bpmux

v8.2.1

Published

2 years ago

Node stream multiplexing with back-pressure on each stream

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stream back-pressure backpressure high-water mark duplex readable writable multiplex mux demux

bpmux

Node stream multiplexing with back-pressure on each stream.

Run more than one stream.Duplex over a carrier Duplex.
Exerts back-pressure on each multiplexed stream and the underlying carrier stream.
Each multiplexed stream's back-pressure is handled separately while respecting the carrier's capacity. This prevents a slow or paused stream affecting other streams. This does incur an overhead so if you don't care about this feature you might want to look elsewhere.
Unit tests with 100% coverage.
Tested with TCP streams. You'll get better performance if you disable Nagle.
Works in the browser!
- Tested with Primus (using primus-backpressure).
- Tested with HTTP/2 streams (using browser-http2-duplex). Also tested Node-to-Node using http2.
- Browser unit tests using webpack and nwjs.
See the errors section for information on why multiplexed streams error when their carrier stream closes before they do.

The API is described here.

Example

Multiplexing multiple streams over a single TCP stream:

var net = require('net'),
    crypto = require('crypto'),
    assert = require('assert'),
    BPMux = require('bpmux').BPMux,
    sent = [];

net.createServer(function (c)
{
    var received = [], ended = 0;

    new BPMux(c).on('handshake', function (duplex)
    {
        var accum = '';

        duplex.on('readable', function ()
        {
            var data = this.read();
            if (data)
            {
                accum += data.toString('hex');
            }
        });

        duplex.on('end', function ()
        {
            received.push(accum);

            ended += 1;
            assert(ended <= 10);
            if (ended === 10)
            {
                assert.deepEqual(received.sort(), sent.sort());
            }
        });
    });
}).listen(7000, function ()
{
    var mux = new BPMux(net.createConnection(7000)), i;

    function multiplex(n)
    {
        var data = crypto.randomBytes(n * 100);
        mux.multiplex().end(data);
        sent.push(data.toString('hex'));
    }

    for (i = 1; i <= 10; i += 1)
    {
        multiplex(i);
    }
});

Another Example

Multiple return pipes to the browser, multiplexed over a single Primus connection:

var PrimusDuplex = require('primus-backpressure').PrimusDuplex,
    BPMux = require('bpmux').BPMux,
    http = require('http'),
    path = require('path'),
    crypto = require('crypto'),
    stream = require('stream'),
    assert = require('assert'),
    finalhandler = require('finalhandler'),
    serve_static = require('serve-static'),
    Primus = require('primus'),
    serve = serve_static(__dirname);

http.createServer(function (req, res)
{
    serve(req, res, finalhandler(req, res));
}).listen(7500, function ()
{
    var primus = new Primus(this);

    primus.on('connection', function (spark)
    {
        var mux = new BPMux(new PrimusDuplex(spark)), ended = 0, i;

        function multiplex(n)
        {
            var buf = crypto.randomBytes(10 * 1024),
                buf_stream = new stream.PassThrough(),
                bufs = [],
                duplex = mux.multiplex({ handshake_data: Buffer.from([n]) });

            buf_stream.end(buf);
            buf_stream.pipe(duplex);

            duplex.on('readable', function ()
            {
                var data;

                while (true)
                {
                    data = this.read();
                    if (data === null)
                    {
                        break;
                    }
                    bufs.push(data);
                }
            });

            duplex.on('end', function ()
            {
                console.log('end', n);
                ended += 1;
                assert(ended <= 10);
                assert.deepEqual(Buffer.concat(bufs), buf);
            });
        }

        for (i = 0; i < 10; i += 1)
        {
            multiplex(i);
        }
    });
    
    console.log('Point your browser to http://localhost:7500/loader.html');
});

The HTML (loader.html) for the browser-side of this example:

<html>
  <head>
    <title>BPMux Test Runner</title>
    <script type="text/javascript" src="/primus/primus.js"></script>
    <script type="text/javascript" src="bundle.js"></script>
    <script type="text/javascript" src="loader.js"></script>
  </head>
  <body onload='doit()'>
  </body>
</html>

The browser-side code (loader.js):

function doit()
{
    var mux = new BPMux(new PrimusDuplex(new Primus({ strategy: false })));

    mux.on('handshake', function (duplex, handshake_data)
    {
        console.log("handshake", handshake_data[0]);
        duplex.pipe(duplex);

        duplex.on('end', function ()
        {
            console.log('end', handshake_data[0]);
        });
    });
}

The browser-side dependencies (bundle.js) can be produced by webpack from:

PrimusDuplex = require('primus-backpressure').PrimusDuplex;
BPMux = require('bpmux').BPMux;

Comparison

multiplex library

Multiplexing libraries which don't exert backpressure on individual streams suffer from starvation. A stream which doesn't read its data stops other streams on the multiplex getting their data.

Here's a test using the multiplex library:

// Uses https://github.com/maxogden/multiplex (npm install multiplex)
// Backpressure is exerted across the multiplex as a whole, not individual streams.
// This means a stream which doesn't read its data starves the other streams.

const fs = require('fs');
const net = require('net');
const multiplex = require('multiplex');

require('net').createServer(c => {
    c.pipe(multiplex((stream, id) => {
        stream.on('data', function(d) {
            console.log('data', id, d.length);
            if (id === '0') {
                this.pause();
            }
        });
    }));
}).listen(7000, () => {
    const plex = multiplex();
    plex.pipe(net.createConnection(7000));

    const stream1 = plex.createStream();
    const stream2 = plex.createStream();

    fs.createReadStream('/dev/urandom').pipe(stream1);
    fs.createReadStream('/dev/urandom').pipe(stream2);
});

When the first stream is paused, backpressure is applied to the second stream too, even though it hasn't been paused. If you run this example, you'll see:

$ node multiplex.js 
data 0 65536
data 1 65536

bpmux doesn't suffer from this problem since backpressure is exerted on each stream separately. Here's the same test:

// BPMux exerts backpressure on individual streams so a stream which doesn't
// read its data doesn't starve the other streams.

const fs = require('fs');
const net = require('net');
const { BPMux } = require('bpmux');

require('net').createServer(c => {
    new BPMux(c).on('handshake', stream => {
        stream.on('data', function (d) {
            console.log('data', stream._chan, d.length);
            if (stream._chan === 0) {
                this.pause();
            }
        });
    });
}).listen(7000, () => {
    const mux = new BPMux(net.createConnection(7000));

    const stream1 = mux.multiplex();
    const stream2 = mux.multiplex();

    fs.createReadStream('/dev/urandom').pipe(stream1);
    fs.createReadStream('/dev/urandom').pipe(stream2);
});

The second stream continues to receive data when the first stream is paused:

data 0 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
data 1 16384
...

HTTP/2 sessions

HTTP/2 sessions do exert backpressure on individual streams, as this test shows:

const fs = require('fs');
const http2 = require('http2');

const server = http2.createServer();
server.on('stream', (stream, headers) => {
    stream.on('data', function (d) {
        console.log('data', headers[':path'], d.length);
        if (headers[':path'] === '/stream1') {
            this.pause();
        }
    });
});
server.listen(8000);

const client = http2.connect('http://localhost:8000');

const stream1 = client.request({ ':path': '/stream1' }, { endStream: false });
const stream2 = client.request({ ':path': '/stream2' }, { endStream: false });

fs.createReadStream('/dev/urandom').pipe(stream1);
fs.createReadStream('/dev/urandom').pipe(stream2);

data /stream1 16384
data /stream2 16384
data /stream2 16348
data /stream2 35
data /stream2 16384
data /stream2 16384
data /stream2 1
data /stream2 16384
data /stream2 16366
data /stream2 18
data /stream2 16384
data /stream2 16382
data /stream2 2
data /stream2 16384
...

If you pass a pair of sessions (one client, one server) to BPMux(), they will be used for multiplexing streams, with no additional overhead. This is useful if you want to use the bpmux API.

Errors

bpmux will emit error events on multiplexed streams if their underlying (carrier) stream closes before they have closed. The error object will have one of the following messages:

carrier stream finished before duplex finished
carrier stream ended before end message received

and have a property carrier_done set to true.

As this is an error event, you must register an event listener on multiplexed streams if you don't want the Node process to exit.

The reasoning behind emitting error events on open multiplexed streams when their carrier closes is:

If you're reading from a stream and it hasn't ended before the carrier closes then there may be some data that you'll never receive. This is an error state.
If you're writing to a stream and it hasn't finished before the carrier closes then your application should be informed about it straight away. If it's performing some heavy calculation, for example, then it has a chance to cancel it before writing the result to the stream.

If you do register error event listeners, make sure you do so for streams you multiplex using multiplex() and for streams you receive using the handshake or peer_multiplex events.

BPMux objects will also re-emit any error events their carrier stream emits.

Installation

npm install bpmux

Licence

MIT

Test

Over TCP (long test):

grunt test

Over TCP (quick test):

grunt test-fast

Over Primus (using nwjs to run browser- and server-side):

grunt test-browser

The examples at the top of this page:

grunt test-examples

Code Coverage

grunt coverage

c8 results are available here.

Coveralls page is here.

Lint

grunt lint

API

new Http2Sessions(client, server)

Class for holding a pair of HTTP/2 sessions.

Pass this to BPMux() and it will use the sessions' existing support for multiplexing streams. Both client and server sessions are required because HTTP/2 push streams are unidirectional.

Parameters:

{ClientHttp2Session} client Client session
{ServerHttp2Session} server Server session

Go: TOC

BPMux(carrier, [options])

Constructor for a BPMux object which multiplexes more than one stream.Duplex over a carrier Duplex.

Parameters:

{Duplex | Http2Sessions} carrier The Duplex stream over which other Duplex streams will be multiplexed.
{Object} [options] Configuration options. This is passed down to frame-stream. It also supports the following additional properties:
- {Object} [peer_multiplex_options] When your BPMux object detects a new multiplexed stream from the peer on the carrier, it creates a new Duplex and emits a peer_multiplex event. When it creates the Duplex, it uses peer_multiplex_options to configure it with the following options:
  - {Integer} [max_write_size] Maximum number of bytes to write to the Duplex at once, regardless of how many bytes the peer is free to receive. Defaults to 0 (no limit).
  - {Boolean} [check_read_overflow] Whether to check if more data than expected is being received. If true and the Duplex's high-water mark for reading is exceeded then the Duplex emits an error event. This should not normally occur unless you add data yourself using readable.unshift — in which case you should set check_read_overflow to false. Defaults to true.
- {Function} [parse_handshake_data(handshake_data)] When a new stream is multiplexed, the BPMux objects at each end of the carrier exchange a handshake message. You can supply application-specific handshake data to add to the handshake message (see BPMux.prototype.multiplex and BPMux.events.handshake). By default, when handshake data from the peer is received, it's passed to your application as a raw Buffer. Use parse_handshake_data to specify a custom parser. It will receive the Buffer as an argument and should return a value which makes sense to your application.
- {Boolean} [coalesce_writes] Whether to batch together writes to the carrier. When the carrier indicates it's ready to receive data, its spare capacity is shared equally between the multiplexed streams. By default, the data from each stream is written separately to the carrier. Specify true to write all the data to the carrier in a single write. Depending on the carrier, this can be more performant.
- {Boolean} [high_channels] BPMux assigns unique channel numbers to multiplexed streams. By default, it assigns numbers in the range [0..2^31). If your application can synchronise the two BPMux instances on each end of the carrier stream so they never call multiplex at the same time then you don't need to worry about channel number clashes. For example, one side of the carrier could always call multiplex and the other listen for handshake events. Or they could take it in turns. If you can't synchronise both sides of the carrier, you can get one side to use a different range by specifying high_channels as true. The BPMux with high_channels set to true will assign channel numbers in the range [2^31..2^32).
- {Integer} [max_open] Maximum number of multiplexed streams that can be open at a time. Defaults to 0 (no maximum).
- {Integer} [max_header_size] BPMux adds a control header to each message it sends, which the receiver reads into memory. The header is of variable length — for example, handshake messages contain handshake data which can be supplied by the application. max_header_size is the maximum number of header bytes to read into memory. If a larger header is received, BPMux emits an error event. Defaults to 0 (no limit).
- {Integer|false} keep_alive Send a single byte keep-alive message every N milliseconds. Defaults to 30000 (30 seconds). Pass false to disable.

Go: TOC

BPMux.prototype.multiplex([options])

Multiplex a new stream.Duplex over the carrier.

Parameters:

{Object} [options] Configuration options:
- {Buffer} [handshake_data] Application-specific handshake data to send to the peer. When a new stream is multiplexed, the BPMux objects at each end of the carrier exchange a handshake message. You can optionally supply handshake data to add to the handshake message here. The peer application will receive this when its BPMux object emits a handshake event. Defaults to a zero-length Buffer.
- {Integer} [max_write_size] Maximum number of bytes to write to the Duplex at once, regardless of how many bytes the peer is free to receive. Defaults to 0 (no limit).
- {Boolean} [check_read_overflow] Whether to check if more data than expected is being received. If true and the Duplex's high-water mark for reading is exceeded then the Duplex emits an error event. This should not normally occur unless you add data yourself using readable.unshift — in which case you should set check_read_overflow to false. Defaults to true.
- {Integer} [channel] Unique number for the new stream. BPMux identifies each multiplexed stream by giving it a unique number, which it allocates automatically. If you want to do the allocation yourself, specify a channel number here. It's very unlikely you'll need to do this but the option is there. Duplex objects managed by BPMux expose a get_channel method to retrieve their channel number. Defaults to automatic allocation.

Return:

{Duplex} The new Duplex which is multiplexed over the carrier. This supports back-pressure using the stream readable event and write method.

Throws:

{Error} If there are no channel numbers left to allocate to the new stream, the maximum number of open multiplexed streams would be exceeded or the carrier has finished or ended.

Go: TOC | BPMux.prototype

BPMux.events.peer_multiplex(duplex)

peer_multiplex event

A BPMux object emits a peer_multiplex event when it detects a new multiplexed stream from its peer on the carrier stream.

Parameters:

{Duplex} duplex The new stream.

Go: TOC | BPMux.events

BPMux.events.handshake(duplex, handshake_data, [delay_handshake])

handshake event

A BPMux object emits a handshake event when it receives a handshake message from its peer on the carrier stream. This can happen in two cases:

The BPMux object is processing a handshake message for a new multiplexed stream the peer created and it hasn't seen before. Note the handshake event is emitted after the peer_multiplex event.
Your application previously called multiplex on its BPMux object to multiplex a new stream over the carrier and now the peer has replied with a handshake message.

Parameters:

{Duplex} duplex The multiplexed stream for which a handshake message has been received. Please note that a handshake event is also emitted on duplex immediately after BPMux's handshake event finishes processing. duplex's handshake event is passed the same handshake_data and delay_handshake parameters decribed below.
{Object} handshake_data Application-specific data which the peer sent along with the handshake message. If you specified a parse_handshake_data function in the BPMux constructor then handshake_data will be the return value from calling that function.
{Function} [delay_handshake] This parameter will be null in case 2 (your application previously created duplex). Otherwise (case 1), this parameter will be a function. By default, the BPMux object replies to the peer's handshake message as soon as your event handler returns and doesn't attach any application-specific handshake data. If you wish to delay the handshake message or provide handshake data, call delay_handshake. It returns another function which you can call at any time to send the handshake message. The returned function takes a single argument:
- {Buffer} [handshake_data] Application-specific handshake data to attach to the handshake message sent to the peer. Defaults to a zero-length Buffer.

Go: TOC | BPMux.events

BPMux.events.handshake_sent(duplex, complete)

handshake_sent event

A BPMux object emits a handshake_sent event after it sends a handshake message to its peer on the carrier stream.

Parameters:

{Duplex} duplex The multiplexed stream for which a handshake has been sent. Please note that a handshake_sent event is also emitted on duplex immediately after BPMux's handshake event finishes processing. duplex's handshake_sent event is passed the same complete parameter described below.
{Boolean} complete Whether the handshake message was completely sent (true) or the carrier stream buffered it (false). You can use this to apply back-pressure to stream multiplexing. For example, if complete is false then you could avoid calling multiplex until a drain event is emitted.

Go: TOC | BPMux.events

BPMux.events.drain()

drain event

A BPMux object emits a drain event when its carrier stream emits a drain event.

Go: TOC | BPMux.events

BPMux.events.end()

end event

A BPMux object emits a end event after the carrier stream ends (will receive no more data).

Go: TOC | BPMux.events

BPMux.events.finish()

finish event

A BPMux object emits a finish event after the carrier stream finishes (won't write any more data).

Go: TOC | BPMux.events

BPMux.events.full()

full event

A BPMux object emits a full event when it wants to add a new multiplexed stream on the carrier stream but the number of multiplexed streams is at its maximum. It will remain at maximum until a removed event is emitted.

Go: TOC | BPMux.events

BPMux.events.removed(duplex)

removed event

A BPMux object emits a removed event when a multiplexed stream has closed (finished and ended) and been removed from the list of multiplexed streams.

Parameters:

{Duplex} duplex The stream which has closed.

Go: TOC | BPMux.events

BPMux.events.keep_alive()

keep_alive event

A BPMux object emits a keep_alive event when it receives a keep-alive message from its peer.

Go: TOC | BPMux.events

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Readme

bpmux

Example

Another Example

Comparison

multiplex library

HTTP/2 sessions

Errors

Installation

Licence

Test

Code Coverage

Lint

API

new Http2Sessions(client, server)

BPMux(carrier, [options])

BPMux.prototype.multiplex([options])

BPMux.events.peer_multiplex(duplex)

BPMux.events.handshake(duplex, handshake_data, [delay_handshake])

BPMux.events.handshake_sent(duplex, complete)

BPMux.events.drain()

BPMux.events.end()

BPMux.events.finish()

BPMux.events.full()

BPMux.events.removed(duplex)

BPMux.events.keep_alive()