qpsmtpd/docs/plugins.pod

#
# This file is best read with ``perldoc plugins.pod''
#

### 
# Conventions:
#  plugin names:  F<myplugin>, F<qpsmtpd-async>
#  constants:     I<LOGDEBUG>
#  smtp commands, answers: B<HELO>, B<250 Queued!>
#
# Notes: 
#  * due to restrictions of some POD parsers, no C<<$object->method()>>
#    are allowed, use C<$object-E<gt>method()> 
# 

=head1 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 I<hooks> provided by the qpsmtpd core engine.

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

=head2 Loading Plugins

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

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

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

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

=head1 Anatomy of a plugin

A plugin has at least one method, which inherits from the 
C<Qpsmtpd::Plugin> object. The first argument for this method is always the 
plugin object itself (and usually called C<$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.

=head2 Initialisation

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

=over 4

=item $self 

the current plugin object, usually called C<$self>

=item $qp

the Qpsmtpd object, usually called C<$qp>.

=item @args

the values following the plugin name in the F<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, ...

=back

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

The next step is to register the hooks the plugin provides. Any method which 
is named C<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 C<s/\W/_/g;>, see 
L</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 C<register()> method (see below) with the 
C<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 C<register()> method is called last. It receives the same arguments as 
C<init()>. There is no restriction, what you can do in C<register()>, but 
creating database connections and reuse them later in the process may not be
a good idea. This initialisation happens before any C<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 F<qpsmtpd-async> and the pperl flavours, but 
not for F<qpsmtpd> started by (x)inetd or tcpserver. 

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

=head2 Hook - Subroutine translations

As mentioned above, the hook name needs to be translated to a valid perl 
C<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

=head3 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

=head2 Inheritance

Inheriting methods from other plugins is an advanced topic. You can alter 
arguments for the underlying plugin, prepare something for the I<real> 
plugin or skip a hook with this. Instead of modifying C<@ISA>
directly in your plugin, use the C<isa_plugin()> method from the 
C<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 C<Changing return values> and 
F<contrib/vetinari/rcpt_ok_maxrelay> in SVN.

=head2 Config files

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

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

All empty lines and lines starting with C<#> 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 C<config>
hook. 

=head2 Logging

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

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

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

=over 4

=item * 

LOGDEBUG

=item *

LOGINFO

=item *

LOGNOTICE

=item *

LOGWARN

=item *

LOGERROR

=item *

LOGCRIT

=item *

LOGALERT

=item *

LOGEMERG

=back

While debugging your plugins, you want to set the log level in the F<logging>
config file to I<LOGDEBUG>. This will log very much data. To restrict this 
output just to the plugin you are debugging, you can use the following plugin: 

=cut

FIXME: Test if this really works as inteded ;-)

=pod

 # logging/debug_plugin - just show LOGDEBUG messages of one plugin
 # Usage: 
 #  logging/debug_plugin my_plugin LOGLEVEL
 #
 #  LOGLEVEL is the log level for all other log messages
 use Qpsmtpd::Constants;
 
 sub register {
   my ($self, $qp, $plugin, $loglevel) = @_;
   die "no plugin name given"
     unless $plugin;
   $loglevel = "LOGWARN"
     unless defined $loglevel;
   $self->{_plugin} = $plugin;
   $self->{_level}  = Qpsmtpd::Constants::log_level($loglevel);
   $self->{_level}  = LOGWARN 
     unless defined $self->{_level};
 }
 
 sub hook_logging {
   my ($self, $transaction, $trace, $hook, $plugin, @log) = @_;
   return(OK) # drop these lines
     if $plugin ne $self->{_plugin} and $trace > $self->{_level};
   return(DECLINED);
 }

The above plugin should be loaded before the default logging plugin, which 
logs with I<LOGDEBUG>. The plugin name must be the one returned by the 
C<plugin_name()> method of the debugged plugin. This is probably not 
the same as the name of the plugin (i.e. not the same you write in the 
F<plugins> config file). In doubt: take a look in the log file for lines 
like C<queue::qmail_2dqueue hooking queue> (here: F<queue/qmail-queue> 
=E<gt> F<queue::qmail_2dqueue>).

=head2 Information about the current plugin

Each plugin inherits the public methods from C<Qpsmtpd::Plugin>. 

=over 4

=item plugin_name()

Returns the name of the currently running plugin

=item hook_name()

Returns the name of the running hook

=item auth_user()

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

=item auth_mechanism()

Returns the auth mechanism if authentication is used

=item connection()

Returns the C<Qpsmtpd::Connection> object associated with the current 
connection

=item transaction()

Returns the C<Qpsmtpd::Transaction> object associated with the current 
transaction

=back

=head2 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.

=over 4

=item 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).

=item 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 C<$self-E<gt>qp-E<gt>temp_dir()>, which takes a 
single parameter for the permissions requested (see L<mkdir> for details). 
A directory created like this will not be deleted when the transaction 
is ended.

=item spool_dir()

Returns the configured system-wide spool directory.

=back


=head2 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 F<count_unrecognized_commands> plugin from the qpsmtpd core
distribution.

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


=head1 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 I<DECLINED>.

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

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

=over 4

=item DECLINED

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

=item OK

Action allowed.

=item DENY

Action denied.

=item DENYSOFT

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

=item 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.

=item DENYSOFT_DISCONNECT

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

=item DONE

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

=back

The I<YIELD> constant is not mentioned here, because it is not used by
plugins directly.

=head1 SMTP hooks

This section covers the hooks, which are run in a normal SMTP connection. 
The order of these hooks is like you will (probably) see them, while a mail
is received. 

Every hook receives a C<Qpsmtpd::Plugin> object of the currently 
running plugin as the first argument. A C<Qpsmtpd::Transaction> object is 
the second argument of the current transaction in the most hooks, exceptions 
are noted in the description of the hook. If you need examples how the 
hook can be used, see the source of the plugins, which are given as 
example plugins.

B<NOTE>: for some hooks (post-fork, post-connection, disconnect, deny, ok) the
return values are ignored. This does B<not> mean you can return anything you
want. It just means the return value is discarded and you can not disconnect
a client with I<DENY_DISCONNECT>. The rule to return I<DECLINED> to run the
next plugin for this hook (or return I<OK> / I<DONE> to stop processing) 
still applies.

=head2 hook_pre_connection

Called by a controlling process (e.g. forkserver or prefork) after accepting 
the remote server, but before beginning a new instance (or handing the 
connection to the worker process).

Useful for load-management and rereading large config files at some
frequency less than once per session.

This hook is available in the F<qpsmtpd-forkserver>, F<qpsmtpd-prefork> and
F<qpsmtpd-async> flavours. 

=cut 

NOT FOR: apache, -server and inetd/pperl

=pod

B<NOTE:> You should not use this hook to do major work and / or use lookup 
methods which (I<may>) take some time, like DNS lookups. This will slow down
B<all> incoming connections, no other connection will be accepted while this
hook is running!

Arguments this hook receives are (B<NOTE>: currently no C<%args> for 
F<qpsmtpd-async>):

  my ($self,$transaction,%args) = @_;
  # %args is:
  # %args = ( remote_ip    => inet_ntoa($iaddr),
  #           remote_port  => $port,
  #           local_ip     => inet_ntoa($laddr),
  #           local_port   => $lport,
  #           max_conn_ip  => $MAXCONNIP,
  #           child_addrs  => [values %childstatus],
  #         );

B<NOTE:> the C<$transaction> is of course C<undef> at this time.

Allowed return codes are

=over 4

=item DENY / DENY_DISCONNECT

returns a B<550> to the client and ends the connection

=item DENYSOFT / DENYSOFT_DISCONNECT

returns a B<451> to the client and ends the connection

=back

Anything else is ignored.

Example plugins are F<hosts_allow> and F<connection_time>. 

=head2 hook_connect

It is called at the start of a connection before the greeting is sent to 
the connecting client.

Arguments for this hook are

  my $self = shift;

B<NOTE:> in fact you get passed two more arguments, which are C<undef> at this
early stage of the connection, so ignore them.

Allowed return codes are

=over 4

=item OK

Stop processing plugins, give the default response

=item DECLINED

Process the next plugin

=item DONE

Stop processing plugins and dont give the default response, i.e. the plugin 
gave the response

=item DENY

Return hard failure code and disconnect

=item DENYSOFT

Return soft failure code and disconnect

=back

Example plugin for this hook is the F<check_relay> plugin. 

=head2 hook_helo / hook_ehlo

It is called after the client sent B<EHLO> (hook_ehlo) or B<HELO> (hook_helo)
Allowed return codes are

=over 4

=item DENY

Return a 550 code

=item DENYSOFT

Return a B<450> code

=item DENY_DISCONNECT / DENYSOFT_DISCONNECT

as above but with disconnect

=item DONE

Qpsmtpd wont do anything, the plugin sent the message

=item DECLINED 

Qpsmtpd will send the standard B<EHLO>/B<HELO> answer, of course only 
if all plugins hooking I<helo/ehlo> return I<DECLINED>.

=back

Arguments of this hook are

  my ($self, $transaction, $host) = @_;
  # $host: the name the client sent in the 
  # (EH|HE)LO line

B<NOTE:> C<$transaction> is C<undef> at this point.

=head2 hook_mail_pre

After the B<MAIL FROM: > line sent by the client is broken into 
pieces by the C<hook_mail_parse()>, this hook recieves the results.
This hook may be used to pre-accept adresses without the surrounding 
I<E<lt>E<gt>> (by adding them) or addresses like 
I<E<lt>user@example.com.E<gt>> or I<E<lt>user@example.com E<gt>> by 
removing the trailing I<"."> / C<" ">.

Expected return values are I<OK> and an address which must be parseable
by C<Qpsmtpd::Address-E<gt>parse()> on success or any other constant to
indicate failure.

Arguments are 

  my ($self, $transaction, $addr) = @_;

=head2 hook_mail

Called right after the envelope sender line is parsed (the B<MAIL FROM: >
command). The plugin gets passed a C<Qpsmtpd::Address> object, which means 
the parsing and verifying the syntax of the address (and just the syntax, 
no other checks) is already done. Default is to allow the sender address. 
The remaining arguments are the extensions defined in RFC 1869 (if sent by 
the client).

B<NOTE:> According to the SMTP protocol, you can not reject an invalid
sender until after the B<RCPT> stage (except for protocol errors, i.e.
syntax errors in address). So store it in an C<$transaction-E<gt>note()> and 
process it later in an rcpt hook.

Allowed return codes are

=over 4

=item OK

sender allowed

=item DENY

Return a hard failure code

=item DENYSOFT

Return a soft failure code

=item DENY_DISCONNECT / DENYSOFT_DISCONNECT

as above but with disconnect

=item DECLINED

next plugin (if any)

=item DONE

skip further processing, plugin sent response

=back

Arguments for this hook are 

  my ($self,$transaction, $sender, %args) = @_;
  # $sender: an Qpsmtpd::Address object for 
  # sender of the message

Example plugins for the C<hook_mail> are F<require_resolvable_fromhost>
and F<check_badmailfrom>.

=head2 hook_rcpt_pre

See C<hook_mail_pre>, s/MAIL FROM:/RCPT TO:/.

=head2 hook_rcpt

This hook is called after the client sent an I<RCPT TO: > command (after 
parsing the line). The given argument is parsed by C<Qpsmtpd::Address>, 
then this hook is called. Default is to deny the mail with a soft error 
code. The remaining arguments are the extensions defined in RFC 1869
(if sent by the client).

Allowed return codes

=over 4

=item OK

recipient allowed

=item DENY

Return a hard failure code, for example for an I<User does not exist here> 
message.

=item DENYSOFT

Return a soft failure code, for example if the connect to a user lookup 
database failed

=item DENY_DISCONNECT / DENYSOFT_DISCONNECT

as above but with disconnect

=item DONE

skip further processing, plugin sent response

=back

Arguments are

  my ($self, $transaction, $recipient, %args) = @_;
  # $rcpt = Qpsmtpd::Address object with 
  # the given recipient address

Example plugin is F<rcpt_ok>.

=head2 hook_data

After the client sent the B<DATA> command, before any data of the message
was sent, this hook is called. 

B<NOTE:> This hook, like B<EHLO>, B<VRFY>, B<QUIT>, B<NOOP>, is an 
endpoint of a pipelined command group (see RFC 1854) and may be used to 
detect ``early talkers''. Since svn revision 758 the F<check_earlytalker>
plugin may be configured to check at this hook for ``early talkers''.

Allowed return codes are

=over 4

=item DENY

Return a hard failure code

=item DENYSOFT

Return a soft failure code

=item DENY_DISCONNECT / DENYSOFT_DISCONNECT

as above but with disconnect

=item DONE

Plugin took care of receiving data and calling the queue (not recommended)

B<NOTE:> The only real use for I<DONE> is implementing other ways of
receiving the message, than the default... for example the CHUNKING SMTP
extension (RFC 1869, 1830/3030) ... a plugin for this exists at 
http://svn.perl.org/qpsmtpd/contrib/vetinari/experimental/chunking, but it
was never tested ``in the wild''.

=back

Arguments:

  my ($self, $transaction) = @_;

Example plugin is F<greylisting>.

=head2 hook_received_line

If you wish to provide your own Received header line, do it here. You can use
or discard any of the given arguments (see below).

Allowed return codes:

=over 4

=item OK, $string

use this string for the Received header.

=item anything else

use the default Received header

=back

Arguments are

 my ($self, $transaction, $smtp, $auth, $sslinfo) = @_;
 # $smtp - the SMTP type used (e.g. "SMTP" or "ESMTP").
 # $auth - the Auth header additionals.
 # $sslinfo - information about SSL for the header.

=head2 data_headers_end

This hook fires after all header lines of the message data has been received.
Defaults to doing nothing, just continue processing. At this step,
the sender is not waiting for a reply, but we can try and prevent him from
sending the entire message by disconnecting immediately. (Although it is
likely the packets are already in flight due to buffering and pipelining).

B<NOTE:> BE CAREFUL! If you drop the connection legal MTAs will retry again 
and again, spammers will probably not. This is not RFC compliant and can lead
to an unpredictable mess. Use with caution.

Why this head may be useful for you, see 
L<http://www.nntp.perl.org/group/perl.qpsmtpd/2009/02/msg8502.html>, ff.

Allowed return codes:

=over 4

=item DENY_DISCONNECT

Return B<554 Message denied> and disconnect

=item DENYSOFT_DISCONNECT

Return B<421 Message denied temporarily> and disconnect

=item DECLINED

Do nothing

=back

Arguments:

  my ($self, $transaction) = @_; 

B<FIXME:> check arguments

=head2 hook_data_post

The C<data_post> hook is called after the client sent the final C<.\r\n> 
of a message, before the mail is sent to the queue.

Allowed return codes are

=over 4

=item DENY

Return a hard failure code

=item DENYSOFT

Return a soft failure code

=item DENY_DISCONNECT / DENYSOFT_DISCONNECT

as above but with disconnect

=item DONE

skip further processing (message will not be queued), plugin gave the response.

B<NOTE:> just returning I<OK> from a special queue plugin does (nearly) 
the same (i.e. dropping the mail to F</dev/null>) and you don't have to 
send the response on your own.

If you want the mail to be queued, you have to queue it manually!

=back

Arguments:

  my ($self, $transaction) = @_;

Example plugins: F<spamassassin>, F<virus/clamdscan>

=head2 hook_queue_pre

This hook is run, just before the mail is queued to the ``backend''. You 
may modify the in-process transaction object (e.g. adding headers) or add 
something like a footer to the mail (the latter is not recommended).

Allowed return codes are 

=over 4

=item DONE

no queuing is done

=item OK / DECLINED

queue the mail

=back

=head2 hook_queue

When all C<data_post> hooks accepted the message, this hook is called. It 
is used to queue the message to the ``backend''.

Allowed return codes:

=over 4

=item DONE

skip further processing (plugin gave response code)

=item OK

Return success message, i.e. tell the client the message was queued (this
may be used to drop the message silently).

=item DENY

Return hard failure code

=item DENYSOFT

Return soft failure code, i.e. if disk full or other temporary queuing 
problems

=back

Arguments:

  my ($self, $transaction) = @_;

Example plugins: all F<queue/*> plugins

=head2 hook_queue_post

This hook is called always after C<hook_queue>. If the return code is 
B<not> I<OK>, a message (all remaining return values) with level I<LOGERROR> 
is written to the log.
Arguments are

 my $self = shift;
 
B<NOTE:> C<$transaction> is not valid at this point, therefore not mentioned.


=head2 hook_reset_transaction

This hook will be called several times. At the beginning of a transaction 
(i.e. when the client sends a B<MAIL FROM:> command the first time), 
after queueing the mail and every time a client sends a B<RSET> command.
Arguments are 

 my ($self, $transaction) = @_;

B<NOTE:> don't rely on C<$transaction> being valid at this point.

=head2 hook_quit

After the client sent a B<QUIT> command, this hook is called (before the
C<hook_disconnect>).

Allowed return codes

=over 4

=item DONE

plugin sent response

=item DECLINED

next plugin and / or qpsmtpd sends response

=back

Arguments: the only argument is C<$self>

=cut 

### XXX: FIXME pass the rest of the line to this hook?

=pod

Expample plugin is the F<quit_fortune> plugin.

=head2 hook_disconnect

This hook will be called from several places: After a plugin returned 
I<DENY(|SOFT)_DISCONNECT>, before connection is disconnected or after the 
client sent the B<QUIT> command, AFTER the quit hook and ONLY if no plugin 
hooking C<hook_quit> returned I<DONE>.

All return values are ignored, arguments are just C<$self>

Example plugin is F<logging/file>

=head2 hook_post_connection

This is the counter part of the C<pre-connection> hook, it is called 
directly before the connection is finished, for example, just before the 
qpsmtpd-forkserver instance exits or if the client drops the connection 
without notice (without a B<QUIT>). This hook is not called if the qpsmtpd
instance is killed.

=cut 

FIXME: we should run this hook on a ``SIGHUP'' or some other signal?

=pod 

The only argument is C<$self> and all return codes are ignored, it would 
be too late anyway :-).

Example: F<connection_time>

=head1 Parsing Hooks

Before the line from the client is parsed by 
C<Qpsmtpd::Command-E<gt>parse()> with the built in parser, these hooks 
are called. They can be used to supply a parsing function for the line,
which will be used instead of the built in parser.

The hook must return two arguments, the first is (currently) ignored,
the second argument must be a (CODE) reference to a sub routine. This sub 
routine receives three arguments:

=over 4

=item $self

the plugin object

=item $cmd

the command (i.e. the first word of the line) sent by the client

=item $line

the line sent by the client without the first word

=back

Expected return values from this sub are I<DENY> and a reason which is 
sent to the client or I<OK> and the C<$line> broken into pieces according
to the syntax rules for the command.

B<NOTE: ignore the example from C<Qpsmtpd::Command>, the C<unrecognized_command_parse> hook was never implemented,...>

=head2 hook_helo_parse / hook_ehlo_parse

The provided sub routine must return two or more values. The first is 
discarded, the second is the hostname (sent by the client as argument 
to the B<HELO> / B<EHLO> command). All other values are passed to the 
helo / ehlo hook. This hook may be used to change the hostname the client
sent... not recommended, but if your local policy says only to accept
I<HELO> hosts with FQDNs and you have a legal client which can not be 
changed to send his FQDN, this is the right place.

=head2 hook_mail_parse / hook_rcpt_parse

The provided sub routine must return two or more values. The first is 
either I<OK> to indicate that parsing of the line was successfull
or anything else to bail out with I<501 Syntax error in command>. In
case of failure the second argument is used as the error message for the 
client.

If parsing was successfull, the second argument is the sender's / 
recipient's address (this may be without the surrounding I<E<lt>> and 
I<E<gt>>, don't add them here, use the C<hook_mail_pre()> / 
C<hook_rcpt_pre()> methods for this). All other arguments are 
sent to the C<mail / rcpt> hook as B<MAIL> / B<RCPT> parameters (see 
RFC 1869 I<SMTP Service Extensions> for more info). Note that 
the mail and rcpt hooks expect a list of key/value pairs as the 
last arguments.

=head2 hook_auth_parse

B<FIXME...>

=head1 Special hooks

Now some special hooks follow. Some of these hooks are some internal hooks, 
which may be used to alter the logging or retrieving config values from 
other sources (other than flat files) like SQL databases.

=head2 hook_logging

This hook is called when a log message is written, for example in a plugin 
it fires if someone calls C<$self-E<gt>log($level, $msg);>. Allowed
return codes are

=over 4

=item DECLINED

next logging plugin

=item OK

(not I<DONE>, as some might expect!) ok, plugin logged the message

=back

Arguments are

  my ($self, $transaction, $trace, $hook, $plugin, @log) = @_;
  # $trace: level of message, for example 
  #          LOGWARN, LOGDEBUG, ...
  # $hook:  the hook in/for which this logging 
  #          was called
  # $plugin: the plugin calling this hook
  # @log:   the log message

B<NOTE:> C<$transaction> may be C<undef>, depending when / where this hook
is called. It's probably best not to try acessing it.

All F<logging/*> plugins can be used as example plugins.

=head2 hook_deny

This hook is called after a plugin returned I<DENY>, I<DENYSOFT>, 
I<DENY_DISCONNECT> or I<DENYSOFT_DISCONNECT>. All return codes are ignored, 
arguments are

  my ($self, $transaction, $prev_hook, $return, $return_text) = @_;

B<NOTE:> C<$transaction> may be C<undef>, depending when / where this hook
is called. It's probably best not to try acessing it.

Example plugin for this hook is F<logging/adaptive>.

=head2 hook_ok

The counter part of C<hook_deny>, it is called after a plugin B<did not>
return I<DENY>, I<DENYSOFT>, I<DENY_DISCONNECT> or I<DENYSOFT_DISCONNECT>. 
All return codes are ignored, arguments are

  my ( $self, $transaction, $prev_hook, $return, $return_text ) = @_;

B<NOTE:> C<$transaction> may be C<undef>, depending when / where this hook
is called. It's probably best not to try acessing it.

=head2 hook_config

Called when a config file is requested, for example in a plugin it fires 
if someone calls C<my @cfg = $self-E<gt>qp-E<gt>config($cfg_name);>. 
Allowed return codes are

=over 4

=item DECLINED

plugin didn't find the requested value

=item OK

requested values as C<@list>, example:

  return (OK, @{$config{$value}}) 
    if exists $config{$value};
  return (DECLINED);

=back

Arguments:

  my ($self,$transaction,$value) = @_; 
  # $value: the requested config item(s)

B<NOTE:> C<$transaction> may be C<undef>, depending when / where this hook
is called. It's probably best not to try acessing it.

Example plugin is F<http_config> from the qpsmtpd distribution.

=head2 hook_unrecognized_command

This is called if the client sent a command unknown to the core of qpsmtpd.
This can be used to implement new SMTP commands or just count the number 
of unknown commands from the client, see below for examples.
Allowed return codes:

=over 4

=item DENY_DISCONNECT

Return B<521> and disconnect the client

=item DENY

Return B<500>

=item DONE

Qpsmtpd wont do anything; the plugin responded, this is what you want to 
return, if you are implementing new commands

=item Anything else...

Return B<500 Unrecognized command>

=back

Arguments:

  my ($self, $transaction, $cmd, @args) = @_;
  # $cmd  = the first "word" of the line 
  #         sent by the client
  # @args = all the other "words" of the 
  #         line sent by the client
  #         "word(s)": white space split() line

B<NOTE:> C<$transaction> may be C<undef>, depending when / where this hook
is called. It's probably best not to try acessing it.

Example plugin is F<tls>.

=head2 hook_help

This hook triggers if a client sends the B<HELP> command, allowed return
codes are:

=over 4

=item DONE

Plugin gave the answer.

=item DENY

The client will get a C<syntax error> message, probably not what you want, 
better use

  $self->qp->respond(502, "Not implemented.");
  return DONE;

=back

Anything else will be send as help answer.

Arguments are
   my ($self, $transaction, @args) = @_;

with C<@args> being the arguments from the client's command.

=head2 hook_vrfy

If the client sents the B<VRFY> command, this hook is called. Default is to 
return a message telling the user to just try sending the message.
Allowed return codes:

=over 4

=item OK

Recipient Exists

=item DENY

Return a hard failure code

=item DONE

Return nothing and move on

=item Anything Else...

Return a B<252>

=back

Arguments are:

 my ($self) = shift;

=cut 

FIXME: this sould be changed in Qpsmtpd::SMTP to pass the rest of the line
as arguments to the hook

=pod

=head2 hook_noop 

If the client sents the B<NOOP> command, this hook is called. Default is to
return C<250 OK>.

Allowed return codes are:

=over 4

=item DONE

Plugin gave the answer

=item DENY_DISCONNECT

Return error code and disconnect client

=item DENY

Return error code.

=item Anything Else...

Give the default answer of B<250 OK>.

=back

Arguments are

  my ($self,$transaction,@args) = @_;

=head2 hook_post_fork

B<NOTE:> This hook is only available in qpsmtpd-async.

It is called while starting qpsmtpd-async. You can run more than one 
instance of qpsmtpd-async (one per CPU probably). This hook is called 
after forking one instance.

Arguments: 

 my $self = shift;

The return values of this hook are discarded.

=head1 Authentication hooks

=cut 

B<FIXME missing:> auth_parse

#=head2 auth

B<FIXME>

#=head2 auth-plain

B<FIXME>

#=head2 auth-login

B<FIXME>

#=head2 auth-cram-md5

B<FIXME>

=pod

See F<README.authentication> in the qpsmtpd base dir.

=head1 Writing your own plugins

This is a walk through a new queue plugin, which queues the mail to a (remote)
QMQP-Server.

First step is to pull in the necessary modules

 use IO::Socket;
 use Text::Netstring qw( netstring_encode 
                         netstring_decode 
                         netstring_verify 
                         netstring_read );

We know, we need a server to send the mails to. This will be the same 
for every mail, so we can use arguments to the plugin to configure this 
server (and port).

Inserting this static config is done in C<register()>:

  sub register {
    my ($self, $qp, @args) = @_;
  
    die "No QMQP server specified in qmqp-forward config"
      unless @args;
  
    $self->{_qmqp_timeout} = 120;
  
    if ($args[0] =~ /^([\.\w_-]+)$/) {
      $self->{_qmqp_server} = $1;
    }
    else {
      die "Bad data in qmqp server: $args[0]";
    }
  
    $self->{_qmqp_port} = 628;
    if (@args > 1 and $args[1] =~ /^(\d+)$/) {
      $self->{_qmqp_port} = $1;
    }
  
    $self->log(LOGWARN, "WARNING: Ignoring additional arguments.") 
      if (@args > 2);
  }

We're going to write a queue plugin, so we need to hook to the I<queue>
hook.

  sub hook_queue {
    my ($self, $transaction) = @_;
  
    $self->log(LOGINFO, "forwarding to $self->{_qmqp_server}:"
                       ."$self->{_qmqp_port}");

The first step is to open a connection to the remote server.

   my $sock = IO::Socket::INET->new(
                 PeerAddr => $self->{_qmqp_server},
                 PeerPort => $self->{_qmqp_port},
                 Timeout  => $self->{_qmqp_timeout},
                 Proto    => 'tcp')
      or $self->log(LOGERROR, "Failed to connect to "
                      ."$self->{_qmqp_server}:"
                      ."$self->{_qmqp_port}: $!"),
        return(DECLINED);
    $sock->autoflush(1);

=over 4

=item *

The client starts with a safe 8-bit text message. It encodes the message
as the byte string C<firstline\012secondline\012 ... \012lastline>. (The
last line is usually, but not necessarily, empty.) The client then encodes
this byte string as a netstring. The client also encodes the envelope
sender address as a netstring, and encodes each envelope recipient address
as a netstring.

The client concatenates all these netstrings, encodes the concatenation
as a netstring, and sends the result.

(from L<http://cr.yp.to/proto/qmqp.html>)

=back

The first idea is to build the package we send, in the order described
in the paragraph above:

  my $message = $transaction->header->as_string;
  $transaction->body_resetpos;
  while (my $line = $transaction->body_getline) {
    $message .= $line;
  }
  $message  = netstring_encode($message);
  $message .= netstring_encode($transaction->sender->address);
  for ($transaction->recipients) {
    push @rcpt, $_->address;
  }
  $message .= join "", netstring_encode(@rcpt);
  print $sock netstring_encode($message)
    or do {
      my $err = $!;
      $self->_disconnect($sock);
      return(DECLINED, "Failed to print to socket: $err");
    };

This would mean, we have to hold the full message in memory... Not good 
for large messages, and probably even slower (for large messages).

Luckily it's easy to build a netstring without the help of the
C<Text::Netstring> module if you know the size of the string (for more
info about netstrings see L<http://cr.yp.to/proto/netstrings.txt>).

We start with the sender and recipient addresses:

  my ($addrs, $headers, @rcpt);
  $addrs = netstring_encode($transaction->sender->address);
  for ($transaction->recipients) {
    push @rcpt, $_->address;
  }
  $addrs .= join "", netstring_encode(@rcpt);

Ok, we got the sender and the recipients, now let's see what size the
message is.

  $headers   = $transaction->header->as_string;
  my $msglen = length($headers) + $transaction->body_length;

We've got everything we need. Now build the netstrings for the full package
and the message.

First the beginning of the netstring of the full package

  # (+ 2: the ":" and "," of the message's netstring)
  print $sock ($msglen + length($msglen) + 2 + length($addrs))
               .":"
               ."$msglen:$headers" ### beginning of messages netstring
    or do { 
      my $err = $!;
      $self->_disconnect($sock);
      return(DECLINED, 
             "Failed to print to socket: $err");
    };

Go to beginning of the body

  $transaction->body_resetpos;

If the message is spooled to disk, read the message in
blocks and write them to the server

  if ($transaction->body_fh) {
    my $buff;
    my $size = read $transaction->body_fh, $buff, 4096;
    unless (defined $size) {
      my $err = $!;
      $self->_disconnect($sock);
      return(DECLINED, "Failed to read from body_fh: $err");
    }
    while ($size) {
      print $sock $buff
        or do { 
          my $err = $!;
          $self->_disconnect($sock);
          return(DECLINED, "Failed to print to socket: $err");
        };
  
      $size = read $transaction->body_fh, $buff, 4096;
      unless (defined $size) {
        my $err = $!;
        $self->_disconnect($sock);
        return(DECLINED, 
               "Failed to read from body_fh: $err");
      }
    }
  }

Else we have to read it line by line ...

  else { 
    while (my $line = $transaction->body_getline) {
      print $sock $line
        or do { 
          my $err = $!;
          $self->_disconnect($sock);
          return(DECLINED, "Failed to print to socket: $err");
        };
    }
  }

Message is at the server, now finish the package.

  print $sock ","    # end of messages netstring
             .$addrs # sender + recpients
             .","    # end of netstring of 
                     #   the full package
    or do { 
      my $err = $!;
      $self->_disconnect($sock);
      return(DECLINED, 
             "Failed to print to socket: $err");
    };

We're done. Now let's see what the remote qmqpd says...


=over 4

=item *

(continued from L<http://cr.yp.to/proto/qmqp.html>:)

The server's response is a nonempty string of 8-bit bytes, encoded as a
netstring.
  
The first byte of the string is either K, Z, or D. K means that the
message has been accepted for delivery to all envelope recipients. This
is morally equivalent to the 250 response to DATA in SMTP; it is subject
to the reliability requirements of RFC 1123, section 5.3.3. Z means
temporary failure; the client should try again later. D means permanent
failure.
   
Note that there is only one response for the entire message; the server
cannot accept some recipients while rejecting others.

=back


    my $answer = netstring_read($sock);
    $self->_disconnect($sock);
    
    if (defined $answer and netstring_verify($answer)) {
      $answer = netstring_decode($answer);
  
      $answer =~ s/^K// and return(OK,
                                 "Queued! $answer");
      $answer =~ s/^Z// and return(DENYSOFT, 
                                 "Deferred: $answer");
      $answer =~ s/^D// and return(DENY,
                                 "Denied: $answer");
    }

If this is the only F<queue/*> plugin, the client will get a 451 temp error:

    return(DECLINED, "Protocol error");
  }

  sub _disconnect {
    my ($self,$sock) = @_;
    if (defined $sock) {
      eval { close $sock; };
      undef $sock;
    }
  }

=head1 Advanced Playground

=head2 Discarding messages

If you want to make the client think a message has been regularily accepted,
but in real you delete it or send it to F</dev/null>, ..., use something
like the following plugin and load it before your default queue plugin.

  sub hook_queue {
    my ($self, $transaction) = @_;
    if ($transaction->notes('discard_mail')) {
      my $msg_id = $transaction->header->get('Message-Id') || '';
      $msg_id =~ s/[\r\n].*//s;
      return(OK, "Queued! $msg_id");
    }
    return(DECLINED);
  }


=head2 Changing return values

This is an example how to use the C<isa_plugin> method.

The B<rcpt_ok_maxrelay> plugin wraps the B<rcpt_ok> plugin. The B<rcpt_ok>
plugin checks the F<rcpthosts> and F<morercpthosts> config files for
domains, which we accept mail for. If not found it tells the
client that relaying is not allowed. Clients which are marked as
C<relay clients> are excluded from this rule. This plugin counts the
number of unsuccessfull relaying attempts and drops the connection if
too many were made.

The optional parameter I<MAX_RELAY_ATTEMPTS> configures this plugin to drop
the connection after I<MAX_RELAY_ATTEMPTS> unsuccessful relaying attempts.
Set to C<0> to disable, default is C<5>.

Note: Do not load both (B<rcpt_ok> and B<rcpt_ok_maxrelay>). This plugin
should be configured to run I<last>, like B<rcpt_ok>.

 use Qpsmtpd::DSN;
 
 sub init {
   my ($self, $qp, @args) = @_;
   die "too many arguments"
     if @args > 1;
   $self->{_count_relay_max} = defined $args[0] ? $args[0] : 5;
   $self->isa_plugin("rcpt_ok");
 }

 sub hook_rcpt {
   my ($self, $transaction, $recipient) = @_;
   my ($rc, @msg) = $self->SUPER::hook_rcpt($transaction, $recipient);
 
   return ($rc, @msg)
      unless (($rc == DENY) and $self->{_count_relay_max});

   my $count = 
     ($self->qp->connection->notes('count_relay_attempts') || 0) + 1;
   $self->qp->connection->notes('count_relay_attempts', $count);

   return ($rc, @msg) unless ($count > $self->{_count_relay_max});
   return Qpsmtpd::DSN->relaying_denied(DENY_DISCONNECT, 
           "Too many relaying attempts"); 
 }

=head2 Results of other hooks

B<NOTE:> just copied from README.plugins

If we're in a transaction, the results of a callback are stored in

    $self->transaction->notes( $code->{name})->{"hook_$hook"}->{return}

If we're in a connection, store things in the connection notes instead.
B<FIXME>: does the above (regarding connection notes) work?

=cut

# vim: ts=2 sw=2 expandtab