[Spice-devel] Questions regarding Bug 62033 - Means to detect local-only

[Fedor Lyakhov]

Hello Zeeshan, Marc-André and other Spice developers,

I think about implementing a solution for this bug 62033 (
https://bugs.freedesktop.org/show_bug.cgi?id=62033).

First of all, need to clarify what is requested and what is really needed
in this request. Zeeshan suggests as a simple yet acceptable solution for
vdagent to report 'local-only' connection non-dynamically.. as I understand
this means reporting only once, at startup (?). I think it isn't enough
because this connection state may change easily during X session lifetime -
in general user is free to connect locally and then re-connect from remote
host, and vise versa. So I propose more generic approach, when vdagent
reports current connection state dynamically when state is changed. It will
be up to gnome-settings-daemon to act on this signal and toggle animations
accordingly.

If this is acceptable, we need to decide on the interface. I think there
are 2 appropriate technologies:
1. raw socket [or something like this]
2. D-Bus

I'm not an expert in D-Bus and freedesktop in general (good opportunity for
me to learn!) but looks like it is appropriate to use it here. 2 questions
arise:
1. vdagentd and vdagent daemons already communicate via socket using simple
homebrew protocol (at least afaik). Probably this was done on purpose. So
is it true vdagent wants to avoid dependency on D-Bus?
2. It seems to better use some higher-level D-Bus bindings (GLib, Qt...)
instead of its low-level API. So is it acceptable to add a dependency of
GLib to vdagent? Or are you aware of some other D-Bus bindings to be used
in vdagent to avoid this extra dependency?

BTW, reporting of connection state can be implemented independently of the
actual transport (socket/D-Bus):
1. Client app (e.g. gnome-settings-daemon) establishes connection to
vdagent being a server (e.g. listening at the socket, or providing D-Bus
interface method RegisterConnectionStateObserver or w/e we name it)
2. vdagent sends the state to registered clients (e.g. D-Bus signal); and
continues to do so each time the state is changed.
So we can even have 2 back-ends for this (additional work, unfortunately).

And last question: while this isn't needed on Windows version of vdagent
right now, additional use cases of this vdagent interface in guest
userspace may arise [e.g. I'm thinking about remote media engine provided
by spice client]. So I think we should target for similar extendable
interface at both Windows and Linux guests (as much as possible). I haven't
looked in vdagent for Windows code yet but guess D-Bus won't be the best
choice there (while D-Bus reportedly works on Windows as well...).
Something like socket and D-Bus and native DCOM would be the best and
future-proof.. What do you think?

[Note: I haven't talked about implementation of new messages between
vdagent and vdagentd, and spice-server, and the actual local/remote
detection code - will ask questions later]

-- 
Best regards,
Fedor
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