Provided by: libprpc-perl_0.1005-21_all 
NAME
RPC::pServer - Perl extension for writing pRPC servers
SYNOPSIS
use RPC::pServer;
$sock = IO::Socket::INET->new('LocalPort' => 9000,
'Proto' => 'tcp',
'Listen' = 5,
'Reuse' => 1);
$connection = new RPC::pServer('sock' => $sock,
'configFile' => $file,
'funcTable' => $funcTableRef,
# other attributes #
);
while ($running) {
$connection->Loop();
if ($connection->error) {
# Do something
}
}
DESCRIPTION
pRPC (Perl RPC) is a package that simplifies the writing of Perl based client/server
applications. RPC::pServer is the package used on the server side, and you guess what
Net::pRPC::Client is for. See Net::pRPC::Client(3) for this part.
pRPC works by defining a set of of functions that may be executed by the client. For
example, the server might offer a function "multiply" to the client. Now a function call
@result = $con->Call('multiply', $a, $b);
on the client will be mapped to a corresponding call
multiply($con, $data, $a, $b);
on the server. (See the funcTable description below for $data.) The function call's result
will be returned to the client and stored in the array @result. Simple, eh? :-)
Server methods
new The server constructor. Unlike the usual constructors, this one will in general not
return immediately, at least not for a server running as a daemon. Instead it will
return if a connection is established with a connection object as result. The result
will be an error string or the connection object, thus you will typically do a
$con = RPC::pServer->new ( ...);
if (!ref($con)) {
print "Error $con.\n";
} else {
# Accept connection
...
}
Accept
Deny
After a connection is established, the server should call either of these methods. If
he calls Accept(), he should continue with calling the Loop() method for processing
the clients requests.
Loop
When a connection is established, the Loop method must be called. It will process the
client's requests. If Loop() returns FALSE, an error occurred. It is the main programs
task to decide what to do in that case.
Encrypt
This method can be used to get or set the cipher attribute, thus the encryption mode.
If the method is passed an argument, the argument will be used as the new encryption
mode. ('undef' for no encryption.) In either case the current encryption mode will be
returned. Example:
# Get the current encryption mode
$mode = $server->Encrypt();
# Currently disable encryption
$server->Encrypt(undef);
# Switch back to the old mode
$server->Encrypt($mode);
Server attributes
Server attributes will typically be supplied with the "new" constructor.
configFile
RPC::pServer has a builtin authorization mechanism based on a configuration file. If
you want to use this mechanism, just supply the name of a configuration file with the
attribute configFile and the server will accept or deny connections based on the
configuration file.
The authorization scheme is host based, but you may add user based functionality with
the user and password attributes. See "CONFIGURATION FILE" below.
client
This attribute is useful in conjunction with the configFile. If the server has
authorized a client by using the config file, he will create a hash ref with all the
client attributes and store a reference to this hash under the key client. Thus you
can easily extend the configuration file for your own purposes, at least as long as
host based configuration is sufficient for you.
sock
An object of type IO::Socket, if this program is running as a daemon. An accept() call
will be executed on this socket in order to wait for connections. See IO::Socket(3).
An inetd based server should leave this attribute empty: The method will use STDIN and
STDOUT instead.
Note: The latter is not yet functionable, I first need to work out how to create an
object of type IO::socket for an inetd based server's STDIN and STDOUT. It seems this
is currently not supported by IO::Socket.
cipher
This attribute can be used to add encryption quite easily. pRPC is not bound to a
certain encryption method, but to a block encryption API. The attribute is an object
supporting the methods blocksize, encrypt and decrypt. For example, the modules
Crypt::DES and Crypt::IDEA support such an interface.
Do not modify this attribute directly, use the encrypt method instead! However, it is
legal to pass the attribute to the constructor.
Example:
use Crypt::DES;
$crypt = DES->new(pack("H*", "0123456789abcdef"));
$client->Encrypt($crypt);
# or, to stop encryption
$client->Encrypt(undef);
You might prefer encryption being client dependent, so there is the additional
possibility to setup encryption in the server configuration file. See "CONFIGURATION
FILE". Client encryption definitions take precedence over the cipher attribute.
However, you can set or remove encryption on the fly (putting "undef" as attribute
value will stop encryption), but you have to be sure, that both sides change the
encryption mode.
funcTable
This attribute is a hash reference. The hash keys are the names of methods, that the
client may execute on the server. The hash values are hash references (again). The
RPC::pServer module will use the key 'code' only: It contains a code reference to the
function performing the clients function call. The first argument of the function call
will be the connection object itself, the second will be the 'funcTable' value. You
are free to use this hash reference in any way you want, the exception being the
'code' key. The function must return a list: In case of errors the results will be the
values 0, followed by a textual error message. In case of success, it ought to return
nonzero, followed by the result list being sent to the client.
stderr
a value of TRUE will enable logging messages to STDERR, the default is using syslog();
if the stderr attribute is FALSE, you might call openlog() to configure the
application name and facility. See Sys::Syslog(3).
debug
this will cause the server to log debugging information about client requests using
the Log method. A value of 0 disables debugging.
application
version
user
password
it is part of the pRPC authorization process, that the client must obeye a login
procedure where he will pass an application name, a protocol version and optionally a
user name and password. These are not used by pRPC, but when the new method returns
with a connection object, the main program may use these for additional authorization.
These attributes are read-only.
io this attribute is a Storable object created for communication with the client. You may
use this, for example, when you want to change the encryption mode with
Storable::Encrypt(). See Storable(3).
CONFIGURATION FILE
The server configuration file is currently not much more than a collection of client names
or ip numbers that should be permitted or denied to connect to the server. Any client is
represented by a definition like the following:
accept .*\.neckar-alb\.de
encryption DES
key 063fde7982defabc
encryptModule Crypt::DES
deny .*
In other words a client definition begins with either "accept pattern" or "deny pattern",
followed by some client attributes, each of the attributes being on a separate line,
followed by the attribute value. The "pattern" is a perl regular expression matching
either the clients host name or IP number. In particular this means that you have to
escape dots, for example a client with IP number 194.77.118.1 is represented by the
pattern "194\.77\.118\.1".
Currently known attributes are:
encryption
key
encryptionModule
These will be used for creating an encryption object which is used for communication
with the client, see Storable(3) for details. The object is created with a sequence
like
use $encryptionModule;
$cipher = $encryption->new(pack("H*", $key));
encryptionModule defaults to encryption, the reason why we need both is the brain
damaged design of the Crypt::IDEA and Crypt::DES modules, which use different module
and package names without any obvious reason.
You may add any other attribute you want, thus extending your authorization file. The
RPC::pServer module will simply ignore them, but your main program will find them in the
client attribute of the RPC::pServer object. This can be used for additional client
dependent configuration.
PREDEFINED FUNCTIONS
RPC::pServer offers some predefined methods which are designed for ease in work with
objects. In short they allow creation of objects on the server, passing handles to the
client and working with these handles in a fashion similar to the use of the true objects.
The handle functions need to share some common data, namely a hash array of object handles
(keys) and objects (values). The problem is, how to allocate these variables. By keeping a
multithreaded environment in mind, we suggest to store the hash on the stack of the
server's main loop.
The handle functions get access to this loop, by looking into the 'handles' attribute of
the respective entry in the 'funcTables' hash. See above for a description of the
'funcTables' hash.
See below for an example of using the handle functions.
NewHandle
This method can be inserted into the servers function table. The client may call this
function to create objects and receive handles to the objects. The corresponding entry
in the function table must have a key classes: This is a list reference with class
names. The client is restricted to create objects of these classes only.
The NewHandle function expects, that the constructor returns an object in case of
success or 'undef' otherwise. Note, that this isn't true in all cases, for example the
RPC::pServer and Net::pRPC::Client classes behave different. In that cases you have to
write your own constructor with a special error handling. The StoreHandle method below
will help you. Constructors with a different name than new are another example when
you need StoreHandle directly.
StoreHandle
After you have created an object on behave of the clients request, you'd like to store
it for later use. This is what StoreHandle does for you. It returns an object handle
which may be passed back to the client. The client can pass the objects back to the
server for use in CallMethod or UseHandle.
NewHandle
The NewHandle is mainly a wrapper for StoreHandle. It creates an object of the given
class, passes it to StoreHandle and returns the result. The NewHandle method is
designed for direct use within the servers function table.
UseHandle
This is the counterpart of StoreHandle: It gets an object handle, passed by the
client, as argument and returns the corresponding object, if any. An 'undef' value
will be returned for an invalid handle.
CallMethod
This function receives an object handle as argument and the name of a method being
executed. The method will be invoked on the corresponding object and the result will
be returned.
A special method is 'DESTROY', valid for any object handle. It disposes the object,
the handle becomes invalid.
All handle functions are demonstrated in the following example.
EXAMPLE
Enough wasted time, spread the example, not the word. :-) Let's write a simple server, say
a spreadsheet server. Of course we are not interested in the details of the spreadsheet
part (which could well be implemented in a separate program), the spreadsheet example is
chosen, because it is obvious, that such a server is dealing with complex data structures.
For example, a "sum" method should be able to add over complete rows, columns or even
rectangular regions of the spreadsheet. And another thing, obviously a spread- sheet could
easily be represented by perl data structures: The spreadsheet itself could be a list of
lists, the elements of the latter lists being hash references, each describing one column.
You see, such a spreadsheet is an ideal object for the Storable(3) class. But now, for
something completely different:
#!/usr/local/bin/perl -wT # Note the -T switch! I mean it!
use 5.0004; # Yes, this really *is* required.
use strict; # Always a good choice.
use IO::Socket();
use RPC::pServer;
# Constants
$MY_APPLICATION = "Test Application";
$MY_VERSION = 1.0;
# Functions that the clients may execute; for simplicity
# these aren't designed in an object oriented manner.
# Function returning a simple scalar
sub sum ($$$$$) {
my($con, $data, $spreadsheet, $from, $to) = @_;
# Example: $from = A3, $to = B5
my($sum) = SpreadSheet::Sum($spreadsheet, $from, $to);
return (1, $sum);
}
# Function returning another spreadsheet, thus a complex object
sub double ($$$$$) {
my($con, $data, $spreadsheet, $from, $to);
# Doubles the region given by $from and $to, returns
# a spreadsheet
my($newSheet) = SpreadSheet::Double($spreadsheet, $from, $to);
(1, $newSheet);
}
# Quit function; showing the use of $data
sub quit ($$) {
my($con, $data) = @_;
$$data = 0; # Tell the server's Loop() method, that we
# are done.
(1, "Bye!");
}
# Now we give the handle functions a try. First of all, a
# spreadsheet constructor:
sub spreadsheet ($$$$) {
my ($con, $data, $rows, $cols) = @_;
my ($sheet, $handle);
if (!defined($sheet = SpreadSheet::Empty($rows, $cols))) {
$con->error = "Cannot create spreadsheet";
return (0, $con->error);
}
if (!defined($handle = StoreHandle($con, $data, $sheet))) {
return (0, $con->error); # StoreHandle stored error message
}
(1, $handle);
}
# Now a similar function to "double", except that a spreadsheet
# is doubled, which is stored locally on the server and not
# remotely on the client
sub rdouble ($$$$$) {
my($con, $data, $sHandle, $from, $to);
my($spreadsheet) = UseHandle($con, $data, $sHandle);
if (!defined($spreadsheet)) {
return (0, $con->error); # UseHandle stored an error message
}
# Doubles the region given by $from and $to, returns
# a spreadsheet
my($newSheet) = SpreadSheet::Double($spreadsheet, $from, $to);
my($handle);
if (!defined($handle = StoreHandle($con, $data, $newSheet))) {
return (0, $con->error); # StoreHandle stored error message
}
(1, $newSheet);
}
# This function is called for any valid connection to a client
# In a loop it processes the clients requests.
#
# Note, that we are using local data only, thus we should be
# safe in a multithreaded environment. (Of course, noone knows
# about the spreadsheet functions ... ;-)
sub Server ($) {
my($con) = shift;
my($con, $configFile, %funcTable);
my($running) = 1;
my(%handles) = (); # Note: handle hash is on the local stack
# First, create the servers function table. Note the
# references to the handle hash in entries that access
# the handle functions.
%funcTable = {
'sum' => { 'code' => &sum },
'double' => { 'code' => &list },
'quit' => { 'code' => &quit,
'data' = \$running }
'spreadsheet' => { 'code' => \&spreadsheet,
'handles' => \%handles },
'rdouble' => { 'code' => \&rdouble,
'handles' = \%handles },
# An alternative to the 'spreadsheet' entry above;
'NewHandle' => { 'code' => \&RPC::pServer::NewHandle,
'handles' => \%handles,
'classes' => [ 'Spreadsheet' ] },
# Give client access to *all* (!) spreadsheet methods
'CallMethod' => { 'code' => \&RPC::pServer::CallMethod,
'handles' => \%handles }
};
$con->{'funcTable'} = \%funcTable;
while($running) {
if (!$con->Loop()) {
$con->Log('err', "Exiting.\n"); # Error already logged
exit 10;
}
}
$con->Log('notice', "Client quits.\n");
exit 0;
}
# Avoid Zombie ball ...
sub childGone { my $pid = wait; $SIG{CHLD} = \&childGone; }
# Now for main
{
my ($iAmDaemon, $sock);
# Process command line arguments ...
...
# If running as daemon: Create a socket object.
if ($iAmDaemon) {
$sock = IO::Socket->new('Proto' => 'tcp',
'Listen' => SOMAXCONN,
'LocalPort' => 'wellKnownPort(42)',
'LocalAddr' => Socket::INADDR_ANY
);
} else {
$sock = undef; # Let RPC::pServer create a sock object
}
while (1) {
# Wait for a client establishing a connection
my $con = RPC::pServer('sock' => $sock,
'configFile' => 'testapp.conf');
if (!ref($con)) {
print STDERR "Cannot create server: $con\n";
} else {
if ($con->{'application'} ne $MY_APPLICATION) {
# Whatever this client wants to connect to:
# It's not us :-)
$con->Deny("This is a $MY_APPLICATION server. Go away");
} elsif ($con->{'version'} > $MY_VERSION) {
# We are running an old version of the protocol :-(
$con->Deny("Sorry, but this is version $MY_VERSION");
} elsif (!IsAuthorizedUser($con->{'user'},
$con->{'password'})) {
$con->Deny("Access denied");
} else {
# Ok, we accept the client. Spawn a child and let
# the child do anything else.
my $pid = fork();
if (!defined($pid)) {
$con->Deny("Cannot fork: $!");
} elsif ($pid == 0) {
# I am the child
$con->Accept("Welcome to the pleasure dome ...");
Server();
}
}
}
}
}
SECURITY
It has to be said: pRPC 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 in a a proper format
(currently integer numbers, but don't rely on that, it could change). If it is, then
it will still be verified, that an object with the given handle exists.
Be restrictive
Think twice, before you give a client access to a function. In particular, think
twice, before you give a client access to objects via the handle methods: If a client
can coerce CallMethod() on an object, he has access to *all* methods of that object!
perlsec
And just in case I forgot it: Read the "perlsec" man page. :-)
Protection against untrusted users
Host based authorization
pRPC has a builtin host based authorization scheme; use it! See "CONFIGURATION FILE".
User based authorization
pRPC has no builtin user based authorization scheme; that doesn't mean, that you
should not implement one.
Encryption
Using encryption with pRPC 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 DBD::pNET
agent for an example.
AUTHOR
Jochen Wiedmann, wiedmann@neckar-alb.de
SEE ALSO
Net::pRPC::Client(3), Storable(3), Sys::Syslog(3)
See DBD::pNET(3) for an example application.