qpsmtpd/README.plugins.md

Introduction

Plugins are the heart of qpsmtpd. The core implements only basic SMTP protocol functionality. No useful function can be done by qpsmtpd without loading plugins.

Plugins are loaded on startup where each of them register their interest in various hooks provided by the qpsmtpd core engine.

At least one plugin must allow or deny the RCPT command to enable receiving mail. The check_relay plugin is the standard plugin for this. Other plugins provide extra functionality related to this; for example the resolvable_fromhost plugin.

Loading Plugins

The list of plugins to load are configured in the config/plugins configuration file. One plugin per line, empty lines and lines starting with # are ignored. The order they are loaded is the same as given in this config file. This is also the order the registered hooks are run. The plugins are loaded from the plugins/ directory or from a subdirectory of it. If a plugin should be loaded from such a subdirectory, the directory must also be given, like the virus/clamdscan in the example below. Alternate plugin directories may be given in the config/plugin_dirs config file, one directory per line, these will be searched first before using the builtin fallback of plugins/ relative to the qpsmtpd root directory. It may be necessary, that the config/plugin_dirs must be used (if you're using Apache::Qpsmtpd, for example).

Some plugins may be configured by passing arguments in the plugins config file.

A plugin can be loaded two or more times with different arguments by adding :N to the plugin filename, with N being a number, usually starting at 0.

Another method to load a plugin is to create a valid perl module, drop this module in perl's @INC path and give the name of this module as plugin name. The only restriction to this is, that the module name must contain ::, e.g. My::Plugin would be ok, MyPlugin not. Appending of :0, :1, ... does not work with module plugins.

check_relay
virus/clamdscan
spamassassin reject_threshold 7
my_rcpt_check example.com
my_rcpt_check:0 example.org
My::Plugin

Anatomy of a plugin

A plugin has at least one method, which inherits from the Qpsmtpd::Plugin object. The first argument for this method is always the plugin object itself (and usually called $self). The most simple plugin has one method with a predefined name which just returns one constant.

# plugin temp_disable_connection
sub hook_connect {
   return(DENYSOFT, "Sorry, server is temporarily unavailable.");
}

While this is a valid plugin, it is not very useful except for rare circumstances. So let us see what happens when a plugin is loaded.

Initialisation

After the plugin is loaded the init() method of the plugin is called, if present. The arguments passed to init() are

• $self

  the current plugin object, usually called $self

• $qp

  the Qpsmtpd object, usually called $qp.

• @args

  the values following the plugin name in the plugins config, split by white space. These arguments can be used to configure the plugin with default and/or static config settings, like database paths, timeouts, ...

This is mainly used for inheriting from other plugins, but may be used to do the same as in register().

The next step is to register the hooks the plugin provides. Any method which is named hook_$hookname is automagically added.

Plugins should be written using standard named hook subroutines. This allows them to be overloaded and extended easily. Because some of the callback names have characters invalid in subroutine names , they must be translated. The current translation routine is s/\W/_/g;, see "Hook - Subroutine translations" for more info. If you choose not to use the default naming convention, you need to register the hooks in your plugin in the register() method (see below) with the register_hook() call on the plugin object.

sub register {
  my ($self, $qp, @args) = @_;
  $self->register_hook("mail", "mail_handler");
  $self->register_hook("rcpt", "rcpt_handler");
}
sub mail_handler { ... }
sub rcpt_handler { ... }

The register() method is called last. It receives the same arguments as init(). There is no restriction, what you can do in register(), but creating database connections and reuse them later in the process may not be a good idea. This initialisation happens before any fork() is done. Therefore the file handle will be shared by all qpsmtpd processes and the database will probably be confused if several different queries arrive on the same file handle at the same time (and you may get the wrong answer, if any). This is also true for the pperl flavor but not for qpsmtpd started by (x)inetd or tcpserver.

In short: don't do it if you want to write portable plugins.

Hook - Subroutine translations

As mentioned above, the hook name needs to be translated to a valid perl sub name. This is done like

($sub = $hook) =~ s/\W/_/g;
$sub = "hook_$sub";

Some examples follow, for a complete list of available (documented ;-)) hooks (method names), use something like

$ perl -lne 'print if s/^=head2\s+(hook_\S+)/$1/' docs/plugins.pod

All valid hooks are defined in lib/Qpsmtpd/Plugins.pm, our @hooks.

Translation table

hook                          method
----------                    ------------
config                        hook_config
queue                         hook_queue
data                          hook_data
data_post                     hook_data_post
quit                          hook_quit
rcpt                          hook_rcpt
mail                          hook_mail
ehlo                          hook_ehlo
helo                          hook_helo
auth                          hook_auth
auth-plain                    hook_auth_plain
auth-login                    hook_auth_login
auth-cram-md5                 hook_auth_cram_md5
connect                       hook_connect
reset_transaction             hook_reset_transaction
unrecognized_command          hook_unrecognized_command

Inheritance

Inheriting methods from other plugins is an advanced topic. You can alter arguments for the underlying plugin, prepare something for the real plugin or skip a hook with this. Instead of modifying @ISA directly in your plugin, use the isa_plugin() method from the init() subroutine.

# rcpt_ok_child
sub init {
  my ($self, $qp, @args) = @_;
  $self->isa_plugin("rcpt_ok");
}

sub hook_rcpt {
  my ($self, $transaction, $recipient) = @_;
  # do something special here...
  $self->SUPER::hook_rcpt($transaction, $recipient);
}

See also chapter Changing return values and contrib/vetinari/rcpt_ok_maxrelay in SVN.

Config files

Most of the existing plugins fetch their configuration data from files in the config/ sub directory. This data is read at runtime and may be changed without restarting qpsmtpd. (FIXME: caching?!) The contents of the files can be fetched via

@lines = $self->qp->config("my_config");

All empty lines and lines starting with # are ignored.

If you don't want to read your data from files, but from a database you can still use this syntax and write another plugin hooking the config hook.

Logging

Log messages can be written to the log file (or STDERR if you use the logging/warn plugin) with

$self->log($loglevel, $logmessage);

The log level is one of (from low to high priority)

• LOGDEBUG
• LOGINFO
• LOGNOTICE
• LOGWARN
• LOGERROR
• LOGCRIT
• LOGALERT
• LOGEMERG

While debugging your plugins, set your plugins loglevel to LOGDEBUG. This will log every logging statement within your plugin.

For more information about logging, see docs/logging.pod.

Information about the current plugin

Each plugin inherits the public methods from Qpsmtpd::Plugin.

• plugin_name()

  Returns the name of the currently running plugin

• hook_name()

  Returns the name of the running hook

• auth_user()

  Returns the name of the user the client is authed as (if authentication is used, of course)

• auth_mechanism()

  Returns the auth mechanism if authentication is used

• connection()

  Returns the Qpsmtpd::Connection object associated with the current connection

• transaction()

  Returns the Qpsmtpd::Transaction object associated with the current transaction

Temporary Files

The temporary file and directory functions can be used for plugin specific workfiles and will automatically be deleted at the end of the current transaction.

• temp_file()

  Returns a unique name of a file located in the default spool directory, but does not open that file (i.e. it is the name not a file handle).

• temp_dir()

  Returns the name of a unique directory located in the default spool directory, after creating the directory with 0700 rights. If you need a directory with different rights (say for an antivirus daemon), you will need to use the base function $self->qp->temp_dir(), which takes a single parameter for the permissions requested (see mkdir for details). A directory created like this will not be deleted when the transaction is ended.

• spool_dir()

  Returns the configured system-wide spool directory.

Connection and Transaction Notes

Both may be used to share notes across plugins and/or hooks. The only real difference is their life time. The connection notes start when a new connection is made and end, when the connection ends. This can, for example, be used to count the number of none SMTP commands. The plugin which uses this is the count_unrecognized_commands plugin from the qpsmtpd core distribution.

The transaction note starts after the MAIL FROM: command and are just valid for the current transaction, see below in the reset_transaction hook when the transaction ends.

Return codes

Each plugin must return an allowed constant for the hook and (usually) optionally a ``message'' for the client. Generally all plugins for a hook are processed until one returns something other than DECLINED.

Plugins are run in the order they are listed in the plugins configuration file.

The return constants are defined in Qpsmtpd::Constants and have the following meanings:

• DECLINED

  Plugin declined work; proceed as usual. This return code is always allowed unless noted otherwise.

• OK

  Action allowed.

• DENY

  Action denied.

• DENYSOFT

  Action denied; return a temporary rejection code (say 450 instead of 550).

• DENY_DISCONNECT

  Action denied; return a permanent rejection code and disconnect the client. Use this for "rude" clients. Note that you're not supposed to do this according to the SMTP specs, but bad clients don't listen sometimes.

• DENYSOFT_DISCONNECT

  Action denied; return a temporary rejection code and disconnect the client. See note above about SMTP specs.

• DONE

  Finishing processing of the request. Usually used when the plugin sent the response to the client.