# CodeIgniter User Guide Version 2.0.0

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# Trackback Class

The Trackback Class provides functions that enable you to send and receive Trackback data.

If you are not familiar with Trackbacks you'll find more information here.

## Initializing the Class

Like most other classes in CodeIgniter, the Trackback class is initialized in your controller using the $this->load->library function:

`$this->load->library('trackback');`

Once loaded, the Trackback library object will be available using: $this->trackback

## Sending Trackbacks

A Trackback can be sent from any of your controller functions using code similar to this example:

`$this->load->library('trackback');
$tb_data = array(
'ping_url' => 'http://example.com/trackback/456',
'url' => 'http://www.my-example.com/blog/entry/123',
'title' => 'The Title of My Entry',
'excerpt' => 'The entry content.',
'blog_name' => 'My Blog Name',
'charset' => 'utf-8'
);
if ( ! $this->trackback->send($tb_data))
{
echo $this->trackback->display_errors();
}
else
{
echo 'Trackback was sent!';
}`

Description of array data:

- ping_url - 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.
- url - The URL to YOUR site where the weblog entry can be seen.
- title - The title of your weblog entry.
- excerpt - 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.
- blog_name - The name of your weblog.
- charset - The character encoding your weblog is written in. If omitted, UTF-8 will be used.

The Trackback sending function returns TRUE/FALSE (boolean) on success or failure. If it fails, you can retrieve the error message using:

`$this->trackback->display_errors();`

## Receiving Trackbacks

Before you can receive Trackbacks you must create a weblog. If you don't have a blog yet there's no point in continuing.

Receiving Trackbacks is a little more complex than sending them, only because you will need a database table in which to store them, and you will need to validate the incoming trackback data. You are encouraged to implement a thorough validation process to guard against spam and duplicate data. You may also want to limit the number of Trackbacks you allow from a particular IP within a given span of time to further curtail spam. The process of receiving a Trackback is quite simple; the validation is what takes most of the effort.

## Your Ping URL

In order to accept Trackbacks you must display a Trackback URL next to each one of your weblog entries. This will be the URL that people will use to send you Trackbacks (we will refer to this as your "Ping URL").

Your Ping URL must point to a controller function where your Trackback receiving code is located, and the URL must contain the ID number for each particular entry, so that when the Trackback is received you'll be able to associate it with a particular entry.

For example, if your controller class is called Trackback, and the receiving function is called receive, your Ping URLs will look something like this:

`http://example.com/index.php/trackback/receive/`entry_id``

Where `entry_id` represents the individual ID number for each of your entries.

## Creating a Trackback Table

Before you can receive Trackbacks you must create a table in which to store them. Here is a basic prototype for such a table:

CREATE TABLE trackbacks ( tb_id int(10) unsigned NOT NULL auto_increment, entry_id int(10) unsigned NOT NULL default 0, url varchar(200) NOT NULL, title varchar(100) NOT NULL, excerpt text NOT NULL, blog_name varchar(100) NOT NULL, tb_date int(10) NOT NULL, ip_address varchar(16) NOT NULL, PRIMARY KEY `tb_id` (`tb_id`), KEY `entry_id` (`entry_id`) );

The Trackback specification only requires four pieces of information to be sent in a Trackback (url, title, excerpt, blog_name), but to make the data more useful we've added a few more fields in the above table schema (date, IP address, etc.).

## Processing a Trackback

Here is an example showing how you will receive and process a Trackback. The following code is intended for use within the controller function where you expect to receive Trackbacks.

`$this->load->library('trackback');
$this->load->database();
if ($this->uri->segment(3) == FALSE)
{
$this->trackback->send_error("Unable to determine the entry ID");
}
if ( ! $this->trackback->receive())
{
$this->trackback->send_error("The Trackback did not contain valid data");
}
$data = array(
'tb_id' => '',
'entry_id' => $this->uri->segment(3),
'url' => $this->trackback->data('url'),
'title' => $this->trackback->data('title'),
'excerpt' => $this->trackback->data('excerpt'),
'blog_name' => $this->trackback->data('blog_name'),
'tb_date' => time(),
'ip_address' => $this->input->ip_address()
);
$sql = $this->db->insert_string('trackbacks', $data);
$this->db->query($sql);
$this->trackback->send_success();`

#### Notes:

The entry ID number is expected in the third segment of your URL. This is based on the URI example we gave earlier:

`http://example.com/index.php/trackback/receive/`entry_id``

Notice the entry_id is in the third URI segment, which you can retrieve using:

`$this->uri->segment(3);`

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 reason to continue.

The $this->trackback->receive() function is simply a validation function that looks at the incoming data and makes sure it contains the four pieces of data that are required (url, title, excerpt, blog_name). It returns TRUE on success and FALSE on failure. If it fails you will issue an error message.

The incoming Trackback data can be retrieved using this function:

`$this->trackback->data('item')`

Where item represents one of these four pieces of info: url, title, excerpt, or blog_name

If the Trackback data is successfully received, you will issue a success message using:

`$this->trackback->send_success();`

Note: The above code contains no data validation, which you are encouraged to add.