Add 'drain'-event

[VanCoding]

Is it possible to add the 'drain'-event?

I looked at the WebSocket specification and there is no such event and I'm not sure if there's a way to do it. But it would be great!

Maybe, you have any idea on how to implement it...

[maxogden]

i'm not doing any buffering at all so it should be drained every time write is called (i think). @dominictarr said that the send method on a websocket returns a boolean in the same way writable streams write returns booleans but I don't actually know if that is true (though binaryjs is using the return value binaryjs/streamws@7034fc1#L3R195). there is also a bufferedAmount property

[maxogden]

Oh I just realized the above comment is wrong. sorry, coffee hasnt kicked in yet. lemme research this a bit more

[maxogden]

seems like the only way to do it is by polling http://marcelojabali.blogspot.com/2012/07/websocket-bufferedamount-attribute.html

[VanCoding]

That's a pity. Polling will not be near to performant.. Hope there will come an extension to the API anytime...

[dominictarr]

It's not as bad as you think, because you only need so start polling when send(data) == false
i.e. when you should be slowing down anyway.

[NodeGuy]

The return type of send has been changed from boolean to void in the WebSocket spec so we can't check it anymore.

Perhaps after each write we can poll every 50 ms until the bufferedAmount is zero, and then stop and emit a drain event.

[dominictarr]

why would they do that?

polling an in memory structure isn't that bad... also, you don't need to poll it all the time, only after the buffer has filled.

[NodeGuy]

Looks like this message was the inspiration for the change.

[dominictarr]

hmm, that looks much more serious! it actually closes the connection when the buffer fills!
maybe just make it return false if bufferedAmount is above a certain water mark...

[Raynos]

@dominictarr @maxogden

We should check bufferedAmount streams2 style. If its below the hwm then return true if its above return false and set up a poller at certain rate to emit "drain" once below hwm.

[dominictarr]

yes +1

[maxogden]

I rewrote this module using streams2. Maybe it's easier to implement this now?

[jnordberg]

I'm using this patched socketWriteBrowser function to do this:

function socketWriteBrowser(chunk, enc, next) {

  if (socket.bufferedAmount > 16384) {
    setTimeout(function(){
      socketWriteBrowser(chunk, enc, next)
    }, 10)
    return
  }

  try {
    socket.send(chunk)
  } catch(err) {
    return next(err)
  }

  next()
}

Not sure if this is the best way to go about this but it's been working well so far. With this patch I can upload large (>1gb) files over websockets without chrome eating all memory and cpu.

[mcollina]

@jnordberg I think we should avoid to allocate a closure, it would give us more speed :). Something like:

function socketWriteBrowser(chunk, enc, next) {

  if (socket.bufferedAmount > 16384) {
    return setTimeout(socketWriteBrowser, 10, chunk, enc, next)
  }

  try {
    socket.send(chunk)
  } catch(err) {
    return next(err)
  }

  next()
}

I'm 👍 on this. PR?

[jnordberg]

Neat, I didn't know you could pass along arguments to setTimeout.

I'll prepare a PR