Setting Response Headers
As
we’ve already discussed, the HTTP response that a
server sends back to a client contains headers that identify the type
of content in the body of the response, the server that sent the
response, how many bytes are in the body, when the response was sent,
etc. PHP and Apache normally take care of the headers for you,
identifying the document as HTML, calculating the length of the HTML
page, and so on. Most web applications never need to set headers
themselves. However, if you want to send back something
that’s not HTML, set the expiration time for a page,
redirect the client’s browser, or generate a
specific HTTP error, you’ll need to use the
header( ) function.
The only catch to setting headers is that you must do so before any
of the body is generated. This means that all calls to
header( )
(or setcookie( ),
if you’re setting cookies) must happen at the very
top of your file, even before the <html>
tag. For example:
<?php
header('Content-Type: text/plain');
?>
Date: today
From: fred
To: barney
Subject: hands off!
My lunchbox is mine and mine alone. Get your own,
you filthy scrounger!Attempting to set headers after the document has started results in this warning:
Warning: Cannot add header information - headers already sentDifferent Content Types
The
Content-Type header identifies the type of document being returned.
Ordinarily this is "text/html", indicating an HTML
document, but there are other useful document types. For example,
"text/plain" ...
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