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CSC 2720 Building Web Applications

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

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CSC 2720 Building Web Applications

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  1. CSC 2720Building 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 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 data in the HTTP header contains info about client/server and the data embedded in the HTTP body. 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. Redirecting the web client to another URL • header() must be called before any actual output is sent! 1 2 3 4 5 <?php header('Location: http://www.yahoo.com/'); exit(); // Return immediately ?> When a web client access the above file, it will go to http://www.yahoo.comimmeidately. 1 2 3 4 5 <?php header('Location: http://www.yahoo.com/'); exit(); ?> Even with only one empty space sent, subsequent calls to header() will fail.

  11. Send a different HTTP status code 1 2 3 4 5 6 <?php header("HTTP/1.0 404 Not Found"); ?> <html> <!-- Content of the error page goes here … --> </html> 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. Tell the web client whether to cache the current document or not 1 2 3 4 <?php // HTTP/1.1 header("Cache-Control: no-cache, must-revalidate"); ?> • 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. Requesting the web client to download a file 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 <?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"); ?>

  14. References • 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 • PHP Manual • http://www.php.net/manual/en/index.php

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