image caching...

Anon

Have an interesting problem. Maybe some of you can shed light on it. 😉

-MSN Conversation---
Jeremiah says:
Is there a way in php to make an image refresh?
Jeremiah says:
see.. in my image uploader program
Jeremiah says:
it displays the image
Jeremiah says:
say you upload car.jpg
Jeremiah says:
it will upload and show the car and that photo will be in the cache
Jeremiah says:
but say you upload a different picture named car.jpg and that photo is still in the cache
Jeremiah says:
it will still display that old photo even though you replaced it because it's the same name
Jeremiah says:
and make you think you didn't actually replace it
Jeremiah says:
So I need to refresh it.

andrew says:
hmm, I'm not sure
andrew says:
try phpbuilder.com

Jeremiah says:

k

end conversation.

vsego

image.php:
<?php
header("Content-type: image/jpeg");
// Next 4 lines are copied from manual (function header()):
header ("Expires: Mon, 26 Jul 1997 05:00:00 GMT"); // Date in the past
header ("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT"); // always modified
header ("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
header ("Pragma: no-cache"); // HTTP/1.0
readfile("$path_to_images/$f"); // $f is parameter
?>

Call: image.php?f=car.jpg

rrijnders

Personally, I don't let users name thier own images when they upload them. I track the images they upload in a db file that stores
image info like:

image_name
  image_description
  image_file

where image_file is the actual name of the file on disk. This file name is generated uniquely for each uploaded image. Even if they replace image_name = "car", the new image will have a unique, different name in the image_file column.

This method completely avoids the image caching problems you face, prevents different users from accidently over writing each others (or their own) image files, and prevents users from trying to cause mischeif by naming an uploaded file the same name as some other image on your site and replacing it.

-- HTH
-- Rich

Anon

This method completely avoids the image
caching problems you face, prevents
different users from accidently over
writing each others (or their own) image
files,

This should be accomplished with checking existing files first and reporting any errors to user rather (and asking to than with just naming files differently.

and prevents users from trying to cause
mischeif by naming an uploaded file the
same name as some other image on your
site and replacing it.

What if they want to replace the image? Suppose previously uploaded image was poor in quality or had visible errors or whatnot? You just keep piling images in your directory?

Of course, I don't know exactly what your image db is doing or what is it built for but still I'd prefer more flexible approach.

rrijnders

You misinterpret my technique. The user car is always car, but that is stored in the image_name field. Only the image_file value gets changed and is always unique.

IE:

User uploads an image and calls it car.
Application stores it as:
  image_name = "car"
  image_value = "img0001.jpg"
User wants to display car so the application generates
  <img src="img0001.jpg">

If the user wants to replace car they can.

User uploads a new image for car
Application stores it as:
  image_name = "car"
  image_value = "img0002.jpg"
User wants to display car so the application generates
  <img src="img0002.jpg">

Get the idea? Since the generated <IMG> tag is different now, no cache problems.

-- Rich

vsego

I still find my solution to be easier...