public bool TryReadFrame(ref ReadOnlySequence <byte> buffer, out Frame frame)
{
var sequenceReader = new SequenceReader <byte>(buffer);
frame = Frame.InvalidFrame;
if (!headerReader.TryReadHeader(ref sequenceReader, out var header))
{
return(false);
}
var frameSizeIncludingOpeningAndEndingFlags = header.FrameSize + 2;
// Ensure that we have a complete frame.
if (sequenceReader.Remaining < (frameSizeIncludingOpeningAndEndingFlags - sequenceReader.Consumed))
{
return(false);
}
/// Check
var frameBody = sequenceReader.Sequence.Slice(header.StartPosition, header.FrameSize - FRAME_CHECK_SEQUENCE_LENGTH).ToArray();
var frameCheckSequenceBytes = sequenceReader.Sequence.Slice((header.StartPosition + header.FrameSize) - 2, FRAME_CHECK_SEQUENCE_LENGTH).ToArray();
var frameCheckSequence = (ushort)(frameCheckSequenceBytes[1] << 8 | frameCheckSequenceBytes[0]);
if (!cyclicRedundancyChecker.Check(frameCheckSequence, frameBody))
{
return(false);
}
// Advance past the LLC PDU section. Nothing relevant here.
sequenceReader.Advance(8);
// Skip reading this byte since not all meters sends this byte
// 09 which indicates the COSEM datatype "octet-string" is propably found to be redundant as we will always have a timestamp here.
if (sequenceReader.TryPeek(out var dataType))
{
if (dataType == 0x09)
{
sequenceReader.Advance(1);
}
}
var timeStamp = dateTimeReader.Read(ref sequenceReader);
var payload = payLoadReader.Read(ref sequenceReader);
frame = new Frame(header, timeStamp, payload);
// Advance past the frame check sequence bytes and the end flag;
sequenceReader.Advance(3);
return(true);
}
public bool TryReadHeader(ref SequenceReader <byte> sequenceReader, out Header header)
{
header = Header.InvalidHeader;
if (!sequenceReader.TryAdvanceTo(START_FLAG))
{
return(false);
}
var headerStartPosition = sequenceReader.Consumed;
if (sequenceReader.Remaining < 2)
{
// We don't have enough bytes to read the frame format field.
return(false);
}
sequenceReader.TryRead(out var firstFrameFormatByte);
sequenceReader.TryRead(out var secondFrameFormatByte);
int frameFormat = firstFrameFormatByte << 8 | secondFrameFormatByte;
// Right shift the frame size and segmentation bit (12 bits) leaving only the frame format type (4 bits).
var frameFormatType = frameFormat >> 12;
// Get the frame size from the last 11 bits.
var frameSize = frameFormat & 0b0000011111111111;
if (!TryReadPastAddress(ref sequenceReader) || !TryReadPastAddress(ref sequenceReader))
{
return(false);
}
// Ensure that we have at least the control byte and the two bytes containing the check sum
if (sequenceReader.Remaining < 3)
{
return(false);
}
// Advance past the control byte
sequenceReader.Advance(1);
sequenceReader.TryRead(out var firstHeaderCheckSequenceByte);
sequenceReader.TryRead(out var secondHeaderCheckSequenceByte);
var headerCheckSequence = (ushort)(secondHeaderCheckSequenceByte << 8 | firstHeaderCheckSequenceByte);
var headerBody = sequenceReader.Sequence.Slice(headerStartPosition, (sequenceReader.Consumed - headerStartPosition) - 2).ToArray();
if (!cyclicRedundancyChecker.Check(headerCheckSequence, headerBody))
{
return(false);
}
var frameSizeIncludingOpeningAndEndingFlags = frameSize + 2;
// Ensure that we have a complete frame.
if (sequenceReader.Remaining < (frameSizeIncludingOpeningAndEndingFlags - sequenceReader.Consumed))
{
return(false);
}
var frameBody = sequenceReader.Sequence.Slice(headerStartPosition, frameSize - 2).ToArray();
var frameCheckSequenceBytes = sequenceReader.Sequence.Slice((headerStartPosition - 2) + frameSize, 2).ToArray();
var frameCheckSequence = (ushort)(frameCheckSequenceBytes[1] << 8 | frameCheckSequenceBytes[0]);
if (!cyclicRedundancyChecker.Check(frameCheckSequence, frameBody))
{
return(false);
}
var headerSize = sequenceReader.Consumed - headerStartPosition;
header = new Header(frameSize, headerStartPosition, headerSize);
return(true);
}
