combined-stream2

A drop-in Streams2-compatible replacement for the combined-stream module.

Supports most of the combined-stream API. Automatically wraps Streams1 streams, so that they work as well.

Both Promises and nodebacks are supported.

License

WTFPL or CC0, whichever you prefer. A donation and/or attribution are appreciated, but not required.

Donate

My income consists entirely of donations for my projects. If this module is useful to you, consider making a donation!

You can donate using Bitcoin, PayPal, Gratipay, Flattr, cash-in-mail, SEPA transfers, and pretty much anything else.

Contributing

Pull requests welcome. Please make sure your modifications are in line with the overall code style, and ensure that you're editing the .coffee files, not the .js files.

Build tool of choice is gulp; simply run gulp while developing, and it will watch for changes.

Be aware that by making a pull request, you agree to release your modifications under the licenses stated above.

Migrating from combined-stream

Note that there are a few important differences between combined-stream and combined-stream2:

• You cannot supply strings, only Buffers and streams. This is because combined-stream2 doesn't know what the encoding of your string would be, and can't guess safely. You will need to manually encode strings to a Buffer before passing them on to combined-stream2.
• The pauseStreams option does not exist. All streams are read lazily in non-flowing mode; that is, no data is read until something explicitly tries to read the combined stream.
• The maxDataSize option does not exist.
• The .write(), .end() and .destroy() methods are not (yet) implemented.
• There is a .getCombinedStreamLength() method that asynchronously returns the total length of all streams (or an error if it cannot be determined). This method will 'resolve' all callback-supplied streams, as if the stream were being read.

Most usecases will not be affected by these differences, but your mileage may vary.

Using combined-stream2 with request

There's an important caveat when trying to append a request stream to a combined-stream2.

Because request does a bunch of strange non-standard hackery with streams, it doesn't play nicely with combined-stream2 (and many other writable/transform streams). For convenience, combined-stream2 contains a built-in workaround using a PassThrough stream specifically for dealing with request streams, but this workaround will likely result in the entire response being buffered into memory.

Passing in response objects (that is, the object provided in the response event handler for a request call) is completely unsupported - trying to do so will likely break combined-stream2. You must pass in the request object, rather than the response object.

I seriously suggest you consider using bhttp instead - it has much more predictable behaviour.

Usage

var CombinedStream = require('combined-stream2');
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'));

Appending a stream asynchronously (lazily)

The function will only be called when you try to either read/pipe the combined stream, or retrieve the total stream length.

combinedStream.append(function(next){
	next(fs.createReadStream('file3.txt'));
});

Getting the combined length of all streams

See the API documentation below for more details.

Promise = require("bluebird");

Promise.try(function(){
	combinedStream.getCombinedStreamLength()
}).then(function(length){
	console.log("Total stream length is " + length + " bytes.");
}).catch(function(err){
	console.log("Could not determine the total stream length!");
});

... or using nodebacks:

combinedStream.getCombinedStreamLength(function(err, length){
	if(err) {
		console.log("Could not determine the total stream length!");
	} else {
		console.log("Total stream length is " + length + " bytes.");
	}
});

API

Since combined-stream2 is a stream.Readable, it inherits the regular Readable stream properties. Aside from that, the following methods exist:

CombinedStream.create()

Creates and returns a new combinedStream. Contrary to the .create() method for the original combined-stream module, this method does not accept options.

combinedStream.append(source, [options])

Adds a source to the combined stream. Valid sources are streams, Buffers, and callbacks that return either of the two (asynchronously).

• source: The source to add.
• options: Optional. Additional stream options.
  • contentLength: The length of the stream. Useful if your stream type is not supported by stream-length, but you know the length of the stream in advance. Also available as knownLength for backwards compatibility reasons.

combinedStream.getCombinedStreamLength([callback])

This method will 'resolve' all callback-supplied streams, as if the stream were being read.

Asynchronously returns the total length of all streams (and Buffers) together. If the total length cannot be determined (ie. at least one of the streams is of an unsupported type), an error is thrown asynchronously.

If you specify a callback, it will be treated as a nodeback. If you do not specify a callback, a Promise will be returned.

This functionality uses the stream-length module.

combinedStream.pipe(target)

Like for other Streams2 Readable streams, this will start piping the combined stream contents into the target stream.

After calling this, you can no longer append new streams.