CODEWITHSUNDEEP
phpbrowser-cache
Omid Kamangar
Omid Kamangar

Reputation: 5778

Cache a dynamically generated image

I am generating some images using a PHP script.
I want to cache the images, so the browser doesn't have to load them each time. I have added these headers:

'max-age' => 3600
'Etag' => md5($image->getSlug())
'last-modified' => $image->getUpdatedAt()
'Vary' => 'Accept-Encoding'
'content-length' => (size of the image)
'Content-type' => 'image/jpeg'

but the image is not cached, and it is loaded every time by the browser.

The response headers look like these (using Firebug):

Date             Sun, 04 Sep 2011 00:25:45 GMT
Server           Apache/2.2.16 (Debian)
X-Powered-By     PHP/5.3.3-7+squeeze1
Cache-Control    max-age=3600, private
Etag            "9280c6c672c6535c13b7481972f9ac39"
Last-Modified    Sat, 27 Aug 2011 01:36:24 GMT
Vary             Accept-Encoding
Content-Length   26231
Connection       close
Content-Type     image/jpeg

Does anyone have any idea what is wrong here?

Upvotes: 2

Views: 1158

Answers (2)

kirb
kirb

Reputation: 2049

One way you can force an image to be cached is to set the Last-Modified tag to the date and time that the image you want to use was created. For example:

<?php
error_reporting(0); //disable error reporting as it will corrupt the image
session_start(); //start a php session
$date = date(DATE_RFC822);
//some code to connect to a mysql database
$query = mysqli_query($link, "SELECT * FROM images WHERE sessionid='$sessionid'");
if ($query and mysqli_num_rows($query) == 1) { //if mysql returned one row
    $row = mysqli_fetch_array($query); //get the row as an array
    $date = $row["date"]; //set the date to the one in the database
} else { //if the user has never seen the image before
    mysqli_query($link, "INSERT INTO images SET sessionid='$sessionid', date='$date'"); //put the session id and date into the database for later use
}
header("Last-Modified: $date");
//some code that would generate and send the image

Don't forget to create a database (in any database program) that contains a table called images with sessionid, which should be the primary key, and date. Both should be strings.

Upvotes: 2

gview
gview

Reputation: 15361

You need to calculate and add an Expires: header. For example:

Expires: Fri, 30 Oct 2011 14:19:41 GMT

Upvotes: 0

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