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