I'm facing with an old known issue related with Bluetooth RFCOMM SPP serial port devices but I couldn't find a reasonable solution/workaround to detect if the DataReader socket is empty without closing the connection.
What I've tried until now:
1) using CancellationTokenSource the underlying streamSocket is closed when is nothing to read. In this case, I need to do a full await streamSocket.ConnectAsync(...).AsTask() and sometimes is generating an exception "Element not found. (Exception from HRESULT: 0x80070490)". why? there is any other solution to detect that the datareader is empty without closing the streamSocket ?
[here is the c# code]
//connect your Windows.Devices.Bluetooth.Rfcomm.RfcommDeviceService
// see the Bluetooth chat example
[...]
StreamSocket streamSocket = new StreamSocket();
await streamSocket.ConnectAsync(...); //connect to Bluetooth device
DataReader dataReader = new DataReader(inputStream); // to read from the stream
uint ReadBufferLength = 1024;
// Set InputStreamOptions to complete the asynchronous read operation when one or more bytes is available
dataReader.InputStreamOptions = InputStreamOptions.Partial;
try
{
using (CancellationTokenSource cts = new CancellationTokenSource(timeout))
{
cts.Token.Register(() => { ErrorInfoHandling.SetError("Timeout"); });
Task<uint> loadAsyncTask = dataReader.LoadAsync(ReadBufferLength ).AsTask(cts.Token);
uint bytesRead = await loadAsyncTask;
...
}
}
catch (Exception)
{
// we will get here, and everything looks fine, but the problem is:
// The underlying streamSocket is also closed!
// we can not re-use the streamSocket. Any more calls to LoadAsync results in exceptions (something about the object being not assigned...)
// we need to do a full await streamSocket.ConnectAsync(...) sometimes is generating an exception
// TimeoutExceptionRead:Element not found. (Exception from HRESULT: 0x80070490)
// at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
// at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
//at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
}
2) using dataReader.UnconsumedBufferLength
In this case I do not know why every time UnconsumedBufferLength is 0 even if there is data available on the socket. (also when I run the first scenario and there is data on the socket dataReader.UnconsumedBufferLength is 0). Why dataReader.UnconsumedBufferLength is always 0 even there is data available?
Could someone please give me a hint how to solve this issue?
