combined-stream

What is combined-stream?

The combined-stream npm package is used to create a stream that emits events from multiple other streams in sequence. It is useful for treating a series of streams as a single continuous stream, which can be particularly handy when dealing with file uploads, data concatenation, or stream transformation.

What are combined-stream's main functionalities?

Creating a combined stream from multiple sources

This feature allows you to combine multiple readable streams into one. In the code sample, two text files are read as streams and appended to the combined stream, which is then piped to the standard output.

const CombinedStream = require('combined-stream');
const fs = require('fs');

const combinedStream = CombinedStream.create();
combinedStream.append(fs.createReadStream('file1.txt'));
combinedStream.append(fs.createReadStream('file2.txt'));

combinedStream.pipe(process.stdout);

Appending streams with delayed execution

This feature allows you to append streams with a function that will be called when the stream is ready for more data. The code sample demonstrates appending a stream with a function that provides the stream asynchronously.

const CombinedStream = require('combined-stream');
const fs = require('fs');

const combinedStream = CombinedStream.create();
combinedStream.append(next => {
  next(fs.createReadStream('file3.txt'));
});

combinedStream.pipe(process.stdout);

Appending data directly

This feature allows you to append raw data directly to the combined stream. The code sample shows how to append string data to the stream, which is then piped to the standard output.

const CombinedStream = require('combined-stream');

const combinedStream = CombinedStream.create();
combinedStream.append('Hello ');
combinedStream.append('World!');

combinedStream.pipe(process.stdout);

Other packages similar to combined-stream

multistream

Multistream is similar to combined-stream in that it allows you to combine multiple streams into a single stream. However, multistream provides more control over the order and manner in which streams are combined, such as lazy stream creation and handling of stream errors.

pumpify

Pumpify combines streams using pump and stream.pipeline under the hood for better error handling. It is similar to combined-stream but focuses on creating a pipeline of transform streams that can be treated as a single duplex stream.

stream-combiner2

Stream-combiner2 is a successor to stream-combiner, and it is used to turn a pipeline of streams into a single duplex stream. It differs from combined-stream by focusing on transforming streams and providing a duplex interface.

README

combined-stream

A stream that emits multiple other streams one after another.

Installation

npm install combined-stream

Usage

Here is a simple example that shows how you can use combined-stream to combine two files into one:

var CombinedStream = require('combined-stream');
var fs = require('fs');

var combinedStream = CombinedStream.create();
combinedStream.append(fs.createReadStream('file1.txt'));
combinedStream.append(fs.createReadStream('file2.txt'));

combinedStream.pipe(fs.createWriteStream('combined.txt'));

While the example above works great, it will pause all source streams until they are needed. If you don't want that to happen, you can set pauseStreams to false:

var CombinedStream = require('combined-stream');
var fs = require('fs');

var combinedStream = CombinedStream.create({pauseStreams: false});
combinedStream.append(fs.createReadStream('file1.txt'));
combinedStream.append(fs.createReadStream('file2.txt'));

combinedStream.pipe(fs.createWriteStream('combined.txt'));

However, what if you don't have all the source streams yet, or you don't want to allocate the resources (file descriptors, memory, etc.) for them right away? Well, in that case you can simply provide a callback that supplies the stream by calling a next() function:

var CombinedStream = require('combined-stream');
var fs = require('fs');

var combinedStream = CombinedStream.create();
combinedStream.append(function(next) {
  next(fs.createReadStream('file1.txt'));
});
combinedStream.append(function(next) {
  next(fs.createReadStream('file2.txt'));
});

combinedStream.pipe(fs.createWriteStream('combined.txt'));

API

CombinedStream.create([options])

Returns a new combined stream object. Available options are:

• maxDataSize
• pauseStreams

The effect of those options is described below.

combinedStream.pauseStreams = true

Whether to apply back pressure to the underlaying streams. If set to false, the underlaying streams will never be paused. If set to true, the underlaying streams will be paused right after being appended, as well as when delayedStream.pipe() wants to throttle.

combinedStream.maxDataSize = 2 * 1024 * 1024

The maximum amount of bytes (or characters) to buffer for all source streams. If this value is exceeded, combinedStream emits an 'error' event.

combinedStream.dataSize = 0

The amount of bytes (or characters) currently buffered by combinedStream.

combinedStream.append(stream)

Appends the given stream to the combinedStream object. If pauseStreams is set to `true, this stream will also be paused right away.

streams can also be a function that takes one parameter called next. next is a function that must be invoked in order to provide the next stream, see example above.

Regardless of how the stream is appended, combined-stream always attaches an 'error' listener to it, so you don't have to do that manually.

Special case: stream can also be a String or Buffer.

combinedStream.write(data)

You should not call this, combinedStream takes care of piping the appended streams into itself for you.

combinedStream.resume()

Causes combinedStream to start drain the streams it manages. The function is idempotent, and also emits a 'resume' event each time which usually goes to the stream that is currently being drained.

combinedStream.pause();

If combinedStream.pauseStreams is set to false, this does nothing. Otherwise a 'pause' event is emitted, this goes to the stream that is currently being drained, so you can use it to apply back pressure.

combinedStream.end();

Sets combinedStream.writable to false, emits an 'end' event, and removes all streams from the queue.

combinedStream.destroy();

Same as combinedStream.end(), except it emits a 'close' event instead of 'end'.

License

combined-stream is licensed under the MIT license.