Ubuntu Manpage: Courier::Filter - Purely Perl-based mail filter framework for the Courier MTA

Provided by: courier-filter-perl_0.200+ds-6_all

NAME

       Courier::Filter - Purely Perl-based mail filter framework for the Courier MTA

VERSION

       0.200

SYNOPSIS

           use Courier::Filter;
           use Courier::Filter::Logger::Moo;
           use Courier::Filter::Module::Foo;
           use Courier::Filter::Module::Bar;

           my $filter = Courier::Filter->new(
               mandatory   => 1,
               logger      => Courier::Filter::Logger::Moo->new( ... ),
               modules     => [
                   Courier::Filter::Module::Foo->new( ... ),
                   Courier::Filter::Module::Bar->new( ... )
               ],
               testing     => 0,
               debugging   => 0
           );

           my $exit_code = $filter->run() || 0;

           exit($exit_code);

DESCRIPTION

For an architectural and administrative overview of the Courier::Filter framework, see
Courier::Filter::Overview.

The Courier::Filter class is the heart of the Courier::Filter framework. To drive a
courierfilter filter process, create a Courier::Filter object, passing the filter modules
and loggers you want to use to the constructor, and call the "run()" method.

Courier::Filter will then take care of creating the courierfilter socket in the right
place in a safe manner, listening for connections from Courier, asking filter modules for
consideration of messages, notifying Courier of whether messages should be accepted or
rejected, logging message rejections, catching and logging errors, and finally removing
the socket when being terminated by Courier.

Constructor
The following constructor is provided:

new(%options): returns Courier::Filter; throws Courier::Error, Perl exceptions
Creates a new "Courier::Filter" object. Also creates the courierfilter socket in the
right place in a safe manner.

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

name
The name of the filter process. Used to build the socket name. Defaults to the
base name of the process ($0).

mandatory
A boolean value controlling whether the filter process should act as a mandatory
courierfilter. If true, users will not be able to bypass the filter modules in
this filter process from their individual localmailfilter filters. Technically,
this controls whether the courierfilter socket will be created in the "allfilters"
(true) or the "filters" (false) directory in Courier's run-time state directory
(see "runtime_dir" in Courier::Config). Defaults to true.

logger
A Courier::Filter::Logger object that will be used for logging message rejections
and error messages. You may override this for individual filter modules for which
you do not want the global logger to be used. If no logger is specified, logging
is disabled.

modules
Required. A so-called filter module group structure. A module group is a
reference to an array that may contain filter module objects (i.e. instances of
sub-classes of Courier::Filter::Module), as well as other module groups. Thus, a
module group is essentially a tree structure with filter modules as its leaves.
When considering messages, Courier::Filter walks the tree in a recursive-descent,
depth-first order, asking every filter module for consideration of the message's
acceptability.

For instance, given the following filter module group:

[$m1, $m2, [$m3, [$m4, $m5]], $m6]

Courier::Filter queries the filter modules in ascending order from 1 to 6.

The acceptability result returned by each module determines how Courier::Filter
proceeds with considering the current message:

• If a module states an explicit reject, Courier::Filter aborts the
consideration process and rejects the message.

• If a module states an implicit accept, Courier::Filter just proceeds to the
next module in turn.

• If a module states an explicit accept, Courier::Filter skips the rest of the
current module group and proceeds to the next item in the superordinate module
group, assuming the whole group to be an implicit accept.

For instance, take the nested filter module group from above:

Let's assume Courier::Filter queries the filter module $m3. If $m3 states an
explicit reject, the consideration process is aborted and the current message is
rejected. If $m3 states an implicit accept, Courier::Filter proceeds to $m4. If
$m3 states an explicit accept, the rest of group 2 (including all of group 3) is
skipped and the acceptability result of group 2 is assumed an implicit accept, so
Courier::Filter proceeds to $m6.

If no explicit reject has occured when Courier::Filter reaches the end of the main
module group, or a module in the main group states an explicit accept, the message
is accepted.

Using nested groups of filter modules with normal or inverse polarity, it should
be possible to implement sufficiently complex filtering policies to satisfy very
most needs.

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

testing
A boolean value controlling whether the whole filter process 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.

NOTE: You may also enable testing mode on individual filter module objects, see
"new" in Courier::Filter::Module. Enabling testing mode globally is not the same
as individually enabling testing mode on all filter modules, though. When global
testing mode is enabled, Courier::Filter only ignores the final result, but still
follows the rules of the normal consideration process, e.g. aborting as soon as a
filter module states an explicit reject, etc. When an individual filter module is
in testing mode, its individual result is ignored, and the consideration process
is continued with the next filter module. So individually enabling testing mode
on all filter modules allows you to thoroughly test the correctness and
performance of all installed filter modules, or even to gather stochastically
indepent statistics on the hit/miss rates of your filter modules.

debugging
A boolean value controlling whether extra debugging information should be logged
by Courier::Filter. Defaults to false. You need to enable debugging mode for
filter modules separately.

Instance methods
The following instance methods are provided:

run: throws Courier::Error, Perl exceptions
Runs the Courier::Filter. Listens for connections from Courier on the courierfilter
socket, asks the configured filter modules for consideration of messages, notifies
Courier of whether messages should be accepted or rejected, and logs message
rejections. When Courier requests termination of the courierfilter, removes the
socket and returns.

name: returns string
Returns the name of the filter process, as set through the constructor's "name"
option.

mandatory: returns boolean
Returns a boolean value indicating whether the filter process is a mandatory
courierfilter, as set through the constructor's "mandatory" option.

logger: returns Courier::Filter::Logger
logger($logger): returns Courier::Filter::Logger
If $logger is specified, installs a new global logger. Returns the (newly) configured
global logger.

modules: returns array-ref
modules(\@modules): returns array-ref
If "\@modules" is specified, installs a new filter module group structure. Returns
the (newly) configured filter modules group structure.

trusting: returns boolean
Returns a boolean value indicating the trusting mode, as set through the constructor's
"trusting" option.

testing: returns boolean
Returns a boolean value indicating the global testing mode, as set through the
constructor's "testing" option.

debugging: returns boolean
debugging($debugging): returns boolean
If $debugging is specified, sets the global debugging mode. Returns a boolean value
indicating the (newly) configured global debugging mode.

REFERENCES

       The courierfilter interface
           <http://www.courier-mta.org/courierfilter.html>

AUTHOR