trusty (3) RPC::PlServer.3pm.gz
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 ...)
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 "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.
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.