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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.