func responsePacket(local net.IP, remote net.IP, lPort uint16, rPort uint16, respPayload []byte) *udpPacket {
ip := packet.NewIPv4()
udp := packet.NewUDP()
ip.Version = 4
ip.SrcIP = make(net.IP, len(remote))
copy(ip.SrcIP, remote)
ip.DstIP = make(net.IP, len(local))
copy(ip.DstIP, local)
ip.TTL = 64
ip.Protocol = packet.IPProtocolUDP
udp.SrcPort = rPort
udp.DstPort = lPort
udp.Payload = respPayload
pkt := newUDPPacket()
pkt.ip = ip
pkt.udp = udp
buf := newBuffer()
pkt.mtuBuf = buf
payloadL := len(udp.Payload)
payloadStart := MTU - payloadL
if payloadL != 0 {
copy(pkt.mtuBuf[payloadStart:], udp.Payload)
}
udpHL := 8
udpStart := payloadStart - udpHL
pseduoStart := udpStart - packet.IPv4_PSEUDO_LENGTH
ip.PseudoHeader(pkt.mtuBuf[pseduoStart:udpStart], packet.IPProtocolUDP, udpHL+payloadL)
udp.Serialize(pkt.mtuBuf[udpStart:payloadStart], pkt.mtuBuf[pseduoStart:])
ipHL := ip.HeaderLength()
ipStart := udpStart - ipHL
ip.Serialize(pkt.mtuBuf[ipStart:udpStart], udpHL+payloadL)
pkt.wire = pkt.mtuBuf[ipStart:]
return pkt
}
func copyUDPPacket(raw []byte, ip *packet.IPv4, udp *packet.UDP) *udpPacket {
iphdr := packet.NewIPv4()
udphdr := packet.NewUDP()
pkt := newUDPPacket()
if len(udp.Payload) == 0 {
// shallow copy headers
// for now, we don't need deep copy if no payload
*iphdr = *ip
*udphdr = *udp
pkt.ip = iphdr
pkt.udp = udphdr
} 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.ParseUDP(iphdr.Payload, udphdr)
pkt.ip = iphdr
pkt.udp = udphdr
}
return pkt
}