bytesAvailable() returns 4,294,967,295

[GoogleCodeExporter]

System:
Windows 7 64bit
QExtSerialPort 1.2beta1 (built with Mingw-gcc4.6 or Msvc2010 (static and 
dynamic libraries))
Using a USB to serial dongle (These generally cause odd behaviour but older 
versions of QExtSerialPort do not have this problem)

Problem:
Using a loop like below to read data from a QExtSerialPort named serialPort 
works fine for a period (10 seconds up to 2 minutes) then 
serialPort->bytesAvailible() starts returning 4,294,967,295, which is not good. 

QByteArray dataBuffer;
while(true)
{
   Sleep(1);
   while(serialPort->bytesAvailible() > 0)
   {
      dataBuffer.append(serialPort->realAll());

      // do stuff with data buffer to read messages
   }
}

Initial Investigation:
The problem seems to come from qextserialport_win.cpp line 157.  Where 
Status.cbInQue which is a DWORD (unsigned long) gets the number 4,294,967,295 
placed in it and is put into a qint64.  It seems like this value should 
actually be seen as a -1 because it is an error (I don;t thing we should ever 
have 4GB of data).  Replacing the line with

return static_cast<qint32>(Status.cbInQue);

results in it returning a -1 which I think is more correct.

Bigger Issue:
That's not the whole issue though because, even with is now returning -1 the 
port just starts returning errors after a short period of working and the only 
way to make it go again seems to be deleting the QExtSerialPort and creating a 
new one.  This behaviour does not occur with version 1.1 or a source tarball I 
downloaded in November 2011 (I can upload the tarball to compare against if 
needed).

Original issue reported on code.google.com by Ben.Arc...@gmail.com on 25 Apr 2012 at 11:45

[GoogleCodeExporter]

Hi Ben,

Perhaps you can try to initialize Errors and Status to Zeros. 
Output the value of Errors when you get 4,294,967,295. and output the return 
value of GetLastError() too.

qint64 QextSerialPortPrivate::bytesAvailable_sys() const
{
    DWORD Errors;
    COMSTAT Status;
    if (ClearCommError(Win_Handle, &Errors, &Status)) {
        return Status.cbInQue;
    }
    return (qint64)-1;
}

Seems you are using Polling Mode, if so, only ReadFile() will be called once 
port is opened.

qint64 QextSerialPortPrivate::readData_sys(char *data, qint64 maxSize)
{
    DWORD bytesRead = 0;
    if (!ReadFile(Win_Handle, (void*)data, (DWORD)maxSize, & bytesRead, NULL))
        return -1;
    return (qint64)bytesRead;
}

You can output the return value of GetLastError() here too when error occur.

Hope this is useful to you.

Original comment by dbzhang...@gmail.com on 26 Apr 2012 at 2:04

[GoogleCodeExporter]

How to use ReadData() prototype 

Original comment by sushantb...@gmail.com on 23 Jul 2013 at 5:17