PHP中的重定向标题之后的所有代码都会被执行吗？

Question

So I know the general rule of thumb is after doing a header redirect in PHP, you should call exit() to avoid having extra code running, but I want to know if you put code after the redirect header, if it will always run?

I was doing some research on various ways of tracking referrals in Google Analytics and came across this post: Google Analytics Tips & Tricks – Tracking 301 Redirects in Google Analytics

It recommends doing something like this:

<?
Header( “HTTP/1.1 301 Moved Permanently” );
Header( “Location: http://www.new-url.com” );
?>

<script type=”text/javascript”>
var gaJsHost = ((“https:” == document.location.protocol) ? “https://ssl.” : “http://www.”);
document.write(unescape(“%3Cscript src=’” + gaJsHost + “google-analytics.com/ga.js’ type=’text/javascript’%3E%3C/script%3E”));
</script>
<script type=”text/javascript”>
try {
var pageTracker = _gat._getTracker(“UA-YOURPROFILE-ID”);
pageTracker._trackPageview();
} catch(err) {}</script>

From the way I've always understood the header() function, it's up to the browser and it can run the redirect whenever it wants to. So there's no guarantee the JavaScript would actually begin or finish executing prior to the redirect occurring.

PHP's documentation for the header() function indicates the reason for exiting after a redirect is to "make sure that code below does not get executed when we redirect." That doesn't sound like they guarantee all following code will run, just that it could happen.

Regardless, I found a different way to actually manage the tracking, but I wanted to see if I could find out how exactly header() worked in this situation..

Thanks for your help.

Answer 1

Using the header function in PHP only adds to the headers of the response returned by the server. It does not immediately send any data and does not immediately terminate the connection. Any code after the header call will be executed.

In particular, it's a good idea to add a response body even after doing a 301 redirect so that clients that do not support the redirect also get some descriptive response. Infact according to the HTTP 1.1 specification Section 10.3.2 -

Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s). If the 301 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.