/// <summary>
/// Search through all fragments we've collected to
/// see if one fits.
/// </summary>
/// <param name="conn"></param>
/// <param name="dir"></param>
/// <param name="ack"></param>
/// <returns>Return true if a fragment is found match the stream and added to the stream.</returns>
private bool checkFragment(TcpConnection conn, int dir, UInt32 ack)
{
// Handy object cache
TcpStream stream = conn.Stream(dir);
TCB tcb = conn.ControlBlock(dir);
UInt32 lowestseq = UInt32.MaxValue;
for (TcpFrag cur = stream.FragListHead, prev = null;
cur != null;
prev = cur, cur = cur.next)
{
lowestseq = Math.Min(lowestseq, cur.seq);
if (cur.seq < tcb.seq)
{
// the sequence number seems dated,
// but check the end to make sure it has no more
// info than we have seen.
UInt32 endseq = cur.seq + cur.len;
if (endseq > tcb.seq)
{
// here's more than we have seen.
// Get the payload that we have not seen.
UInt32 new_offset = tcb.seq - cur.seq;
// Only when we have captured the data
if (cur.data.Length > new_offset)
{
Byte[] tmp = new Byte[cur.data.Length - new_offset];
Array.Copy(cur.data, new_offset, tmp, 0, tmp.Length);
conn.WritePacketData(dir, tmp);
}
tcb.seq += (cur.len - new_offset);
if (cur.flags.HasFlag(TcpControlBits.Fin))
{
if (conn.CloseStream(dir))
{
CloseConnection(conn);
}
}
}
// Remove it from list.
if (prev != null)
{
prev.next = cur.next;
}
else // is list head
{
stream.FragListHead = cur.next;
}
cur.data = null;
cur = null;
return(true);
}
if (cur.seq == tcb.seq)
{
// Got one match the stream
tcb.seq += cur.len;
if (cur.data != null)
{
conn.WritePacketData(dir, cur.data);
}
if (cur.flags.HasFlag(TcpControlBits.Fin))
{
if (conn.CloseStream(dir))
{
CloseConnection(conn);
}
}
// Remove it from list.
if (prev != null)
{
prev.next = cur.next;
}
else // is list head
{
stream.FragListHead = cur.next;
}
cur.data = null;
cur = null;
return(true);
}
}
if (ack > lowestseq)
{
// There are frames missing in the capture file that were
// seen by the receiving host.
// Add a dummy string here.
string dummy = String.Format("[%d bytes missing in capture file]", lowestseq - tcb.seq);
conn.WritePacketData(dir, Encoding.Default.GetBytes(dummy));
tcb.seq = lowestseq;
return(true);
}
return(false);
}
/// <summary>
/// Reassembly tcp stream
/// </summary>
/// <param name="sequence">Sequence number of the tcp packet</param>
/// <param name="acknowledgement">Acknowledgement number of the tcp packet</param>
/// <param name="length">Length of the original payload data</param>
/// <param name="data">Actual captured data</param>
/// <param name="flags">All control bits of the tcp packet</param>
/// <param name="pair">Tcp end point pair, we use its AEP as source and BEP as destination</param>
private void tcp_reassemble(UInt32 sequence, UInt32 acknowledgement, UInt32 length, Byte[] data,
TcpControlBits flags, TcpPair pair)
{
// First to get a TcpConnection object, which can either be seen before
// or a newly created one.
TcpConnection conn = GetConnection(pair);
// Check our direction.
int dir = conn.Pair.AEP.Equals(pair.AEP) ? 0 : 1;
// Cache some useful object, this is packet receiver. (Only reference here.)
TCB tcb = conn.ControlBlock(dir);
TcpStream stream = conn.Stream(dir);
// Whether we have trunced the packet
if (data.Length < length)
{
stream.IsTrunced = true;
}
// Before adding data for this flow to the data_out_file, check whether
// this frame acks fragments that were already seen. This happens when
// frames are not in the capture file, but were actually seen by the
// receiving host.
if (conn.Stream(1 - dir).FragListHead != null)
{
while (checkFragment(conn, 1 - dir, acknowledgement))
{
;
}
}
// now lets get the sequence number stuff figured out
if (tcb.State == TcpState.CLOSED)
{
// Transmit FSM state.
tcb.Transit(flags, true);
conn.ControlBlock(1 - dir).Transit(flags, false); // the other side.
// This is the first time we see sequence number (in this direction)
tcb.seq = sequence + length;
if (flags.HasFlag(TcpControlBits.Synchronize))
{
tcb.seq++; // we hold next seq, and in case of syn, next seq is sequence+1
}
else
{
// A new conversation should start with three-way handshake, thus syn should be set
// but if not, it may means that we are dealing with a connection
// which was captured half way.
stream.IsTrunced = true;
}
conn.WritePacketData(dir, data);
return;
}
// If we got here, it means we've seen packets in this connection and direction
// transit fsm state.
tcb.Transit(flags, true);
conn.ControlBlock(1 - dir).Transit(flags, false);
// Warning: I didn't care about sequence number wrap-around in
// all comparisons of sequence numbers. I'm not sure if this will
// cause problems.
// check if this packet is in right place
if (sequence < tcb.seq)
{
// the sequence number seems dated,
// but check the end to make sure it has no more
// info than we have seen.
UInt32 endseq = sequence + length;
if (endseq > tcb.seq)
{
// here's more than we have seen.
// Get the payload that we have not seen.
UInt32 new_offset = tcb.seq - sequence;
if (data.Length <= new_offset)
{
// Unfortunately, we didn't captured that.
// so only useless data left.
data = null;
stream.IsTrunced = true;
}
else
{
Byte[] tmp = new Byte[data.Length - new_offset];
Array.Copy(data, new_offset, tmp, 0, tmp.Length);
data = tmp;
}
// Make things appear to be right on time.
sequence = tcb.seq;
length = endseq - sequence;
}
}
if (sequence == tcb.seq)
{
// right on time
tcb.seq += length;
if (flags.HasFlag(TcpControlBits.Synchronize))
{
tcb.seq++;
}
if (data != null)
{
conn.WritePacketData(dir, data);
}
if (flags.HasFlag(TcpControlBits.Fin))
{
if (conn.CloseStream(dir))
{
CloseConnection(conn);
}
}
// done with the packet, see if it cause a fragment to fit.
// pass 0 to ack because we don't need to check ack here.
// should been checked above, before add data.
while (checkFragment(conn, dir, 0))
{
;
}
}
else
{
// out of order packet
if (data.Length > 0 && sequence > tcb.seq)
{
TcpFrag frag = new TcpFrag()
{
seq = sequence,
len = length,
data = data,
flags = flags
};
// Add to fragment list
if (stream.FragListHead == null)
{
frag.next = null;
stream.FragListHead = frag;
}
else
{
frag.next = stream.FragListHead;
stream.FragListHead = frag;
}
}
}
}