feat: update engine.io to capture and forward sticky session header

.editorconfig

@@ -0,0 +1,12 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.md]
+trim_trailing_whitespace = false

.travis.yml

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+language: node_js
+cache:
+  directories:
+    - node_modules
+notifications:
+  email: false
+node_js:
+  - '7'
+  - '6'
+  - '4'
+before_script:
+  - npm prune
+after_success:
+  - npm run semantic-release
+branches:
+  except:
+    - /^v\d+\.\d+\.\d+$/

README.md

@@ -1,2 +1,31 @@
 # socket.io-sticky-headers
+
 Use custom header to maintain sticky sessions with socket.io
+
+## Problem
+
+For cluster of socket.io servers Socket.io connections made by the client requires a handshake process that involves sending several XHR requests. If any of those requests fail to connect to the same instance the handshake will fail and socket.io will be in a reconnect loop (failing with 401 errors).
+
+Sticky sessions are need to successfully connect to a cluster of socket.io servers. Usually this can be managed with a Cookie. However browsers such as Safari has very strict third party cookie rules which could prevent this from working. An example could be a chat client placed on a customers site.
+
+This module patches the engine.io XHR polling to capture a custom http header response of your choosing. Any future requests made will use the same http header. Future requests will update the header if that header ever changed.
+
+## Install
+
+```bash
+npm install socket.io-sticky-headers --save
+```
+
+## Usage
+
+### Socket.io
+
+```javascript
+require('socket.io-sticky-headers')(require('socket.io-client/node_modules/engine.io-client/lib/transports/polling-xhr'), 'My-Session-Id');
+```
+
+### Engine.io
+
+```javascript
+require('socket.io-sticky-headers')(require('engine.io-client/lib/transports/polling-xhr'), 'My-Session-Id');
+```

index.js

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+'use strict'
+
+const debug = require('debug')('engine.io-sticky-headers')
+
+let initialized = false
+
+function initialize (XHR, stickyHeader) {
+  if (initialized) return
+
+  if (stickyHeader == null) {
+    stickyHeader = 'Session-Id'
+  }
+
+  if (XHR == null || typeof XHR !== 'function') {
+    throw new Error('Please provide XHR function constructor ie require("engine.io-client/lib/transports/polling-xhr"')
+  }
+
+  const Request = XHR.Request
+
+  const originalXHRRequest = XHR.prototype.request
+  if (originalXHRRequest == null) {
+    throw new Error('XHR.prototype.request is not set')
+  }
+
+  const originalOnLoad = Request.prototype.onLoad
+
+  if (originalOnLoad == null) {
+    throw new Error('Request.prototype.onLoad is not set')
+  }
+
+  Request.prototype.onLoad = function () {
+    this.emit('onLoad')
+    originalOnLoad.call(this)
+  }
+
+  XHR.prototype.request = function (opts) {
+    let request = originalXHRRequest.call(this, opts)
+    request.once('onLoad', createStickyUpdater(this))
+    return request
+  }
+
+  // Update sticky header after every successful request
+  function createStickyUpdater (xhr) {
+    return function updateSticky () {
+      let newStickyValue = this.xhr.getResponseHeader(stickyHeader)
+      if (newStickyValue != null) {
+        debug('setting header %s to %s', stickyHeader, newStickyValue)
+        if (xhr.extraHeaders == null) {
+          xhr.extraHeaders = {}
+        }
+        xhr.extraHeaders[stickyHeader] = newStickyValue
+      }
+    }
+  }
+
+  initialized = true
+}
+
+module.exports = initialize

package.json

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+{
+  "name": "socket.io-sticky-headers",
+  "version": "0.0.0-development",
+  "description": "Use custom header to maintain sticky sessions with socket.io",
+  "main": "index.js",
+  "scripts": {
+    "test": "standard && mocha",
+    "semantic-release": "semantic-release pre && npm publish && semantic-release post"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/hyperlink/socket.io-sticky-headers.git"
+  },
+  "files": [
+    "index.js"
+  ],
+  "keywords": [
+    "socket.io",
+    "sticky sessions",
+    "headers"
+  ],
+  "author": "Xiaoxin Lu <[email protected]>",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/hyperlink/socket.io-sticky-headers/issues"
+  },
+  "homepage": "https://github.com/hyperlink/socket.io-sticky-headers#readme",
+  "devDependencies": {
+    "mocha": "^3.2.0",
+    "semantic-release": "^6.3.2",
+    "engine.io-client": "^2.0.2",
+    "standard": "^10.0.0"
+  },
+  "dependencies": {
+    "debug": "^2.6.3"
+  },
+  "peerDependencies": {
+    "engine.io-client": "2"
+  }
+}

test/test.js

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+/* eslint-env node, mocha */
+
+'use strict'
+
+const stickyHeaders = require('../')
+const assert = require('assert')
+
+describe('sticky-headers', function () {
+  describe('verify patching', function () {
+    it('should throw exception if passing in undefined XHR polling', function () {
+      assert.throws(function () {
+        stickyHeaders()
+      }, Error)
+    })
+
+    it('should throw exception if passing in null XHR polling', function () {
+      assert.throws(function () {
+        stickyHeaders(null)
+      }, Error)
+    })
+
+    it('should throw exception if missing prototype methods to patch', function () {
+      assert.throws(function () {
+        stickyHeaders(function () {})
+      }, Error)
+    })
+  })
+})