Requests
========

Requests made to an application are represented in terms of [[yii\web\Request]] objects which provide information
such as request parameters, HTTP headers, cookies, etc. For a given request, you can get access to the corresponding
request object via the `request` [application component](structure-application-components.md) which is an instance
of [[yii\web\Request]], by default. In this section, we will describe how you can make use of this component in your applications.


## Request Parameters <span id="request-parameters"></span>

To get request parameters, you can call [[yii\web\Request::get()|get()]] and [[yii\web\Request::post()|post()]] methods
of the `request` component. They return the values of `$_GET` and `$_POST`, respectively. For example,

```php
$request = Yii::$app->request;

$get = $request->get(); 
// equivalent to: $get = $_GET;

$id = $request->get('id');   
// equivalent to: $id = isset($_GET['id']) ? $_GET['id'] : null;

$id = $request->get('id', 1);   
// equivalent to: $id = isset($_GET['id']) ? $_GET['id'] : 1;

$post = $request->post(); 
// equivalent to: $post = $_POST;

$name = $request->post('name');   
// equivalent to: $name = isset($_POST['name']) ? $_POST['name'] : null;

$name = $request->post('name', '');   
// equivalent to: $name = isset($_POST['name']) ? $_POST['name'] : '';
```

> Info: Instead of directly accessing `$_GET` and `$_POST` to retrieve the request parameters, it is recommended
  that you get them via the `request` component as shown above. This will make writing tests easier because
  you can create a mock request component with faked request data.

When implementing [RESTful APIs](rest-quick-start.md), you often need to retrieve parameters that are submitted
via PUT, PATCH or other [request methods](#request-methods). You can get these parameters by calling
the [[yii\web\Request::getBodyParam()]] methods. For example,

```php
$request = Yii::$app->request;

// returns all parameters
$params = $request->bodyParams;

// returns the parameter "id"
$param = $request->getBodyParam('id');
```

> Info: Unlike `GET` parameters, parameters submitted via `POST`, `PUT`, `PATCH` etc. are sent in the request body.
  The `request` component will parse these parameters when you access them through the methods described above.
  You can customize the way how these parameters are parsed by configuring the [[yii\web\Request::parsers]] property.
  

## Request Methods <span id="request-methods"></span>

You can get the HTTP method used by the current request via the expression `Yii::$app->request->method`.
A whole set of boolean properties are also provided for you to check if the current method is of certain type.
For example,

```php
$request = Yii::$app->request;

if ($request->isAjax) { // the request is an AJAX request }
if ($request->isGet)  { // the request method is GET }
if ($request->isPost) { // the request method is POST }
if ($request->isPut)  { // the request method is PUT }
```

## Request URLs <span id="request-urls"></span>

The `request` component provides many ways of inspecting the currently requested URL. 

Assuming the URL being requested is `http://example.com/admin/index.php/product?id=100`, you can get various
parts of this URL as summarized in the following:

* [[yii\web\Request::url|url]]: returns `/admin/index.php/product?id=100`, which is the URL without the host info part. 
* [[yii\web\Request::absoluteUrl|absoluteUrl]]: returns `http://example.com/admin/index.php/product?id=100`,
  which is the whole URL including the host info part.
* [[yii\web\Request::hostInfo|hostInfo]]: returns `http://example.com`, which is the host info part of the URL.
* [[yii\web\Request::pathInfo|pathInfo]]: returns `/product`, which is the part after the entry script and 
  before the question mark (query string).
* [[yii\web\Request::queryString|queryString]]: returns `id=100`, which is the part after the question mark. 
* [[yii\web\Request::baseUrl|baseUrl]]: returns `/admin`, which is the part after the host info and before
  the entry script name.
* [[yii\web\Request::scriptUrl|scriptUrl]]: returns `/admin/index.php`, which is the URL without path info and query string.
* [[yii\web\Request::serverName|serverName]]: returns `example.com`, which is the host name in the URL.
* [[yii\web\Request::serverPort|serverPort]]: returns 80, which is the port used by the Web server.


## HTTP Headers <span id="http-headers"></span> 

You can get the HTTP header information through the [[yii\web\HeaderCollection|header collection]] returned 
by the [[yii\web\Request::headers]] property. For example,

```php
// $headers is an object of yii\web\HeaderCollection 
$headers = Yii::$app->request->headers;

// returns the Accept header value
$accept = $headers->get('Accept');

if ($headers->has('User-Agent')) { // there is User-Agent header }
```

The `request` component also provides support for quickly accessing some commonly used headers, including:

* [[yii\web\Request::userAgent|userAgent]]: returns the value of the `User-Agent` header.
* [[yii\web\Request::contentType|contentType]]: returns the value of the `Content-Type` header which indicates
  the MIME type of the data in the request body.
* [[yii\web\Request::acceptableContentTypes|acceptableContentTypes]]: returns the content MIME types acceptable by users.
  The returned types are ordered by their quality score. Types with the highest scores will be returned first.
* [[yii\web\Request::acceptableLanguages|acceptableLanguages]]: returns the languages acceptable by users.
  The returned languages are ordered by their preference level. The first element represents the most preferred language.

If your application supports multiple languages and you want to display pages in the language that is the most preferred
by the end user, you may use the language negotiation method [[yii\web\Request::getPreferredLanguage()]].
This method takes a list of languages supported by your application, compares them with [[yii\web\Request::acceptableLanguages|acceptableLanguages]],
and returns the most appropriate language.

> Tip: You may also use the [[yii\filters\ContentNegotiator|ContentNegotiator]] filter to dynamically determine 
  what content type and language should be used in the response. The filter implements the content negotiation
  on top of the properties and methods described above.


## Client Information <span id="client-information"></span>

You can get the host name and IP address of the client machine through [[yii\web\Request::userHost|userHost]]
and [[yii\web\Request::userIP|userIP]], respectively. For example,

```php
$userHost = Yii::$app->request->userHost;
$userIP = Yii::$app->request->userIP;
```
