feat: Add retry with backoff to requests

This adds a bit more tolerance to network outages etc. If a 40x status code is recieved from the API
it will not retry as this indicates a bad request – so no need to keep sening the same
request.

There were no end-to-end tests predating this feature so I added some.

Fixes bugsnag/webpack-bugsnag-plugins#17.

index.js

@@ -1,7 +1,7 @@
 'use strict';
 
 const fs = require('graceful-fs');
-const request = require('request');
+const request = require('./lib/request');
 const path = require('path');
 const os = require('os');
 
@@ -330,18 +330,7 @@ function sendRequest(args) {
   // { options, formData }
   const options = args.options
   const formData = args.formData
-  return new Promise((resolve, reject) => {
-    request.post({
-      url: options.endpoint,
-      formData,
-    }, function (err, res, body) {
-      if (err || res.statusCode !== 200) {
-        reject(err || new Error(`${res.statusMessage} (${res.statusCode}) - ${body}`));
-      } else {
-        resolve(options);
-      }
-    });
-  });
+  return request(options.endpoint, formData).then(() => options)
 }
 
 /**

lib/request.js

@@ -0,0 +1,32 @@
+const request = require('request')
+const Backoff = require('backo')
+const MAX_ATTEMPTS = 5
+const MIN_BACKOFF_INTERVAL = process.env.BUGSNAG_MIN_BACKOFF_INTERVAL || 500
+const MAX_BACKOFF_INTERVAL = process.env.BUGSNAG_MAX_BACKOFF_INTERVAL || 5000
+
+module.exports = (url, formData) => {
+  return new Promise((resolve, reject) => {
+    const backoff = new Backoff({ min: MIN_BACKOFF_INTERVAL, max: MAX_BACKOFF_INTERVAL })
+
+    const onSuccess = () => resolve()
+    const onError = (err) => {
+      if (backoff.attempts >= MAX_ATTEMPTS - 1) return reject(err)
+      if (err.statusCode >= 400 && err.statusCode < 500) return reject(err)
+      setTimeout(() => req(url, formData, { onSuccess, onError }), backoff.duration())
+    }
+
+    req(url, formData, { onError, onSuccess })
+  })
+}
+
+const req = (url, formData, { onError, onSuccess }) => {
+  request.post({ url, formData }, function (err, res, body) {
+    if (err || res.statusCode !== 200) {
+      err = err || new Error(`${res.statusMessage} (${res.statusCode}) - ${body}`)
+      if (res.statusCode) err.statusCode = res.statusCode
+      onError(err)
+    } else {
+      onSuccess()
+    }
+  })
+}