[packagekit] Setting the proxy

[Richard Hughes]

I've been debugging a problem with using different sessions, and using
a network proxy.

The issues are threefold:

* The session proxy setting is only set when the session process is
started, or when the gconf keys change
* The packagekitd does not save the proxies when it times out,
therefore, on next auto-start it's as if a proxy has never been set
* The proxy is systemwide, not tracked per-session

So, how to fix this properly... The key issue is that the SetProxy()
method is on the main interface, and not the transaction interface.
This means that if we have multiple sessions with different proxies,
then the proxy used is the last one set, which isn't ideal at all.

So, we have two solutions:

1. Track the session in packagekitd when the proxy gets set, and use
ConlsoleKit to get the session when we get the transaction method, and
choose the proxy based on that.

2. Break the API and move the SetProxy method to the transaction
interface, and then set the proxy on each method call. This fixes
things, but requires every application using PackageKit to also query
the proxy settings, which could quickly become tiresome, and also ties
us to a GConf dep in an otherwise GLib library.

The first has the disadvantage of calling into ConsoleKit for every
method, which adds some delay.
The second has the disadvantage of breaking API, and requiring normal
applications to track the proxy, or adding a GConf dep to the
PkControl instance.

I have chosen option 1 as this avoids breaking API and also doesn't
require clients to track the session proxy.

For the 0.4.x clients, I've patched GpkWatch (the part of
gpk-update-icon that sets the proxy) to re-set the proxy when
packagekitd re-appears on the bus. That should fix things in the
single user login case, but will suffer the over-write problem
mentioned earlier. I've spent yesterday evening writing up a plan of
action, and this
morning coding it up in PackageKit git master.

The implementation notes are here:
http://cgit.freedesktop.org/packagekit/plain/docs/setting-the-proxy.txt and the
security implication notes are here:
http://cgit.freedesktop.org/packagekit/plain/docs/security.txt

So, basically, using a proxy server using git head nor works reliably,
but before it was flaky. No client code has to change for kpackagekit
or packagekit-qt. I would appreciate some testing if you use a proxy,
or any code review. One thing I'm still not sure about is sending the
proxy username and password across the system DBus unencrypted, but I
figure for HTTP proxies it's sent over the network unencrypted anyway,
so this isn't a big deal. Ideas welcome.

Richard.