sivaprabug · December 8, 2016 10:45
diff --git a/eTag-cache.php b/eTag-cache.php
 <?php
 // Start output buffering, this will
 // catch all content so that we can
 // do some calculations
 ob_start();


 // Some example HTML
 print '<html>';

 // put your content in here:
 print '<h1>Example content</h1>';

 print '<ul>';
 for ($x=0; $x < 100; $x++)
    print "<li>List item $x</li>";

 print '</ul>';
 print '</html>';

 // or include() something here


 // Now save all the content from above into
 // a variable
 $PageContent = ob_get_contents();
 echo $PageContent;

 // And clear the buffer, so the
 // contents will not be submitted to
 // the client (we do that later manually)
 ob_end_clean();


 // Generate unique Hash-ID by using MD5
 $HashID = md5($PageContent);

 // Specify the time when the page has
 // been changed. For example this date
 // can come from the database or any
 // file. Here we define a fixed date value:
 $LastChangeTime = 1144055759;

 // Define the proxy or cache expire time
 $ExpireTime = 3600; // seconds (= one hour)

 // Get request headers:
 $headers = apache_request_headers();
 // you could also use getallheaders() or $_SERVER
 // or HTTP_SERVER_VARS

 // Add the content type of your page
 header('Content-Type: text/html');

 // Content language
 header('Content-language: en');

 // Set cache/proxy informations:
 header('Cache-Control: max-age=' . $ExpireTime); // must-revalidate
 header('Expires: '.gmdate('D, d M Y H:i:s', time()+$ExpireTime).' GMT');

 // Set last modified (this helps search engines
 // and other web tools to determine if a page has
 // been updated)
 header('Last-Modified: '.gmdate('D, d M Y H:i:s', $LastChangeTime).' GMT');

 // Send a "ETag" which represents the content
 // (this helps browsers to determine if the page
 // has been changed or if it can be loaded from
 // the cache - this will speed up the page loading)
 header('ETag: ' . $HashID);


 // The browser "asks" us if the requested page has
 // been changed and sends the last modified date he
 // has in it's internal cache. So now we can check
 // if the submitted time equals our internal time value.
 // If yes then the page did not get updated

 $PageWasUpdated = !(isset($headers['If-Modified-Since']) and
    strtotime($headers['If-Modified-Since']) == $LastChangeTime);


 // The second possibility is that the browser sends us
 // the last Hash-ID he has. If he does we can determine
 // if he has the latest version by comparing both IDs.

 $DoIDsMatch = (isset($headers['If-None-Match']) and
    ereg($HashID, $headers['If-None-Match']));

 // Does one of the two ways apply?
 if (!$PageWasUpdated or $DoIDsMatch){

    // Okay, the browser already has the
    // latest version of our page in his
    // cache. So just tell him that
    // the page was not modified and DON'T
    // send the content -> this saves bandwith and
    // speeds up the loading for the visitor

    header('HTTP/1.1 304 Not Modified');

    // That's all, now close the connection:
    header('Connection: close');

    // The magical part:
    // No content here ;-)
    // Just the headers

 }
 else {

    // Okay, the browser does not have the
    // latest version or does not have any
    // version cached. So we have to send him
    // the full page.

    header('HTTP/1.1 200 OK');

    // Tell the browser which size the content
    header('Content-Length: ' . strlen($PageContent));

    // Send the full content
    print $PageContent;
 }
 ?>
	<?php
	// Start output buffering, this will
	// catch all content so that we can
	// do some calculations
	ob_start();


	// Some example HTML
	print '<html>';

	// put your content in here:
	print '<h1>Example content</h1>';

	print '<ul>';
	for ($x=0; $x < 100; $x++)
	print "<li>List item $x</li>";

	print '</ul>';
	print '</html>';

	// or include() something here


	// Now save all the content from above into
	// a variable
	$PageContent = ob_get_contents();
	echo $PageContent;

	// And clear the buffer, so the
	// contents will not be submitted to
	// the client (we do that later manually)
	ob_end_clean();


	// Generate unique Hash-ID by using MD5
	$HashID = md5($PageContent);

	// Specify the time when the page has
	// been changed. For example this date
	// can come from the database or any
	// file. Here we define a fixed date value:
	$LastChangeTime = 1144055759;

	// Define the proxy or cache expire time
	$ExpireTime = 3600; // seconds (= one hour)

	// Get request headers:
	$headers = apache_request_headers();
	// you could also use getallheaders() or $_SERVER
	// or HTTP_SERVER_VARS

	// Add the content type of your page
	header('Content-Type: text/html');

	// Content language
	header('Content-language: en');

	// Set cache/proxy informations:
	header('Cache-Control: max-age=' . $ExpireTime); // must-revalidate
	header('Expires: '.gmdate('D, d M Y H:i:s', time()+$ExpireTime).' GMT');

	// Set last modified (this helps search engines
	// and other web tools to determine if a page has
	// been updated)
	header('Last-Modified: '.gmdate('D, d M Y H:i:s', $LastChangeTime).' GMT');

	// Send a "ETag" which represents the content
	// (this helps browsers to determine if the page
	// has been changed or if it can be loaded from
	// the cache - this will speed up the page loading)
	header('ETag: ' . $HashID);


	// The browser "asks" us if the requested page has
	// been changed and sends the last modified date he
	// has in it's internal cache. So now we can check
	// if the submitted time equals our internal time value.
	// If yes then the page did not get updated

	$PageWasUpdated = !(isset($headers['If-Modified-Since']) and
	strtotime($headers['If-Modified-Since']) == $LastChangeTime);


	// The second possibility is that the browser sends us
	// the last Hash-ID he has. If he does we can determine
	// if he has the latest version by comparing both IDs.

	$DoIDsMatch = (isset($headers['If-None-Match']) and
	ereg($HashID, $headers['If-None-Match']));

	// Does one of the two ways apply?
	if (!$PageWasUpdated or $DoIDsMatch){

	// Okay, the browser already has the
	// latest version of our page in his
	// cache. So just tell him that
	// the page was not modified and DON'T
	// send the content -> this saves bandwith and
	// speeds up the loading for the visitor

	header('HTTP/1.1 304 Not Modified');

	// That's all, now close the connection:
	header('Connection: close');

	// The magical part:
	// No content here ;-)
	// Just the headers

	}
	else {

	// Okay, the browser does not have the
	// latest version or does not have any
	// version cached. So we have to send him
	// the full page.

	header('HTTP/1.1 200 OK');

	// Tell the browser which size the content
	header('Content-Length: ' . strlen($PageContent));

	// Send the full content
	print $PageContent;
	}
	?>
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