NAME

POEST::Config - Details of Writing a POEST Configurator

ABSTRACT

Details for writing a plugin configurator.

DESCRIPTION

poest needs to be configured. Yes folks, that means writing (or at least editing) a configuration of some sort. I say "of some sort" because there may be lots of different approaches to configuration. This is the default configuration method. This is also the reference implementation.

Conventions

Package setup

Configuration modules are really classes. Yes, classes. An object instance is created and used to get configuration sets. There are a certain number of methods a configuration must provide, as well as a certain functionality, described below.

The actual setup and type of configuration that a class accepts is completley out in the open. The most common is a configuration file. There are many more avenues that can be explored, some much more useful than a configuration file. Consider storing configuration in a database or LDAP directory. Perhaps in a DBM file or something else all together. It's up to you.

Functionality

Plugins need to have a couple of ways to represent configuration information. First is a single key/value pair. Second is a slightly more complex key/list of values. A plugin configurator must provide both options. As an example configuration file.

# key/value
Port 25

# key/list of values
Plugin POEST::Plugin::Queue::DiskHash
Plugin POEST::Plugin::Deliver::Local

These configuration options should boil down to a data structure such as this.

{
  port   => 25,
  plugin => [
              'POEST::Plugin::Queue::DiskHash',
              'POEST::Plugin::Deliver::Local',
            ],
};

Note that the keys, or configuration parameter names, have been lower-cased in the data structure. This was on purpose, because it should always happen.

Public method API

The public API for configuration classes is pretty well set. After all, it is only used in one place, server initialization.

new()

new() is the constructor. Arguments are passed to new() as a list of key/value pairs. Any arguments recieved by new() were what was passes directly to POEST::Server->new(). Arguments must be validated and checked for accuracy, and existence. If something is wrong, an exception should be thrown. This will end the server initialization and terminate the server so the problem can be fixed.

new() returnes an instance object of your configuration class.

As this is a base class for poest configuration classes, we do provide a simple constructor.

sub new {
  my ($class, %args) = @_;

  return bless \%args, $self;
}

This should be overriden, to at least include configuration checking.

sub new {
  my $self = shift->SUPER::new( @_ );
  
  # .. do validation ..
  
  return $self;
}

config()

This method returns the entire configuration data structure. Useful for serialization, should the need arise. This data structure should be returned as a hash reference as described previously in the section on functionality.

Here is a simple example.

sub config {
  my ($self) = @_;

  return $self;
}

This very method is provided in this base class, and that's the very reason it should be overriden.

get()

This method accepts a list of configuration parameters to get. For all that exist in the configuration, they will be returned as a hash reference. This is analigous to retrieving a slice of the configuration.

Here is the example in this base class.

sub get {
  my ($self, @configs) = @_;
  
  my %conf = ();
  foreach ( @configs ) {
    $conf{$_} = $self->{$_} if exists $self->{$_};
  }
  
  return \%conf;
}

Again, this method should be overriden in the sub-class.

set()

Now you too can set configuration parameters at run time. This goes against everything daemon methedology believes in, but then, it's also useful. There may be some odd and rather insane situations where you want to set a configration parameter (or change an existing one) during runtime. It will not be serialized to the original source of configuration, that's just going too far. Instead it is a modification of the in-memory copy.

Here is an example.

sub set {
  my ($self, %set) = @_;

  my @keys = keys %set;

  @{$self}{@keys} = @set{@keys};
}

This method is provided in the base class and should be overriden.

AUTHOR

Casey West, <casey@dyndns.org>

COPYRIGHT AND LICENSE

Copyright 2003 DynDNS.org

You may distribute this package under the terms of either the GNU General Public License or the Artistic License, as specified in the Perl README file, with the exception that it may not be placed on physical media for distribution without the prior written approval of the author.

THIS PACKAGE IS PROVIDED WITH USEFULNESS IN MIND, BUT WITHOUT GUARANTEE OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. USE IT AT YOUR OWN RISK.

For more information, please visit http://opensource.dyndns.org

SEE ALSO

perl, POEST::Server, POEST::Config::General.