DO NOT REPLY [Bug 22030] New: - 4097+ bytes of stderr from cgi script causes script to hang

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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=22030

4097+ bytes of stderr from cgi script causes script to hang

           Summary: 4097+ bytes of stderr from cgi script causes script to
                    hang
           Product: Apache httpd-2.0
           Version: 2.0.47
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: Normal
          Priority: Other
         Component: mod_cgi
        AssignedTo: bugs@httpd.apache.org
        ReportedBy: brandon@tryplec.com


If a cgi script under mod_cgi outputs more than 4096 bytes of stderr before it 
finishes writing to and closing its stdout, the write() inthe cgi script 
containing the 4097th byte of stderr will hang indefinitely, hanging the 
script's execution.

This appears to be cause by the fact that mod_cgi reads all stdout output 
first, and then begins reading stderr output.  APR's file_io which is handling 
the streams will only buffer 4096 characters before further writes by the 
script to stderr will hang, waiting for mod_cgi to read some of the data from 
the stream via APR file_io.

This occured for me where a perl cgi script was producing a large volume of 
harmless warning messages to ssl_error_log before it got to the part of it's 
execution where it actually wrote the stdout output, and causing the script to 
hang and produce no output to the end user.  Below is a test script to 
demonstrate:

#!/usr/bin/perl
# 24x170 = 4080 bytes to stderr
foreach my $x (1..24) {
  print STDERR 'X' x 169 . "\n";
}
# + 17 more bytes, putting us at 4097
# Delete one char from the print below to make
# it work again
print STDERR "0123456789ABCDEF\n";
# Our actual script output, which never comes
print "Content-type: text/plain\n\nASDF\n";

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