I started a (now defunct) website last year, powered by WordPress. It never got too popular, and in the beginning I was excited every time I got a “New Comment” or “New Trackback” e-mail. Then I realized they were mostly all spam.

A few minutes ago, I checked my e-mail and had a spam comment in my inbox. I thought, “Ahh, here comes the spam.”

When I logged into the dashboard, I spammed the comment and was about to move away. Then I happened to look at the dashboard again – and I remembered that I had set up Akismet this time around.

I just added the widget to the left sidebar because I was so impressed. Akismet apparently blocked 84 spam comments – and this was the first one that got through. I’d say that’s pretty impressive.

If you’re running a WordPress blog, or something else that uses comments and can utilize an Akismet plug-in, do so. There’s nothing more frustrating than wading through spam comments and trackbacks all day long.

Akismet is apparently pretty effective at cutting them down. A few of them might sift through, but you can never get rid of all the spam. So be happy if you can eliminate 84/85.

You can download the Akismet plugin for WordPress, but all new builds come with Akismet pre-installed. All you have to do is fill in the Akismet API number – which you can get for free with a WordPress account.

Happy spam-free comment logs.

Assuming you do know what a trackback is, how do you send one – technically speaking? And how can we write a php script to send one?

A trackback is a simple ping – an HTTP Request. It is specially formatted with a limited amount of information. The receiving server is set up to handle that information and use it to create the comment based on your trackback ping.

The Trackback API As Per Moveable Type

Since Moveable Type introduced the trackback, they were the ones responsible for writing the standards and API. You can read through the trackback technical specs on the SixApart website.

In order to send a trackback ping with a PHP script, there’s a few things we need to know…

• The ping is in the form of an HTTP Post Request.
• The ping is sent to the trackback URI of the receiving post.
• The request must have a content-type header defining it as application/x-www-url-encoded
• All of the parameters included in the content should be url encoded.
• The standard parameters are “title,” “excerpt,” “url,” and “blog.” Only the “url” parameter is required.
• The server will send a short XML response – containing <error>0</error> if there was no error, and <error>1</error> along with a <message></message> element if there was an error.

With that in mind, we can begin to write our script. We need to do four things.

• Receive input from the user (the blog url, title, excerpt, etc).
• Create the header and format the information correctly
• Send the header and get a response
• Read the XML to see if it was successful or not

Getting Input From the User

Getting input is pretty simple. We’ll create a form in HTML, set the action to the page containing the script, and set the method to post.

You’ll want a text input for the URL, title, and blog. You could use either a text input or a small textarea box to take the excerpt.

Here’s some sample HTML to create the form. You’d want to add some css to make it look pretty, but you can do that some other time.

<form id="trackback-form" method="post"
        action="trackback.html">
<fieldset id="trackback">
<label for="trackback-uri">Trackback URI:</label>
<input id="trackback-uri" name="trackback-uri" 
        type="text" /><br />
 
<label for="title">Post Title:</label>
<input id="title" name="title" type="text" /><br />
 
<label for="url">Post URL:</label>
<input id="url" name="url" type="text" /><br />
 
<label for="excerpt">Excerpt:</label>
<input id="excerpt" name="excerpt" type="text" /><br />
 
<label for="blog">Blog Name:</label>
<input id="blog" name="blog" type="text" /><br />
 
<label for="submit"></label>
<input value="Send Trackback Ping" name="submit" 
        id="submit" type="submit" /> </fieldset></form>');

Simple… but effective. Set the “action” to the name of the file with the form in it. We’ll add the php script to the top, and the form will just return the information to itself.

Reading the Information from the Form and Encoding It

Once you hit submit, all of the form information will get sent to the file so that the script – at the beginning of the file – can handle it.

All of this form information is in the $_POST array. The ‘key’ for each element is the ‘name’ attribute of the form element.

We’ll also need to use the urlencode() function. This takes the input and escapes any special characters (like spaces) so that the input is in the proper format.

Here’s a snippet to read the $_POST variables, encode them, and store the information in some new variables. Note that you’d probably want to include some error checking (i.e. check to see if the $_POST[] element is empty, and set an error message if it is). I’ll leave that up to you.

$title = urlencode($_POST['title']);
$url = urlencode($_POST['url']);
$excerpt = urlencode($_POST['excerpt']);
$blog_name = urlencode($_POST['blog']);
 
$trackback_uri = $_POST['trackback-uri'];

Now that have all of our information, we need to create the HTTP header.

You could format this as a special string, but php has a built in function – stream_context_create – that will take a formatted array and use it to send an HTTP header. That’s what we’ll be using.

A HTTP header looks something like this…

POST http://targeturl.com
Content-Type: application/x-www-form-urlencoded; charset=utf-8

paramvar=Param+Value&paramvar2=Param+Value+2

In order to use stream_context_create, we need to create an array in the following format.

• $params['http']['method'] is the method (POST)
• $params['http']['header'] is the optional headers (in this case the Content-Type)
• $params['http']['content'] is the actual content – the parameter variables and values. This will be the string containing all of the trackback information (the post url, post title, blog name, and excerpt).

So, to create the array we need, here’s a short snippet of code, picking up where we left off before…

$params['http']['method'] = 'POST';
$params['http']['header'] = 'Content-Type: 
    application/x-www-form-urlencoded';
$params['http']['content'] = "title=$title&url=$url&
    blog_name=$blog_name&excerpt=$excerpt";

Note that because we used double-quotes (” “) when declaring $params['http']['content'], we could simply include the variables in the string – and PHP will punch in the values for us.

Send the Header! Pings Away!

Now that we’ve created the array, we’re ready to create a context and actually send the HTTP request to the target website.

Like I said before, we’ll use the function stream_context_create to do the work. Then we’ll fopen the target, write the header, fclose the target, and save the response.

stream_context_create just needs one parameter – our formatted array.

fopen will take a few parameters – the target URL ($trackback_uri), the mode (‘rb’ for read-only, binary), a boolean option which is false for us, and the context we created with stream_context_create.

Here’s the actual code snippet. (Note: You can only use a context in fopen() in PHP 5 or greater. You’ll need to manually make the header if you’re using PHP 4)

//  Create the context from the formatted array
$context = stream_context_create($params);
 
//  Open a stream to the url, save it in the pointer $fp
$fp = @fopen($trackback_uri, 'rb', false, $context);
 
//  Send the header and get the results, saved in $response
$response = @stream_get_contents($fp);
 
//  Always close for good measure
fclose($fp);

At this point, you should be able to send trackbacks just fine.

Read the Result Message – Error or No?

Now we need to read the results (saved in $response) and find out if we were successful.

You could just echo it. The xml tags will be hidden by the browser, so the user will just see the output. However I like to have the script read it so that I can output a customized message.

One way to do this would be to build an xml parser and find out directly what’s in the <error></error> element. This is a lot of work for one error message, though.

Instead, we can use our knowledge of the standard format of the message to good use.

First, we know that a success is always returned with <error>0</error>. If we do a stripos or substr search to see if that string is included in $response, we’ll know if the test was successful or not.

Then, we can isolate the <message></message> element and echo that.

Here’s the code I used to do it. Not sure if it’s the most efficient way to do it, but it works… so why not?

//  If this is true, there was no error
if (stripos($response, '<error>0</error>'))
    $outcome = "All clear! Trackback 
        was sent successfully.";
else
    {
    //  Find the beginning and end of the message element
    $start_resp = stripos($response, '<message>');
    $end_resp = stripos($response, '</message>');
 
    //  substr will return the actual message element, 
    //    with the tags included
    $outcome = substr($response, $start_resp, 
        $end_resp - $start_resp - 1);
 
    //  Replace the tags with blank space
    $outcome = str_replace('<message>', '', $outcome);
    $outcome = str_replace('</message>', '', $outcome);
    $outcome = "Error: " . $outcome;
    }
 
//  Echo the results.  I formatted 'error' to be red.
echo "<p class='error>$outcome</p>";

Recap

Well, there you have it. Put all that code together and you should have a functioning example.

Of course, instead of building your own script, you could simply use the form I already created to do this. Or you could head over there to see how it works.

This is a pretty good learning activity, though. You get to see how contexts and streams work, sending an HTTP header to get a response.

We also make use of the urlencode() function and use stripos() and substr() to do some half-assed xml parsing. You could use a similar method for reading HTML and parsing tags.

Enjoy, and be sure to leave a comment if there’s something else you’d like to see explained in a tutorial.

Trackbacks are strange things. Blogs all over the internet have them enabled, but I’d bet a lot of the blog owners don’t have a clue what they are.

Here’s the short version. Trackbacks are citation systems for blogs. Trackbacks are also a system for remote commenting.

That’s how they’re typically explained, but that doesn’t help a whole lot, now does it?

So here are a few questions answered to get you started on understanding the trackback.

• What is a trackback and what does it do?
• Do all blogs support trackbacks?
• How can I create a trackback
• Why would I want to create a trackback?

What is it? It’s a form that let’s you send a trackback to a blog from any website. It might sound silly, but trust me… it’s not.

I faced this problem with another website of mine (Babel). I was using a CMS (cmsmadesimple) instead of a blogging platform.

Still, I had some blog-like posts using a module in the CMS. I wanted to be able to trackback to someone else’s blog to signal that I was referencing their post, but there was no trackback functionality in cmsmadesimple.

I looked into writing a full plugin and tag for cmsmadesimple, but I decided it would be easier to just write a simple form and a script to do the work for me. Thus, the trackback-via-form tool was born.

You can read more about trackbacks and why you need this form, or just head over to the form and start submitting pings to blogs.

Browse through and use what you need. If you have an idea for a new kind of tool that you need, and I could build, leave a comment. Maybe I’ll put it on my to-do list.

Submit Trackbacks with a Form

Trackbacks are great, but not all blogging platforms and websites support them. Solution? Submit them from a third-party form – like the trackback-via-form tool I wrote.

You provide all the necessary information – the trackback URI and your webpage’s information – and the script sends the trackback to your target. Pretty nifty tool for publicizing websites that don’t have built in support for trackbacks.

Text Cleaner Tool: Remove Newline Characters

This is a simple tool that can come in handy for uploading articles to your own site or to article directories. If you used hard line-breaks to format the article for print or for e-mail, you’ll need to get rid of those new-lines. Just copy and paste into the form, and those newline characters will be a thing of the past.

You can access the Text Cleaner Form here.

Form to Encode Sample HTML for Display

If you want to display sample HTML for the user to see, you need to jump through a few hurdles. With this tool, you can copy and paste HTML into the textarea, hit submit, and get text that has all of the special characters escaped for you.

Copy and paste that on to your page, and it should appear as a perfect snippet of sample markup. Check out the HTML encoding form here.

Fill out the form below, and we’ll do the trackbacking for you.The Trackback URI comes from the website you’re sending the ping to. The other sections are pretty self-explanatory – describe the post you’re trackbacking from.

If you want to test it out, trackback to this page and watch the magic work. You should get a response if it works, or an error message if something goes wrong.

These trackback pings will show up in the target post’s comment section, and sometimes the author will separate trackbacks out to show at the beginning of the list. Although they won’t always get you search engine ju-ju, thanks to rel=nofollow, they are a great way to get people to come to your website.

Why Trackback If the Search Engine Doesn’t Care?

I know that every time I get a trackback to one of my websites, I immediately check out the source. To some extent I want to check for spam, but I’m also concerned with, “Who’s this new guy talking to me?”

When I’m viewing another person’s blog, I also usually follow the trackbacks if I was interested in the original post. I rarely click on the typical name-link included in a comment, though.

The trackback signals to both the target website’s author and to its readers that this comment has something worth while for them to read. So often they’ll click the link and see what you have to say.

Ok, How Do I Send a Trackback?

Well, if you’re using a standard blogging platform like WordPress, it’s pretty easy. At the bottom of your post editing screen, you’ll probably see a space to enter a trackback URI. This is the link from the original website that you send the trackback ping to.

Just enter the URI in your editor, and you’re all set. The problem, though, is that not every blogging platform supports sending trackbacks. You might also want to send a trackback from a non-blog website, if you’ve added some content that speaks to the original post.

Enter the trackback-via-form tool. This form will do all the work for you. Enter the necessary information (Trackback URI, your page’s title, your page’s URL, an excerpt of your page, and your blog name), and hit submit.

You should see a response with either an “All clear! Trackback was sent successfully.” or some kind of error message.

Enjoy, and good luck trackbacking. Test it out by sending a trackback to this page or the form’s page.

If you’re done with the trackback form, why don’t you go back and browse through some other online tools?