Response

Your Slim app's routes and middleware are given a PSR-7 response object that represents the current HTTP response to be returned to the client. The response object implements the PSR-7 ResponseInterface with which you can inspect and manipulate the HTTP response status, headers, and body.

How to get the Response object

The PSR-7 response object is injected into your Slim application routes as the second argument to the route callback like this:

use Psr\Http\Message\ResponseInterface as Response; use Psr\Http\Message\ServerRequestInterface as Request; use Slim\Factory\AppFactory;

require DIR . '/../vendor/autoload.php';

$app = AppFactory::create();

$app->get('/hello', function (Request $request, Response $response) { $response->getBody()->write('Hello World'); return $response; });

$app->run();

<figcaption>Figure 1: Inject PSR-7 response into application route callback.</figcaption>
</figure>

## The Response Status

Every HTTP response has a numeric [status code][statuscodes]. 
The status code identifies the _type_ of HTTP response to be returned to the client. 
The PSR-7 Response object's default status code is `200` (OK). 
You can get the PSR-7 Response object's status code with the `getStatusCode()` method like this.

[statuscodes]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

<figure markdown="1">
```php
$status = $response->getStatusCode();

You can copy a PSR-7 Response object and assign a new status code like this:

The Response Headers

Every HTTP response has headers. These are metadata that describe the HTTP response but are not visible in the response's body. The PSR-7 Response object provides several methods to inspect and manipulate its headers.

Get All Headers

You can fetch all HTTP response headers as an associative array with the PSR-7 Response object's getHeaders() method. The resultant associative array's keys are the header names and its values are themselves a numeric array of string values for their respective header name.

Get One Header

You can get a single header's value(s) with the PSR-7 Response object's getHeader($name) method. This returns an array of values for the given header name. Remember, a single HTTP header may have more than one value!

You may also fetch a comma-separated string with all values for a given header with the PSR-7 Response object's getHeaderLine($name) method. Unlike the getHeader($name) method, this method returns a comma-separated string.

Detect Header

You can test for the presence of a header with the PSR-7 Response object's hasHeader($name) method.

Set Header

You can set a header value with the PSR-7 Response object's withHeader($name, $value) method.

Append Header

You can append a header value with the PSR-7 Response object's withAddedHeader($name, $value) method.

Remove Header

You can remove a header with the Response object's withoutHeader($name) method.

The Response Body

An HTTP response typically has a body.

Just like the PSR-7 Request object, the PSR-7 Response object implements the body as an instance of Psr\Http\Message\StreamInterface. You can get the HTTP response body StreamInterface instance with the PSR-7 Response object's getBody() method. The getBody() method is preferable if the outgoing HTTP response length is unknown or too large for available memory.

The resultant Psr\Http\Message\StreamInterface instance provides the following methods to read from, iterate, and write to its underlying PHP resource.

• getSize()
• tell()
• eof()
• isSeekable()
• seek()
• rewind()
• isWritable()
• write($string)
• isReadable()
• read($length)
• getContents()
• getMetadata($key = null)

Most often, you'll need to write to the PSR-7 Response object. You can write content to the StreamInterface instance with its write() method like this:

You can also replace the PSR-7 Response object's body with an entirely new StreamInterface instance. This is particularly useful when you want to pipe content from a remote destination (e.g. the filesystem or a remote API) into the HTTP response. You can replace the PSR-7 Response object's body with its withBody(StreamInterface $body) method. Its argument MUST be an instance of Psr\Http\Message\StreamInterface.

$newStream = new LazyOpenStream('/path/to/file', 'r'); $newResponse = $oldResponse->withBody($newStream);

<figcaption>Figure 14: Replace the HTTP response body</figcaption>
</figure>

<div class="alert alert-info">
    <div><strong>Reminder</strong></div>
    <div>
        The Response object is immutable. This method returns a <em>copy</em>
        of the Response object that contains the new body.
    </div>
</div>

## Returning JSON

In it's simplest form, JSON data can be returned with a default 200 HTTP status code.

<figure markdown="1">
```php
$data = array('name' => 'Bob', 'age' => 40);
$payload = json_encode($data);

$response->getBody()->write($payload);
return $response
          ->withHeader('Content-Type', 'application/json');

We can also return JSON data with a custom HTTP status code.

$response->getBody()->write($payload); return $response ->withHeader('Content-Type', 'application/json') ->withStatus(201);

<figcaption>Figure 16: Returning JSON with a 201 HTTP status code.</figcaption>
</figure>

<div class="alert alert-info">
    <div><strong>Reminder</strong></div>
    <div>
        The Response object is immutable. This method returns a <em>copy</em> of
        the Response object that has a new Content-Type header. <strong>This method is destructive</strong>, and it <em>replaces</em> the existing Content-Type header.
    </div>
</div>

[json_encode]: http://php.net/manual/en/function.json-encode.php
[json_last_error]: http://php.net/manual/en/function.json-last-error.php
[json_last_error_msg]: http://php.net/manual/en/function.json-last-error-msg.php

## Returning a Redirect

You can redirect the HTTP client by using the `Location` header.

<figure markdown="1">
```php
return $response
  ->withHeader('Location', 'https://www.example.com')
  ->withStatus(302);