XP bug when talking to CUPS through http proxy

[Luigi Rizzo]

> > This posting is mostly for the archives in case someone has
> > the same problem and doesn't want to waste a lot of time debugging it.
> >
> > I think i have hit an annoying bug with Windows XP (including SP2)
> > when trying to access a CUPS printer through an http/https proxy,
> > _and_ the printer requires authentication.
> >
> > In our setting, some PCs on a private network need to access
> > an external CUPS server through an HTTP proxy. The proxy is
> > correctly configured in "Internet Options" on windows.
> >
> > When you try to "Add a printer" from the Windows panel, Windows
> > does a first request to CUPS through the proxy, and receives back a
> >     '401 Unauthorized'
> > response, with a challenge for the authentication.
> > At this point, unfortunately, Windows <b>stops using the proxy</b>
> > and sends the next request directly to the server without going
> > through the proxy. As a result, the printer is not accessed
> > because there isn't a direct path to the server.
...

> I used CUPS at home with 5 clients(3 Windows XP, 1 Windows 98, 1 Vista)
> and I don't seem to have the issue you're experiencing. My CUPS server
> is running under FC5 with CUPS 1.2 installed.
>
> All of the clients goes through my proxy server all of which requires
> basic authentication(PAM module).
>
> I may not understand your problem correctly but just for verification,
> I can access my CUPS server web interface through any of my clients via
> proxy server.

the web interface is not involved here. Explorer obeys the
proxy setting and talks to the proxy even after the 401.
Also note that if you have a direct path to the CUPS server
(e.g. through a nat box etc that lets you bypass the proxy)
the problem is hidden and you may not notice that it exists.

> Check your host files. Do some ping test, etc. Access the CUPS server's
> web interface locally(not through proxy) to check configuration is set
> correctly.

everything is set correctly on the cups side - i have verified the behaviour i documented above with a tcpdump on the client side
(showing that it does the first requests to the proxy, and then
switches to direct connection after the 401), and with the logs
of the proxy server.

This is with BasicDigest authentication , but even Basic does
the same thing.

cheers
luigi