Add support of msgpack format

[mrniko]

I think it will be useful to add support of msgpack and have ability to switch between json and msgpack formats in configuration. http://msgpack.org/

[rase-]

i think alternative formats would serve better as plugins. I'd be happy to merge in any hooks needed to make that happen.

Thought, @rauchg?

[rauchg]

Agreed on hooks. Pluggable codecs is something we've been meaning to introduce for a while!
As a matter of fact, the current "codec" is highly opinionated in several areas (performance, usage of UTF8 JSON even in binary stream, etc), and many applications would definitely be better served with a custom one.

[rauchg]

It'd be interesting to test the performance of a demo app that shows users cursors on a page in realtime using the default codec and a custom codec that can only receive integer tuples over a binary stream (x,y).

In other words:

io.emit('position', x, y)

could be encoded in a very minimal way instead of using JSON.

[legomind]

any progress on this? I have msgpack working via monkey-patching - something I would like to avoid.

[darrachequesne]

I'd be happy to merge in any hooks needed to make that happen.

Related: #1946

[darrachequesne]

Question: aren't most users already using something like io.emit(<message id>, msgpack.encode({ x: x, y: y }));?

[legomind]

@darrachequesne that is the only way to do it right now, but it would be far more convenient if there were a way to preprocess all outgoing and incoming messages automatically.

As far as hooks go, what would you like them named?

I was thinking something like:

server

const socket = new SocketIO(httpServer, {
  prepareMessage: msgpack.encode,
  unprepareMessage: msgpack.decode,
})

client

const socket = new SocketIO({
  prepareMessage: msgpack.encode,
  unprepareMessage: msgpack.decode,
})

[legomind]

Or closer to the request in #1946,

server

const codec = {
  encode: msgpack.encode,
  decode: msgpack.decode,
}
const socket = new SocketIO(httpServer, {
  codec,
})

client

const codec = {
  encode: msgpack.encode,
  decode: msgpack.decode,
}
const socket = new SocketIO({
  codec,
})

[darrachequesne]

On a per-event level

Maybe something like the following?
io.registerCodec(<eventName>, { encode: <encode>, decode: <decode> });

That would allow to use not only msgpack, but also protobuf or schemapack (among others).

Question: since socket.io does add some metadata to the payload (i.e. the event name, the packet type, the namespace name, the optional acknowledgment id), should the user be aware of that?

Example: socket.emit('hello', 'world', function () {}) results in the following packet:

{
  type: parser.EVENT,
  data: ['hello', 'world'],
  id: 1,
  nsp: '/test'
}

[darrachequesne]

That may make sense too: socketio/socket.io-parser#61

[darrachequesne]

What do you think of #2829?

[darrachequesne]

Closed by #2829.