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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 PlRPC::Client(3) and RPC::PlServer::Comm 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. "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 Net::Daemon(3) 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
    "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. MD5(3). We present the server source here, the client is part
    of the RPC::PlClient man page. See RPC::PlClient(3).

        #!/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 ...)

    Due to implementation of PlRPC, it's hard to use internal authentication
    mechanisms properly to achieve secured remote calls. Therefore users are
    advised to use an external authentication mechanism like TLS or IPsec.

    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.

    Use of Storable
        Storable module used for serialization and deserialization
        underneath is inherently insecure. Deserialized data can contain
        objects which lead to loading foreign modules and executing possible
        attached destructors. Do not accept host-based unauthorized
        connections. The Storable module is exercised before checking user
        password.

    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
        "CONFIGURATION FILE".

    User based authorization
        PlRPC has a builtin user based authorization scheme; use it! See
        "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.

        Please note PlRPC encryption does not protect from reply attacks.
        You should have implement it on the application or the cipher level.

AUTHOR AND COPYRIGHT
    The PlRPC-modules are

      Copyright (C) 1998, Jochen Wiedmann
                          Email: jochen.wiedmann at freenet.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
    RPC::PlClient(3), RPC::PlServer::Comm(3), Net::Daemon(3),
    Net::Daemon::Log(3), Storable(3), Sys::Syslog(3), Win32::EventLog(3)

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