6. Using XML-RPC with Perl

Ken MacLeod has implemented XML-RPC for Perl. You can find his Frontier::RPC module at his website or through CPAN.

To install Frontier::RPC, download the package and compile it in the standard fashion:

bash$ gunzip -c Frontier-RPC-0.07b1.tar.gz | tar xvf -
bash$ cd Frontier-RPC-0.07b1
bash$ perl Makefile.PL
bash$ make
bash$ make test
bash$ su -c 'make install'

(The process will be slightly different on Windows systems, or if you don't have root access. Consult your Perl documentation for details.)

6.1. A Perl Client

The following program shows how to call an XML-RPC server from Perl:

use Frontier::Client;

# Make an object to represent the XML-RPC server.
$server_url = 'http://xmlrpc-c.sourceforge.net/api/sample.html';
$server = Frontier::Client->new(url => $server_url);

# Call the remote server and get our result.
$result = $server->call('sample.sumAndDifference', 5, 3);
$sum = $result->{'sum'};
$difference = $result->{'difference'};

print "Sum: $sum, Difference: $difference\n";

6.2. A Stand-Alone Perl Server

The following program shows how to write an XML-RPC server in Perl:

use Frontier::Daemon;

sub sumAndDifference {
    my ($x, $y) = @_;
    return {'sum' => $x + $y, 'difference' => $x - $y};
}

# Call me as http://localhost:8080/RPC2
$methods = {'sample.sumAndDifference' => \&sumAndDifference};
Frontier::Daemon->new(LocalPort => 8080, methods => $methods)
    or die "Couldn't start HTTP server: $!";

6.3. A CGI-Based Perl Server

Frontier::RPC2 doesn't provide built-in support for CGI-based servers. It does, however, provide most of the pieces you'll need.

Save the following code as sumAndDifference.cgi in your web server's cgi-bin directory. (On Unix systems, you'll need to make it executable by typing chmod +x sumAndDifference.cgi.)

#!/usr/bin/perl -w

use strict;
use Frontier::RPC2;

sub sumAndDifference {
    my ($x, $y) = @_;
    return {'sum' => $x + $y, 'difference' => $x - $y};
}

process_cgi_call({'sample.sumAndDifference' => \&sumAndDifference});


#==========================================================================
#  CGI Support
#==========================================================================
#  Simple CGI support for Frontier::RPC2. You can copy this into your CGI
#  scripts verbatim, or you can package it into a library.
#  (Based on xmlrpc_cgi.c by Eric Kidd <http://xmlrpc-c.sourceforge.net/>.)

# Process a CGI call.
sub process_cgi_call ($) {
    my ($methods) = @_;

    # Get our CGI request information.
    my $method = $ENV{'REQUEST_METHOD'};
    my $type = $ENV{'CONTENT_TYPE'};
    my $length = $ENV{'CONTENT_LENGTH'};

    # Perform some sanity checks.
    http_error(405, "Method Not Allowed") unless $method eq "POST";
    http_error(400, "Bad Request") unless $type eq "text/xml";
    http_error(411, "Length Required") unless $length > 0;

    # Fetch our body.
    my $body;
    my $count = read STDIN, $body, $length;
    http_error(400, "Bad Request") unless $count == $length; 

    # Serve our request.
    my $coder = Frontier::RPC2->new;
    send_xml($coder->serve($body, $methods));
}

# Send an HTTP error and exit.
sub http_error ($$) {
    my ($code, $message) = @_;
    print <<"EOD";
Status: $code $message
Content-type: text/html

<title>$code $message</title>
<h1>$code $message</h1>
<p>Unexpected error processing XML-RPC request.</p>
EOD
    exit 0;
}

# Send an XML document (but don't exit).
sub send_xml ($) {
    my ($xml_string) = @_;
    my $length = length($xml_string);
    print <<"EOD";
Status: 200 OK
Content-type: text/xml
Content-length: $length

EOD
    # We want precise control over whitespace here.
    print $xml_string;
}

You can copy the utility routines into your own CGI scripts.