last-modified.php

<?php
// Autor: gallir@uib.es, header implementation for weak y strong
// HTTP validator according to RFC2616 of HTTP/1.1
// It's also compatible with HTTP/1.0 and 
// take care of Netscape non-standard headers
// If more than 10800 secs have gone since last load
// it makes the client/cache to reload the page

// Call this function before doing anything else with databases or similar.

if(function_exists('getallheaders')){
	function DoHeaders($lastModified, $logged=FALSE) {
	// $lastModified: last database modification, in "epochs"
	// $logged: FALSE/TRUE // It takes in account that pages can be accessed
	// as public or authorised

		$now = time();
		$maxCache = $now - 10800; // Max. time before refreshing
		$headers = getallheaders();
		$refresh=TRUE; // refresh, as default

		if(isset($headers["If-Modified-Since"])) { 
			// Netscape sends ";length = xxx" after the date
			$arraySince = explode(";", $headers["If-Modified-Since"]);
			$since = strtotime($arraySince[0]);
			if($since >= $lastModified) $refresh=FALSE;
		}

		if($logged == TRUE) {
			$tag="\"AUT".$lastModified."\"";  // A private page
		} else {
			$tag="\"PUB".$lastModified."\"";  // and public one
		}

		if(isset($headers["If-None-Match"])) { // check ETag
			if(strcmp($headers["If-None-Match"], $tag) == 0 ){
				$refresh=FALSE;
			}else{
				$refresh=TRUE;
			}
		}
		if(!$refresh) {
			header("HTTP/1.1 304 Not changed");
		// The first header must be this
		// otherwise Netscape gives "No Data" error
			$strLastModified = gmdate("r", $lastModified);
		}else{
			$strLastModified = gmdate("r", $now);
		}
		header("Content-type: text/html; charset=utf-8");
		header("ETag: $tag");  // The new TAG
		header("Last-Modified: $strLastModified");
		header("Expires: " . gmdate("r", time()+1));
		header("Cache-Control: max-age=1, must-revalidate"); // HTTP/1.1
	// Netscape doesn't handle very well the header("Pragma: no-cache");
		if(!$refresh) {
			ob_end_clean(); // Just in case..
			die; // Don't do anything more
		}
		ob_start(); // We start buffering to allow "Content-length" header
	// at the end of the output to allow HTTP/1.0 persistent connections.
	}
	
}else{
	function DoHeaders($lastModified, $logged=FALSE) {
	// $lastModified: last database modification, in "epochs"
	// $logged: FALSE/TRUE // It takes in account that pages can be accessed
	// as public or authorised

		$now = time();
		$maxCache = $now - 10800; // Max. time before refreshing
		//$headers = getallheaders();
		$refresh=TRUE; // refresh, as default

		if(isset($_SERVER["If-Modified-Since"])) { 
			// Netscape sends ";length = xxx" after the date
			$arraySince = explode(";", $_SERVER["If-Modified-Since"]);
			$since = strtotime($arraySince[0]);
			if($since >= $lastModified) $refresh=FALSE;
		}

		if($logged == TRUE) {
			$tag="\"AUT".$lastModified."\"";  // A private page
		} else {
			$tag="\"PUB".$lastModified."\"";  // and public one
		}

		if(isset($_SERVER["If-None-Match"])) { // check ETag
			if(strcmp($_SERVER["If-None-Match"], $tag) == 0 ){
				$refresh=FALSE;
			}else{
				$refresh=TRUE;
			}
		}
		if(!$refresh) {
			header("HTTP/1.1 304 Not changed");
		// The first header must be this
		// otherwise Netscape gives "No Data" error
			$strLastModified = gmdate("r", $lastModified);
		}else{
			$strLastModified = gmdate("r", $now);
		}
		header("Content-type: text/html; charset=utf-8");
		header("ETag: $tag");  // The new TAG
		header("Last-Modified: $strLastModified");
		header("Expires: " . gmdate("r", time()+1));
		header("Cache-Control: max-age=1, must-revalidate"); // HTTP/1.1
	// Netscape doesn't handle very well the header("Pragma: no-cache");
		if(!$refresh) {
			ob_end_clean(); // Just in case..
			die; // Don't do anything more
		}
		ob_start(); // We start buffering to allow "Content-length" header
	// at the end of the output to allow HTTP/1.0 persistent connections.
	}
}


// Add following code at the end of your output

// If we allowed buffering before, we send the length
// to allow HTTP/1.0 persistent connections
function SendLength() {
	if(ob_get_length()) {
		header("Content-Length: " . ob_get_length());
		ob_end_flush();
		die;  // Delete it if you don't want to finish the script
	}
}
?>