private byte[] getFrame()
{
int addressOffset = parameters.serverAddress.Length + 1;
stream.WriteByte(0x00); //fcs
stream.WriteByte(0x00); //fcs
stream.WriteByte((byte)HDLC_FLAG);
byte[] data = stream.ToArray();
data[1] = (byte)(data[1] | ((data.Length - 2) >> 8));
data[2] = (byte)(data.Length - 2);
short fcs = HdlcLinkLayer.calcFcs(data, 1, addressOffset + 3);
data[4 + addressOffset] = (byte)fcs;
data[5 + addressOffset] = (byte)(fcs >> 8);
if (data.Length > (addressOffset + 7))
{
fcs = HdlcLinkLayer.calcFcs(data, 1, data.Length - 4);
data[data.Length - 3] = (byte)fcs;
data[data.Length - 2] = (byte)(fcs >> 8);
}
return(data);
}
private void verifyReceivedData(byte[] data)
{
if ((data[1] & 0xF0) != HDLC_FORMAT)
{
throw new LinkLayerException(LinkLayerExceptionReason.RECEIVED_INVALID_FRAME_FORMAT);
}
int frameSize = ((data[1] & 0x0F) << 8) | (data[2] & 0xFF);
if (frameSize != data.Length - 2)
{
throw new LinkLayerException(LinkLayerExceptionReason.RECEIVED_INVALID_FRAME_FORMAT);
}
if (parameters.clientAddress != data[3])
{
throw new LinkLayerException(LinkLayerExceptionReason.RECEIVED_INVALID_ADDRESS);
}
int offset = 4;
while (offset < frameSize && (data[offset++] & 0x01) != 0x01)
{
}
connection.receivedControl = data[offset++] & 0xFF;
if (data.Length - offset > 3)
{
connection.receivedData = helper.extensions.copyOfRange(data, offset + 2, data.Length - 3);
}
else
{
connection.receivedData = new byte[0];
}
short fcs = BitConverter.ToInt16((new byte[] { data[offset], data[offset + 1] }), 0);
if (fcs != HdlcLinkLayer.calcFcs(data, 1, offset - 1))
{
throw new LinkLayerException(LinkLayerExceptionReason.RECEIVED_INVALID_CHECK_SEQUENCE);
}
fcs = BitConverter.ToInt16((new byte[] { data[data.Length - 3], data[data.Length - 3 + 1] }), 0);
if (fcs != HdlcLinkLayer.calcFcs(data, 1, data.Length - 4))
{
throw new LinkLayerException(LinkLayerExceptionReason.RECEIVED_INVALID_CHECK_SEQUENCE);
}
connection.isFinalPoll = (connection.receivedControl & 0x10) == 0x10;
connection.receivedControl &= 0xEF; //remove p/f bit from control
connection.receivedRrr = 0;
connection.receivedSss = 0;
if ((connection.receivedControl & 0x01) == 0x00)
{
connection.receivedRrr = ((int)((uint)connection.receivedControl >> 5)) & 0x07;
connection.receivedSss = ((int)((uint)connection.receivedControl >> 1)) & 0x07;
connection.receivedControl &= 0x01; //remove sss and rrr bits from control
connection.lastFrameHadSss = true;
}
else if ((connection.receivedControl & 0x02) == 0x00)
{
connection.receivedRrr = ((int)((uint)connection.receivedControl >> 5)) & 0x07;
connection.receivedControl &= 0x0F; //remove rrr bits from control
}
if (connection.receivedControl == FRMR_CONTROL)
{
throw new LinkLayerException(LinkLayerExceptionReason.SERVER_REPORTS_FRAME_REJECTED);
}
}