Re: p2: Expect: 100-continue and "final" status codes

Willy Tarreau <w@1wt.eu> Wed, 24 April 2013 17:48 UTC

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Date: Wed, 24 Apr 2013 19:47:16 +0200
From: Willy Tarreau <w@1wt.eu>
To: Ken Murchison <murch@andrew.cmu.edu>
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Subject: Re: p2: Expect: 100-continue and "final" status codes
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On Wed, Apr 24, 2013 at 01:34:51PM -0400, Ken Murchison wrote:
> 
> On Wed, 24 Apr 2013 13:06:38 -0400, Willy Tarreau wrote:
> > On Wed, Apr 24, 2013 at 01:00:42PM -0400, Ken Murchison wrote:
> > > >2. If the client receives a final status code instead of 100 
> > > >(Continue), it
> > > >should stop sending request body if it is doing so; it must close the
> > > >connection after the response is received.
> > > 
> > > I don't understand point #2.  If the client submits a request with 
> > > Expect:100-continue, I would assume that the client MUST NOT send any 
> > > part of the body until it receives 100 (Continue) from the server.  If 
> > > the server rejects the request based on the headers (with 412, 415, 417, 
> > > etc) there should be no body data in the pipe for either the client or 
> > > server to worry about, correct?
> > 
> > In fact the client can decide that it's been waiting too long for 100
> > and decides to send anyway (because some old servers or intermediaries
> > do not know about Expect and will wait).
> > 
> > So what is generally done is that the client sends the headers, waits a
> > bit then starts to send data if the server does not respond.
> 
> Fair enough. But I would expect that a compliant 1.1 server would respond
> with 100 (Continue) or failure pretty quickly -- well within the client's
> "wait" interval.     Given that RFC 2616 is over a decade old, I would like
> to think that any 1.1 implementation would be compliant with the Expect
> behavior or should be deprecated. 
> 
> Unless we are worried about Expect:100-continue being sent to a 1.0 server,
> allowing a client to start sending a body in the absence of 100 (Continue)
> seems like a bad idea to me.  But if this behavior IS needed a client should
> at least wait several seconds or something longer than the expected roundtrip
> time.
> 
> Am I way off base here?  I'm not privy to all of the history of HTTP.  I only
> started developing our CalDAV server a couple of years ago.

No you're perfectly right, but you forgot about the messy case where the 1.1
client sends via a 1.0 gateway to an 1.1 server and the 1.0 gateway needs to
validate the contents before passing the request :-)

Willy