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<td><h1>CodeIgniter User Guide Version 2.1.3</h1></td>
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<h1>Trackback Class</h1>
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<p>The Trackback Class provides functions that enable you to send and receive Trackback data.</p>
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<p>If you are not familiar with Trackbacks you'll find more information <a href="http://en.wikipedia.org/wiki/Trackback">here</a>.</p>
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<h2>Initializing the Class</h2>
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<p>Like most other classes in CodeIgniter, the Trackback class is initialized in your controller using the <dfn>$this->load->library</dfn> function:</p>
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<code>$this->load->library('trackback');</code>
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<p>Once loaded, the Trackback library object will be available using: <dfn>$this->trackback</dfn></p>
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<h2>Sending Trackbacks</h2>
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<p>A Trackback can be sent from any of your controller functions using code similar to this example:</p>
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<code>$this->load->library('trackback');<br />
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$tb_data = array(<br />
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'ping_url' => 'http://example.com/trackback/456',<br />
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'url' => 'http://www.my-example.com/blog/entry/123',<br />
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'title' => 'The Title of My Entry',<br />
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'excerpt' => 'The entry content.',<br />
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'blog_name' => 'My Blog Name',<br />
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'charset' => 'utf-8'<br />
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);<br />
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if ( ! $this->trackback->send($tb_data))<br />
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echo $this->trackback->display_errors();<br />
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echo 'Trackback was sent!';<br />
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<p>Description of array data:</p>
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<li><strong>ping_url</strong> - The URL of the site you are sending the Trackback to. You can send Trackbacks to multiple URLs by separating each URL with a comma.</li>
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<li><strong>url</strong> - The URL to YOUR site where the weblog entry can be seen.</li>
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<li><strong>title</strong> - The title of your weblog entry.</li>
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<li><strong>excerpt</strong> - The content of your weblog entry. Note: the Trackback class will automatically send only the first 500 characters of your entry. It will also strip all HTML.</li>
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<li><strong>blog_name</strong> - The name of your weblog.</li>
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<li><strong>charset</strong> - The character encoding your weblog is written in. If omitted, UTF-8 will be used.</li>
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<p>The Trackback sending function returns TRUE/FALSE (boolean) on success or failure. If it fails, you can retrieve the error message using:</p>
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<code>$this->trackback->display_errors();</code>
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<h2>Receiving Trackbacks</h2>
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<p>Before you can receive Trackbacks you must create a weblog. If you don't have a blog yet there's no point in continuing.</p>
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<p>Receiving Trackbacks is a little more complex than sending them, only because you will need a database table in which to store them,
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and you will need to validate the incoming trackback data. You are encouraged to implement a thorough validation process to
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guard against spam and duplicate data. You may also want to limit the number of Trackbacks you allow from a particular IP within
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a given span of time to further curtail spam. The process of receiving a Trackback is quite simple;
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the validation is what takes most of the effort.</p>
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<h2>Your Ping URL</h2>
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<p>In order to accept Trackbacks you must display a Trackback URL next to each one of your weblog entries. This will be the URL
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that people will use to send you Trackbacks (we will refer to this as your "Ping URL").</p>
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<p>Your Ping URL must point to a controller function where your Trackback receiving code is located, and the URL
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must contain the ID number for each particular entry, so that when the Trackback is received you'll be
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able to associate it with a particular entry.</p>
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<p>For example, if your controller class is called <dfn>Trackback</dfn>, and the receiving function is called <dfn>receive</dfn>, your
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Ping URLs will look something like this:</p>
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<code>http://example.com/index.php/trackback/receive/<samp>entry_id</samp></code>
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<p>Where <samp>entry_id</samp> represents the individual ID number for each of your entries.</p>
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<h2>Creating a Trackback Table</h2>
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<p>Before you can receive Trackbacks you must create a table in which to store them. Here is a basic prototype for such a table:</p>
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<textarea class="textarea" style="width:100%" cols="50" rows="13">
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CREATE TABLE trackbacks (
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tb_id int(10) unsigned NOT NULL auto_increment,
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entry_id int(10) unsigned NOT NULL default 0,
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url varchar(200) NOT NULL,
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title varchar(100) NOT NULL,
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excerpt text NOT NULL,
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blog_name varchar(100) NOT NULL,
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tb_date int(10) NOT NULL,
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ip_address varchar(16) NOT NULL,
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PRIMARY KEY `tb_id` (`tb_id`),
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KEY `entry_id` (`entry_id`)
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<p>The Trackback specification only requires four pieces of information to be sent in a Trackback (url, title, excerpt, blog_name),
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but to make the data more useful we've added a few more fields in the above table schema (date, IP address, etc.).</p>
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<h2>Processing a Trackback</h2>
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<p>Here is an example showing how you will receive and process a Trackback. The following
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code is intended for use within the controller function where you expect to receive Trackbacks.</p>
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<code>$this->load->library('trackback');<br />
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$this->load->database();<br />
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if ($this->uri->segment(3) == FALSE)<br />
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$this->trackback->send_error("Unable to determine the entry ID");<br />
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if ( ! $this->trackback->receive())<br />
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$this->trackback->send_error("The Trackback did not contain valid data");<br />
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'tb_id' => '',<br />
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'entry_id' => $this->uri->segment(3),<br />
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'url' => $this->trackback->data('url'),<br />
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'title' => $this->trackback->data('title'),<br />
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'excerpt' => $this->trackback->data('excerpt'),<br />
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'blog_name' => $this->trackback->data('blog_name'),<br />
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'tb_date' => time(),<br />
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'ip_address' => $this->input->ip_address()<br />
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);<br />
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$sql = $this->db->insert_string('trackbacks', $data);<br />
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$this->db->query($sql);<br />
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$this->trackback->send_success();</code>
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<p>The entry ID number is expected in the third segment of your URL. This is based on the URI example we gave earlier:</p>
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<code>http://example.com/index.php/trackback/receive/<samp>entry_id</samp></code>
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<p>Notice the entry_id is in the third URI segment, which you can retrieve using:</p>
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<code>$this->uri->segment(3);</code>
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<p>In our Trackback receiving code above, if the third segment is missing, we will issue an error. Without a valid entry ID, there's no
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reason to continue.</p>
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<p>The <dfn>$this->trackback->receive()</dfn> function is simply a validation function that looks at the incoming data
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and makes sure it contains the four pieces of data that are required (url, title, excerpt, blog_name).
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It returns TRUE on success and FALSE on failure. If it fails you will issue an error message.</p>
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<p>The incoming Trackback data can be retrieved using this function:</p>
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<code>$this->trackback->data('<var>item</var>')</code>
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<p>Where <var>item</var> represents one of these four pieces of info: url, title, excerpt, or blog_name</p>
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<p>If the Trackback data is successfully received, you will issue a success message using:</p>
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<code>$this->trackback->send_success();</code>
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<p class="important"><strong>Note:</strong> The above code contains no data validation, which you are encouraged to add.</p>
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