man Apache2::PerlSections (3): write Apache configuration files in Perl

Synopsis

  <Perl>
  @PerlModule = qw(Mail::Send Devel::Peek);
  
  #run the server as whoever starts it
  $User  = getpwuid(>) || >;
  $Group = getgrgid()) || );
  
  $ServerAdmin = $User;
  
  </Perl>

Description

With "<Perl>"..."</Perl>" sections, it is possible to configure your server entirely in Perl.

"<Perl>" sections can contain any and as much Perl code as you wish. These sections are compiled into a special package whose symbol table mod_perl can then walk and grind the names and values of Perl variables/structures through the Apache core configuration gears.

Block sections such as "<Location>".."</Location>" are represented in a %Location hash, e.g.:

  <Perl>
  $Location{"/~dougm/"} = {
    AuthUserFile   => '/tmp/htpasswd',
    AuthType       => 'Basic',
    AuthName       => 'test',
    DirectoryIndex => [qw(index.html index.htm)],
    Limit          => {
        "GET POST"    => {
            require => 'user dougm',
        }
    },
  };
  </Perl>

If an Apache directive can take two or three arguments you may push strings (the lowest number of arguments will be shifted off the @list) or use an array reference to handle any number greater than the minimum for that directive:

  push @Redirect, "/foo", "http://www.foo.com/";
  
  push @Redirect, "/imdb", "http://www.imdb.com/";
  
  push @Redirect, [qw(temp "/here" "http://www.there.com")];

Other section counterparts include %VirtualHost, %Directory and %Files.

To pass all environment variables to the children with a single configuration directive, rather than listing each one via "PassEnv" or "PerlPassEnv", a "<Perl>" section could read in a file and:

  push @PerlPassEnv, [$key => $val];

  Apache2->httpd_conf("PerlPassEnv $key $val");

These are somewhat simple examples, but they should give you the basic idea. You can mix in any Perl code you desire. See eg/httpd.conf.pl and eg/perl_sections.txt in the mod_perl distribution for more examples.

Assume that you have a cluster of machines with similar configurations and only small distinctions between them: ideally you would want to maintain a single configuration file, but because the configurations aren't exactly the same (e.g. the "ServerName" directive) it's not quite that simple.

"<Perl>" sections come to rescue. Now you have a single configuration file and the full power of Perl to tweak the local configuration. For example to solve the problem of the "ServerName" directive you might have this "<Perl>" section:

  <Perl>
  $ServerName = `hostname`;
  </Perl>

For example if you want to allow personal directories on all machines except the ones whose names start with secure:

  <Perl>
  $ServerName = `hostname`;
  if ($ServerName !~ /^secure/) {
      $UserDir = "public.html";
  }
  else {
      $UserDir = "DISABLED";
  }
  </Perl>

API

"Apache2::PerlSections" provides the following functions and/or methods:

server

Get the current server's object for the <Perl> section

  <Perl>
    $s = Apache2::PerlSections->server();
  </Perl>

obj: "Apache2::PerlSections" (class name)
ret: $s ( "Apache2::ServerRec object" )
since: 2.0.03

@PerlConfig and $PerlConfig

This array and scalar can be used to introduce literal configuration into the apache configuration. For example:

  push @PerlConfig, 'Alias /foo /bar';

Or:
$PerlConfig .= ``Alias /foo /bar\n'';

Configuration Variables

There are a few variables that can be set to change the default behaviour of "<Perl>" sections.

$Apache2::PerlSections::Save

Each "<Perl>" section is evaluated in its unique namespace, by default residing in a sub-namespace of "Apache2::ReadConfig::", therefore any local variables will end up in that namespace. For example if a "<Perl>" section happened to be in file /tmp/httpd.conf starting on line 20, the namespace: "Apache2::ReadConfig::tmp::httpd_conf::line_20" will be used. Now if it had:

  <Perl>
    $foo     = 5;
    my $bar  = 6;
    $My::tar = 7;
  </Perl>

The local global variable $foo becomes $Apache2::ReadConfig::tmp::httpd_conf::line_20::foo, the other variable remain where they are.

By default, the namespace in which "<Perl>" sections are evaluated is cleared after each block closes. In our example nuking $Apache2::ReadConfig::tmp::httpd_conf::line_20::foo, leaving the rest untouched.

By setting $Apache2::PerlSections::Save to a true value, the content of those namespaces will be preserved and will be available for inspection by "Apache2::Status" and "Apache2::PerlSections->dump" In our example $Apache2::ReadConfig::tmp::httpd_conf::line_20::foo will still be accessible from other perl code, after the "<Perl>" section was parsed.

PerlSections Dumping

Apache2::PerlSections->dump

This method will dump out all the configuration variables mod_perl will be feeding to the apache config gears. The output is suitable to read back in via "eval".

  my $dump = Apache2::PerlSections->dump;

ret: $dump ( string / "undef" ): A string dump of all the Perl code encountered in <Perl> blocks, suitable to be read back via "eval"

For example:

  <Perl>
  
  $Apache2::PerlSections::Save = 1;
  
  $Listen = 8529;
  
  $Location{"/perl"} = {
     SetHandler => "perl-script",
     PerlHandler => "ModPerl::Registry",
     Options => "ExecCGI",
  };
  
  @DirectoryIndex = qw(index.htm index.html);
  
  $VirtualHost{"www.foo.com"} = {
     DocumentRoot => "/tmp/docs",
     ErrorLog => "/dev/null",
     Location => {
       "/" => {
         Allowoverride => 'All',
         Order => 'deny,allow',
         Deny  => 'from all',
         Allow => 'from foo.com',
       },
     },
  };
  </Perl>
  
  <Perl>
  print Apache2::PerlSections->dump;
  </Perl>

This will print something like this:

  $Listen = 8529;
  
  @DirectoryIndex = (
    'index.htm',
    'index.html'
  );
  
  $Location{'/perl'} = (
      PerlHandler => 'Apache2::Registry',
      SetHandler => 'perl-script',
      Options => 'ExecCGI'
  );
  
  $VirtualHost{'www.foo.com'} = (
      Location => {
        '/' => {
          Deny => 'from all',
          Order => 'deny,allow',
          Allow => 'from foo.com',
          Allowoverride => 'All'
        }
      },
      DocumentRoot => '/tmp/docs',
      ErrorLog => '/dev/null'
  );
  
  1;
  __END__

It is important to put the call to "dump" in it's own "<Perl>" section, otherwise the content of the current "<Perl>" section will not be dumped.

Apache2::PerlSections->store

This method will call the "dump" method, writing the output to a file, suitable to be pulled in via "require" or "do".

  Apache2::PerlSections->store($filename);

arg1: $filename (string): The filename to save the dump output to
ret: no return value

Advanced API

mod_perl 2.0 now introduces the same general concept of handlers to "<Perl>" sections. Apache2::PerlSections simply being the default handler for them.

To specify a different handler for a given perl section, an extra handler argument must be given to the section:

  <Perl handler="My::PerlSection::Handler" somearg="test1">
    $foo = 1;
    $bar = 2;
  </Perl>

And in My/PerlSection/Handler.pm:

  sub My::Handler::handler : handler {
      my ($self, $parms, $args) = @_;
      #do your thing!
  }

So, when that given "<Perl>" block in encountered, the code within will first be evaluated, then the handler routine will be invoked with 3 arguments:

arg1: $self

self-explanatory

arg2: $parms ( "Apache2::CmdParms" )

$parms is specific for the current Container, for example, you might want to call "$parms->server()" to get the current server.

arg3: $args ( "APR::Table object")

the table object of the section arguments. The 2 guaranteed ones will be:

  $args->{'handler'} = 'My::PerlSection::Handler';
  $args->{'package'} = 'Apache2::ReadConfig';

Other "name="value"" pairs given on the "<Perl>" line will also be included.

At this point, it's up to the handler routing to inspect the namespace of the $args->{'package'} and chooses what to do.

The most likely thing to do is to feed configuration data back into apache. To do that, use Apache2::Server->add_config(``directive''), for example:

  $parms->server->add_config("Alias /foo /bar");

Would create a new alias. The source code of "Apache2::PerlSections" is a good place to look for a practical example.

Verifying <Perl> Sections

If the "<Perl>" sections include no code requiring a running mod_perl, it is possible to check those from the command line. But the following trick should be used:

  # file: httpd.conf
  <Perl>
  #!perl
  
  # ... code here ...
  
  __END__
  </Perl>

Now you can run:

  % perl -c httpd.conf

Bugs

<Perl> directive missing closing '>'

httpd-2.0.47 had a bug in the configuration parser which caused the startup failure with the following error:

  Starting httpd:
  Syntax error on line ... of /etc/httpd/conf/httpd.conf:
  <Perl> directive missing closing '>'     [FAILED]

This has been fixed in httpd-2.0.48. If you can't upgrade to this or a higher version, please add a space before the closing '>' of the opening tag as a workaround. So if you had:

  <Perl>
  # some code
  </Perl>

change it to be:

  <Perl >
  # some code
  </Perl>

<Perl>[...]> was not closed.

On encountering a one-line <Perl> block, httpd's configuration parser will cause a startup failure with an error similar to this one:

  Starting httpd:
  Syntax error on line ... of /etc/httpd/conf/httpd.conf:
  <Perl>use> was not closed.

If you have written a simple one-line <Perl> section like this one :

  <Perl>use Apache::DBI;</Perl>