Re: [hybi] Multiplexing extension spec draft 03

[Takeshi Yoshino <[e-mail]>]

On Fri, Mar 23, 2012 at 17:14, Arman Djusupov <[e-mail]> wrote:

> Hello Takeshi,****
>
> ** **
>
> Using both a DropChannel and a close frame to close a logical channel
> seems like overkill.
>
The original aim of addition of DropChannel was only to provide a way to
terminate logical channel which is behaving abnormally by some command out
of that logical channel.

To make abstraction simple, I gave it a role to terminate a logical channel
normally, too. But I'm ok with getting normal close done by only one
command (one close frame, one DropChannel command, etc.)

> Exchanging DropChannel control messages should be enough for mutual
> shutdown of a logical channel. A more important issue is that if a close
> frame is sent through an intermediary that does not understand the mux
> extension, the intermediary may simply drop the physical channel /
> connection.
>
I understand your concern. Actually, IIRC it was one of the motivation to
introduce close frame that a close frame tells intermediaries the end of
session instead of unreliable TCP FIN so that they can release resource for
the session more quickly.

John's original proposal was adding a new framing onto WebSocket framing to
implement multiplexing. There was some discussion about this and some
suggested  reuse of opcode in base framing. See this thread for example
http://www.ietf.org/mail-archive/web/hybi/current/msg07240.html.

> It’s easy to imagine a frame compression intermediary that would simply
> stop reading from the network connection once it encounters a close frame
> (as per WS spec no data is expected to follow the close frame). So probably
> the sending of a close frame should be avoided (i.e. prohibited) for
> logical channels.
>
I'd like to disallow any control frame with channel ID != 0 and have
corresponding mux commands for each of them if we take this approach rather
than just converting close frame into DropChannel ad-hoc.

Also we need to give DropChannel some field to hold the information close
frame has (status and reason).