Merge branch 'future' of https://github.com/yggdrasil-network/yggdrasil-go into future

src/core/icmpv6.go

@@ -0,0 +1,80 @@
+package core
+
+// The ICMPv6 module implements functions to easily create ICMPv6
+// packets. These functions, when mixed with the built-in Go IPv6
+// and ICMP libraries, can be used to send control messages back
+// to the host. Examples include:
+// - NDP messages, when running in TAP mode
+// - Packet Too Big messages, when packets exceed the session MTU
+// - Destination Unreachable messages, when a session prohibits
+//   incoming traffic
+
+import (
+	"encoding/binary"
+	"net"
+
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv6"
+)
+
+type ICMPv6 struct{}
+
+// Marshal returns the binary encoding of h.
+func ipv6Header_Marshal(h *ipv6.Header) ([]byte, error) {
+	b := make([]byte, 40)
+	b[0] |= byte(h.Version) << 4
+	b[0] |= byte(h.TrafficClass) >> 4
+	b[1] |= byte(h.TrafficClass) << 4
+	b[1] |= byte(h.FlowLabel >> 16)
+	b[2] = byte(h.FlowLabel >> 8)
+	b[3] = byte(h.FlowLabel)
+	binary.BigEndian.PutUint16(b[4:6], uint16(h.PayloadLen))
+	b[6] = byte(h.NextHeader)
+	b[7] = byte(h.HopLimit)
+	copy(b[8:24], h.Src)
+	copy(b[24:40], h.Dst)
+	return b, nil
+}
+
+// Creates an ICMPv6 packet based on the given icmp.MessageBody and other
+// parameters, complete with IP headers only, which can be written directly to
+// a TUN adapter, or called directly by the CreateICMPv6L2 function when
+// generating a message for TAP adapters.
+func CreateICMPv6(dst net.IP, src net.IP, mtype ipv6.ICMPType, mcode int, mbody icmp.MessageBody) ([]byte, error) {
+	// Create the ICMPv6 message
+	icmpMessage := icmp.Message{
+		Type: mtype,
+		Code: mcode,
+		Body: mbody,
+	}
+
+	// Convert the ICMPv6 message into []byte
+	icmpMessageBuf, err := icmpMessage.Marshal(icmp.IPv6PseudoHeader(src, dst))
+	if err != nil {
+		return nil, err
+	}
+
+	// Create the IPv6 header
+	ipv6Header := ipv6.Header{
+		Version:    ipv6.Version,
+		NextHeader: 58,
+		PayloadLen: len(icmpMessageBuf),
+		HopLimit:   255,
+		Src:        src,
+		Dst:        dst,
+	}
+
+	// Convert the IPv6 header into []byte
+	ipv6HeaderBuf, err := ipv6Header_Marshal(&ipv6Header)
+	if err != nil {
+		return nil, err
+	}
+
+	// Construct the packet
+	responsePacket := make([]byte, ipv6.HeaderLen+ipv6Header.PayloadLen)
+	copy(responsePacket[:ipv6.HeaderLen], ipv6HeaderBuf)
+	copy(responsePacket[ipv6.HeaderLen:], icmpMessageBuf)
+
+	// Send it back
+	return responsePacket, nil
+}