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From "William A. Rowe, Jr." <ad...@rowe-clan.net>
Subject Re: cvs commit: httpd-2.0 STATUS
Date Mon, 02 Jul 2001 19:09:10 GMT
From: "Bill Stoddard" <bill@wstoddard.com>
Sent: Monday, July 02, 2001 2:02 PM


> > On Mon, 2 Jul 2001, Bill Stoddard wrote:
> >
> > > > >cgi on all platforms is broken.  Specifically, with the addition of
> > > > >filters, we have lost the ability to flush partially written buffers
> > > > >received from CGI scripts to the network.
> > > > [...]
> > > > >Apache 2.0 always does a blocking read (in the content length filter)
> > > >
> > > > Partial writes to the network from a CGI and content length are
> > > > mutually exclusive.
> > >
> > > No S**t!! :-) That's why it's broken!
> >
> > Bill, there is no fix for this.  If the content_length filter determines
> > that a C-L is required, then we can't stream CGI's.  It looks like the
> > problem is simply that we are using the wrong options to apr_bucket_read.
> > Switch that to a APR_NONBLOCK_READ, and the problem should go away.
> >
> > Ryan
> 
> I don't think changing the read in the content_length filter to nonblocking is the right
> solution to this problem because we still need to force the network flush. I will
> investigate your suggestion though because I might be overlooking something.

This is DSS [dirt simple stupid].  mod_cgi needs to read the *first* part of the request
into a buffer, following the 1.3 convention, and append a flush bucket when it gets to the
various 1.3 contentions that the buffer should flush.  The C-L filter can STILL interpose
and block the flush, but if it's simply a chunked http/1.1 connection, this isn't a problem.

> IMO the decision to flush or not and how to read from the pipe should be entirely
> controlled by mod_cgi.  We need a function similar to the old ap_send_fb() code.

No... what you could create, for simplicity, is a cgi_pipe bucket type that has the same
integellegence as 1.3 and ap_send_fb().  It would have to permit morphing into another 
bucket type, and might need to learn how to signal a flush itself.

> I also want to play with making the interface between Apache and CGI scripts full duplex
> as well (to allow a CGI script to read a large POST request and begin responding to that
> POST immediately) which will require controlling the byte stream at the top of the filter
> stack as well.

This is big brokenness on 1.3 under Win32 right now.  I'd be strongly ++1 to getting the
full duplex logic correct, but only under the caviat that we do so 'with the system' and
we don't simply write dirty hacks around it.

Since filters must prove themselves to 1.3 module authors, here's our chance to prove we
'got it right', even if that means demonstrating how to extend a new, more intellegent
bucket type.

Bill


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