Webmaster in a Nutshell, Third Edition

mod_perl Handlers

To understand mod_perl, you should understand how the Apache server works. When Apache receives a request, it processes it in several stages. First, it translates the URL to the associated resource (i.e., filename, CGI script, etc.) on the server machine. Then it checks to see if the user is authorized to access that resource, perhaps by requesting and checking an ID and password. Once the user has passed inspection, the server figures out what kind of data it’s sending back (e.g., it decides a file ending in .html is probably a text/html file), creates some headers, and sends those headers back to the client with the resource itself. When all is said and done, the server makes a log entry.

At each stage of this process, Apache looks for routines to “handle” the request. Apache supplies its own handlers; for example, one of the default handlers is cgi-script, often seen applied to /cgi-bin:

<Location /cgi-bin>
  ...
SetHandler cgi-script
  ...
</Location>

mod_perl allows you to write your own handlers in Perl, by embedding the Perl runtime library directly into the Apache httpd server executable. To use mod_perl for CGI (which is all that most people want to do with it), assign the SetHandler directive to perl-script, and then assign the mod_perl-specific PerlHandler directive to a special Perl module called Apache::Registry:

SetHandler perl-script
PerlHandler Apache::Registry

PerlHandler is the mod_perl handler for the content retrieval stage of the transaction. ...