IIS 8.5, serving corrupt zip files

compressionhttpiisiis-8web-server

I have a WS2012r2 web server with multiple sites. We host zip files that are accessed though a direct URL (http://mysite.me/Test.zip").

These files are used to update our software and are downloaded using a c# WebClient but the same issue occurs when downloading via browsers.

The issue is only affecting one client, the file is being corrupted as a part of the download, it looks like it is one KB smaller than what it should be. But if i put the same zip on dropbox and download it, it works fine.

  • I have disabled static content compression
  • I have changed the mime type to application/zip or application/octet-stream
  • I have disabled output caching

these are the headers being returned:

Accept-Ranges : bytes

Content-Length : 1289611

Content-Type : application/zip

Date : Fri, 18 Jul 2014 01:00:20 GMT

ETag : "e3b794fa2cf1:0"

Last-Modified : Thu, 17 Jul 2014 22:36:40 GMT

Server : Microsoft-IIS/8.5

X-Powered-By : ASP.NET

Like I say this is only happening to one client, but only on my server.

Any idea?

Best Answer

This could be caused by an HTTP proxy at the client site (e.g. an office firewall, SQUID cache server) or on the client computer.

An interesting test would be to rule out anything along the way being able to interfere with the download, by serving the file over HTTPS.