Table of Contents for
Node.js 8 the Right Way

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition Node.js 8 the Right Way by Jim Wilson Published by Pragmatic Bookshelf, 2018
  1. Title Page
  2. Node.js 8 the Right Way
  3. Node.js 8 the Right Way
  4. Node.js 8 the Right Way
  5. Node.js 8 the Right Way
  6.  Acknowledgments
  7.  Preface
  8. Why Node.js the Right Way?
  9. What’s in This Book
  10. What This Book Is Not
  11. Code Examples and Conventions
  12. Online Resources
  13. Part I. Getting Up to Speed on Node.js 8
  14. 1. Getting Started
  15. Thinking Beyond the web
  16. Node.js’s Niche
  17. How Node.js Applications Work
  18. Aspects of Node.js Development
  19. Installing Node.js
  20. 2. Wrangling the File System
  21. Programming for the Node.js Event Loop
  22. Spawning a Child Process
  23. Capturing Data from an EventEmitter
  24. Reading and Writing Files Asynchronously
  25. The Two Phases of a Node.js Program
  26. Wrapping Up
  27. 3. Networking with Sockets
  28. Listening for Socket Connections
  29. Implementing a Messaging Protocol
  30. Creating Socket Client Connections
  31. Testing Network Application Functionality
  32. Extending Core Classes in Custom Modules
  33. Developing Unit Tests with Mocha
  34. Wrapping Up
  35. 4. Connecting Robust Microservices
  36. Installing ØMQ
  37. Publishing and Subscribing to Messages
  38. Responding to Requests
  39. Routing and Dealing Messages
  40. Clustering Node.js Processes
  41. Pushing and Pulling Messages
  42. Wrapping Up
  43. Node.js 8 the Right Way
  44. Part II. Working with Data
  45. 5. Transforming Data and Testing Continuously
  46. Procuring External Data
  47. Behavior-Driven Development with Mocha and Chai
  48. Extracting Data from XML with Cheerio
  49. Processing Data Files Sequentially
  50. Debugging Tests with Chrome DevTools
  51. Wrapping Up
  52. 6. Commanding Databases
  53. Introducing Elasticsearch
  54. Creating a Command-Line Program in Node.js with Commander
  55. Using request to Fetch JSON over HTTP
  56. Shaping JSON with jq
  57. Inserting Elasticsearch Documents in Bulk
  58. Implementing an Elasticsearch Query Command
  59. Wrapping Up
  60. Node.js 8 the Right Way
  61. Part III. Creating an Application from the Ground Up
  62. 7. Developing RESTful Web Services
  63. Advantages of Express
  64. Serving APIs with Express
  65. Writing Modular Express Services
  66. Keeping Services Running with nodemon
  67. Adding Search APIs
  68. Simplifying Code Flows with Promises
  69. Manipulating Documents RESTfully
  70. Emulating Synchronous Style with async and await
  71. Providing an Async Handler Function to Express
  72. Wrapping Up
  73. 8. Creating a Beautiful User Experience
  74. Getting Started with webpack
  75. Generating Your First webpack Bundle
  76. Sprucing Up Your UI with Bootstrap
  77. Bringing in Bootstrap JavaScript and jQuery
  78. Transpiling with TypeScript
  79. Templating HTML with Handlebars
  80. Implementing hashChange Navigation
  81. Listing Objects in a View
  82. Saving Data with a Form
  83. Wrapping Up
  84. 9. Fortifying Your Application
  85. Setting Up the Initial Project
  86. Managing User Sessions in Express
  87. Adding Authentication UI Elements
  88. Setting Up Passport
  89. Authenticating with Facebook, Twitter, and Google
  90. Composing an Express Router
  91. Bringing in the Book Bundle UI
  92. Serving in Production
  93. Wrapping Up
  94. Node.js 8 the Right Way
  95. 10. BONUS: Developing Flows with Node-RED
  96. Setting Up Node-RED
  97. Securing Node-RED
  98. Developing a Node-RED Flow
  99. Creating HTTP APIs with Node-RED
  100. Handling Errors in Node-RED Flows
  101. Wrapping Up
  102. A1. Setting Up Angular
  103. A2. Setting Up React
  104. Node.js 8 the Right Way

Routing and Dealing Messages

The REQ/REP socket pair we explored makes request/reply logic easy to code by operating sequentially. The Node.js code for a given responder will only ever be aware of one message at a time.

For parallel message processing, ØMQ includes the more advanced socket types ROUTER and DEALER. Let’s explore these a bit; then we’ll be ready to construct our Node.js cluster.

Routing Messages

You can think of a ROUTER socket as a parallel REP socket. Rather than replying to only one message at a time, a ROUTER socket can handle many requests simultaneously. It remembers which connection each request came from and will route reply messages accordingly.

Recall from ​Implementing a Messaging Protocol​, that any time you do networked programming, you’re working with one or more protocols. ØMQ uses the ZeroMQ Message Transport Protocol (ZMTP) for exchanging messages.[30] This protocol uses a sequence of low-overhead frames to compose messages. A ROUTER socket uses these frames to route each reply message back to the connection that issued the request.

Most of the time your Node.js programs can ignore the underlying details of ØMQ frames because the simpler socket types only need one frame per message. But the ROUTER socket type uses multiple frames.

Here’s an example of how to create a ROUTER socket in Node.js, with a message handler that grabs all the incoming frames:

​ ​const​ router = zmq.socket(​'router'​);
​ router.on(​'message'​, (...frames) => {
​  ​// Use frames.​
​ });

Previously our message handlers would take a data parameter, but this handler takes an array of frames instead.

The three dots (...) introduce an ECMAScript 2015 feature called rest parameters. When used in a function declaration, this syntax allows you to collect any number of arguments passed into the function as an array.

Now that we can get all the frames, let’s look at the DEALER socket type.

Dealing Messages

If a ROUTER socket is a parallel REP socket, then a DEALER is a parallel REQ. A DEALER socket can send multiple requests in parallel.

Let’s see how a dealer and router work together in Node. Take a look at this code sample:

​ ​const​ router = zmq.socket(​'router'​);
​ ​const​ dealer = zmq.socket(​'dealer'​);
​ 
​ router.on(​'message'​, (...frames) => dealer.send(frames));
​ dealer.on(​'message'​, (...frames) => router.send(frames));

Here we create both a ROUTER socket and a DEALER socket. Whenever either receives a message, it sends the frames to the other socket.

This creates a passthrough relationship where incoming requests to the router will be passed off to the dealer to send out to its connections. Likewise, incoming replies to the dealer will be forwarded back to the router, which directs each reply back to the connection that requested it.

The following figure shows the structure we’ll implement shortly, using the techniques we’ve just discussed.

images/router-dealer.png

The box in the center of the figure is the Node.js program. An incoming REQ socket connects to the ROUTER. When the REQ socket issues a request, the ROUTER bounces it over to the DEALER. The DEALER then picks the next one of the REP sockets connected to it (round-robin style) and forwards the request.

When the REP connection produces a reply, it follows the reverse route. The DEALER receives the reply and bounces it back to the ROUTER. The ROUTER looks at the message’s frames to determine its origin and sends the reply back to the connected REQ that sent the initial request.

From the perspective of the REQ and REP sockets, nothing has changed. Each still works on one message at a time. Meanwhile, the ROUTER/DEALER pair can distribute (round-robin) among the REQ and REP sockets connected on both ends.

Now we’re ready to develop a clustered Node.js application on top of the REQ, REP, ROUTER, and DEALER sockets we’ve just explored.