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Re: ISSUE: MUST a client wait for 100 when doing PUT or POST requests?

From: Henrik Frystyk Nielsen <frystyk@w3.org>
Date: Tue, 10 Jun 1997 14:10:12 -0400
Message-Id: <3.0.1.32.19970610141012.00b00d80@pop.w3.org>
To: John Franks <john@math.nwu.edu>
Cc: "David W. Morris" <dwm@xpasc.com>, http-wg@cuckoo.hpl.hp.com, lawrence@agranat.com, rlgray@raleigh.ibm.com
At 12:50 PM 6/10/97 -0500, John Franks wrote:

>> Yes, but unfortunately, HTTP/1.0 is broken and this is the only way to get
>> PUT to work reliably. If you have ever tried to PUT across the Atlantic
>> then you would know what I am talking about.
>> 
>
>Could you explain why trans-Atlantic POSTs would be more reliable with
>100 Continue?  I honestly don't understand.

A typical HTTP request header is small enough to not force a TCP reset
which may cause the HTTP response to get lost. As I said in my first mail,
the problem is illustrated in the connection draft, section 8:

   The scenario is as follows: an HTTP/1.1 client talking to a HTTP/1.1
   server starts pipelining a batch of requests, for example 15 on an
   open TCP connection.  The server decides that it will not serve more
   than 5 requests per connection and closes the TCP connection in both
   directions after it successfully has served the first five requests.
   The remaining 10 requests that are already sent from the client will
   along with client generated TCP ACK packets arrive on a closed port
   on the server. This "extra" data causes the server's TCP to issue a
   reset which makes the client TCP stack pass the last ACK'ed packet to
   the client application and discard all other packets. This means that
   HTTP responses that are either being received or already have been
   received successfully but haven't been ACK'ed will be dropped by the
   client TCP. In this situation the client does not have any means of
   finding out which HTTP messages were successful or even why the
   server closed the connection. The server may have generated a

In general, the problem can occur if the client sends a lot of data and the
server closes the connection before having read the whole bit.

>Here is my point.  Superficially HTTP/1.0 POSTS seems to work well.
>The proposed change seems likely to cause a dramatic degredation of
>service.  I suspect that it will always be fairly rare for a server to
>reject a POST.  Do we really have evidence that requiring 100 Continue
>for every POST is a good thing?

I don't believe I said that - the proposed resolution was:

   a client SHOULD wait for a 100 (Continue) code before sending the
   body but can send the whole thing if it believes that the server
   will react properly.

This covers exactly the situation of small POST requests, you are referring
to. I believe that being conservative in the specification guaranteeing
correct behavior but allowing optimized applications is better than the
other way round.

Thanks,

Henrik
--
Henrik Frystyk Nielsen, <frystyk@w3.org>
World Wide Web Consortium
http://www.w3.org/People/Frystyk
Received on Tuesday, 10 June 1997 11:13:24 EDT

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