Julian Mehnle

NAME

Courier::Filter::Module - Abstract Perl base class for filter modules used by the Courier::Filter framework

SYNOPSIS

Courier::Filter message filtering

    use Courier::Filter::Module::My;  # Need to use a non-abstract sub-class.
    
    my $module = Courier::Filter::Module::My->new(
        logger      => $logger,
        inverse     => 0,
        trusting    => 0,
        testing     => 0,
        debugging   => 0
    );
    
    my $filter = Courier::Filter->new(
        ...
        modules     => [ $module ],
        ...
    );

Deriving new filter module classes

    package Courier::Filter::Module::My;
    use base qw(Courier::Filter::Module);

DESCRIPTION

Sub-classes of Courier::Filter::Module are used by the Courier::Filter mail filtering framework to determine the acceptability of messages. See Courier::Filter::Overview for an overview of how filter modules are used and for how to write them.

When overriding a method in a derived class, do not forget calling the inherited method from your overridden method.

Constructor

The following constructor is provided and may be overridden:

new(%options): returns Courier::Filter::Module

Creates a new filter module using the %options. Initializes the filter module, by opening I/O handles, connecting to databases, creating temporary files, initializing parser libraries, etc..

%options is a list of key/value pairs representing any of the following options:

logger

A Courier::Filter::Logger object that will be used for logging message rejections and error messages caused by this individual filter module. If no logger is specified, Courier::Filter's global logger will be used.

inverse

A boolean value controlling whether the filter module should operate with inverse polarity (true) as opposed to normal polarity (false). Under inverse polarity, the result of the match method is negated by the consider method before returning it. For details on how Courier::Filter translates match results into acceptability results, see "How filter modules work" in Courier::Filter::Overview. Defaults to false.

trusting

A boolean value controlling whether the filter module should not be applied to trusted messages. For details on how the trusted status is determined, see the description of the trusted property in Courier::Message. In most configurations, this option can be used to white-list so-called outbound messages. Defaults to false.

testing

A boolean value controlling whether the filter module should run in testing mode. In testing mode, planned message rejections will be logged as usual, but no messages will actually be rejected. Defaults to false.

debugging

A boolean value controlling whether the filter module should log extra debugging information. Defaults to false.

Derived classes may support additional options.

Courier::Filter::Module::new() creates a hashref as an object of the invoked class, and stores the %options in it, but does nothing else.

Destructor

The following destructor is provided and may be overridden:

destroy

Uninitializes the filter module, by closing I/O handles, disconnecting from databases, deleting temporary files, uninitializing parser libraries, etc..

Courier::Filter::Module::destroy() does nothing. Sub-classes may override this method and define clean-up behavior.

Class methods

The following class methods are provided and may be overridden:

warn($text)

Writes a warning message to syslog. This method may also be used as an instance method.

Instance methods

The following instance methods are provided and may be overridden:

consider($message): returns string, [string]; throws Perl exceptions

Calls the match method, passing it the $message object. Returns the result of match, negating it beforehand if the filter module has inverse polarity. There is usually no need at all to override this method.

match($message): returns string, [string]; throws Perl exceptions

Examines the Courier::Message object given as $message. Returns a so-called match result consisting of an SMTP status response text, and an optional numerical SMTP status response code. For details about how match results are used by Courier::Filter, see "How filter modules work" in Courier::Filter::Overview and "Writing filter modules" in Courier::Filter::Overview.

Courier::Filter::Module::match() does nothing and returns undef. Sub-classes should override this method and define their own matching rule.

logger: returns Courier::Filter::Logger
logger($logger): returns Courier::Filter::Logger

If $logger is specified, installs a new logger for this individual filter module. Returns the current (new) logger.

inverse: returns boolean

Returns a boolean value indicating whether the filter module is operating with inverse polarity, as set through the constructor's inverse option.

trusting: returns boolean

Returns a boolean value indicating whether the filter module does not apply to trusted messages, as set through the constructor's trusting option.

testing: returns boolean

Returns a boolean value indicating whether the filter module is in testing mode, as set through the constructor's testing option.

debugging: returns boolean
debugging($debugging): returns boolean

If $debugging is specified, sets the debugging mode for this individual filter module. Returns the (newly) configured debugging mode.

SEE ALSO

Courier::Filter, Courier::Filter::Module.

For a list of prepared loggers that come with Courier::Filter, see "Bundled Courier::Filter loggers" in Courier::Filter::Overview.

For AVAILABILITY, SUPPORT, and LICENSE information, see Courier::Filter::Overview.

AUTHOR

Julian Mehnle <julian@mehnle.net>