Phalcon, HTTP Cache of a generated image - php

Question

I'm writing a web service who generate thumbs of images with Phalcon.
I try to HTTP cache it.
This is my code :
$seconds = 43200;
$expireDate = new DateTime();
$expireDate->modify("+ $seconds seconds");
$finfo = new finfo(FILEINFO_MIME_TYPE);
$app->response->setHeader('Content-Type', 'Content-type: ' . $finfo->buffer($data));
$app->response->setExpires($expireDate);
$app->response->setHeader('Pragma', 'cache');
$app->response->setHeader('Cache-Control', "private, max-age=$seconds");
$app->response->setHeader('E-Tag', md5(filemtime($path)));
$app->response->setHeader('Last-Modified', gmdate('D, d M Y H:i:s', filemtime($path)).' GMT');
$app->response->sendHeaders();
echo $data;
The image is corretly displayed. But when you refresh it, the http code is always 200, I try on another image of another website and I've got 200, 304, 304, 304...
This is my raw response header :
HTTP/1.1 200 OK
Date: Thu, 27 Aug 2015 18:38:41 GMT
Server: Apache/2.4.10 (Debian)
Expires: Fri, 28 Aug 2015 06:38:41 GMT
Pragma: cache
Cache-Control: private, max-age=43200
E-Tag: 501a8d62f276eb5b165b8a709bf4e5b4
Last-Modified: Sun, 05 Jul 2015 20:34:14 GMT
Keep-Alive: timeout=5, max=90
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: image/jpeg
Someone see what i'm doing wrong ?
Thanks in advance.

Answer 1

Your php code needs to return the 304 Not Modified header when the browser asks if the cached image is still valid. Put an if statement at the top of your script to handle that request before sending the image again.
You are always sending the image that's why the browser is showing a 200 response.

Answer 2

If you add the max-age to the last-modified date you get an expiry time in the past.
Your code is a mess of every possible way to influence caching (and btw http does not define a "pragma: cache" header). As to the question of what you should be doing, that depends on what you are trying to acheive - just getting load off the server, faster page rendering or caching up to apre-planned replacement or something else. And you haven't told us what this is.

Answer 3

Thanks PaulS !
$filemtimeOk = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && $filemtime <= strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']);
$etagOk = isset($_SERVER['HTTP_IF_NONE_MATCH']) && $_SERVER['HTTP_IF_NONE_MATCH'] == $etag;
if ($filemtimeOk && $etagOk) {
$app->response->setStatusCode(304, "Not Modified");
$app->response->sendHeaders();
} else {
// Normal case... (send data and headers)
}