Antwort: [Mod_gzip] corrupted images???

[Jody Brownell]

After a few days of testing and the removal of mod_gzip from our
configuration we are still getting the corrupted images. (it took 
a while *sigh*).

It appears the corruption is happening on the client side for whatever
reason. We will have to track this down, when we come to a definative 
conclusion I will make a post to the list and let you folks know.

BTW, mod_gzip is a great module. Glad to see more work being done on it!

thanks for the help,
jody

-----Original Message-----
From: Michael.Schroepl@telekurs.de [mailto:Michael.Schroepl@telekurs.de]
Sent: Wednesday, September 25, 2002 8:56 AM
To: mod_gzip@lists.over.net
Subject: Antwort: [Mod_gzip] corrupted images???



Hi Jody,


> I am having a weird issue that, sometimes (intermitent) I have
> partial images being served.

could you please give us a little more information about
- which MIME types these images have and
- why you want to compress them at all?
If you have optimized GIF and/or PNG images you will not
get any advantage by compressing these files using mod_gzip.
You will save some one-digit percentage of size, if any -
in a large percentage of cases you will get no savings at
all, but a mod_gzip status code telling you that the com-
ressed file indeed was larger than the original file.

> The server itself hosts 3 main sites which means 2 virtual hosts
> for each site. (One for SSL and one for mod_jk/gzip pair).
> Everything works frin 95% of the time, every now and then I get
> a corrupted image.

What do you mean with "get a corrupted file"?

Do your Apache logs tell you that the size of this file
changes from request to request, i. e. mod_gzip produces
different output (which would surprise me a lot) or do
some of your visitors use some broken browser that isn't
able to decompress compressed images properly?
If your get some "corrupted file", then are you able to
save this file from the browser to a disk file? And when
you click "reload" in the browser, will the same image
still be broken? If not, and you store this file as well,
are the resulting files identical or not?
Does cleaning the browser cache make the problem fo away?

I have read about problems that some browsers might have
displaying gzip-compressed images, but as I am optimizing
my images statically (and the dynamically generated GIFs
are already compressed so well that mod_gzip would'n save
a bit there) I don't have any experience about which brow-
ser is able to interpret which image types in compressed
form.

> I am wondering if anyone else has ever noticed any issues with
> similar setups?

There have been postings about problems with compressed
images some time in the past. But noone seems to have
tried to find out which browser has which bugs in this
area.

> Or is this system too complicated to begin with?

It doesn't look like this were a problem of the server
configuration. I would rather suspect browsers and/or
caching proxies to be responsible for this effect.

> Mod gzip is configured to not serve any content with a mime
> type of image/*

Then why should the Apache serve broken images at all?
Do the HTTP headers of the response indicate that the
file has been compressed?

Regards, Michael


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