Async Lazy Streams

Create streams lazily (event using promises) when they are read from or written to.
async-lazystream: 1.0.0

Why?

Sometimes you feel the itch to open all the files at once. You want to pass a bunch of streams around, so the consumer does not need to worry where the data comes from. From a software design point-of-view this sounds entirely reasonable. Then there is that neat little function fs.createReadStream() that opens a file and gives you a nice fs.ReadStream to pass around, so you use what the mighty creator deities of node bestowed upon you.

Error: EMFILE, too many open files
─ node

This package provides two classes based on the node's Streams3 API (courtesy of readable-stream to ensure a stable version).

Class: lazystream.Readable

A wrapper for readable streams. Extends stream.PassThrough.

new lazystream.Readable(fn [, options])

• fn {Function}
  The function that the lazy stream will call to obtain the stream to actually read from.
• options {Object}
  Options for the underlying PassThrough stream, accessible by fn.

Creates a new readable stream. Once the stream is accessed (for example when you call its read() method, or attach a data-event listener) the fn function is called with the outer lazystream.Readable instance bound to this.

If you pass an options object to the constuctor, you can access it in your fn function.

const lazystream = require('async-lazystream');

new lazystream.Readable(function (options) {
  return fs.createReadStream('/dev/urandom');
});

or async variant:

const lazystream = require('async-lazystream');

new lazystream.Readable(async function (options) {
  // ... some async code
  return fs.createReadStream('/dev/urandom');
});

Class: lazystream.Writable

A wrapper for writable streams. Extends stream.PassThrough.

new lazystream.Writable(fn [, options])

• fn {Function}
  The function that the lazy stream will call to obtain the stream to actually write to.
• options {Object}
  Options for the underlying PassThrough stream, accessible by fn.

Creates a new writable stream. Just like the one above but for writable streams.

const lazystream = require('async-lazystream');

new lazystream.Writable(function () {
  return fs.createWriteStream('/dev/null');
});

or async variant:

const lazystream = require('async-lazystream');

new lazystream.Writable(async function () {
  //... some async code
  return fs.createWriteStream('/dev/null');
});

Install

$ npm install async-lazystream --save

Changelog

v1.0.0

• Initial release

Contributing

Fork it, branch it, send me a pull request. We'll work out the rest together.

Credits

J. Pommerening - code for this module was based on 'lazystream'.

LICENSE

See License