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From Brian Candler <B.Cand...@pobox.com>
Subject Re: [PATCH] Re: Pluggable mod_log_config
Date Fri, 07 Oct 2005 15:33:03 GMT
On Thu, Oct 06, 2005 at 03:49:10PM -0400, Brian Akins wrote:
> Colm MacCarthaigh wrote:
> 
> >If httpd writes a complete line, to any kind of a file descriptor,
> >anything beyond that is out of our control and becomes a question of the
> >quality of the piped logger, filesystem or whatever else is on the other
> >side of that file-descriptor.
> 
> Maybe I'm just being difficult, but I'm still not sold on it :)  While I 
>  understand all that you wrote, the possibilities of getting "partial 
> line" with normal piped logs irks me.  Maybe it's just a personal thing...
> 
> I prefer to have something like:
> 
> length of message, message, sync bit
> 
> (message could be many log lines)

Or you could just do read() on a pipe. If the last character you receive is
'\n' then you have a high degree of confidence that you have received an
entire line or a number of whole lines.

I don't think it's possible for logs generated by Apache to contain newlines
mid-way (if there are any such cases, they probably should be fixed)

If you're talking about log output from a CGI, then there's nothing to
guarantee that a CGI will write anything sensible which ends with newline,
or that it will write whole lines atomically rather than writing a few
characters at a time (which therefore could get mixed up with stderr output
from other CGI processes); but equally you cannot enforce that a CGI uses
your tagged protocol either.

CGI error logs are a bit of a pain. Since Apache is the parent process, and
the CGI is the child, Apache would be a good place to:
(a) receive bytes from stderr and reformat them into whole log lines,
prefixed by timestamp, server_name etc to allow post-processing; and
(b) log the CPU time used by a CGI after it has completed

Since Apache does neither of these, I have been doing this in a hacked
version of suexec to avoid having to hack mod_cgi itself. This costs an
extra fork() in suexec though.

Regards,

Brian.

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