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: joe@ispsoft.de

      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.

