Node streams

in Projects, Programming, Technology

How to inherit from node stream

I recently had a project where I wanted my node javascript class to support pipe to and from (in other words, to be a duplex stream). I couldn’t find sufficient examples of implementing streams (probably because the node API has changed so many times). The current node stream docs are pretty clear, but miss a couple points.

After solving the problem, I created this Node Stream Inheritance sample project with code to share. The project contains sample code showing how to subclass node’s Readable, Writeable, Transform, and Duplex streams as they exist in node v0.12.2.

The node streaming API has a long history. For the purposes of this project, I wanted to make my class support streaming in the simplest way possible without any external dependencies.

Specific node stream inheritance questions

I implemented this project to demonstrate the following:

  1. What event should I wait for to know stream is complete? This depends on the stream you are piping to (the sink). In the case of a FileStream, handle the 'close' event.
  2. What events should I implement (emit) to indicate my writable stream has received everything it can handle? In this case I opted to implement my own 'full' event – indicating that my custom stream had no room for further input.
  3. How do I handle errors? _write and _transform provide callbacks. If you pass your error out, the underlying implementation will automatically emit an ‘error’ event. In the case of _read, you need to use this.emit('error', err);

Sample code

Here is some sample code from the project.

Duplex stream subclass test

Duplex stream subclass example

Alternatives

If you do want to use a library for a simpler API (that is more consistent across node versions), look into through2 and event-stream. Thanks @collinwat for the code review and recommendations!

Related: Top 6 problems with node.js

Write a Comment

Comment

  1. Thanks for this. I’ve been searching everywhere for recent example code showing how to work with node streams.