# 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.

- Using the Trackback Class
  - Initializing the Class
  - Sending Trackbacks
  - Receiving Trackbacks
  - Your Ping URL
  - Creating a Trackback Table
  - Processing a Trackback
    - Notes:
- Class Reference

## Using the Trackback Class

### Initializing the Class

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

    $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.
- blog_name - The name of your weblog.
- charset - The character encoding your weblog is written in. If omitted, UTF-8 will be used.

Note

The Trackback class will automatically send only the first 500 characters of your entry. It will also strip all HTML.

The Trackback sending method 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(45) 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.

## Class Reference

class `CI_Trackback`
  `$data = array('url' => '', 'title' => '', 'excerpt' => '', 'blog_name' => '', 'charset' => '')`

    Trackback data array.

  `$convert_ascii = TRUE`

    Whether to convert high ASCII and MS Word characters to HTML entities.

  `send`($tb_data)

    Parameters: | $tb_data (array) – Trackback data
    Returns: | TRUE on success, FALSE on failure
    Return type: | bool

    Send trackback.

  `receive`()

    Returns: | TRUE on success, FALSE on failure
    Return type: | bool

    This method simply validates the incoming TB data, returning TRUE on success and FALSE on failure. If the data is valid it is set to the `$this->data` array so that it can be inserted into a database.

  `send_error([$message = 'Incomplete information')`

    Parameters: | $message (string) – Error message
    Return type: | void

    Responses to a trackback request with an error message.

    Note

    This method will terminate script execution.

  `send_success`()

    Return type: | void

    Responses to a trackback request with a success message.

    Note

    This method will terminate script execution.

  `data`($item)

    Parameters: | $item (string) – Data key
    Returns: | Data value or empty string if not found
    Return type: | string

    Returns a single item from the reponse data array.

  `process`($url, $data)

    Parameters: | $url (string) – Target url $data (string) – Raw POST data
    Returns: | TRUE on success, FALSE on failure
    Return type: | bool

    Opens a socket connection and passes the data to the server, returning TRUE on success and FALSE on failure.

  `extract_urls`($urls)

    Parameters: | $urls (string) – Comma-separated URL list
    Returns: | Array of URLs
    Return type: | array

    This method lets multiple trackbacks to be sent. It takes a string of URLs (separated by comma or space) and puts each URL into an array.

  `validate_url`(&$url)

    Parameters: | $url (string) – Trackback URL
    Return type: | void

    Simply adds the http:// prefix it it’s not already present in the URL.

  `get_id`($url)

    Parameters: | $url (string) – Trackback URL
    Returns: | URL ID or FALSE on failure
    Return type: | string

    Find and return a trackback URL’s ID or FALSE on failure.

  `convert_xml`($str)

    Parameters: | $str (string) – Input string
    Returns: | Converted string
    Return type: | string

    Converts reserved XML characters to entities.

  `limit_characters`($str[, $n = 500[, $end_char = '&#8230;']])

    Parameters: | $str (string) – Input string $n (int) – Max characters number $end_char (string) – Character to put at end of string
    Returns: | Shortened string
    Return type: | string

    Limits the string based on the character count. Will preserve complete words.

  `convert_ascii`($str)

    Parameters: | $str (string) – Input string
    Returns: | Converted string
    Return type: | string

    Converts high ASCII text and MS Word special characterss to HTML entities.

  `set_error`($msg)

    Parameters: | $msg (string) – Error message
    Return type: | void

    Set an log an error message.

  `display_errors`([$open = '<p>'[, $close = '</p>']])

    Parameters: | $open (string) – Open tag $close (string) – Close tag
    Returns: | HTML formatted error messages
    Return type: | string

    Returns error messages formatted in HTML or an empty string if there are no errors.