XP bug when talking to CUPS through http proxy

Luigi Rizzo rizzo at icir.org
Thu Jul 5 09:33:03 PDT 2007


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.

A similar problem occurs if the response is '426' (e.g.
because CUPS' default is to always use encryption when passing
authentication info): the initial request goes through the
proxy, then upon the 401/426 response windows XP stops using
the proxy and goes directly to the server.

I don't think that this problem can be solved on the CUPS side,
but wonder if is there anyone else who experienced the same issue,
and maybe (I know this is not the forum to ask) whether there is
a Microsoft patch that fixes this.
If not, I think it is worthwhile mentioning the problem on
the CUPS notes.





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