1. CSC 2720 Building Web Applications Getting and Setting HTTP Headers (With PHP Examples)

2. Outline  What kinds of data are embedded in the HTTP request/response headers?  How useful could these data be?  What can we achieve by setting HTTP response header?  PHP APIs for getting headers from HTTP request  PHP APIs for setting HTTP response headers  Examples

3. Introduction  The data in the HTTP header contains info about client/server and the data embedded in the HTTP body. HTTP/1.1 200 OK Date: Mon, 23 May 2005 22:38:34 GMT Server: Apache/1.3.3.7 (Unix) (Red-Hat/Linux) Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT Etag: "3f80f-1b6-3e1cb03b" Accept-Ranges: bytes Content-Length: 438 Connection: close Content-Type: text/html; charset=UTF-8 Body of the contents goes here … The header section of a HTTP response

4. HTTP Request Headers  You can find out more about your client.  For examples  accept, accept-encoding, accept-language, accept-charset : Content types, compression schemes, languages, and character sets that the web client can handle.  user-agent : Info about the web client and operating system  referer : The URL of the webpage that "brings" the client to the requested page  cookie : Cookies

5. Obtaining HTTP Header Fields  Header fields of the current request is stored in $_SERVER.  For a complete list of predefined names, please refer to http://www.php.net/manual/en/reserved.variables.server.php  Some of the useful info include  $_SERVER['HTTP_USER_AGENT']  Contains info about the web client  $_SERVER['HTTP_REFERER']  URL of the page (if any) which referred the web client to the current page. (May not be reliable)  Cookies should be access through $_COOKIE instead.

6. HTTP Response Headers  You can modify the HTTP response header to  Redirect the web client to another URL  Send a different HTTP status code  Tell the web client whether to cache the current document or not  Tell web client what language is used in the current document  Change the content type of the current document  You can use PHP to dynamically create text file, CSV file, image, etc.  Requesting the web client to download another file.  Set cookies (but in PHP, cookies should be set through $_COOKIE instead.)

7. Examples of HTTP 1.1 Response Headers  Cache-Control  Tells all caching mechanisms from server to client whether they may cache this object.  To tells a client not to cache the requested resource, set the its value to no-cache.  Content-Language  The language the content is in  Content-Type  The MIME type of the content being returned

8. Examples of HTTP 1.1 Response Headers  Expires  The time at which document should be considered as out- of-date  Last-Modified  The time in which the requested resource was last modified.  Location  To redirect the web client to a new URL  Set-Cookie  The cookies that browser should remember.

9. Functions for Dealing with Header Fields in the HTTP Response  header()  Set a raw HTTP header  headers_list()  Return a list of headers to be sent to the web client  The list is a numerically indexed array  headers_sent()  Return FALSE if no HTTP headers have already been sent or TRUE otherwise

10. <?php header('Location: http://www.yahoo.com/');http://www.yahoo.com/ exit(); // Return immediately ?> 1234512345 Redirecting the web client to another URL  header() must be called before any actual output is sent! When a web client access the above file, it will go to http://www.yahoo.com immeidately.http://www.yahoo.com <?php header('Location: http://www.yahoo.com/');http://www.yahoo.com/ exit(); ?> 1234512345 Even with only one empty space sent, subsequent calls to header() will fail.

11. <?php header("HTTP/1.0 404 Not Found"); ?> 123456123456 Send a different HTTP status code Creating a custom-made page to display the error message when a requested resource cannot be found by the server. You also need to configure the web server to use your custom-made page.

12. <?php // HTTP/1.1 header("Cache-Control: no-cache, must-revalidate"); ?> 12341234 Tell the web client whether to cache the current document or not For the format of HTTP header fields, please refer to HTTP/1.1: Header Field Definitions http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html The above example is extracted from: http://www.php.net/header

13. <?php $imagename = 'test.jpg'; $info = getimagesize($imagename); $fs = filesize($imagename); // Setting the mime-type of the file header("Content-type: {$info['mime']}\n"); // Send as attachment (request client to download) header("Content-Disposition: attachment;". " filename=\"$imagename\"\n"); header("Content-Length: $fs\n"); readfile("$imagename"); ?> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Requesting the web client to download a file

14. References  Wiki: List of HTTP headers  http://en.wikipedia.org/wiki/List_of_HTTP_headers http://en.wikipedia.org/wiki/List_of_HTTP_headers  HTTP/1.1: Header Field Definitions  http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html  PHP Manual  http://www.php.net/manual/en/index.php http://www.php.net/manual/en/index.php