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Re: Server-side roles in the HTTP

From: Julien Pierre <jpierre@netscape.com>
Date: Thu, 02 Sep 1999 14:17:07 -0700
Message-ID: <37CEE953.3076CE93@netscape.com>
To: kugler@us.ibm.com
CC: http-wg@cuckoo.hpl.hp.com, http-wg@hplb.hpl.hp.com
Hi,

kugler@us.ibm.com wrote:

> If the full content is immediately available, it would be sent as one chunk.

Not necessarily.
It depends how the CGI is writing to stdout, on the OS, pipe buffer size, and on the
load on the machine.
If a dumb CGI writes one byte at a time to stdout, even in a tight loop, it's
possible that the kernel will make the daemon thread wake up and return it that
single byte, which would then be sent as a chunk if no buffer thresholds are set.
Every other 1-byte write may also result in another chunk. Some thresholds are
necessary to avoid those cases.

> >This won't work for some content generators.
> >For example, you can't start a CGI before you know the length of the POST data
> >because you have to set it in the CGI process environment variables.
>
> The one pathological case is CGI/1.1 and chunked POST requests.  Supposedly,
> future versions of CGI will deal with chunking.  And if the request provides
> Content-Length, you don't have to buffer it, even for CGI/1.1.

True - and we don't buffer the POST data in our daemon.

This reminds me of a case I was debugging a few weeks ago :
an echo CGI script writes the POST data to stdout as it comes, in a simple loop. The
problem is that most HTTP/1.0 clients send the full request first, then wait for the
server reply.

But if the POST data is large, at some point, the server's socket buffer gets full
when trying to send the reply, since the client isn't reading the reply yet (it's
still not done POSTing the request). At that point, both the clients and the server
are trying to send() and one of them times out (typically the server).

I haven't seen anything in the CGI spec that requires a script to first read all its
input before its starts writing to stdout. The script should be the proper place to
do the buffering for this case.

--
for a good time, try kill -9 -1




Received on Thursday, 2 September 1999 22:17:38 EDT

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