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From "Bill Stoddard" <stodd...@raleigh.ibm.com>
Subject HTTP compliance and pipelined requests
Date Wed, 28 Jun 2000 19:18:19 GMT
I am looking for the correct interpretation of Section 8.1.2.2 in RFC 2068. It states:

"A client that supports persistent connections MAY "pipeline" its requests.  A server MUST
send its responses to those requests in the same order that the requests were received."

My questions...
1. Is there a way for the server to determine if an HTTP/1.1 compliant browser is capable
of pipelining requests?
    My understanding is that there is no way for the server to know if an HTTP/1.1 browser
can pipeline requests unless it actually starts sending pipelined requests.

2. Is it possible, upon receiving the first request from a client, to determine whether
that client intends to or is capable of pipelining requests?
    This is really the same question as above, just wanted to ask it in a different way.

3. Can a client pipeline some request and non pipeline other requests (all on the same
connection) and still be HTTP/1.1 compliant?

There are a couple of cases where the answer to this question is important.....

case 1. - Bill, Ryan, Rasmus, et. al. in the past tossed around the idea of an request
dispatcher. The distapcther receives a request and dispatches it to a back-end process
running under a a security context (user id) suitable for that request. If two or more
pipelined requests are dispatched to different back-end processes, then  it is possible
for the responses to those requests to be sent out of order, unless the responses go back
through the dispatcher process.

case 2 - If you are using an in-kernel static file cache (IBM's AFPA, khttpd, etc.) and
pipelined requests are received, some of which are served out of the kernel cache and some
of which are served out of user space.  Unless special precautions are taken, responses to
pipelined requests could get out of order.

If it were possible to determine, when the connection is first established between the
browser and the server (or when the first request is received) that a browser is
guaranteed to NEVER pipeline requests, then this would make handling these 'special
precautions' trivial easy.  I don't think the server has a way of determining this though.

Thoughts?

________________________________________________
Bill Stoddard stoddard@raleigh.ibm.com


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