AJAX and PHP: Building Responsive Web Applications源代码

								// reference the file containing the Chat class
				require_once("chat.class.php");
				// retrieve the operation to be performed
				$mode = $_POST['mode'];
				 
				// default the last id to 0
				$id = 0;
				// create a new Chat instance
				$chat = new Chat();
				// if the operation is SendAndRetrieve
				if($mode == 'SendAndRetrieveNew')
				{
				  // retrieve the action parameters used to add a new message
				  $name = $_POST['name']; 
				  $message = $_POST['message'];
				  $color = $_POST['color'];
				  $id = $_POST['id'];
				  
				  // check if we have valid values 
				  if ($name != '' && $message != '' && $color != '') 
				  {
				    // post the message to the database     
				    $chat->postMessage($name, $message, $color); 
				  }
				}
				// if the operation is DeleteAndRetrieve
				elseif($mode == 'DeleteAndRetrieveNew')
				{
				  // delete all existing messages
				  $chat->deleteMessages();         
				}
				// if the operation is Retrieve
				elseif($mode == 'RetrieveNew')
				{
				  // get the id of the last message retrieved by the client
				  $id = $_POST['id'];    
				}
				// Clear the output
				if(ob_get_length()) ob_clean();
				// Headers are sent to prevent browsers from caching
				header('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); 
				header('Last-Modified: ' . gmdate('D, d M Y H:i:s') . 'GMT'); 
				header('Cache-Control: no-cache, must-revalidate'); 
				header('Pragma: no-cache');
				header('Content-Type: text/xml');
				// retrieve new messages from the server
				echo $chat->retrieveNewMessages($id);
				?>