initial: ZeroTier-like P2P mesh VPN server with multi-tenant Web UI

internal/vl2/frame.go

@@ -0,0 +1,92 @@
+package vl2
+
+import (
+	"encoding/binary"
+	"fmt"
+	"net"
+	"sync"
+)
+
+const (
+	MinFrameSize    = 14
+	MaxFrameSize    = 65535
+	EtherTypeIPv4   = 0x0800
+	EtherTypeARP    = 0x0806
+	EtherTypeIPv6   = 0x86DD
+)
+
+type EthernetFrame struct {
+	DstMAC   net.HardwareAddr
+	SrcMAC   net.HardwareAddr
+	EtherType uint16
+	Payload  []byte
+}
+
+func ParseEthernetFrame(data []byte) (*EthernetFrame, error) {
+	if len(data) < MinFrameSize {
+		return nil, fmt.Errorf("frame too short: %d < %d", len(data), MinFrameSize)
+	}
+	return &EthernetFrame{
+		DstMAC:   net.HardwareAddr(data[0:6]),
+		SrcMAC:   net.HardwareAddr(data[6:12]),
+		EtherType: binary.BigEndian.Uint16(data[12:14]),
+		Payload:  data[14:],
+	}, nil
+}
+
+func (f *EthernetFrame) Encode() []byte {
+	buf := make([]byte, MinFrameSize+len(f.Payload))
+	copy(buf[0:6], f.DstMAC)
+	copy(buf[6:12], f.SrcMAC)
+	binary.BigEndian.PutUint16(buf[12:14], f.EtherType)
+	copy(buf[14:], f.Payload)
+	return buf
+}
+
+func (f *EthernetFrame) IsBroadcast() bool {
+	for _, b := range f.DstMAC {
+		if b != 0xff {
+			return false
+		}
+	}
+	return true
+}
+
+func (f *EthernetFrame) IsMulticast() bool {
+	return len(f.DstMAC) > 0 && f.DstMAC[0]&0x01 == 0x01 && !f.IsBroadcast()
+}
+
+func (f *EthernetFrame) IsARP() bool {
+	return f.EtherType == EtherTypeARP
+}
+
+func (f *EthernetFrame) IsIPv4() bool {
+	return f.EtherType == EtherTypeIPv4
+}
+
+func (f *EthernetFrame) IsIPv6() bool {
+	return f.EtherType == EtherTypeIPv6
+}
+
+type MACKey [6]byte
+
+func MACToKey(mac net.HardwareAddr) MACKey {
+	var key MACKey
+	copy(key[:], mac)
+	return key
+}
+
+var frameBufPool = sync.Pool{
+	New: func() interface{} {
+		buf := make([]byte, MaxFrameSize)
+		return &buf
+	},
+}
+
+func GetFrameBuf() *[]byte {
+	return frameBufPool.Get().(*[]byte)
+}
+
+func PutFrameBuf(buf *[]byte) {
+	frameBufPool.Put(buf)
+}