HTTP_HOST vs. SERVER_NAME in PHP: Which Variable Should I Use?

Understanding the Distinction between HTTP_HOST and SERVER_NAME in PHP

PHP provides two variables, $_SERVER['HTTP_HOST'] and $_SERVER['SERVER_NAME'], that convey information about the web request's host. This article will delve into the differences between these variables and provide guidance on when to use each.

HTTP_HOST

The HTTP_HOST variable is gathered from the HTTP request header and represents the target host specified by the client. This value can be manipulated by the user agent and is not necessarily reliable for security purposes.

SERVER_NAME

The SERVER_NAME variable is configured in the server's configuration files and represents the hostname of the server hosting the PHP script. It is generally more reliable as it is under the server's control.

Choosing Between HTTP_HOST and SERVER_NAME

The appropriate choice between HTTP_HOST and SERVER_NAME depends on the intended usage:

• Use HTTP_HOST if you need the host information as perceived by the client browser.
• Use SERVER_NAME if you require a reliable hostname for security-critical operations or server configuration purposes.

Reliability Considerations

It is important to note that the reliability of SERVER_NAME is contingent upon the web server's configuration. If the UseCanonicalName directive is not enabled in Apache HTTP Server's VirtualHost section, it may incorrectly return the HTTP Host header's value for SERVER_NAME.

Setting UseCanonicalName to "on" ensures that Apache HTTP Server provides an accurate SERVER_NAME value. It is recommended to verify the server configuration to guarantee the reliability of this variable.

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