Malcolm H. Nooning > PlRPC-0.2020 > RPC::PlClient

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NAME ^

RPC::PlClient - Perl extension for writing PlRPC clients

SYNOPSIS ^

  require RPC::PlClient;

  # Create a client object and connect it to the server
  my $client = RPC::PlClient->new('peeraddr' => 'joes.host.de',
                                  'peerport' => 2570,
                                  'application' => 'My App',
                                  'version' => '1.0',
                                  'user' => 'joe',
                                  'password' => 'hello!');

  # Create an instance of $class on the server by calling $class->new()
  # and an associated instance on the client.
  my $object = $client->Call('NewHandle', $class, 'new', @args);


  # Call a method on $object, effectively calling the same method
  # on the associated server instance.
  my $result = $object->do_method(@args);

DESCRIPTION ^

PlRPC (Perl RPC) is a package that simplifies the writing of Perl based client/server applications. RPC::PlServer is the package used on the server side, and you guess what RPC::PlClient is for. See RPC::PlServer(3) for this part.

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 a function call

    @result = $client->Call('multiply', $a, $b);

on the client will be mapped to a corresponding call

    $server->multiply($a, $b);

on the server. The function calls result will be transferred to the client and returned as result of the clients method. Simple, eh? :-)

Client methods

$client = new(%attr);

(Class method) The client constructor. Returns a client object, connected to the server. A Perl exception is thrown in case of errors, thus you typically use it like this:

    $client = eval { RPC::PlClient->new ( ... ) };
    if ($@) {
        print STDERR "Cannot create client object: $@\n";
        exit 0;
    }

The method accepts a list of key/value pairs as arguments. Known arguments are:

peeraddr
peerport
socket_proto
socket_type
timeout

These correspond to the attributes PeerAddr, PeerPort, Proto, Type and Timeout of IO::Socket::INET. The server connection will be established by passing them to IO::Socket::INET->new().

socket

After a connection was established, the IO::Socket instance will be stored in this attribute. If you prefer establishing the connection on your own, you may as well create an own instance of IO::Socket and pass it as attribute socket to the new method. The above attributes will be ignored in that case.

application
version
user
password

it is part of the PlRPC 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 arguments are handled by the servers Application, Version and User methods.

compression

Set this to off (default, no compression) or gzip (requires the Compress::Zlib module).

cipher

This attribute can be used to add encryption quite easily. PlRPC 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.

Note that 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.

Example:

    use Crypt::DES;
    $cipher = Crypt::DES->new(pack("H*", "0123456789abcdef"));
    $client = RPC::PlClient->new('cipher' => $cipher,
                                ...);
maxmessage

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.

debug

Enhances logging level by emitting debugging messages.

logfile

By default the client is logging to syslog (Unix) or the event log (Windows). If neither is available or you pass a TRUE value as logfile, then logging will happen to the given file handle, an instance of IO::Handle. If the value is scalar, then logging will occur to stderr.

Examples:

  # Logging to stderr:
  my $client = RPC::PlClient->new('logfile' => 1, ...);

  # Logging to 'my.log':
  my $file = IO::File->new('my.log', 'a')
      || die "Cannot create log file 'my.log': $!";
  my $client = RPC::PlClient->new('logfile' => $file, ...);
@result = $client->Call($method, @args);

(Instance method) Calls a method on the server; the arguments are a method name of the server class and the method call arguments. It returns the method results, if successfull, otherwise a Perl exception is thrown.

Example:

  @results = eval { $client->Call($method, @args };
  if ($@) {
      print STDERR "An error occurred while executing $method: $@\n";
      exit 0;
  }
$cobj = $client->ClientObject($class, $method, @args)

(Instance method) A set of predefined methods is available that make dealing with client side objects incredibly easy: In short the client creates a representation of the server object for you. Say we have an object $sobj on the server and an associated object $cobj on the client: Then a call

  @results = $cobj->my_method(@args);

will be immediately mapped to a call

  @results = $sobj->my_method(@args);

on the server and the results returned to you without any additional programming. Here's how you create $cobj, an instance of RPC::PlClient::Object:

  my $cobj = $client->ClientObject($class, 'new', @args);

This will trigger a call

  my $sobj = $class->new(@args);

on the server for you. Note that the server has the ability to restrict access to both certain classes and methods by setting $server->{'methods'} appropriately.

EXAMPLE ^

We'll create a simple example application, an MD5 client. The server will have installed the MD5 module and create digests for us. We present the client part only, the server example is part of the RPC::PlServer man page. See RPC::PlServer(3).

    #!/usr/local/bin/perl

    use strict;               # Always a good choice.

    require RPC::PlClient;

    # Constants
    my $MY_APPLICATION = "MD5_Server";
    my $MY_VERSION = 1.0;
    my $MY_USER = "";           # The server doesn't require user
    my $MY_PASSWORD = "";       # authentication.

    my $hexdigest = eval {
        my $client = RPC::PlClient->new
            ('peeraddr'    => '127.0.0.1',
             'peerport'    => 2000,
             'application' => $MY_APPLICATION,
             'version'     => $MY_VERSION,
             'user'        => $MY_USER,
             'password'    => $MY_PASSWORD);

        # Create an MD5 object on the server and an associated
        # client object. Executes a
        #     $context = MD5->new()
        # on the server.
        my $context = $client->ClientObject('MD5', 'new');

        # Let the server calculate a digest for us. Executes a
        #     $context->add("This is a silly string!");
        #     $context->hexdigest();
        # on the server.
        $context->add("This is a silly string!");
        $context->hexdigest();
    };
    if ($@) {
        die "An error occurred: $@";
    }

    print "Got digest $hexdigest\n";

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 ^

PlRPC::Server(3), Net::Daemon(3), Storable(3), Sys::Syslog(3), Win32::EventLog

An example application is the DBI Proxy client:

DBD::Proxy(3).

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