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

internal/vl1/packet.go

@@ -0,0 +1,117 @@
+package vl1
+
+import (
+	"encoding/binary"
+	"fmt"
+)
+
+const (
+	Version      = 1
+	MaxPacketSize = 65535
+	HeaderSize   = 8
+	MaxFrameSize  = 65535
+	MinFrameSize  = 14
+
+	PacketTypeHandshake = byte(1)
+	PacketTypeData      = byte(2)
+	PacketTypeKeepalive = byte(3)
+)
+
+type Header struct {
+	Version   byte
+	Type      byte
+	NetworkID uint32
+	Length    uint16
+}
+
+func (h *Header) Encode(buf []byte) {
+	buf[0] = h.Version
+	buf[1] = h.Type
+	binary.BigEndian.PutUint32(buf[2:6], h.NetworkID)
+	binary.BigEndian.PutUint16(buf[6:8], h.Length)
+}
+
+func (h *Header) Decode(buf []byte) error {
+	if len(buf) < HeaderSize {
+		return fmt.Errorf("header too short: %d < %d", len(buf), HeaderSize)
+	}
+	h.Version = buf[0]
+	h.Type = buf[1]
+	h.NetworkID = binary.BigEndian.Uint32(buf[2:6])
+	h.Length = binary.BigEndian.Uint16(buf[6:8])
+	return nil
+}
+
+type Packet struct {
+	Header  Header
+	Payload []byte
+}
+
+func NewHandshakePacket(payload []byte) Packet {
+	return Packet{
+		Header: Header{
+			Version: Version,
+			Type:    PacketTypeHandshake,
+			Length:  uint16(len(payload)),
+		},
+		Payload: payload,
+	}
+}
+
+func NewDataPacket(networkID uint32, payload []byte) Packet {
+	return Packet{
+		Header: Header{
+			Version:   Version,
+			Type:      PacketTypeData,
+			NetworkID: networkID,
+			Length:    uint16(len(payload)),
+		},
+		Payload: payload,
+	}
+}
+
+func NewKeepalivePacket() Packet {
+	return Packet{
+		Header: Header{
+			Version: Version,
+			Type:    PacketTypeKeepalive,
+			Length:  0,
+		},
+	}
+}
+
+func (p *Packet) Encode() []byte {
+	total := HeaderSize + len(p.Payload)
+	buf := make([]byte, total)
+	p.Header.Length = uint16(len(p.Payload))
+	p.Header.Encode(buf[:HeaderSize])
+	copy(buf[HeaderSize:], p.Payload)
+	return buf
+}
+
+func DecodePacket(data []byte) (*Packet, error) {
+	var p Packet
+	if err := p.Header.Decode(data); err != nil {
+		return nil, err
+	}
+	payloadLen := int(p.Header.Length)
+	if HeaderSize+payloadLen > len(data) {
+		return nil, fmt.Errorf("packet truncated: header claims %d + %d > %d", HeaderSize, payloadLen, len(data))
+	}
+	p.Payload = make([]byte, payloadLen)
+	copy(p.Payload, data[HeaderSize:HeaderSize+payloadLen])
+	return &p, nil
+}
+
+func DecodePacketInto(p *Packet, data []byte) error {
+	if err := p.Header.Decode(data); err != nil {
+		return err
+	}
+	payloadLen := int(p.Header.Length)
+	if HeaderSize+payloadLen > len(data) {
+		return fmt.Errorf("packet truncated")
+	}
+	p.Payload = make([]byte, payloadLen)
+	copy(p.Payload, data[HeaderSize:HeaderSize+payloadLen])
+	return nil
+}