[Interest] UDP broadcast on Winphone

[Andrew Knight]

Hi Federico,

On 10/19/2015 08:55 PM, Federico Buti wrote:
> Hi list.
>
> According to multiple sources, UDP broadcast is supported on WinPhone 
> 8+ (e.g. look here 
> <http://stackoverflow.com/questions/23504957/windows-phone-8-1-doesnt-send-udp-broadcast>, 
> here 
> <http://metronuggets.com/2013/03/18/how-to-send-and-receive-a-udp-broadcast-in-windows-phone-8-and-win8/> or 
> here 
> <http://01siddharth.blogspot.it/2014/08/send-and-receive-udp-broadcast-in.html>) 
> but it seems that the feature in not supported in Qt since 
> CanBroadcast flag is set to false in QNetworkInterface (or am I 
> misinterpreting?)
> The test code I've used is as simple as the following:
>

That missing flag likely indicates that this has not been 
tested/implemented. While UDP is supported, broadcasts may only work by 
accident.

>
> udpSocket->bind(BROADCAST_PORT);
> udpSocket->writeDatagram(data, length, a.broadcast(), BROADCAST_PORT);
>
>
> A 4-bytes message is sent on a network where our target device is 
> connected. The sent message is correctly received by the target BUT 
> the answer we receive back is plain wrong. At least, the length of the 
> messages match the expected lengths:
>
>
> \0x00cdcdcd// original message sent by my code - 4 bytes
> \0x00cdcdcdcdcdcdcdcdcdcdcdcdcdcd// answer from the target device - 15 
> bytes
>
>
> The very same code works fine on other platforms. Any idea or suggestion?

Yes, those lengths are clearly wrong. The repeating 0xcd is 
uninitialized memory.

The truth is, despite passing autotests and having gone through several 
Qt minor revisions worth of bug fixes, the Qt network stack for Windows 
Phone (Runtime) has goblins. This can be blamed on the large difference 
in design and behavior between the WinRT API and traditional (BSD-style) 
sockets that most of QtNetwork uses.

So, please test against a released Qt version (or better yet, the 5.6 
branch) and file a bug report with your case.

> Thanks in advance,
> F.
>

Cheers,
Andrew