch(function(error) {
  // error = Any occurred error
})

How to define your own retry strategy

A retry strategy let you specify when request-retry should retry a request

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

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 request-retry 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
});

Modifying `request` options

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

var request = require('requestretry').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.