lazystream

What is lazystream?

The lazystream npm package provides a way to lazily create streams, meaning the stream is not created until it is actually needed. This can be useful for optimizing performance and resource usage in applications that deal with streams.

What are lazystream's main functionalities?

Lazy Stream Creation

This feature allows you to create a stream that is only instantiated when it is actually used. In this example, a read stream for 'example.txt' is created lazily, meaning the file is not opened until data is actually read from the stream.

const LazyStream = require('lazystream');
const fs = require('fs');

const lazyStream = new LazyStream(() => fs.createReadStream('example.txt'));

lazyStream.on('data', (chunk) => {
  console.log(chunk.toString());
});

Lazy Stream with Options

This feature allows you to pass options to the stream creation function. In this example, the read stream is created with the 'utf8' encoding option, and the file is read as a UTF-8 encoded string.

const LazyStream = require('lazystream');
const fs = require('fs');

const lazyStream = new LazyStream(() => fs.createReadStream('example.txt', { encoding: 'utf8' }));

lazyStream.on('data', (chunk) => {
  console.log(chunk);
});

Other packages similar to lazystream

streamifier

The streamifier package allows you to convert various data types into readable streams. Unlike lazystream, which focuses on lazy instantiation, streamifier is more about converting existing data into stream form.

through2

The through2 package provides a thin wrapper around Node.js streams2 Transform to avoid explicit subclassing noise. It is more focused on transforming data as it passes through the stream, whereas lazystream is about lazy instantiation.

from2

The from2 package is a small utility for creating readable streams in a simple way. It is similar to lazystream in that it helps with stream creation, but it does not specifically focus on lazy instantiation.

README

Lazy Streams

Create streams lazily when they are read from or written to.
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.

new lazystream.Readable(function (options) {
  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.

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

Install

$ npm install lazystream --save
lazystream@1.0.0 node_modules/lazystream
└── readable-stream@2.0.5

Changelog

v1.0.0

• #2: unconditionally use readable-stream 2.x.

v0.2.0

• #1: error events are now propagated

v0.1.0

• (this was the first release)

Contributing

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

Credits

Chris Talkington and his node-archiver for providing a use-case.

License

Copyright (c) 2013 J. Pommerening, contributors.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.