/// <summary>
/// This returns the next complete payload. This involves defragmenting any fragments
/// </summary>
/// <returns>byte array containing the IP payload.</returns>
public unsafe byte[] GetNextIPPayload()
{
if (Fragments.Count == 0)
{
return(null);
}
List <byte[]> nextFragments;
// optimize single packet processing
if (Fragments.Count == 1)
{
nextFragments = Fragments;
}
else
{
nextFragments = Fragments.OrderBy(x =>
Utility.ntohs(BitConverter.ToUInt16(x, 4))) // identification
.ThenBy(x =>
Utility.ntohs(BitConverter.ToUInt16(x, 6)) & 0x1fff) // fragment offset
.ToList();
}
ushort currentId = 0;
ushort fragmentOffset = 0;
byte[] payload = null;
for (int i = 0; i < nextFragments.Count; i++)
{
fixed(byte *ptr = nextFragments[i])
{
IPv4Header ip4Header = *(IPv4Header *)ptr;
// every new ID resets the internal state - we dont need to return in order.
if (currentId != ip4Header.Id)
{
currentId = ip4Header.Id;
payload = null;
fragmentOffset = 0;
}
// skip for now if the offset is incorrect, the correct packet may come soon.
if (ip4Header.FragmentOffset == fragmentOffset)
{
int fragmentDataSize;
// correction for fragmented packet
// note: ip4Header.length may be zero if using hardwre offloading to network card.
if (ip4Header.Length == 0 && ip4Header.Id != 0)
{
fragmentDataSize = nextFragments[i].Length - ip4Header.HeaderLength;
}
else
{
fragmentDataSize = ip4Header.Length - ip4Header.HeaderLength;
}
// resize payload array
if (payload == null)
{
payload = new byte[fragmentDataSize];
}
// if this is a fragment, prepare array to accept it and record last fragment time.
if (ip4Header.FragmentOffset > 0)
{
LastIPFragmentTimestamp = DateTime.Now;
Array.Resize(ref payload, payload.Length + fragmentDataSize);
}
// copy packet into payload
Array.Copy(nextFragments[i], ip4Header.HeaderLength, payload, fragmentOffset, fragmentDataSize);
// add data offset
fragmentOffset += (ushort)fragmentDataSize;
// return payload if this is the final fragment
if ((ip4Header.Flags & (byte)IPFlags.MF) == 0)
{
// purge current fragments
if (Fragments.Count == 1) // optimize single packet processing
{
Fragments.Clear();
}
else
{
// remove in reverse order to prevent IEnumerable issues.
for (int j = Fragments.Count - 1; j >= 0; j--)
{
if (Utility.ntohs((ushort)BitConverter.ToUInt16(Fragments[j], 4)) == currentId)
{
Fragments.RemoveAt(j);
}
else if (Utility.ntohs(BitConverter.ToUInt16(Fragments[j], 4)) < currentId - 99)
{
//Trace.WriteLine("IP: Old fragment purged. Current ID: [" + currentId.ToString("X4") + "], Old ID: + [" +
//IPAddress.NetworkToHostOrder((short)BitConverter.ToUInt16(Fragments[j], 4)) + "] " + Utility.ByteArrayToHexString(Fragments[j], 0, 50));
Fragments.RemoveAt(j);
}
}
}
return(payload);
}
}
}
}
return(null);
}
