HTTP request and response headers in PHP

In web development, HTTP request and response headers are very important concepts. They provide a standardized mechanism for transferring data between clients and servers. As a popular web programming language, PHP naturally supports HTTP requests and responses.

HTTP request header is the information sent by the client (such as browser) to the server. It contains a lot of useful information, such as the requested URL, request method (GET or POST, etc.), request parameters, etc. The HTTP response header is the information sent by the server to the client, which includes the response status code, response message type, response time, etc.

In PHP, we can use the $_SERVER array to obtain HTTP request header information. For example, if we want to get the requested URL, we can use the following code:

$url = 'http://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];

Here $_SERVER['HTTP_HOST'] is used to get the host name of the current request, while $_SERVER['REQUEST_URI'] is used To get the URL path of the current request.

On the other hand, through PHP's HTTP response headers, we can control the content output to the browser. For example, we can set the Content-Type response header to specify the output content type. The following is an example of setting the Content-Type in the response header to JSON:

header('Content-Type: application/json');

$data = array('name' => 'John', 'age' => 30);
echo json_encode($data);

Here we use PHP's built-in json_encode() function to convert an array containing the name and age attributes into JSON format characters string and output it to the browser as corresponding content. Note that setting Content-Type to application/json tells the browser the type of content currently being output.

In addition to setting Content-Type, we can also set many other HTTP response headers, such as Cache-Control, Set-Cookie, Location, etc. These header information can help us control functions such as caching and redirection.

It should be noted that once the output content starts to be transmitted to the browser, the HTTP response header can no longer be set. In other words, setting HTTP response headers should be done before outputting the content.

In general, HTTP request and response headers in PHP are very important. They can help us complete the development and maintenance of various web applications.

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