XML-RPC is a standard for sending Procedure Calls (e.g. function calls) to Remote systems. It sends XML data over HTTP that remote system then handles.

LSL receives XML-RPC requests and passes them to the prim specified. It may not establish this connection, but it may reply and keep two-way communication with that server. These responses seem to be able to transport the largest amount of data out of Second Life (vs. Email and HTTP Requests).

IMPORTANT IMPLEMENTATION NOTE:

The current implementation of XML-RPC only allows ONE request to be queued on the front-end server (xmlrpc.secondlife.com) at a time. Any additional requests to the same data channel overwrite any pending one. This has serious ramifications for the design of XML-RPC communications where the in-world object could receive requests faster than it can respond to them. In addition, the 3-second delay in llRemoteDataReply exacerbates this problem even more.

The observed issue is this: if you send multiple quick requests to an in-world object via XML-RPC, one which is scripted to perform some processing and then return a response (via llRemoteDataReply), there is a potential for earlier requests to get lost on the front end server (they still should generate remote_data events, though), and have the response meant for an earlier request end up being passed back to a later one, while the earlier requests will time out back at your external application.

As a result, if you intend to do any serious work with XML-RPC, you will have to design your external client application to manually serialize all requests to each individual RPC channel. That means you have to wait for a response from the previous request before you attempt to send the next one. If you don't care about receiving responses, then this problem is not an issue, as all requests seem to get passed on to the script, regardless of the queueing issue.

Also note that there is NO way to get around the 3-second delay for llRemoteDataReply; you cannot use the multiple-slave-comm-script trick, because XML-RPC channels are *script-specific*, NOT *object-specific*.

For more information, see these forum threads here and here.

Other Resources

• XMLRPC.com
• Incutio's XML-RPC PHP library

Example

php

To initialize a xmlrpc from an external server you'll need some kind of web-application. One language to create a webapplication in is PHP. Here is an example of how to send a xmlrpc message to your SL-script from a webserver using PHP:

<?php
	echo '<pre>';
	$channel = ""; //Fill in the channel you are using (key)
	$xmldata = "<?xml version=\"1.0\"?><methodCall><methodName>llRemoteData</methodName><params><param><value><struct><member><name>Channel</name><value><string>".$channel."</string></value></member><member><name>IntValue</name><value><int>11261979</int></value></member><member><name>StringValue</name><value><string>happy birthday</string></value></member></struct></value></param></params></methodCall>";
	echo sendToHost("xmlrpc.secondlife.com", "POST", "/cgi-bin/xmlrpc.cgi", $xmldata);
	echo '</pre>';
	
	function sendToHost($host,$method,$path,$data,$useragent=0)
	{ 
		$buf="";
		// Supply a default method of GET if the one passed was empty 
		if (empty($method)) 
			$method = 'GET'; 
		$method = strtoupper($method); 
	
		$fp = fsockopen($host, 80, $errno, $errstr, 30);
	
		if( !$fp )
		{
			$buf = "$errstr ($errno)<br />\n";
		}else
		{
			if ($method == 'GET') 
			$path .= '?' . $data; 
			fputs($fp, "$method $path HTTP/1.1\r\n"); 
			fputs($fp, "Host: $host\r\n"); 
			fputs($fp, "Content-type: text/xml\r\n"); 
			fputs($fp, "Content-length: " . strlen($data) . "\r\n"); 
			if ($useragent) 
				fputs($fp, "User-Agent: MSIE\r\n"); 
			fputs($fp, "Connection: close\r\n\r\n"); 
			if ($method == 'POST') 
				fputs($fp, $data); 
			while (!feof($fp)) 
				$buf .= fgets($fp,128); 
			fclose($fp); 
		}
		return $buf; 
	} 
?>

perl

The perl code and corresponding LSL code to contact an object in Second Life is given below. The perl code makes use of the RPC::XML module. You can run the perl code from the command line. It creates an rpc object and sends a message to an object that is rezzed on the grid. Note that you have to supply the UUID of the object within the perl code.

The perl code sends the message that contains the string "Message to pass" and the number "2007." The LSL code responds by sending the string "I got it" and the number "2008."

#!/usr/bin/perl
# 

use RPC::XML;
use RPC::XML::Parser;
use RPC::XML::Client;

my $llURL = "http://xmlrpc.secondlife.com/cgi-bin/xmlrpc.cgi";
$P = RPC::XML::Parser->new();

my $cli = RPC::XML::Client->new($llURL);
my $req = RPC::XML::request->new(
        "llRemoteData",
        {'Channel' => RPC::XML::string->new("UUID for the open channel from the object GOES HERE!"),
        'IntValue' => RPC::XML::int->new(2007),
        'StringValue' => RPC::XML::string->new("message to pass")});

#  Print out the message to send
print "ref(req): ",ref($req),"\n";
$xml = $req->as_string();
print "Length: ",$req->length,"\n\n",$xml,"\n\n";

$res = $P->parse($xml);
print ref($res),"\n";
if (ref($res)) {
    %h = %{$res->args->[0]->value};
    foreach $lupe (keys %h) {
       print "$lupe: $h{$lupe}\n";
    }
}

#  Submit the request to send the information above.
my $resp = $cli->send_request($req);


#  Print out the response
print "\n\n\nResponse\n";
print "ref(resp): ",ref($resp),"\n";
$xml = $resp->as_string();
print "Length: ",$resp->length,"\n\n",$xml,"\n\n";

$res = $P->parse($xml);
print ref($res),"\n";
if (ref($res)) {
    %h = %{$res->value};
    foreach $lupe (keys %h) {
       $val =  $h{$lupe};
       print "$lupe: $val\n";
    }
}

Corresponding LSL code:

key remoteChannel;
init() {
    llOpenRemoteDataChannel(); // create an XML-RPC channel
    llOwnerSay("My key is " + (string)llGetKey());
}

default {
    state_entry() {
        init();
    }
    
    state_exit() {
        return;
    }
                                
    on_rez(integer param) {
        llResetScript();        
    }
                                
    remote_data(integer type, key channel, key message_id, string sender, integer ival, string sval) {
         if (type == REMOTE_DATA_CHANNEL) { // channel created
             llSay(DEBUG_CHANNEL,"Channel opened for REMOTE_DATA_CHANNEL" + 
                (string)channel + " " + (string)message_id + " " + (string)sender + " " +                         
                (string)ival + " " + (string)sval);
             remoteChannel = channel;
             llOwnerSay("Ready to receive requests on channel \"" + (string)channel + "\"");                        
             state receiving; // start handling requests
         } else {
             llSay(DEBUG_CHANNEL,"Unexpected event type"); 
         }                      
     }                 
}                     
                                

state receiving {

    state_entry() {
        llOwnerSay("Ready to receive information from outside SL");
    }  
    
    state_exit() {
        llOwnerSay("No longer receiving information from outside SL.");
         llCloseRemoteDataChannel(remoteChannel);
    }
    
    on_rez(integer param) {
        llResetScript();
    }
    
    remote_data(integer type, key channel, key message_id, string sender, integer ival, string sval) {
        if (type == REMOTE_DATA_REQUEST) { // handle requests sent to us
             llSay(DEBUG_CHANNEL,"Request received for REMOTE_DATA_REQUEST " + (string)channel + " " +
                (string)message_id + " " + (string)sender + " " + (string)ival + " " + (string)sval);
            llRemoteDataReply(channel,NULL_KEY,"I got it",2008);
            llOwnerSay("I just recieved data in "+ llGetRegionName() + 
                        " at position " + (string)llGetPos() + "\n" +
                       "The string was " +  sval + "\nThe number was " + (string)ival + ".");
        }
    }
    
}