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XML-RPC and XML-RPC Server Classes
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<h1>XML-RPC and XML-RPC Server Classes</h1>
<p>Code Igniter's XML-RPC classes permit you to send requests to another server, or set up
your own XML-RPC server to receive requests.</p>
<h2>What is XML-RPC?</h2>
<p>Quite simply it is a way for two computers to communicate over the internet using XML.
One computer, which we will call the <dfn>client</dfn>, sends an XML-RPC <strong>request</strong> to
another computer, which we will call the <dfn>server</dfn>. Once the server receives and processes the request it
will send back a <strong>response</strong> to the client.</p>
<p>For example, using the MetaWeblog API, an XML-RPC Client (usually a desktop publishing tool) will
send a request to an XML-RPC Server running on your site. This request might be a new weblog entry
being sent for publication, or it could be a request for an existing entry for editing.
When the XML-RPC Server receives this request it will examine it to determine which class/method should be called to process the request.
Once processed, the server will then send back a response message.</p>
<p>For detailed specifications, you can visit the <a href="http://www.xmlrpc.com/">XML-RPC</a> site.</p>
<h2>Initializing the Class</h2>
<p>Like most other classes in Code Igniter, the XML-RPC and XML-RPCS classes are initialized in your controller using the <dfn>$this->load->library</dfn> function:</p>
<p>To load the XML-RPC class you will use:
<code>$this->load->library('xmlrpc');</code>
<p>Once loaded, the xml-rpc library object will be available using: <dfn>$this->xmlrpc</dfn></p>
<p>To load the XML-RPC Server class you will use:
<code>
$this->load->library('xmlrpc');<br />
$this->load->library('xmlrpcs');
</code>
<p>Once loaded, the xml-rpcs library object will be available using: <dfn>$this->xmlrpcs</dfn></p>
<p class="important"><strong>Note:</strong> When using the XML-RPC Sever class you must load BOTH the XML-RPC class and the XML-RPC Server class.</p>
<h2>Sending XML-RPC Requests</h2>
<p>To send a request to an XML-RPC server you must specify the following information:</p>
<ul>
<li>The URL of the server</li>
<li>The method on the server you wish to call</li>
<li>The <em>request</em> data (explained below).</li>
</ul>
<p>Here is a basic example that sends a simple Weblogs.com ping to the <a href="http://pingomatic.com/">Ping-o-Matic</a></p>
<code>$this->load->library('xmlrpc');<br />
<br />
$this->xmlrpc->server('http://rpc.pingomatic.com/', 80);<br />
$this->xmlrpc->method('weblogUpdates.ping');<br />
<br />
$request = array('My Photoblog', 'http://www.my-site.com/photoblog/');<br />
$this->xmlrpc->request($request);<br />
<br />
if ( ! $this->xmlrpc->send_request())<br />
{<br />
echo $xmlrpc->display_error();<br />
}
</code>
<h3>Explanation</h3>
<p>The above code initializes the XML-RPC class, sets the server URL and method to be called (weblogUpdates.ping). The
request (in this case, the title and URL of your site) is placed into an array for transportation, and
compiled using the request() function.
Lastly, the full request is sent. If the <dfn>send_request()</dfn> method returns false we will display the error message
sent back from the XML-RPC Server.</p>
<h2>Anatomy of a Request</h2>
<p>An XML-RPC <dfn>request</dfn> is simply the data you are sending to the XML-RPC server. Each piece of data in a request
is referred to as a <dfn>request parameter</dfn>. The above example has two parameters:
The URL and title of your site. When the XML-RPC server receives your request, it will look for parameters it requires.</p>
<p>Request parameters must be placed into an array for transportation, and each parameter can be one
of seven data types (strings, numbers, dates, etc.). If your parameters are something other than strings
you will have to include the data type in the request array.</p>
<p>Here is an example of a simple array with three parameters:</p>
<code>$request = array('John', 'Doe', 'www.some-site.com');<br />
$this->xmlrpc->request($request);</code>
<p>If you use data types other than strings, or if you have several different data types, you will place
each parameter into its own array, with the data type in the second position:</p>
<code>
$request = array (<br />
array('John', 'string'),<br />
array('Doe', 'string'),<br />
array(FALSE, 'boolean'),<br />
array(12345, 'int')<br />
);
<br />
$this->xmlrpc->request($request);</code>
The <a href="#datatypes">Data Types</a> section below has a full list of data types.</p>
<h2>Creating an XML-RPC Server</h2>
<p>An XML-RPC Server acts as a traffic cop of sorts, waiting for incoming requests and redirecting them to the
appropriate functions for processing.</p>
<p>To create your own XML-RPC server involves initializing the XML-RPC Server class in your controller where you expect the incoming
request to appear, then setting up an array with mapping instructions so that incoming requests can be sent to the appropriate
class and method for processing.</p>
<p>Here is an example to illustrate:</p>
<code>
$this->load->library('xmlrpcs');<br />
$this->load->library('xmlrpcs');<br />
<br />
$config['functions']['<var>new_post</var>']; = array('function' => '<dfn>My_blog.new_entry</dfn>');<br />
$config['functions']['<var>update_post</var>'] = array('function' => '<dfn>My_blog.update_entry</dfn>');<br />
<br />
$this->xmlrpcs->initialize($config);<br />
$this->xmlrpcs->serve();</code>
<p>The above example contains an array specifying two method requests that the Server allows.
The allowed methods are on the left side of the array. When either of those are received, they will be mapped to the class and method on the right.
<p>In other words, if an XML-RPC Client sends a request for the <var>new_post</var> method, your
server will load the <dfn>My_blog</dfn> class and call the <dfn>new_entry</dfn> function.
If the request is for the <var>update_post</var> method, your
server will load the <dfn>My_blog</dfn> class and call the <dfn>update_entry</dfn> function.</p>
<p>The function names in the above example are arbitrary. You'll decide what they should be called on your server,
or if you are using standardized APIs, like the Blogger or MetaWeblog API, you'll use their function names.</p>
<h2>Processing Server Requests</h2>
<p>When the XML-RPC Server receives a request and loads the class/method for processing, it will pass
an object to that method containing the data sent by the client.</p>
<p>Using the above example, if the <var>new_post</var> method is requested, the server will expect a class
to exist with this prototype:</p>
<code>class <kbd>My_blog</kbd> extends Controller {<br />
<br />
function <kbd>new_post</kbd>(<var>$request</var>)<br />
{<br />
<br />
}<br />
}
</code>
<p>The <var>$request</var> variable is an object compiled by the Server, which contains the data sent by the XML-RPC Client.
Using this object you will have access to the <em>request parameters</em> enabling you to process the request. When
you are done you will send a <dfn>Response</dfn> back to the Client.<p>
<p>Below is a real-world example, using the Blogger API. One of the methods in the Blogger API is <dfn>getUserInfo()</dfn>.
Using this method, an XML-RPC Client can send the Server a username and password, in return the Server sends
back information about that particular user (nickname, user ID, email address, etc.). Here is how the processing
function might look:</p>
<code>class <kbd>My_blog</kbd> extends Controller {<br />
<br />
function <kbd>getUserInfo</kbd>(<var>$request</var>)<br />
{<br />
$username = 'smitty';<br />
$password = 'secretsmittypass';<br /><br />
$this->load->library('xmlrpc');<br />
<br />
$parameters = $request->output_parameters();<br />
<br />
if ($parameters['1'] != $username AND $parameters['2'] != $password)<br />
{<br />
return $this->xmlrpc->send_error_message('100', 'Invalid Access');<br />
}<br />
<br />
$response = array(array('nickname' => array('Smitty','string'),<br />
'userid' => array('99','string'),<br />
'url' => array('http://yoursite.com','string'),<br />
'email' => array('jsmith@yoursite.com','string'),<br />
'lastname' => array('Smith','string'),<br />
'firstname' => array('John','string')<br />
),<br />
'struct');<br />
<br />
$this->xmlrpc->send_response($response);<br />
}<br />
}
</code>
<h3>Notes:</h3>
<p>The <dfn>output_parameters()</dfn> function retrieves an indexed array corresponding to the request parameters sent by the client.
In the above example, the output parameters will be the username and password.</p>
<p>If the username and password sent by the client were not valid, and error message is returned using <dfn>send_error_message()</dfn>.</p>
<p>If the operation was successful, the client will be sent back a response array containing the user's info.</p>
<h2>Formatting a Response</h2>
<p>Similar to <em>Requests</em>, <em>Responses</em> must be formatted as an array. However, unlike requests, a response is an array
<strong>that contains a single item</strong>. This item can be an array with several additional arrays, but there
can be only one primary array index. In other words, the basic prototype is this:</p>
<code>$request = array('Response data', 'array');</code>
<p>Responses, however, usually contain multiple pieces of information. In order to accomplish this we must put the response into its own
array so that the primary array continues to contain a single piece of data. Here's an example showing how this might be accomplished:</p>
<code>
$request = array (<br />
array(<br />
'first_name' => array('John', 'string'),<br />
'last_name' => array('Doe', 'string'),<br />
'member_id' => array(123435, 'int'),<br />
'todo_list' => array(array('clean house', 'call mom', 'water plants'), 'array'),<br />
),<br />
'struct'<br />
);
</code>
<p class="important">Notice that the above array is formatted as a <dfn>struct</dfn>. This is the most common data type for responses.</p>
<p>As with Requests, a response can be on of the seven data types listed in the <a href="#datatypes">Data Types</a> section.</p>
<h2>Sending an Error Response</h2>
<p>If you need to send the client an error response you will use the following:</p>
<code>return $this->xmlrpc->send_error_message('123', 'Requested data not available');</code>
<p>The first parameter is the error number while the second parameter is the error message.</p>
<h2>Creating Your Own Client and Server</h2>
<p>To help you understand everything we've covered thus far, let's create a couple controllers that act as
XML-RPC Client and Server. You'll use the Client to send a request to the Server and receive a response.</p>
<h3>The Client</h3>
<p>Using a text editor, create a controller called <dfn>xmlrpc_client.php</dfn>.
In it, place this code and save it to your <samp>applications/controllers/</samp> folder:</p>
<textarea class="textarea" style="width:100%" cols="50" rows="32"><?php
class Xmlrpc_client extends Controller {
function index()
{
$this->load->helper('url');
$server_url = site_url('xmlrpc_server');
$this->load->library('xmlrpc');
$this->xmlrpc->server($server_url, 80);
$this->xmlrpc->method('Greetings');
$request = array('How is it going?');
$this->xmlrpc->request($request);
if ( ! $this->xmlrpc->send_request())
{
echo $this->xmlrpc->display_error();
}
else
{
echo '<pre>';
print_r($this->xmlrpc->display_response());
echo '</pre>';
}
}
}
?></textarea>
<p>Note: In the above code we are using a "url helper". You can find more information in the <a href="../general/helpers.html">Helpers Functions</a> page.</p>
<h3>The Server</h3>
<p>Using a text editor, create a controller called <dfn>xmlrpc_server.php</dfn>.
In it, place this code and save it to your <samp>applications/controllers/</samp> folder:</p>
<textarea class="textarea" style="width:100%" cols="50" rows="30"><?php
class Xmlrpc_server extends Controller {
function index()
{
$this->load->library('xmlrpc');
$this->load->library('xmlrpcs');
$config['functions']['Greetings'] = array('function' => 'Xmlrpc_server.process');
$this->xmlrpcs->initialize($config);
$this->xmlrpcs->serve();
}
function process($request)
{
$parameters = $request->output_parameters();
$response = array(
array(
'you_said' => $parameters['0'],
'i_respond' => 'Not bad at all.'),
'struct');
return $this->xmlrpc->send_response($response);
}
}
?></textarea>
<h3>Try it!</h3>
<p>Now visit the your site using a URL similar to this:</p>
<code>www.your-site.com/index.php/<var>xmlrpc_client</var>/</code>
<p>You should now see the message you sent to the server, and its response back to you.</p>
<p>The client you created sends a message ("How's is going?") to the server, along with a reqest for the "Greetings" method.
The Server receives the request and maps it to the "process" function, where a response is sent back.</p>
<p> </p>
<h1>XML-RPC Function Reference</h1>
<h2>$this->xmlrpc->server()</h2>
<p>Sets the URL and port number of the server to which a request is to be sent:</p>
<code>$this->xmlrpc->server('http://www.sometimes.com/pings.php', 80);</code>
<h2>$this->xmlrpc->timeout()</h2>
<p>Set a time out period (in seconds) after which the request will be canceled:</p>
<code>$this->xmlrpc->timeout(6);</code>
<h2>$this->xmlrpc->method()</h2>
<p>Sets the method that will be requested from the XML-RPC server:</p>
<code>$this->xmlrpc->method('<var>method</var>');</code>
<p>Where <var>method</var> is the name of the method.</p>
<h2>$this->xmlrpc->request()</h2>
<p>Takes an array of data and builds request to be sent to XML-RPC server:</p>
<code>$request = array(array('My Photoblog', 'string'), 'http://www.yoursite.com/photoblog/');<br />
$this->xmlrpc->request($request);</code>
<h2>$this->xmlrpc->send_request()</h2>
<p>The request sending function. Returns boolean TRUE or FALSE based on success for failure, enabling it to be used conditionally.</p>
<h2>$this->xmlrpc->set_debug(TRUE);</h2>
<p>Enables debugging, which will display a variety of information and error data helpful during development.</p>
<h2>$this->xmlrpc->display_error()</h2>
<p>Returns an error message as a string if your request failed for some reason.</p>
<code>echo $this->xmlrpc->display_error();</code>
<h2>$this->xmlrpc->display_response()</h2>
<p>Returns the response from the remote server once request is received. The response will typically be an associative array.</p>
<code>$this->xmlrpc->display_response();</code>
<h2>$this->xmlrpc->send_error_message()</h2>
<p>This function lets you send an error message from your server to the client. First parameter is the error number while the second parameter
is the error message.</p>
<code>return $this->xmlrpc->send_error_message('123', 'Requested data not available');</code>
<h2>$this->xmlrpc->send_response()</h2>
<p>Lets you send the response from your server to the client. An array of valid data values must be sent with this method.</p>
<code>$response = array(<br />
array(<br />
'flerror' => array(FALSE, 'boolean'),<br />
'message' => "Thanks for the ping!")<br />
)<br />
'struct');<br />
return $this->xmlrpc->send_response($response);</code>
<a name="datatypes"></a>
<h2>Data Types</h2>
<p>According to the <a href="http://www.xmlrpc.com/spec">XML-RPC spec</a> there are seven types
of values that you can send via XML-RPC:</p>
<ul>
<li><em>int</em> or <em>i4</em></li>
<li><em>boolean</em></li>
<li><em>string</em></li>
<li><em>double</em></li>
<li><em>dateTime.iso8601</em></li>
<li><em>base64</em></li>
<li><em>struct</em> (contains array of values)</li>
<li><em>array</em> (contains array of values)</li>
</ul>
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