# Apache mod\_rewrite External Rewriting Program

**URL:** <https://www.ruby-forum.com/t/apache-mod-rewrite-external-rewriting-program/118898>\
**Category:** Ruby\
**Created:** [November 1, 2007, 5:49am UTC](https://www.ruby-forum.com/t/apache-mod-rewrite-external-rewriting-program/118898 "2007-11-01T05:49:48Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![patrickjoyce](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e9c0ed/32.png) [@patrickjoyce](https://www.ruby-forum.com/u/patrickjoyce)\
**Post date:** [November 1, 2007, 5:49am UTC](https://www.ruby-forum.com/t/apache-mod-rewrite-external-rewriting-program/118898/1 "2007-11-01T05:49:48Z")

</div>

I needed to do a bit of complicated URL rewriting for a project I’m  
working on. Apache’s mod\_rewrite’s built in capabilities wouldn’t do, so  
I decided to make an External Rewriting Program  
([mod\_rewrite - Apache HTTP Server Version 2.2](http://httpd.apache.org/docs/2.2/mod/mod_rewrite.html#rewritemap)) to do  
it.

All the examples I could find were in Perl, but I wanted to take a stab  
at it in Ruby. What I have works most of the time, but occasionally  
fails with what appears to be a concurrency issue.

Here is a simplified version of what I have:

* * *

#!/opt/csw/bin/ruby

# Turn off buffering

STDIN.sync = true  
STDOUT.sync = true

# Enter loop

## while (STDIN) host = gets if host =~ /^(.+).somedomain.com$/ puts $1 else puts ‘NULL’ end end

And here are the pertinent rewrite\_log entries (“key” is what is passed  
to my program via STDIN, “val” is what my program returns to STDOUT):

* * *

## [[somedomain.com](http://mysubdomain.somedomain.com/sid#81b3d48)][rid#837ef38/initial] (5) map lookup OK: map=lookup\_subdomain [key=mysubdomain.somedomain.com](http://key=mysubdomain.somedomain.com) → val=msbomain [[somedomain.com](http://mysubdomain.somedomain.com/sid#81b3d48)][rid#837ef38/initial] (5) map lookup OK: map=lookup\_subdomain [key=mysubdomain.somedomain.com](http://key=mysubdomain.somedomain.com) → val=yudmysubdomain

So… “[mysubdomain.somedomain.com](http://mysubdomain.somedomain.com)” is passed via STDIN to my program  
twice. The first time returns “msbomain” and the second returns  
“yudmysubdomain”

Isn’t this program single threaded? Any ideas as to how my output is  
being interleaved?

I’m running ruby 1.8.5 (2006-12-25 patchlevel 12) [i386-solaris2.8] on a  
Joyent Accelerator.

Thanks is advance for your help.

- Patrick J.

---

<div class="post-metadata">

**Author:** ![patrickjoyce](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e9c0ed/32.png) [@patrickjoyce](https://www.ruby-forum.com/u/patrickjoyce)\
**Post date:** [November 1, 2007, 8:07pm UTC](https://www.ruby-forum.com/t/apache-mod-rewrite-external-rewriting-program/118898/2 "2007-11-01T20:07:21Z")

</div>

OK, so I’m now actually pretty sure this isn’t a problem with my Ruby  
code, but a problem with either Solaris or Apache.

I went ahead and took the Perl example from the Apache docs, modified it  
slightly to match my example, and still got the same problem:  
intermittently interleaved results.

This makes me pretty confident that the problem is outside of Ruby  
(unless of course, and I’m not ruling this out, I somehow made the same  
mistake in both Ruby and Perl).

Since it doesn’t seem to be a Ruby issue I don’t expect any help here,  
but if anyone has ANY idea what could be going on I would be forever in  
your debt.

- Patrick J.

The Perl is below.

* * *

#!/usr/bin/perl

#disable buffered I/O which would lead  
#to deadloops for the Apache serve  
$| = 1;

## #read URLs one per line from stdin and #generate substitution URL on stdout while (\<\>) { /^(.+).somedomain.com$/; print $1, “\n”; }