Corrupted ZIP files when downloaded from IIS

[Igor DR]

Hello, It's a couple of months I'm experiencing the following strange
behaviour.
All ZIP files that are on my IIS intranet, when downloaded become corrupted.
If I open them on the server they are OK.
If I copy them locally on my PC (transferring the file by File Explorer)
they are OK.
But if I create an Intranet page with a link on them and then I download
them using my browser, when they arrive on my PC they are slightly larger and
corrupted.
It seems like IIS is corrupting them during the file transfer.
Has anyone experienced such a strange thing?
Thanks
Igor

[David Wang]

Post by Igor DR
Hello, It's a couple of months I'm experiencing the following strange
behaviour.
All ZIP files that are on my IIS intranet, when downloaded become corrupted.
If I open them on the server they are OK.
If I copy them locally on my PC (transferring the file by File Explorer)
they are OK.
But if I create an Intranet page with a link on them and then I download
them using my browser, when they arrive on my PC they are slightly larger and
corrupted.
It seems like IIS is corrupting them during the file transfer.
Has anyone experienced such a strange thing?
Thanks
Igor

Many people claim such behavior, but I have never replicated it -- IIS
does not corrupt any compressed files like ZIP on download, as I can
verify with all my IIS versions. What I have found, many times in the
past, is that OTHER software on IIS or between IIS and the web browser
which corrupted the file due to a bug and caused issues. For example,
SQUID proxy was truncating some data streams and appending to others.
Or some HTTP headers were altered to cause the web browser to
misunderstand the download. Or sometimes people rename ZIP files to
different extensions to fool browsers, but some browsers sniff the
content and determine ZIP file regardless of file extension, and
strange things happen.

Anyways, you will have to figure out where the corruption is coming
from. It could be between the web server and web browser, or it may be
misinterpretation by the web browser. You can use Network Monitor to
determine the exact bytes flowing across the network to determine if
the extra bytes came from the web server or not. If so, then you need
to look at additional software configured on IIS which may cause
issue.


//David
http://w3-4u.blogspot.com
http://blogs.msdn.com/David.Wang
//

[Igor DR]

David tahnks for the answer, I can immagine that for you is difficult to
understand what's happening on a far LAN. Just to give you more info:

This BUG corrupts only ZIPs, if I use RAR archives they are not corrupted on
download.
ZIPs are corrupted only when downloaded from the intranet, if downloaded
from Internet they are OK.
My Windows 2003 Server, has not third-party software installed on, no
antivirus, no proxies, just a clean Win2003 installation with IIS.
I think that this problem rised when I installed on my network another
Win2003 server with an ISA 2006 server installed on (clean installation with
ISA server).
My network is very simple, there are 4 servers, 1 file server, 1 intranet
server (the one we are speaking of), 1 Data Protection Server and one proxy
(ISA server).

The problem is not on the client side, because every client of the Intranet
suffers the problem, clients with Norton Antivurs, clients with NOD32
antivirus and clients with no antivirus at all.

Thanks again
Igor

Post by David Wang

Post by Igor DR
Hello, It's a couple of months I'm experiencing the following strange
behaviour.
All ZIP files that are on my IIS intranet, when downloaded become corrupted.
If I open them on the server they are OK.
If I copy them locally on my PC (transferring the file by File Explorer)
they are OK.
But if I create an Intranet page with a link on them and then I download
them using my browser, when they arrive on my PC they are slightly larger and
corrupted.
It seems like IIS is corrupting them during the file transfer.
Has anyone experienced such a strange thing?
Thanks
Igor

Many people claim such behavior, but I have never replicated it -- IIS
does not corrupt any compressed files like ZIP on download, as I can
verify with all my IIS versions. What I have found, many times in the
past, is that OTHER software on IIS or between IIS and the web browser
which corrupted the file due to a bug and caused issues. For example,
SQUID proxy was truncating some data streams and appending to others.
Or some HTTP headers were altered to cause the web browser to
misunderstand the download. Or sometimes people rename ZIP files to
different extensions to fool browsers, but some browsers sniff the
content and determine ZIP file regardless of file extension, and
strange things happen.
Anyways, you will have to figure out where the corruption is coming
from. It could be between the web server and web browser, or it may be
misinterpretation by the web browser. You can use Network Monitor to
determine the exact bytes flowing across the network to determine if
the extra bytes came from the web server or not. If so, then you need
to look at additional software configured on IIS which may cause
issue.
//David
http://w3-4u.blogspot.com
http://blogs.msdn.com/David.Wang
//