PHP: How to send HTTP response code?

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I just found this question and thought it needs a more comprehensive answer:

As of PHP 5.4 there are three methods to accomplish this:

Assembling the response code on your own (PHP >= 4.0)

The header() function has a special use-case that detects a HTTP response line and lets you replace that with a custom one

header("HTTP/1.1 200 OK");

However, this requires special treatment for (Fast)CGI PHP:

$sapi_type = php_sapi_name();
if (substr($sapi_type, 0, 3) == 'cgi')
    header("Status: 404 Not Found");
else
    header("HTTP/1.1 404 Not Found");

Note: According to the HTTP RFC, the reason phrase can be any custom string (that conforms to the standard), but for the sake of client compatibility I do not recommend putting a random string there.

Note: php_sapi_name() requires PHP 4.0.1

3rd argument to header function (PHP >= 4.3)

There are obviously a few problems when using that first variant. The biggest of which I think is that it is partly parsed by PHP or the web server and poorly documented.

Since 4.3, the header function has a 3rd argument that lets you set the response code somewhat comfortably, but using it requires the first argument to be a non-empty string. Here are two options:

header(':', true, 404);
header('X-PHP-Response-Code: 404', true, 404);

I recommend the 2nd one. The first does work on all browsers I have tested, but some minor browsers or web crawlers may have a problem with a header line that only contains a colon. The header field name in the 2nd. variant is of course not standardized in any way and could be modified, I just chose a hopefully descriptive name.

http_response_code function (PHP >= 5.4)

The http_response_code() function was introduced in PHP 5.4, and it made things a lot easier.

http_response_code(404);

That's all.