readFile - Image Caching on client side

[Schnulla]

Hello forum,

 

I have the following code to deliver ALL of my website

graphics including the jpg/png files for the interface:

 

if (($FileInfos= stat($File)) or die("File not found!"));

$FileExt= substr($File, -3); // no need to check for >3 cause I always append a path ;-)
    
$FileTypeMIME= array("jpg" => "image/jpeg",
                         "png" => "image/png",
                         "gif" => "image/gif",
                         "ico" => "image/x-icon");

$ContentType= $FileTypeMIME[$FileExt];
if (empty($ContentType)) die("You are not allowed to access this file!");

header("Content-Type: " . $ContentType); 
header("Content-Length: " . $FileInfos[7]);
header("Content-Disposition: filename=" . basename($File));
header("Last-Modified: " . gmdate("D, d M Y H:i:s", $FileInfos[9]) . ' GMT');
readfile($File);

 

But I have the feeling that the images are not cached on client

side so if I load the same page twice it looks a little bit as if the

images are received again from server. I'm new to php btw.

 

Shouldn't the images be in cache so that the browser only compares

the Last-Modified header field and then stops receiving data?

Or is it just stupid from me to think so and I should not deliver

the interface graphics via php (readFile).

 

Thanks!

[Schnulla]

Thanks for no-answer.... 

 

Anyway I found a 2 step solution and hope it is useful for someone who is reading this:

 

1. Tell the client to cache the image when sending the image:

header('Cache-Control: public, must-revalidate, max-age=3600'); // 1 hour

 

2. If the client requests the image again:

// Getting headers sent by the client.
    $ClientHeaders= apache_request_headers();
    
    // Checking if the client is validating his cache and if it is current.
    if (isset($ClientHeaders["If-Modified-Since"]) && (strtotime($ClientHeaders["If-Modified-Since"]) == $FileInfos[9])) {
      // Client's cache IS current, so we just respond '304 Not Modified'.
      header("Last-Modified: " . gmdate("D, d M Y H:i:s", $FileInfos[9]) . " GMT", true, 304);
    } else {
      // Image not cached or cache outdated, we respond '200 OK' and output the image.        
      header('Cache-Control: public, must-revalidate, max-age=3600');
      header("Last-Modified: " . gmdate("D, d M Y H:i:s", $FileInfos[9]) . " GMT", true, 200);
      header("Content-Type: " . $ContentType); 
      header("Content-Length: " . $FileInfos[7]);
      header("Content-Disposition: filename=" . basename($File));
      readfile($File);
    }    

[Schnulla]

CORRECTION:

 

You must also send the cache directive in the 304 response to make it work!

 

 

// Getting headers sent by the client.
    $ClientHeaders= apache_request_headers();
    
    // Checking if the client is validating his cache and if it is current.
    if (isset($ClientHeaders["If-Modified-Since"]) && (strtotime($ClientHeaders["If-Modified-Since"]) == $FileInfos[9])) {
      // Client's cache IS current, so we just respond '304 Not Modified'.
      header('Cache-Control: public, must-revalidate, max-age=3600');
      header("Last-Modified: " . gmdate("D, d M Y H:i:s", $FileInfos[9]) . " GMT", true, 304);
    } else {
      // Image not cached or cache outdated, we respond '200 OK' and output the image.        
      header('Cache-Control: public, must-revalidate, max-age=3600');
      header("Last-Modified: " . gmdate("D, d M Y H:i:s", $FileInfos[9]) . " GMT", true, 200);
      header("Content-Type: " . $ContentType); 
      header("Content-Length: " . $FileInfos[7]);
      header("Content-Disposition: filename=" . basename($File));
      readfile($File);
    }