/// <summary>
/// Factory method parsing <see cref="GsePacket"/>.
/// </summary>
/// <param name="reader"><see cref="PDUStreamReader"/> for stream from which the <see cref="GsePacket"/>
/// should be parsed.</param>
/// <exception cref="InvalidPacketFormatException">If read data does not correspond to valid format.</exception>
/// <returns>Parsed <see cref="GsePacket"/> object.</returns>
public static GsePacket Parse(PDUStreamReader reader)
{
// Header
var h = GseHeader.Parse(reader);
// Type
PacketType type;
if (!h.StartIndicator && !h.EndIndicator && h.LabelTypeIndicator == LabelType.Byte6)
{
type = PacketType.Padding;
}
else if (!h.StartIndicator && !h.EndIndicator && h.LabelTypeIndicator == LabelType.LabelReuse)
{
type = PacketType.Intermediate;
}
else if (h.StartIndicator && !h.EndIndicator)
{
type = PacketType.Start;
}
else if (!h.StartIndicator && h.EndIndicator && h.LabelTypeIndicator == LabelType.LabelReuse)
{
type = PacketType.End;
}
else if (h.StartIndicator && h.EndIndicator)
{
type = PacketType.Complete;
}
else
{
throw new InvalidPacketFormatException(
$"Invalid packet type. StartIndicator={h.StartIndicator}, EndIndicator={h.EndIndicator}, LabelTypeIndicator={h.LabelTypeIndicator}.");
}
// PDU
// Check whether this GSE packet isn't a padding packet
byte[] pdu = null;
if (type != PacketType.Padding)
{
if (h.GSELength == null)
{
throw new InvalidPacketFormatException("GSELength field is missing.");
}
if (h.BytesAfterGseLengthField == null)
{
throw new InvalidPacketFormatException("BytesAfterGseLengthField unknown.");
}
var pduLength = (ushort)h.GSELength - (ushort)h.BytesAfterGseLengthField;
if (!h.StartIndicator && h.EndIndicator) // if CRC is present after PDU
{
pduLength -= 4; // CRC is 4 bytes long
}
pdu = new byte[pduLength];
var readLength = reader.Read(pdu, 0, pduLength);
if (readLength != pduLength)
{
throw new InvalidPacketFormatException(
$"Reader could not read whole PDU. Read {readLength} out of {pduLength} bytes.");
}
}
// CRC-32
int?crc32 = null;
if (!h.StartIndicator && h.EndIndicator)
{
crc32 = reader.ReadInt32();
// CRC-32 can't be verified here, because we need all GSE packets from this fragmentation group.
}
return(new GsePacket(h, pdu, crc32, type, reader.PDUStreamBasedProvider.GetCurrentPDU().FrameList.Last()));
}