HTTP 1.1 and 1.0 Cache Validator

// Autor: [email protected], 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.

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

	if($logged) {
		$tag=""AUT".$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 Netcrap gives "No Data" error
		$strLastModified = gmdate("r", $lastModified);
	} else
		$strLastModified = gmdate("r", $now);

	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-Lenght" 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 lenght
// 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
	}
}