I also have been using the twitter API to write simple twitter apps at appb.in. Felt like, sharing some gyaan on how to write a twitter app in PHP:purpose of this post. Target audience: a n00b or a beginner. Here we start…

First, If you haven’t gone through the  Twitter API wiki,  skim through it. You will get an idea about what we are interacting with. Keep it handy.  

Have PHP manual open for reference. [I have the .chm version of the manual open whenever I do some coding.]

To receive (or send) any info from(to) twitter, you will have to do a POST  or GET  request to twitter. There are different URL’s(methods) for different operations as mentioned in the API documentation. Based upon the application that you are developing, you will use appropriate API methods.

These methods return XML, JSON,  RSS and Atom depending upon the request that you send (http://twitter.com/statuses/public_timeline.format here  format can be xml or json, etc.,) . I generally use  XML, but have also used JSON. PHP has functions that help you easily read these formats, so no worries. Next task is to parse it & interpret the information. Then we need to do the processing as per the applications needs.

Then comes the last but the most challenging part, presenting the information to the user. AJAXy stuff are popular these days, so learn a little bit of jQuery( because there isn’t any other easy way of ajaxyfying that I know of) if you want. I’m not dealing with AJAX here, so let’s keep it aside. You can easily present the information in a HTML page with some neat stying using css.

Now, let us go through a simple app called commontweeps, which lets you find common friends between two people.  This is non-AJAXy and uses XML format.

From the API documentation, to get a list of friends, the URL that we need to use is “http://twitter.com/statuses/friends/username.xml”.  You now need to query twitter for the info. We can do that with a simple function,

 
function getfilecontents($url){
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
curl_setopt($ch, CURLOPT_USERPWD, 'username:password');
$res=curl_exec($ch);
$info=curl_getinfo($ch);
curl_close($ch);
if($res === false || $info['http_code'] !=200 ) { $ret=array(false,$info['http_code'],$res);}
else{$ret=array(true,$info['http_code'],$res);}
return $ret;
}


 It is a function that uses cURL to fetch data from the url being passed to it. This works without replacing the ‘username:password’ (with your username and password) but considering that twitter API has rate limiting, you can get your username whitelisted (i.e, if you are planning to release an app for friends/public).

Next is, how to use this function. Let us write a small piece of code, just to look at the response from twitter and how we can use it. 

http://wg.vinayraikar.com/apps/commontweeps/asktwitter.php.txt  This script will read, parse the xml and show results like this.

Now, I guess we are clear with the querying-twitter part. Next, we need to do some processing to get our desired results. 

Twitter returns only 100 friends per call, so if  someone has more than 100 friends then you should query more than once with a page  parameter in the url. We will do that in our application with a while loop until no more ‘user’s are returned. The code goes something like this…

$xml[$page] = new SimpleXMLElement($fi[2]);
$user1count=0;
while(isset($xml[$page]->user[0])){
      foreach ($xml[$page]->user as $user) {
         $userdet[(string)$user->screen_name]=array( 'screen_name'=> (string)$user->screen_name, 'location'=>(string)$user->location, 'description'=>(string)$user-> description, 'profile_image_url'=> (string)$user-> profile_image_url, 'url'=>(string)$user-> url, 'name'=>(string)$user->name );
         $user1details[$user1count]= (string)$user->screen_name;
         $user1count++;
       } 
      $page++;
      $fi=getfilecontents($friendsurl.$username1.'.xml?page='.$page);
      if($fi[0]===false){
           echo "Error : ".$fi[1];
           $err=new SimpleXMLElement($fi[2]);
           echo " ".$err->error."";
           // echo "";
           die();
      }
   $xml[$page] = new SimpleXMLElement($fi[2]);
}

This piece of code is doing two things,

One: Collecting userdetails in an array $userdet with the username as the key.

Two: Collecting the friends name in an array $user1details .

At the end of the loop, $user1details will have a list of all the followers & $userdet will have all the follower details.

We need to do this for two users and get their friends list. Say, $user1details and $user2details are the arrays for two users, then all you need to get common tweeps is use the array_intersect function:

$commonfriends=array_intersect($user1details, $user2details);

Now, $commonfriends will have a list of all common friends. [You can do much more magic with different ideas by using other array functions like array_diff, array_merge.]

Next is presentation, the most crucial and difficult task.  Let’s keep is simple, displaying an unordered list with this piece of code…

$commoncount=count($commonfriends);
if(is_array($commonfriends)){
echo "<p>You have $commoncount friends in common.</p>";
echo "<ul id='commonlist'>";
foreach($commonfriends as $friend){
echo "<li>";
echo "<span class='nl'><img class='img' src='".$userdet[$friend]['profile_image_url']."'></img><br/>";
echo "<a class='screen-name' href='".$userdet[$friend]['screen_name']."'>".$userdet[$friend]['screen_name']."</a></span>";
echo "<span class='nr'> <p class='desc'> ".$userdet[$friend]['description']." | <a href='".$userdet[$friend]['url']."' title='".$userdet[$friend]['url']."'>web</a> </p></span>";
echo "</li>";
}
echo "</ul>";
}
else{echo "<p>No common Tweeps!</p>";}
}

You can now do some styling using CSS to give it a nice look.

Well, we are done with it, just that we didn’t talk about how to get the input from the user. We need to present a form to the user and then get his input. I hope, you will get it from the final working code.

So, our final commontweeps code is here. The code is more like an procedural hack, lacking proper error handling, cacheing & stuff but it’s one of our first steps right?

Based upon the application idea, you will have to use different API methods and request types (GET or POST) as per the API documentation.

There are PHP libraries for twitter like this one by arc90 that will ease your task. 

OK. That’s it!   Hope I  have been clear and not confusing {let me know in the comments, there’s always scope for improvement  :D}.  You can also catch me on twitter as @vsr  .  Happy tweeting!!

So, you might miss a few posts, but here is a short snapshot of my few lost posts (just 4 posts ;P ).

• Appconverter: converts between units.
• Simple Math Executor: Do some simple math calculations.
• uload: A script to upload files remotely. Have removed it coz. there are a bunch of people who don’t care about doing as simple a task as changing password. Security, is my concern.
• Project Homepage: Thought of doing some web design, so this project. The first and still the only one is apod.

There is also this appb.in where I dump in some at least presentable apps.

I’m quite active on twitter, so may be you can catch me there.