func rst(srcIP net.IP, dstIP net.IP, srcPort uint16, dstPort uint16, seq uint32, ack uint32, payloadLen uint32) *tcpPacket {
iphdr := packet.NewIPv4()
tcphdr := packet.NewTCP()
iphdr.Version = 4
iphdr.DstIP = srcIP
iphdr.SrcIP = dstIP
iphdr.TTL = 64
iphdr.Protocol = packet.IPProtocolTCP
tcphdr.DstPort = srcPort
tcphdr.SrcPort = dstPort
tcphdr.Window = uint16(MAX_RECV_WINDOW)
tcphdr.RST = true
tcphdr.ACK = true
tcphdr.Seq = 0
// RFC 793:
// "If the incoming segment has an ACK field, the reset takes its sequence
// number from the ACK field of the segment, otherwise the reset has
// sequence number zero and the ACK field is set to the sum of the sequence
// number and segment length of the incoming segment. The connection remains
// in the CLOSED state."
tcphdr.Ack = seq + payloadLen
if tcphdr.Ack == seq {
tcphdr.Ack += 1
}
if ack != 0 {
tcphdr.Seq = ack
}
return packTCP(iphdr, tcphdr)
}
func (tt *tcpConnTrack) synAck(syn *tcpPacket) {
iphdr := packet.NewIPv4()
tcphdr := packet.NewTCP()
iphdr.Version = 4
iphdr.SrcIP = tt.remoteIP
iphdr.DstIP = tt.localIP
iphdr.TTL = 64
iphdr.Protocol = packet.IPProtocolTCP
tcphdr.SrcPort = tt.remotePort
tcphdr.DstPort = tt.localPort
tcphdr.Window = uint16(atomic.LoadInt32(&tt.recvWindow))
tcphdr.SYN = true
tcphdr.ACK = true
tcphdr.Seq = tt.nxtSeq
tcphdr.Ack = tt.rcvNxtSeq
tcphdr.Options = []packet.TCPOption{{2, 4, []byte{0x5, 0xb4}}}
synAck := packTCP(iphdr, tcphdr)
tt.send(synAck)
// SYN counts 1 seq
tt.nxtSeq += 1
}
func (tt *tcpConnTrack) ack() {
iphdr := packet.NewIPv4()
tcphdr := packet.NewTCP()
iphdr.Version = 4
iphdr.SrcIP = tt.remoteIP
iphdr.DstIP = tt.localIP
iphdr.TTL = 64
iphdr.Protocol = packet.IPProtocolTCP
tcphdr.SrcPort = tt.remotePort
tcphdr.DstPort = tt.localPort
tcphdr.Window = uint16(atomic.LoadInt32(&tt.recvWindow))
tcphdr.ACK = true
tcphdr.Seq = tt.nxtSeq
tcphdr.Ack = tt.rcvNxtSeq
ack := packTCP(iphdr, tcphdr)
tt.send(ack)
}
func (tt *tcpConnTrack) payload(data []byte) {
iphdr := packet.NewIPv4()
tcphdr := packet.NewTCP()
iphdr.Version = 4
iphdr.SrcIP = tt.remoteIP
iphdr.DstIP = tt.localIP
iphdr.TTL = 64
iphdr.Protocol = packet.IPProtocolTCP
tcphdr.SrcPort = tt.remotePort
tcphdr.DstPort = tt.localPort
tcphdr.Window = uint16(atomic.LoadInt32(&tt.recvWindow))
tcphdr.ACK = true
tcphdr.PSH = true
tcphdr.Seq = tt.nxtSeq
tcphdr.Ack = tt.rcvNxtSeq
tcphdr.Payload = data
pkt := packTCP(iphdr, tcphdr)
tt.send(pkt)
// adjust seq
tt.nxtSeq = tt.nxtSeq + uint32(len(data))
}
func copyTCPPacket(raw []byte, ip *packet.IPv4, tcp *packet.TCP) *tcpPacket {
iphdr := packet.NewIPv4()
tcphdr := packet.NewTCP()
pkt := newTCPPacket()
if len(tcp.Payload) == 0 {
// shallow copy headers
// for now, we don't need deep copy if no payload
*iphdr = *ip
*tcphdr = *tcp
pkt.ip = iphdr
pkt.tcp = tcphdr
} else {
// get a block of buffer, make a deep copy
buf := newBuffer()
n := copy(buf, raw)
pkt.mtuBuf = buf
pkt.wire = buf[:n]
packet.ParseIPv4(pkt.wire, iphdr)
packet.ParseTCP(iphdr.Payload, tcphdr)
pkt.ip = iphdr
pkt.tcp = tcphdr
}
return pkt
}