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Re: 6455 Websockets and the relationship to HTTP

From: Van Catha <vans554@gmail.com>
Date: Sun, 4 Dec 2016 22:23:40 -0500
Message-ID: <CAG-EYCjhoXthjt7HsaV0MprZigJtzUOK=o7ybPwvj+uXwmBO1Q@mail.gmail.com>
To: Andy Green <andy@warmcat.com>
Cc: Jacob Champion <champion.p@gmail.com>, Patrick McManus <mcmanus@ducksong.com>, HTTP Working Group <ietf-http-wg@w3.org>
> The meaning of ws1 PING is different than the h2 link PING, which is
> defined to not be able to have a specific stream context but only
> connectionwide.  For ws1 it means the websockets server (which may be a
> different process or on a different machine than the h2 endpoint) still
> acknowledges the ws1 connection as alive and communication in both ways
> on the stream is working.  For h2 it means the h2 server is still
> connected at the stream bundle level.  They're not actually giving you
> the same assurance.

That is the responsibility of the h2 endpoint (if h2 is proxing/forwarding
the request to another server).

I do not see why this should be the responsibility of ws.  I see your
point, but I see it as out of scope.

On Sun, Dec 4, 2016 at 10:02 PM, Andy Green <andy@warmcat.com> wrote:

> On Sun, 2016-12-04 at 19:59 -0500, Van Catha wrote:
>
> > I do not see the need for Ping, Pong or Close ws frames. The h2/quic
> > transport layer handles this. If you want to measure latency then
> > send your own pings/pongs, do not bake it into the protocol.  There
> > is no need for this, and if there is, please present a compelling
> > reason.
>
> He's making a slightly different point... there are some corner cases
> about ws1 RFC6455 protocol that are not grounded in the JS API,
> although almost everything else is.
>
> 1) ws1 PING / PONG for example aren't exposed in the JS API at all.
>
> But they are in wide use by non-browser clients, who at intervals want
> to confirm their connection to the ws server is still live if it's
> idle.
>
> The meaning of ws1 PING is different than the h2 link PING, which is
> defined to not be able to have a specific stream context but only
> connectionwide.  For ws1 it means the websockets server (which may be a
> different process or on a different machine than the h2 endpoint) still
> acknowledges the ws1 connection as alive and communication in both ways
> on the stream is working.  For h2 it means the h2 server is still
> connected at the stream bundle level.  They're not actually giving you
> the same assurance.
>
> 2) Jacob points out there is implicit serialization in ws1, a fragment
> is atomic, blocking PING, PONG and CLOSE until it is all sent.  Again
> it's not explicit in the JS API.  But again he's suggesting that
> behaviour should be maintained in a ws2.
>
> These are at least reasonable-to-argue points.
>
> > The clientside API should not change, but it should definitely be
> > extended OR more functionality should be added to browsers, like the
> > ability to compress data from inside JS land.
>
> I dunno.  I implemented permessage-deflate nicely, with good control
> over its memory and streaming fixed-size buffers in and out, it can
> pass Autobahn, but personally I have never had (or even seen) a good
> use for it.  I know some people love it... better to discuss with them
> rather than me...
>
> -Andy
>
> >
> >
> > On Fri, Dec 2, 2016 at 4:41 PM, Jacob Champion <champion.p@gmail.com>
> > wrote:
> > > On 12/02/2016 12:58 PM, Andy Green wrote:
> > > > On December 3, 2016 4:18:06 AM GMT+08:00, Jacob Champion <champio
> > > > n.p@gmail.com> wrote:
> > > > > My point is just that this ability to multiplex control frames
> > > > > inside
> > > > > of
> > > > > in-flight messages is not something that is explicitly exposed
> > > > > by the
> > > > > JS
> > > > > API, but it may be something that a (non-browser) client
> > > > > requires for
> > > > > proper operation. I think WS/2 should still support it,
> > > > > regardless of
> > > > > whether or not a JS client can make use of it.
> > > > >
> > > >
> > > > OK.  Although the only relevant control frames are PING / PONG.
> > > >
> > >
> > > CLOSE too, plus any control frames added to the protocol between
> > > now and the release of WS/2.
> > >
> > > > And if a client wants to send control frames inside a huge
> > > > message, that client must have explicitly fragmented the message
> > > > already.
> > > >
> > > > The general idea is just map ws2 payload frames direct to h2
> > > > framing... refragmenting them to fit.  In that way, 'supporting'
> > > > ws1 63-bit frame lengths compatibly doesn't require 63-bit frame
> > > > lengths in ws2 because ws always allows refragmentation of
> > > > frames.
> > > >
> > >
> > > Agreed.
> > >
> > > > So it only creates more fragmentation / opportunities to insert
> > > > control frames, so no problem.
> > > >
> > > > > Let me step back: when you say that your goal is to "provide a
> > > > > transport
> > > > > for JS WS API on h2", my fear is that this could lead to a
> > > > > situation
> > > > > where semantics that are part of WS/1 are removed from WS/2 for
> > > > > no
> > > > > reason other than "Javascript clients don't need it, so no one
> > > > > else
> > > > > does
> > > > > either." I would like to avoid that.
> > > > >
> > > >
> > > > What I meant by that is ws1 wire protocol can go out the window
> > > > completely.  The job is not wrap ws1 verbatim in h2 frames, keep
> > > > ws1 negotiation headers, masking, etc.  It can be radically
> > > > recast to align with h2 while following the JS API, and fully
> > > > exploit new possibilities like roundtrip elimination.
> > > >
> > > > I agree it should make some effort to not break non JS / browser
> > > > uses.  But it's no coincidence there are only a tiny number of
> > > > corner cases about that -- ws1 was itself designed to implement a
> > > > transport for the ws JS API.
> > > >
> > >
> > > It sounds like we're on the same page, as long as the eventual
> > > solution's authors understand those corner cases, and that the
> > > functionality provided by WebSocket is (to a minor extent) a
> > > superset of what's provided by the JS API. In particular, I agree
> > > that we don't necessarily need to be bound by the current wire
> > > format, or the same HTTP-buster security features, as WS/1.
> > >
> > > --Jacob
> > >
> > >
> >
> >
>
Received on Monday, 5 December 2016 03:24:22 UTC

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