/ 
ModPerl2-Tools-0.01
River stage zero No dependents
/ ModPerl2::Tools

NAME

ModPerl2::Tools - a few hopefully useful tools

SYNOPSIS

use ModPerl2::Tools;

ModPerl2::Tools::spawn +{keep_fd=>[3,4,7], survive=>1}, sub {...};
ModPerl2::Tools::spawn +{keep_fd=>[3,4,7], survive=>1}, qw/bash -c .../;

ModPerl2::Tools::safe_die $status;
$r->safe_die($status);
$f->safe_die($status);

$content=ModPerl2::Tools::fetch_url $url;
$content=$r->fetch_url($url);

DESCRIPTION

This module is a collection of functions and methods that I found useful when working with mod_perl. I work mostly under Linux. So, I don't expect all of these functions to work on other operating systems.

Forking off long running processes

Sometimes one needs to spawn off a long running process as the result of a request. Under modperl this is not as simple as calling fork because that way all open file descriptors would be inherited by the child and, more subtle, the long running process would be killed when the administrator shuts down the web server. The former is usually considered a security issue, the latter a design decision.

There is already $r->spawn_proc_prog that serves a similar purpose as the spawn function. However, spawn_proc_prog is not usable for long running processes because it kills the children after a certain timeout.

Solution

$pid=ModPerl2::Tools::spawn \%options, $subroutine, @parameters;

or

$pid=ModPerl2::Tools::spawn \%options, @command_line;

spawn expects as the first parameter an options hash reference. The second parameter may be a code reference or a string.

In case of a code ref no other program is executed but the subroutine is called instead. The remaining parameters are passed to this function.

Note, the perl environment under modperl differs in certain ways from a normal perl environment. For example %ENV is not bound to the C-level environ. These modifications are not undone by this module. So, it's generally better to execute another perl interpreter instead of using the $subroutine feature.

The options parameter accepts these options:

keep_fd => \@fds

here an array of file descriptor numbers (not file handles) is expected. All other file descriptors except for the listed and file descriptor 2 (STDERR) are closed before calling $subroutine or executing @command_line.

survive => $boolean

if passed false the created process will be killed when Apache shuts down. if true it will survive an Apache restart.

The return code on success is the PID of the process. On failure undef or an empty string is returned.

The created process is not related as a child process to the current apache child.

Serving ErrorDocuments

Triggering ErrorDocuments from a registry script or even more from an output filter is not simple. The normal way as a handler is

return Apache2::Const::STATUS;

This does not work for registry scripts. An output filter even if it returns a status can trigger only a SERVER_ERROR.

The main interface to enter standard error processing in Apache is ap_die() at C-level. Its Perl interface is hidden in Apache2::HookRun.

There is one case when an error message cannot be sent to the user. This happens if the HTTP headers are already on the wire. Then it is too late.

The various flavors of safe_die() take this into account.

ModPerl2::Tools::safe_die $status

This function is designed to be called from registry scripts. It uses Apache2::RequestUtil->request to fetch the current request object. So,

PerlOption +GlobalRequest

must be enabled.

Usage example:

ModPerl2::Tools::safe_die 401;
exit 0;
$r->safe_die($status)
$f->safe_die($status)

These 2 methods are to be used if a request object or a filter object are available.

Usage from within a filter:

package My::Filter;
use strict;
use warnings;

use ModPerl2::Tools;
use base 'Apache2::Filter';

sub handler : FilterRequestHandler {
  my ($f, $bb)=@_;
  return $f->safe_die(410);
}

The filter flavor removes the current filter from the request's output filter chain.

Fetching the content of another document

Sometimes a handler or a filter needs the content of another document in the web server's realm. Apache provides subrequests for this purpose.

The 2 fetch_url variants use a subrequest to fetch the content of another document. The document can even be fetched via mod_proxy from another server. However, fetching a document directly as with LWP for example is not (yet) possible.

ModPerl2::Tools::fetch_url needs

PerlOption +GlobalRequest

Usage:

$content=ModPerl2::Tools::fetch_url '/some/where?else=42';

$content=$r->fetch_url('/some/where?else=42');

EXPORTS

None.

SEE ALSO

http://perl.apache.org

AUTHOR

Torsten Förtsch, <torsten.foertsch@gmx.net<gt>

COPYRIGHT AND LICENSE

Copyright (C) 2010 by Torsten Förtsch

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.