/// <summary>
/// Factory method parsing <see cref="BaseBandHeader"/>.
/// </summary>
/// <param name="reader"><see cref="PDUStreamReader"/> for stream from which the <see cref="BaseBandHeader"/>
/// should be parsed.</param>
/// <exception cref="InvalidPacketFormatException">If DFL (Data Field Length) field is not in range [0,58112].</exception>
/// <returns>Parsed <see cref="BaseBandHeader"/> object.</returns>
public static BaseBandHeader Parse(PDUStreamReader reader)
{
// Byte 0, MATYPE-1
var matype1 = Matype1.Parse(reader.ReadByte());
// Byte 1, MATYPE-2
var matype2 = reader.ReadByte();
// Byte 2-3, UPL
var userPacketLenght = reader.ReadUInt16();
// Byte 4-5, DFL
var dataFieldLength = reader.ReadUInt16();
// http://www.etsi.org/deliver/etsi_en/302300_302399/302307/01.01.02_60/en_302307v010102p.pdf#page=18
if (dataFieldLength > 58112)
{
throw new InvalidPacketFormatException(
$"DFL (Data Field Length) field has be in range [0,58112]. {dataFieldLength} > 58112");
}
// Byte 6, SYNC
var sync = reader.ReadByte();
// Byte 7-8, SYNCD
var syncD = reader.ReadUInt16();
// Byte 9, CRC-8
var crc8 = reader.ReadByte();
// NOTE: DVB-S2 base band frame, base band header, CRC-8 is not validated.
return(new BaseBandHeader(matype1, matype2, userPacketLenght, dataFieldLength, sync, syncD, crc8));
}
/// <summary>
/// Factory method parsing <see cref="GseHeader"/>.
/// </summary>
/// <param name="reader"><see cref="PDUStreamReader"/> for stream from which the <see cref="GseHeader"/>
/// should be parsed.</param>
/// <exception cref="InvalidPacketFormatException">If read data does not correspond to valid format.</exception>
/// <returns>Parsed <see cref="GseHeader"/> object.</returns>
/// <remarks>
/// For complete syntax of GSE Packet structure, see Table 2 in
/// <a href="http://www.etsi.org/deliver/etsi_ts/102600_102699/10260601/01.02.01_60/ts_10260601v010201p.pdf#page=13">
/// ETSI TS 102 606-1 V1.2.1.</a>
/// </remarks>
public static GseHeader Parse(PDUStreamReader reader)
{
var b = reader.ReadByte();
// Byte 0-1, Fixed Header Fields
// Bit 15: S
var startIndicator = (b & 0b1000_0000) == 0b1000_0000;
// Bit 14: E
var endIndicator = (b & 0b0100_0000) == 0b0100_0000;
// Bit 13-12: LT
// LabelType enum has 4 values, therefore we use Enum.Parse instead of Enum.TryParse.
var labelTypeIndicator = (LabelType)Enum.Parse(typeof(LabelType), ((b & 0b0011_0000) >> 4).ToString());
// possibly null values which might not be present in packet
ushort?gseLength = null;
ushort?bytesAfterGseLengthField = null;
byte? fragmentID = null;
ushort?totalLength = null;
ushort?protocolType = null;
byte[] label = null;
long?gseLengthFieldStreamPosition = null;
// Bit 11-0
if (!startIndicator && !endIndicator && labelTypeIndicator == LabelType.Byte6)
{
// 4 padding bits
if ((b & 0b0000_1111) != 0b0000_0000)
{
throw new InvalidPacketFormatException($"Expected 4 zero-padding bits.");
}
// N1 Padding bytes (N1 is the number of bytes until the end of the Base-Band frame.)
while (!reader.EndOfPDU)
{
if (reader.ReadByte() != 0)
{
throw new InvalidPacketFormatException(
$"Expected zero-padding bits until the end of the Base-Band frame.");
}
}
}
else
{
// 12 bits
byte[] tmpMaskedBytes =
{
reader.ReadByte(),
(byte)(b & 0b0000_1111)
}; // BigEndian
gseLength = BitConverter.ToUInt16(tmpMaskedBytes, 0);
gseLengthFieldStreamPosition = reader.PDUStreamBasedProvider.Position;
if (!startIndicator || !endIndicator)
{
fragmentID = reader.ReadByte();
}
if (startIndicator && !endIndicator)
{
totalLength = reader.ReadUInt16();
}
if (startIndicator)
{
protocolType = reader.ReadUInt16();
if (labelTypeIndicator == LabelType.Byte6)
{
label = new byte[6];
if (reader.Read(label, 0, 6) != 6)
{
throw new InvalidPacketFormatException("Reader could not read 6 bytes.");
}
}
else if (labelTypeIndicator == LabelType.Byte3)
{
label = new byte[3];
if (reader.Read(label, 0, 3) != 3)
{
throw new InvalidPacketFormatException("Reader could not read 3 bytes.");
}
}
}
}