/* here we search through all the frag we have collected to see if
* one fits */
bool check_fragments(int index, PacketDotNet.TcpPacket tcpPacket)
{
TcpFrag prev = null;
TcpFrag current;
current = frags[index];
while (current != null)
{
if (current.seq == seq[index])
{
/* this fragment fits the stream */
if (current.data != null)
{
write_packet_data(index, current.data, tcpPacket);
}
seq[index] += current.len;
if (prev != null)
{
prev.next = current.next;
}
else
{
frags[index] = current.next;
}
current.data = null;
current = null;
return(true);
}
prev = current;
current = current.next;
}
return(false);
}
/// <summary>
/// Reconstructs the tcp session
/// </summary>
/// <param name="sequence">Sequence number of the tcp packet</param>
/// <param name="length">The size of the original packet data</param>
/// <param name="data">The captured data</param>
/// <param name="data_length">The length of the captured data</param>
/// <param name="synflag"></param>
/// <param name="net_src">The source ip address</param>
/// <param name="net_dst">The destination ip address</param>
/// <param name="srcport">The source port</param>
/// <param name="dstport">The destination port</param>
private void reassemble_tcp(ulong sequence, ulong length, byte[] data,
ulong data_length, bool synflag, long net_src,
long net_dst, uint srcport, uint dstport, PacketDotNet.TcpPacket tcpPacket)
{
long srcx, dstx;
int src_index, j;
bool first = false;
ulong newseq;
TcpFrag tmp_frag;
src_index = -1;
/* Now check if the packet is for this connection. */
srcx = net_src;
dstx = net_dst;
// Check to see if we have seen this source IP and port before.
// Note: We have to check both source IP and port, the connection
// might be between two different ports on the same machine.
for (j = 0; j < 2; j++)
{
if (src_addr[j] == srcx && src_port[j] == srcport)
{
src_index = j;
}
}
// We didn't find it if src_index == -1.
if (src_index < 0)
{
// Assign it to a src_index and get going.
for (j = 0; j < 2; j++)
{
if (src_port[j] == 0)
{
src_addr[j] = srcx;
src_port[j] = srcport;
src_index = j;
first = true;
break;
}
}
}
if (src_index < 0)
{
throw new Exception("ERROR in reassemble_tcp: Too many addresses!");
}
if (data_length < length)
{
incomplete_tcp_stream = true;
}
/* now that we have filed away the srcs, lets get the sequence number stuff
* figured out */
if (first)
{
/* this is the first time we have seen this src's sequence number */
seq[src_index] = sequence + length;
if (synflag)
{
seq[src_index]++;
}
/* write out the packet data */
write_packet_data(src_index, data, tcpPacket);
return;
}
/* if we are here, we have already seen this src, let's
* try and figure out if this packet is in the right place */
if (sequence < seq[src_index])
{
/* this sequence number seems dated, but
* check the end to make sure it has no more
* info than we have already seen */
newseq = sequence + length;
if (newseq > seq[src_index])
{
ulong new_len;
/* this one has more than we have seen. let's get the
* payload that we have not seen. */
new_len = seq[src_index] - sequence;
if (data_length <= new_len)
{
data = null;
data_length = 0;
incomplete_tcp_stream = true;
}
else
{
data_length -= new_len;
byte[] tmpData = new byte[data_length];
for (ulong i = 0; i < data_length; i++)
{
tmpData[i] = data[i + new_len];
}
data = tmpData;
}
sequence = seq[src_index];
length = newseq - seq[src_index];
/* this will now appear to be right on time :) */
}
}
if (sequence == seq[src_index])
{
/* right on time */
seq[src_index] += length;
if (synflag)
{
seq[src_index]++;
}
if (data != null)
{
write_packet_data(src_index, data, tcpPacket);
}
/* done with the packet, see if it caused a fragment to fit */
while (check_fragments(src_index, tcpPacket))
{
;
}
}
else
{
/* out of order packet */
if (data_length > 0 && sequence > seq[src_index])
{
tmp_frag = new TcpFrag();
tmp_frag.data = data;
tmp_frag.seq = sequence;
tmp_frag.len = length;
tmp_frag.data_len = data_length;
if (frags[src_index] != null)
{
tmp_frag.next = frags[src_index];
}
else
{
tmp_frag.next = null;
}
frags[src_index] = tmp_frag;
}
}
}
