[Spice-devel] [PATCH] [vd_agent] close the file handler if file_size = 0

[Christophe Fergeau]

On Sat, Aug 09, 2014 at 06:40:22PM +0800, Cody Chan wrote:
> After dragging a zero-size file, then I open it in guest,
> I get a warning message box which says:
>  "the process cannot access the file because it is being used by another
> process".
> And I get to know the file is occupied by vdagent. Now we look back the
> process:
> 
> a) When dragging a zero-size file, spice-gtk gets the name and size, then
> sends
> the message to vd_agent with VD_AGENT_FILE_XFER_START
> b) vd_agent receives and parsers the message, then gets file name and size,
> creates(open)
> the file and gets the handler, at last, sends
> VD_AGENT_FILE_XFER_STATUS_CAN_SEND_DATA
> c) spice-gtk receives the VD_AGENT_FILE_XFER_STATUS_CAN_SEND_DATA message,
> the sends data with VD_AGENT_FILE_XFER_DATA
> d) vd_agent receives and writes data to the file opened
> e) After finishing the writing, vd_agent closes the handler
> 
> But in step c, we take a look the code:
> //spice-channel.c
> >static void file_xfer_read_cb(...)
> >{
> >    //...
> >    count = g_input_stream_read_finish(G_INPUT_STREAM(task->file_stream),
> res, &error);
> >    if (count > 0) {
> >        task->read_bytes += count;
> >        file_xfer_queue(task, count);
> >        file_xfer_flush_async(channel, task->cancellable,
> >                              file_xfer_data_flushed_cb, task);
> >        task->pending = TRUE;
> >    } else if (error) {
> >        VDAgentFileXferStatusMessage msg = {
> >            .id = task->id,
> >            .result = VD_AGENT_FILE_XFER_STATUS_ERROR,
> >        };
> >        agent_msg_queue_many(task->channel, VD_AGENT_FILE_XFER_STATUS,
> >                             &msg, sizeof(msg), NULL);
> >        spice_channel_wakeup(SPICE_CHANNEL(task->channel), FALSE);
> >        file_xfer_completed(task, error);
> >    }
> >}
> 
> If count == 0, then it does nothing!
> Then vd_agent will receive nothing after opening a file, and always occupy
> the file.
> Here we close the file if file_size = 0, even though it doesn't make sense
> to send
> a zero-size file.

Ah, good catch, from a quick look it seems the linux agent does not
handle this case properly either. This can be fixed in both agents, or
alternatively, this can also be fixed in spice-gtk in file_xfer_read_cb
by sending a dummy empty data message when the file size is 0.
Fixing it in the agents is probably less convoluted.

> 
> ​
> ---
>  vdagent/file_xfer.cpp | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/vdagent/file_xfer.cpp b/vdagent/file_xfer.cpp
> index 34a9ee6..17d842e 100644
> --- a/vdagent/file_xfer.cpp
> +++ b/vdagent/file_xfer.cpp
> @@ -89,6 +89,10 @@ void FileXfer::handle_start(VDAgentFileXferStartMessage*
> start,
>          vd_printf("failed creating %s %lu", file_path, GetLastError());
>          return;
>      }
> +    if (file_size == 0){
> +        CloseHandle(handle);
> +        return;
> +    }

The agent should probably return VD_AGENT_FILE_XFER_STATUS_SUCCESS in
this case to let the client know this is over.

Christophe
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