NAME
   RPC::PlServer - Perl extension for writing PlRPC servers

SYNOPSIS
     # Create a subclass of RPC::PlServer
     use RPC::PlServer;

     package MyServer;
     $MyServer::VERSION = '0.01';
     @MyServer::ISA = qw(RPC::PlServer);

     # Overwrite the Run() method to handle a single connection
     sub Run {
         my $self = shift;
         my $socket = $self->{'socket'};
     }

     # Create an instance of the MyServer class
     package main;
     my $server = MyServer->new({'localport' => '1234'}, \@ARGV);

     # Bind the server to its port to make it actually running
     $server->Bind();

DESCRIPTION
   PlRPC (Perl RPC) is a package for implementing servers and clients that
   are written in Perl entirely. The name is borrowed from Sun's RPC
   (Remote Procedure Call), but it could as well be RMI like Java's "Remote
   Method Interface), because PlRPC gives you the complete power of Perl's
   OO framework in a very simple manner.

   RPC::PlServer is the package used on the server side, and you guess what
   RPC::PlClient is for. Both share the package RPC::PlServer::Comm for
   communication purposes. See the PlRPC::Client(3) manpage and the
   RPC::PlServer::Comm manpage for these parts.

   PlRPC works by defining a set of methods that may be executed by the
   client. For example, the server might offer a method "multiply" to the
   client. Now the clients method call

       @result = $client->multiply($a, $b);

   will be immediately mapped to a method call

       @result = $server->multiply($a, $b);

   on the server. The arguments and results will be transferred to or from
   the server automagically. (This magic has a name in Perl: It's the
   Storable module, my thanks to Raphael Manfredi for this excellent
   package.) Simple, eh? :-)

   The RPC::PlServer and RPC::PlClient are abstract servers and clients:
   You have to derive your own classes from it.

 Additional options

   The RPC::PlServer inherits all of Net::Daemon's options and attributes
   and adds the following:

   *cipher*
           The attribute value is an instance of Crypt::DES, Crypt::IDEA or
           any other class with the same API for block encryption. If you
           supply such an attribute, the traffic between client and server
           will be encrypted using this option.

   *maxmessage* (--maxmessage=size)
           The size of messages exchanged between client and server is
           restricted, in order to omit denial of service attacks. By
           default the limit is 65536 bytes.

   users   This is an attribute of the client object used for Permit/Deny rules
           in the config file. It's value is an array ref of user names
           that are allowed to connect from the given client. See the
           example config file below. the section on "CONFIGURATION FILE".

 Error Handling

   Error handling is simple with the RPC package, because it is based on
   Perl exceptions completely. Thus your typical code looks like this:

     eval {
         # Do something here. Don't care for errors.
         ...
     };
     if ($@) {
         # An error occurred.
         ...
     }

 Server Constructors

     my $server = RPC::PlServer(\%options, \@args);

   (Class method) This constructor is immediately inherited from the
   Net::Daemon package. See the Net::Daemon(3) manpage for details.

 Access Control

     $ok = $self->AcceptApplication($app);
     $ok = $self->AcceptVersion($version);
     $ok = $self->AcceptUser($user, $password);

   The RPC::PlServer package has a very detailed access control scheme:
   First of all it inherits Net::Daemon's host based access control. It
   adds version control and user authorization. To achieve that, the method
   *Accept* from Net::Daemon is split into three methods,
   *AcceptApplication*, *AcceptVersion* and *AcceptUser*, each of them
   returning TRUE or FALSE. The client receives the arguments as the
   attributes *application*, *version*, *user* and *password*. A client is
   accepted only if all of the above methods are returning TRUE.

   The default implementations are as follows: The AcceptApplication method
   returns TRUE, if $self is a subclass of $app. The AcceptVersion method
   returns TRUE, if the requested version is less or equal to
   ${$class}::VERSION, $self being an instance of $class. Whether a user is
   permitted to connect depends on the client configuration. See the
   section on "CONFIGURATION FILE" below for examples.

 Method based access control

   Giving a client the ability to invoke arbitrary methods can be a
   terrible security hole. Thus the server has a *methods* attribute. This
   is a hash ref of class names as keys, the values being hash refs again
   with method names as the keys. That is, if your hash looks as follows:

       $self->{'methods'} = {
           'CalcServer' => {
               'NewHandle' => 1,
               'CallMethod' => 1 },
           'Calculator' => {
               'new' => 1,
               'multiply' => 1,
               'add' => 1,
               'divide' => 1,
               'subtract' => 1 }
           };

   then the client may use the CalcServer's *NewHandle* method to create
   objects, but only via the permitted constructor Calculator->new. Once a
   Calculator object is created, the server may invoke the methods
   multiply, add, divide and subtract.

CONFIGURATION FILE
   The server config file is inherited from Net::Daemon. It adds the
   *users* and *cipher* attribute to the client list. Thus a typical config
   file might look as follows:

       # Load external modules; this is not required unless you use
       # the chroot() option.
       #require DBD::mysql;
       #require DBD::CSV;

       # Create keys
       my $myhost_key = Crypt::IDEA->new('83fbd23390ade239');
       my $bob_key    = Crypt::IDEA->new('be39893df23f98a2');

       {
           # 'chroot' => '/var/dbiproxy',
           'facility' => 'daemon',
           'pidfile' => '/var/dbiproxy/dbiproxy.pid',
           'user' => 'nobody',
           'group' => 'nobody',
           'localport' => '1003',
           'mode' => 'fork',

           # Access control
           'clients' => [
               # Accept the local LAN (192.168.1.*)
               {
                   'mask' => '^192\.168\.1\.\d+$',
                   'accept' => 1,
                   'users' => [ 'bob', 'jim' ],
                   'cipher' => $myhost_key
               },
               # Accept myhost.company.com
               {
                   'mask' => '^myhost\.company\.com$',
                   'accept' => 1,
                   'users' => [ {
                       'name' => 'bob',
                       'cipher' => $bob_key
                       } ]
               },
               # Deny everything else
               {
                   'mask' => '.*',
                   'accept' => 0
               }
           ]
       }

   Things you should note: The user list of 192.168.1.* contains scalar
   values, but the user list of myhost.company.com contains hash refs: This
   is required, because the user configuration is more specific for user
   based encryption.

EXAMPLE
   Enough wasted time, spread the example, not the word. :-) Let's write a
   simple server, say a server for MD5 digests. The server uses the
   external package MD5, but the client doesn't need to install the
   package. the MD5(3) manpage. We present the server source here, the
   client is part of the RPC::PlClient man page. See the RPC::PlClient(3)
   manpage.

       #!/usr/bin/perl -wT
       # Note the -T switch! This is always recommended for Perl servers.

       use strict;               # Always a good choice.

       require RPC::PlServer;
       require MD5;

       package MD5_Server;  # Clients need to request application
                            # "MD5_Server"

       $MD5_Server::VERSION = '1.0'; # Clients will be refused, if they
                                     # request version 1.1
       @MD5_Server::ISA = qw(RPC::PlServer);

       eval {
           # Server options below can be overwritten in the config file or
           # on the command line.
           my $server = MD5_Server->new({
               'pidfile'    => '/var/run/md5serv.pid',
               'configfile' => '/etc/md5serv.conf',
               'facility'   => 'daemon', # Default
               'user'       => 'nobody',
               'group'      => 'nobody',
               'localport'  => 2000,
               'logfile'    => 0,        # Use syslog
               'mode'       => 'fork',   # Recommended for Unix
               'methods'    => {
                   'MD5_Server' => {
                       'ClientObject' => 1,
                       'CallMethod' => 1,
                       'NewHandle' => 1
                       },
                   'MD5' => {
                       'new' => 1,
                       'add' => 1,
                       'hexdigest' => 1
                       },
                   }
           });
           $server->Bind();
       };

SECURITY
   It has to be said: PlRPC based servers are a potential security problem!
   I did my best to avoid security problems, but it is more than likely,
   that I missed something. Security was a design goal, but not *the*
   design goal. (A well known problem ...)

   I highly recommend the following design principles:

 Protection against "trusted" users

   perlsec
       Read the perl security FAQ (`perldoc perlsec') and use the `-T'
       switch.

   taintperl
       Use the `-T' switch. I mean it!

   Verify data
       Never untaint strings withouth verification, better verify twice.
       For example the *CallMethod* function first checks, whether an
       object handle is valid before coercing a method on it.

   Be restrictive
       Think twice, before you give a client access to a method.

   perlsec
       And just in case I forgot it: Read the `perlsec' man page. :-)

 Protection against untrusted users

   Host based authorization
       PlRPC has a builtin host based authorization scheme; use it! See the
       section on "/CONFIGURATION FILE".

   User based authorization
       PlRPC has a builtin user based authorization scheme; use it! See the
       section on "/CONFIGURATION FILE".

   Encryption
       Using encryption with PlRPC is extremely easy. There is absolutely
       no reason for communicating unencrypted with the clients. Even more:
       I recommend two phase encryption: The first phase is the login
       phase, where to use a host based key. As soon as the user has
       authorized, you should switch to a user based key. See the
       DBI::ProxyServer for an example.

AUTHOR AND COPYRIGHT
   The PlRPC-modules are

     Copyright (C) 1998, Jochen Wiedmann
                         Am Eisteich 9
                         72555 Metzingen
                         Germany

                         Phone: +49 7123 14887
                         Email: [email protected]

     All rights reserved.

   You may distribute this package under the terms of either the GNU
   General Public License or the Artistic License, as specified in the Perl
   README file.

SEE ALSO
   the RPC::PlClient(3) manpage, the RPC::PlServer::Comm(3) manpage, the
   Net::Daemon(3) manpage, the Net::Daemon::Log(3) manpage, the Storable(3)
   manpage, the Sys::Syslog(3) manpage, the Win32::EventLog(3) manpage

   See the DBI::ProxyServer(3) manpage for an example application.

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