[Spice-devel] Issues with Clipboard Grab/Release Callbacks

Tue Jun 21 12:08:14 UTC 2022

Hi,

On Mon, Jun 20, 2022 at 10:00 PM Nick Couchman <vnick at apache.org> wrote:

> On Mon, Jun 20, 2022 at 2:46 PM Marc-André Lureau <
> marcandre.lureau at gmail.com> wrote:
>
>> Hi
>>
>> On Mon, Jun 20, 2022 at 6:09 PM Nick Couchman <vnick at apache.org> wrote:
>>
>>> Hello, everyone,
>>> I've posted here, before, with some questions during my journey of
>>> trying to add support for the SPICE protocol to the Guacamole project. The
>>> good news is that I've actually made measurable progress in the
>>> implementation - I can now connect to a SPICE server, and the basics work
>>> (mouse and keyboard - mostly anyway), so I'm moving on to the extra stuff -
>>> clipboard, audio, file transfer, etc.
>>>
>>> In working on the clipboard integration, I'm currently running into an
>>> issue with a couple of the callback functions, specifically the clipboard
>>> grab/release functions, where the number of arguments seems to be
>>> mismatched. According to the documentation, these callbacks should be
>>> called with the following arguments:
>>>
>>> gboolean
>>> user_function (SpiceMainChannel *main,
>>>                guint             selection,
>>>                gpointer          types,
>>>                guint             ntypes,
>>>                gpointer          user_data)
>>>
>>>
>> types is actually guint32*, but that's not the problem here.
>>
>
> Okay, I'll update that.
>
>
>>
>>
>>> void
>>> user_function (SpiceMainChannel *main,
>>>                guint             selection,
>>>                gpointer          user_data)
>>>
>>> I've implemented the callbacks with those arguments, as follows:
>>>
>>> void guac_spice_clipboard_selection_grab_handler(SpiceMainChannel
>>> channel,
>>>         guint selection, gpointer types, guint ntypes, guac_client*
>>> client)
>>>
>>> void guac_spice_clipboard_selection_release_handler(SpiceMainChannel
>>> channel,
>>>         guint selection, guac_client* client)
>>>
>>
>> It looks correct. Can you point to your code connecting the signals with
>> the handlers?
>>
>
> Sure - source code is here:
> https://github.com/necouchman/guacamole-server/tree/working/spice-basic
>
> Here's the section in the src/protocol/spice/client.c file that registers
> the callbacks:
>
>         /* Register clipboard handlers. */
>         g_signal_connect(channel, SPICE_SIGNAL_MAIN_CLIPBOARD_SELECTION,
>                 G_CALLBACK(guac_spice_clipboard_selection_handler),
> client);
>         g_signal_connect(channel,
> SPICE_SIGNAL_MAIN_CLIPBOARD_SELECTION_GRAB,
>                 G_CALLBACK(guac_spice_clipboard_selection_grab_handler),
> client);
>         g_signal_connect(channel,
> SPICE_SIGNAL_MAIN_CLIPBOARD_SELECTION_RELEASE,
>
> G_CALLBACK(guac_spice_clipboard_selection_release_handler), client);
>         g_signal_connect(channel,
> SPICE_SIGNAL_MAIN_CLIPBOARD_SELECTION_REQUEST,
>
> G_CALLBACK(guac_spice_clipboard_selection_request_handler), client);
>
> link to the full function is here:
>
> https://github.com/necouchman/guacamole-server/blob/5e073802a0656e65b1bc8e7e6051831bea0d9508/src/protocols/spice/client.c#L236-L375
>

Try changing the callbacks to accept a pointer, e.g.:
- void guac_spice_clipboard_selection_grab_handler(SpiceMainChannel channel,
+void guac_spice_clipboard_selection_grab_handler(SpiceMainChannel* channel,

 Regards,
    Uri.

>
>>
>> and registered them appropriately. However, if I use them as implemented
>> above, when the callbacks are triggered, the application segfaults when I
>> try to access the "guac_client* client" data structure. I used GDB to try
>> to help track this down, and I noticed that the value of "client" was 0x1,
>> which looks less like a pointer to a memory location and more like the
>> number 1.
>>
>> So, I decided to add another argument to the callback functions, just
>> before the client argument:
>>
>> void guac_spice_clipboard_selection_grab_handler(SpiceMainChannel channel,
>>         guint selection, gpointer types, guint ntypes, guint extra,
>> guac_client* client)
>>
>> void guac_spice_clipboard_selection_release_handler(SpiceMainChannel
>> channel,
>>         guint selection, guint extra, guac_client* client)
>>
>> Strangely, this works - the client data structure can be referenced,
>> there are no segfaults (yet), etc. So, I decided to print the values that
>> are being passed for all of these parameters, and I get the following:
>>
>> guacd[100252]: DEBUG: Notifying client of clipboard grab in the guest.
>> guacd[100252]: DEBUG: Arg: channel: 0x00000000
>> guacd[100252]: DEBUG: Arg: selection: 1275303536
>> guacd[100252]: DEBUG: Arg: types: 0x00000001
>> guacd[100252]: DEBUG: Arg: ntypes: 1276022924
>> guacd[100252]: DEBUG: Arg: extra: 1
>>
>>
> Weird
>
>
>> I printed them in the format I thought they should be in based on what
>> the arguments are supposed to be - I probably should have just done all
>> hex. But, it seems like maybe the "extra" parameter being passed is in
>> front of the channel, since the channel is showing up as all zeros?
>>
>> I was trying to find the code where the callbacks are actually called -
>> I'm guessing, since this is clipboard integration, it'll be in the vdagent
>> code somewhere - but I was having trouble tracking that down.
>>
>>
> The callbacks are not directly called, since those a GObject signals. The
> main channel will call g_signal_emit().
>
>
Okay.

>
>
>> If anyone has any ideas, I'd appreciate the insight into this - I'm
>> puzzled by this apparent mismatch in the number of arguments. Also, if it
>> matters, I'm running CentOS 8 Stream, using Xspice to provide a test SPICE
>> server, and running spice-vdagentd/spice-vdagent within my X session. Yes,
>> I know Xspice is unmaintained, but I just needed something simple and that
>> I didn't have to spend a bunch of time building in order to give me a spice
>> server to point at, and, so far, this has been pretty reliable. Also, at
>> its core, it appears to use the same spice-qxl X driver that x11spice uses,
>> just with a simple Python wrapper script for generating an X config file
>> and starting the X server/display. So, I think it's still pretty "safe" for
>> attempting to develop this Guacamole integration - if for some reason you
>> believe me to be wrong about that, please let me know.
>>
>
> Your testing environment shouldn't be a problem, it's really your
> client-side code integration with spice-glib that looks broken.
>
>
That's what I was thinking, and maybe I'm just messing up something simple!

Thanks,
Nick

>
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