Especially for dynamic content, this code snippet will speed up your page loads (if used correctly). This snippet shows how to use the
Last-Modified
and the
ETag
to optimize the caching of a website.
// 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 < 10; $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();
// 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 $PageContent;
}
// catch all content so that we can
// do some calculations
ob_start();
// Some example HTML
print '<html>';
// put your content in here:
print '<h1>Example content</h1>';
print '<ul>';
for ($x=0; $x < 10; $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();
// 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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