// Assemble reassembles the given TCP packet into its appropriate stream.
// Each Assemble call results in, in order:
//
// zero or one calls to StreamFactory.New, creating a stream
// zero or one calls to Reassembled on a single stream
// zero or one calls to ReassemblyComplete on the same stream
func (a *Assembler) Assemble(netFlow gopacket.Flow, t *layers.TCP) {
// Ignore empty TCP packets
if !t.SYN && !t.FIN && !t.RST && len(t.LayerPayload()) == 0 {
if *debugLog {
log.Println("ignoring useless packet")
}
return
}
a.ret = a.ret[:0]
key := key{netFlow, t.TransportFlow()}
var conn *connection
// This for loop handles a race condition where a connection will close, lock
// the connection pool, and remove itself, but before it locked the connection
// pool it's returned to another Assemble statement. This should loop 0-1
// times for the VAST majority of cases.
for {
conn = a.connPool.getConnection(key, !t.SYN && len(t.LayerPayload()) == 0)
if conn == nil {
if *debugLog {
log.Printf("%v got empty packet on otherwise empty connection", key)
}
return
}
conn.mu.Lock()
if !conn.closed {
break
}
conn.mu.Unlock()
}
conn.lastSeen = time.Now()
seq, bytes := Sequence(t.Seq), t.Payload
if conn.nextSeq == invalidSequence {
if t.SYN {
if *debugLog {
log.Printf("%v saw first SYN packet, returning immediately, seq=%v", key, seq)
}
a.ret = append(a.ret, Reassembly{
Bytes: bytes,
Skip: 0,
Start: true,
Seen: time.Now(),
})
conn.nextSeq = seq.Add(len(bytes) + 1)
} else {
if *debugLog {
log.Printf("%v waiting for start, storing into connection", key)
}
a.insertIntoConn(t, conn)
}
} else if diff := conn.nextSeq.Difference(seq); diff > 0 {
if *debugLog {
log.Printf("%v gap in sequence numbers (%v, %v) diff %v, storing into connection", key, conn.nextSeq, seq, diff)
}
a.insertIntoConn(t, conn)
} else {
bytes, conn.nextSeq = byteSpan(conn.nextSeq, seq, bytes)
if *debugLog {
log.Printf("%v found contiguous data (%v, %v), returning immediately", key, seq, conn.nextSeq)
}
a.ret = append(a.ret, Reassembly{
Bytes: bytes,
Skip: 0,
End: t.RST || t.FIN,
Seen: time.Now(),
})
}
if len(a.ret) > 0 {
a.sendToConnection(conn)
}
conn.mu.Unlock()
}
