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From Mike Varty <m...@bartec.demon.co.uk>
Subject general/7673: Apache reports 'cat: write error: Broken pipe' in error_log file
Date Fri, 04 May 2001 10:58:20 GMT

>Number:         7673
>Category:       general
>Synopsis:       Apache reports 'cat: write error: Broken pipe' in error_log file
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    apache
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Fri May 04 04:00:03 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     mike@bartec.demon.co.uk
>Release:        1.3.12
>Organization:
apache
>Environment:
Apache 3.1.12
Apache Compiled on Solaris 2.5 (uname: SunOS 5.5.1 sun4m SPARCstation-4)
Apache Binaries copied to Solaris 8 machine (uname: SunOS 5.8 sun4u Ultra-5_10)
Apache Running on Solaris 8 (binary compatibility)
Internet Explorer 5 on Windows 98
>Description:
1.  The offending page is a cgi script written in csh, which first sources a file to set environment
variables, then calls an executable.  The 'C' exe uses printfs and system calls to 'cat' to
generate html code to stdout, which apache sends out:

        #!/usr/bin/csh
        source $DOCUMENT_ROOT/setWebEnvironment
        $ISIS_BIN/searchDB

2.  The browser actually displays a blank page and Apache raises a 'cat: write error: Broken
pipe' error in the error_log file.

3.  I redirected the output from the exe to a file (temp_output) and viewed the file:

        $ISIS_BIN/serachDB > temp_output

It contained the complete HTML as it should.  The browser then told me it couldn't find the
page, as expected because the html hadn't gone to apache.

4.  I appended a line to the .cgi script: 'cat temp_output', so that the output might be sent
through apache once again:

        cat temp_output

This time, the browser displayed an incomplete version of the page, and Apache raised the
same Broken pipe error.

5.  I viewed the resulting partial web page source from the browser, and it did indeed contain
only part of the expected HTML, although the temp_output file  contained the entire HTML.

6.  I typed in the URL of the temp_output file and it was displayed perfectly in the browser.

7.  I reverted to a version of Apache, 1.3.2, compiled again on Solaris 2.5 and ported to
my Solaris 8 machine, and it serves the offending page perfectly, with no error message.

8.  I continued investigating Apache 1.3.12 by removing the source command from the cgi and
commenting out the exe which generates temp_output, in case it was filling up the environment
variable table (max variables etc).

        #!/usr/bin/csh
        #source $DOCUMENT_ROOT/setWebEnvironment
        #$ISIS_BIN/searchDB > temp_output
        cat temp_output

This worked perfectly.

8.  I then put the source statement back in and it failed to serve the whole page again, with
the broken pipe error.  So, something to do with the setting of the environment variables

9.  I removed a fair few superfluous variables from the setWebEnvironment script gradually
to see if the page started working.  It did after removing quite a few.  The page was perfect
in the browser.

10. Having got temp_output being served correctly, I put back the running of the exe, and
the page was served correctly.  So definitely something to do with the number or nature of
the environment variables.

11. Finally, with the page working, I removed the redirection of the output so that the exe
sends the pages straight to apache.  This resulted in the blank web page again.

10. So, I have a page that will work with redirection and less environment variables, but
this doesn't really solve my problem really because the web page consists of a form with text
boxes and option menus, then a table which is extracted from a database.  The table will be
as long as there are entries in the database, so I'm left wondering what happens when the
table grows.  I can test for this on my development system, but I cannot test on all versions
of Solaris or SunOS (the SunOS release works OK at the moment).

I'm working on a release, so for us, getting this sorted is important.  Any suggestions will
be very welcome.

If I have not supplied enough info, please ask for some more.
>How-To-Repeat:
I'm don't think you can easily, but you could try declaring a lot of environment variables
then trying to cat an HTML page which contains a form and a long table.
>Fix:

>Release-Note:
>Audit-Trail:
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