DatagramSocket write problem in C++/CX

Question

Consider the following code:

DatagramSocket^ s = ref new DatagramSocket();

later:

WRL::Wrappers::Event evt(CreateEventExW(NULL, NULL, 0, EVENT_ALL_ACCESS));
HRESULT hr = 0;

auto operation = s->ConnectAsync(host, service);
                        
operation->Completed = ref new AsyncActionCompletedHandler(
    [&evt, &hr](IAsyncAction^ asyncInfo)
    {
        hr = asyncInfo->ErrorCode.Value;
        SetEvent(evt.Get());
    }, Platform::CallbackContext::Any);

operation->Start();
            
WaitForSingleObjectEx(evt.Get(), INFINITE, FALSE);
            
assert (hr == 0);

Datagram socket is now associated with host:service, so we send data:

IOutputStream^ os = s->OutputStream;

DataWriter^ writer = ref new DataWriter(os);

array<unsigned char>^ data = ref new array<unsigned char>(len);
::memcpy(data->Data, buf, len);

writer->WriteBytes(data);

auto operation = writer->StoreAsync();

WRL::Wrappers::Event evt(CreateEventExW(NULL, NULL, 0, EVENT_ALL_ACCESS));
HRESULT hr = 0;

operation->Completed = ref new AsyncOperationCompletedHandler<UINT32>(
	[&evt, &hr](IAsyncOperation<UINT32>^ op)
    {
        hr = op->ErrorCode.Value;                    
        SetEvent(evt.Get());
    }, Platform::CallbackContext::Any);

operation->Start();

WaitForSingleObjectEx(evt.Get(), INFINITE, FALSE);
            
// We never get here

And the delegate is never called. If i skip the connect part then delegate will be called here indicating an error which is correct behavior. The problem is in the "success" case, the delegate isn't called so I can't find out if write operations succeeded or not and also, what happens with the delegate, does it get deallocated or its memory is leaked or what ? Note that this only happens in C++/CX, in JavaScript the very same code works fine... Is this a bug in WinRT, C++/CX ?

Answer 1

Ok, worked around the problem like this:

DataWriter^ writer = ref new DataWriter();

array<unsigned char>^ data = ref new array<unsigned char>(len);
::memcpy(data->Data, buf, len);

writer->WriteBytes(data);

auto operation = os->WriteAsync(writer->DetachBuffer());

WRL::Wrappers::Event evt(CreateEventExW(NULL, NULL, 0, EVENT_ALL_ACCESS));
HRESULT hr = 0;

operation->Completed = ref new AsyncOperationWithProgressCompletedHandler<UINT32, UINT32>(
	[&evt, &hr](IAsyncOperationWithProgress<UINT32, UINT32>^ op)
    {
        hr = op->ErrorCode.Value;
        SetEvent(evt.Get());                    
    }, Platform::CallbackContext::Any);

operation->Start();

'hr' is 0 and op->GetResults() returns 'len', but the datagram still doesn't reach the other end. I've also tried calling os->FlushAsync() - no luck...

I've also tried replacing os = s->OutputStream with os = s->GetOutputStream(ref new HostName(ref new Platform::String(host_name)), ref new Platform::String(service_name)) - no luck...

Answer 2

Ok, the datagram is being sent (Wireshark shows it), but is not received by the other side, the delegate:

s->MessageReceived += ref new DatagramSocketMessageReceivedEventHandler(
    []( DatagramSocket^ sender,
            DatagramSocketMessageReceivedEventArgs^ e )
    {
        ...
    });

isn't called. The socket on the other side is bound using:

s->Information->LocalHostName = host; // "127.0.0.1"<br/>s->Information->LocalServiceName = service; // "9124"

auto operation = s->BindServiceNameAsync();

WRL::Wrappers::Event evt(CreateEventExW(NULL, NULL, 0, EVENT_ALL_ACCESS));
HRESULT hr = 0;
            
operation->Completed = ref new AsyncActionCompletedHandler(
    [&evt, &hr](IAsyncAction^ asyncInfo)
    {
        hr = asyncInfo->ErrorCode.Value;
        SetEvent(evt.Get());                    
    }, Platform::CallbackContext::Any);

operation->Start();

WaitForSingleObjectEx(evt.Get(), INFINITE, FALSE);
            
assert (hr == 0);

Another important thing to note, output of "netstat -p udp -a" is:

  Proto  Local Address          Foreign Address        State
  UDP    0.0.0.0:9124           *:*

Inspite of the fact that socket was bound to "127.0.0.1", "127.0.0.1" is not the same as "0.0.0.0", it's very important for my application to bind a socket to "127.0.0.1" so it wouldn't receive datagrams from other computers on the network. How can I bind to "127.0.0.1" and why doesn't my app receive datagrams, it did bind to "0.0.0.0", so it must receive datagrams coming from all interfaces on port 9124...

Answer 3

What was the resolution to this?