Topic 4: POST-based web services and clients

In this session, you will write a web service which updates the database by adding new data, namely a review for a given song.

POST data using Slim

So far we have only looked at GET requests, however to create new data we need to use POST. How do we handle POST data in Slim? Firstly, we set up a 'post' rather than a 'get' route, and then we use the request's getParsedBody() method to extract the POST data. For example, this sets up a POST route /student/create:

// Include all the Slim dependencies. Composer creates an 'autoload.php' inside
// the 'vendor' folder which will, in turn, include all required dependencies.
require 'vendor/autoload.php';


// Create a new Slim App object.
$app = new \Slim\App;

$app->post('/student/create', function ($req, $res, array $args) {
    $post = $req->getParsedBody();
    $res->getBody()->write("Student details : Name: ". $post['name']. " Username: ". $post['username']. " Course: " . $post['course']);
    return $res;
});


$app->run();

In this example, we could set up a form with an action of "/student/create" and fields with names of name, username and course, and the Slim application would read, and display, this data.

Exercise 1

This exercise will involve creating a review for a song, so we will use POST, as per the principles of REST.

• Extend your Slim web service to include a "/review/create" route to create a review for a particular song (defined by ID - so include the ID as a placeholder in your route). It should read in a review, as a POST request, connect to the database, and add a review for that song - there is now a "reviews" table in the "dftitutorials" database so just perform an INSERT statement.

Sending a POST request using cURL

So far we have seen how to connect to a web service using cURL to send a GET request, however what about a POST request?

Rather than adding the data to the end of the URL using a query string, you set the CURLOPT_POSTFIELDS option with the data you want to POST. See the example below, in which $dataToPost is an associative array describing a new flight. It is sent to the REST URL http://www.solentairways.com/flight/create:

$connection = curl_init();
curl_setopt($connection, CURLOPT_URL, "http://www.solentairways.com/flight/create");
$dataToPost = 
    ["origin" => "London" ,
     "dep" => "0900",
     "arr" => "1600",
     "destination" => "New York",
     "aircraft" => "Boeing 777",
     "flightnumber" => "SA123"];
curl_setopt($connection,CURLOPT_RETURNTRANSFER,1);
curl_setopt($connection,CURLOPT_POSTFIELDS,$dataToPost);
$response = curl_exec($connection);
curl_close($connection);

$app->post("/flight/create", function($req, $res, array $args) {
    $postData = $req->getParsedBody();
    // $postData["origin"] is the origin, $postData["dep"] is the departure time, etc.
});

Exercise 2

Return to your "fan" website from last time. On the "fan" website, allow the user the ability to review each song from HT-Tracks. This should be done by writing a new page on your fan site which connects to the HT-Tracks download web service, which you wrote above.

Do this as follows:

• On your fan page, add a "review" form next to each song. This should link to a new, as yet unwritten, script, clientreview.php, and have two fields:
  • a regular field for the review;
  • and a hidden field for the ID.
  Hint: to create your form in your JSON-parsing loop, with a hidden field, use this PHP:

  echo "<form method='post' action='clientreview.php'>";
  echo "<input name='review' />";
  echo "<input name='id' type='hidden' value='(the ID from your JSON - fill this in!)' />";
  echo "<input type='submit' value='review' />";
  echo "</form>";
  

  Or, alternatively, for each song on your fan page, write a link to a separate page which should contain a review form containing a review field, a hidden field for the ID, and an action of clientreview.php.
• Write the new script,clientreview.php. This is part of the "fan" site, and should therefore have the same CSS and look and feel as the main page of the "fan" site. Write some PHP code in this script to read in the ID and the review from the form, and send a cURL POST request to your review web service, passing the chosen review across.
• Finally, add some error handling to your web service. If the review is blank (""), choose an appropriate HTTP code to send back. Look at the REST and Slim topic for information on how to send back a particular HTTP status code from a Slim application.

How to test the HTTP status code from a client

In the last question of the exercise, you were asked to send back an HTTP status code to the client if the review was blank. However, we have not yet looked at how you can test for an HTTP code sent back from a remote script. Luckily, if you are using cURL it's fairly straightforward. Once you have done your cURL request you query the CURLINFO_HTTP_CODE property to obtain the HTTP code returned by the web service, for example:

$connection = curl_init();
curl_setopt($connection, CURLOPT_URL, "http://remoteserver/script.php");
curl_setopt($connection,CURLOPT_RETURNTRANSFER,1);
curl_setopt($connection,CURLOPT_HEADER,0);
$response = curl_exec($connection);

$httpCode = curl_getinfo($connection,CURLINFO_HTTP_CODE);
echo "The script returned the HTTP status code: $httpCode <br />";

curl_close($connection);

Note how the line:

curl_setopt($connection,CURLOPT_HEADER, 0);

Exercise 3

1. Modify your clientreview.php to test which HTTP code is returned from the web service and display an appropriate message accordingly.

2. Add a new route to your web service, getReviews, which returns all reviews for the song with a particular ID as JSON. Modify your fan site to have an additional reviews page, which shows all reviews for a particular song by connecting to your web service and parsing the JSON returned. Link this reviews page to your main fan page, so that each song has a "Review" link. Ensure the fan site's reviews page has the same look and feel as your main fan site page.