Build your own Web Service with PHP and XML-RPC

Preparations

1. Download the code archive for this article -- it'll save you from laboriously cutting and pasting the code from the pages of this tutorial.

2. Download the source code from http://www.keithdevens.com/software/xmlrpc/source.php and save it as "kd_xmlrpc.php".

3. Now create a directory on your Web server called kd_xmlrpc, below your Web root (where your "home page" lives), and place kd_xmlrpc.php there. We'll be putting all the other files we create below in the same directory.

4. Create a table in your MySQL database using this query:

CREATE TABLE kd_xmlrpc_news (    
 news_id mediumint(9) NOT NULL auto_increment,    
 title varchar(255) default NULL,    
 short_desc text,    
 full_desc text,    
 author varchar(100) default NULL,    
 date datetime NOT NULL default '0000-00-00 00:00:00',    
 PRIMARY KEY  (news_id)    
) TYPE=MyISAM COMMENT='XML RPC News';

4. Now INSERT some dummy news items into the table -- or, if you're lacking inspiration, run the "kd_xmlrpc_news.sql" query you'll find in the code archive (downloaded in step 1).

The XML-RPC Server

The database is now ready for action. Next, let's create the XML-RPC server, and call it "server.php":

<?php    
/* server.php */    
   
/* Variables for accessing MySQL */    
$dbserver= "localhost";     // Hostname of your MySQL server    
$db = "database_name";      // Name of your MySQL database    
$dbuser = "username";       // MySQL user with access to $db    
$dbpassword = "password";   // Password for MySQL user    
   
/* Connect to the MySQL server */    
$link = @mysql_connect ($dbserver, $dbuser, $dbpassword);    
if (! $link){    
   echo ( "Unable to connect to db" );    
exit();    
}    
   
/* Select the database */    
if (!mysql_select_db ($db, $link) ){    
exit ();    
}    
   
/* Include Keith's xml-rpc library */    
include("kd_xmlrpc.php");    
   
/* Include a file that defines all the xml-rpc "methods" */    
include("web_service_api.php");    
   
/* Now use the XMLRPC_parse function to take POST    
  data from what xml-rpc client connects and turn    
  it into normal PHP variables */    
$xmlrpc_request = XMLRPC_parse($GLOBALS['HTTP_RAW_POST_DATA']);    
   
/* From the PHP variables generated, let's get the    
  method name ie. server asks "What would you like    
  me to do for you?" */    
$methodName = XMLRPC_getMethodName($xmlrpc_request);    
   
/* Get the parameters associated with that method    
  e.g "So you want to view a news item. Tell me    
  which one you want. What's the id#?" */    
$params = XMLRPC_getParams($xmlrpc_request);    
   
/* Error check - if a method was used that doesn't    
  exist, return the error response to the client */    
if(!isset($xmlrpc_methods[$methodName])){    
   $xmlrpc_methods['method_not_found']($methodName);    
   
/* Otherwise, let's run the PHP function corresponding    
  to that method - note the functions themselves    
  return the correct formatted xml-rpc response    
  to the client */    
}else{    
   
   /* Call the method - notice $params[0] not just $params as the    
   documentation states. */    
   $xmlrpc_methods[$methodName]($params[0]);    
}    
?>

Here's a quick summary of what happens within server.php:

1. Connect to MySQL to give the script access to the database.
2. Include the kd_xmlrpc.php code so we can use Keith's functions.
3. Include web_service_api.php, which defines the XML-RPC methods (see below).
4. Use the XMLRPC_parse() function to take the contents of $GLOBALS['HTTP_RAW_POST_DATA'], which contains the request from an XML-RPC client, and convert the XML into PHP variables.
5. Now determine which XML-RPC method has been called, using the XMLRPC_getMethodName() function. We want the same XML-RPC server to be capable of more than one task (method/function), and here's where we determine which one we'll carry out for the current request (e.g "news.getNewsList" or "news.viewNewsItem").
6. Now check for any parameters sent in the client request, such as an "id" (identifying number) of a news item.
7. Finally we check that the method exists, as defined in web_service_api.php, and if everything looks good, we run th method (i.e. PHP function) required. If we can't find the method, we run the default "method_not_found" method.

The special XML-RPC functions we used were:

• XMLRPC_parse(): this function takes some XML and turns it into PHP variables -- so the XML from the client's request is converted to a form that PHP can work with. At this point, this isn't specific to the XML-RPC standard -- any XML that's sent will be converted to PHP variables.
• XMLRPC_getMethodName() determine which method is being used so we can decide which PHP function to use.
• XMLRPC_getParams() takes any XML-RPC parameters and converts them to PHP variables.

That's basically the XML-RPC server finished. In general, this is what you'd do for every XML-RPC server you build. Not hard, was it? Now all we need are those PHP functions to be used with the methods...