The request

Everything the browser sent — the address, parameters, form data, headers — Slim gathers into one request object. A handler receives it as the first argument, $request. The object follows PSR-7, a shared PHP standard that describes the request and the response, so the same methods appear in other frameworks too.

The $_GET and $_POST superglobals are not used in Slim: all data is read from $request.

Query parameters

Parameters after the question mark are returned by getQueryParams():

// public/index.php
$app->get('/search', function (Request $request, Response $response) {
    $params = $request->getQueryParams();
 
    $query = $params['q'] ?? '';
 
    $response->getBody()->write('Searching for: ' . htmlspecialchars($query));
 
    return $response;
});

Open http://localhost:8080/search?q=slim — the page shows "Searching for: slim". The method returns a plain array; when the parameter is missing, the value after ?? is used. The htmlspecialchars() function neutralises HTML in text you did not write.

Form data and JSON

The request body — form data or JSON — is returned by getParsedBody(). To make Slim parse JSON as well, add one line to public/index.php after creating the application:

// public/index.php
$app = AppFactory::create();
$app->addBodyParsingMiddleware();

Now the data is read the same way in both cases:

// public/index.php
$app->post('/posts', function (Request $request, Response $response) {
    $data = (array) $request->getParsedBody();
 
    $title = trim($data['title'] ?? '');
 
    $response->getBody()->write('Post created: ' . htmlspecialchars($title));
 
    return $response;
});

Try it from the terminal:

curl -X POST -d "title=First post" http://localhost:8080/posts

The answer is "Post created: First post". The (array) cast is needed because the method returns null for an empty body.

Headers

A header is a service line of the request in the form "name: value". It is read with getHeaderLine():

$agent = $request->getHeaderLine('User-Agent');

If the header is missing, an empty string is returned. The letter case of the name does not matter.

What else the request holds

Attributes

Attributes are data added to the request not by the browser but by the application itself on the way to the handler. For example, a middleware checks the login and puts the user into the request, and the handler reads it:

$user = $request->getAttribute('user');

If the attribute is missing, null is returned. How a middleware adds an attribute is shown in the middleware lesson.

Common mistake

getParsedBody() returns null for JSON if you forget $app->addBodyParsingMiddleware() or if the client does not send the Content-Type: application/json header. PHP parses ordinary form data by itself, so the error shows up only on JSON requests — and takes a long time to find.