vppn/node/peer.go

package node

import (
	"fmt"
	"log"
	"net/netip"
	"sync/atomic"
	"time"
	"vppn/m"
)

type remotePeers [256]*remotePeer

type peerRoutingData struct {
	up            bool
	relay         bool
	controlCipher *controlCipher
	dataCipher    *dataCipher
	remoteAddr    netip.AddrPort
	relayIP       byte // Non-zero if we should relay.
}

type remotePeer struct {
	// Immutable data.
	localIP  byte
	remoteIP byte
	iface    *ifWriter
	conn     *connWriter

	// Shared state.
	peers     *remotePeers
	published *atomic.Pointer[peerRoutingData]

	// Only used in HandlePacket / Not synchronized.
	dupCheck   *dupCheck
	decryptBuf []byte

	// Only used in SendData / Not synchronized.
	encryptBuf []byte

	// Used for sending control and data packets. Atomic access only.
	counter uint64

	// For communicating with the supervisor thread.
	peerUpdates    chan *m.Peer
	controlPackets chan controlPacket
}

func newRemotePeer(conf m.PeerConfig, remoteIP byte, iface *ifWriter, conn *connWriter, peers *remotePeers) *remotePeer {
	rp := &remotePeer{
		localIP:        conf.PeerIP,
		remoteIP:       remoteIP,
		iface:          iface,
		conn:           conn,
		peers:          peers,
		published:      &atomic.Pointer[peerRoutingData]{},
		dupCheck:       newDupCheck(0),
		decryptBuf:     make([]byte, bufferSize),
		encryptBuf:     make([]byte, bufferSize),
		counter:        uint64(time.Now().Unix()) << 30,
		peerUpdates:    make(chan *m.Peer),
		controlPackets: make(chan controlPacket, 512),
	}

	pd := peerRoutingData{}
	rp.published.Store(&pd)

	//go newPeerSuper(rp).Run()
	go rp.supervise(conf)
	return rp
}

func (rp *remotePeer) logf(msg string, args ...any) {
	log.Printf(fmt.Sprintf("[%03d] ", rp.remoteIP)+msg, args...)
}

func (rp *remotePeer) HandlePeerUpdate(peer *m.Peer) {
	rp.peerUpdates <- peer
}

// ----------------------------------------------------------------------------

// HandlePacket accepts a raw data packet coming in from the network.
//
// This function is called by a single thread.
func (rp *remotePeer) HandlePacket(addr netip.AddrPort, h header, data []byte) {
	switch h.StreamID {
	case controlStreamID:
		rp.handleControlPacket(addr, h, data)

	case dataStreamID:
		rp.handleDataPacket(data)

	case relayStreamID:
		rp.handleRelayPacket(h, data)

	default:
		rp.logf("Unknown stream ID: %d", h.StreamID)
	}
}

// ----------------------------------------------------------------------------

func (rp *remotePeer) handleControlPacket(addr netip.AddrPort, h header, data []byte) {
	routingData := rp.published.Load()
	if routingData.controlCipher == nil {
		rp.logf("Not connected (control).")
		return
	}

	if h.DestIP != rp.localIP {
		rp.logf("Incorrect destination IP on control packet.")
		return
	}

	out, ok := routingData.controlCipher.Decrypt(data, rp.decryptBuf)
	if !ok {
		rp.logf("Failed to decrypt control packet.")
		return
	}

	if len(out) == 0 {
		rp.logf("Empty control packet from: %d", h.SourceIP)
		return
	}

	if rp.dupCheck.IsDup(h.Counter) {
		rp.logf("Duplicate control packet: %d", h.Counter)
		return
	}

	pkt := controlPacket{
		SrcIP:      h.SourceIP,
		RemoteAddr: addr,
	}

	if err := pkt.ParsePayload(out); err != nil {
		rp.logf("Failed to parse control packet: %v", err)
		return
	}

	select {
	case rp.controlPackets <- pkt:
	default:
		rp.logf("Dropping control packet.")
	}
}

// ----------------------------------------------------------------------------

func (rp *remotePeer) handleDataPacket(data []byte) {
	routingData := rp.published.Load()
	if routingData.dataCipher == nil {
		rp.logf("Not connected (recv).")
		return
	}

	dec, ok := routingData.dataCipher.Decrypt(data, rp.decryptBuf)
	if !ok {
		rp.logf("Failed to decrypt data packet.")
		return
	}

	rp.iface.Write(dec)
}

// ----------------------------------------------------------------------------

func (rp *remotePeer) handleRelayPacket(h header, data []byte) {
	routingData := rp.published.Load()
	if routingData.dataCipher == nil {
		rp.logf("Not connected (recv).")
		return
	}

	dec, ok := routingData.dataCipher.Decrypt(data, rp.decryptBuf)
	if !ok {
		rp.logf("Failed to decrypt data packet.")
		return
	}

	rp.peers[h.DestIP].SendAsIs(dec)
}

// ----------------------------------------------------------------------------

// SendData sends data coming from the interface going to the network.
//
// This function is called by a single thread.
func (rp *remotePeer) SendData(data []byte) {
	rp.encryptAndSend(dataStreamID, rp.remoteIP, data)
}

func (rp *remotePeer) HandleInterfacePacket(data []byte) {
	routingData := rp.published.Load()

	if routingData.dataCipher == nil {
		rp.logf("Not connected (handle interface).")
		return
	}

	h := header{
		StreamID: dataStreamID,
		Counter:  atomic.AddUint64(&rp.counter, 1),
		SourceIP: rp.localIP,
		DestIP:   rp.remoteIP,
	}

	enc := routingData.dataCipher.Encrypt(h, data, rp.encryptBuf)

	if routingData.relayIP != 0 {
		rp.peers[routingData.relayIP].RelayFor(rp.remoteIP, enc)
	} else {
		rp.SendData(data)
	}
}

// ----------------------------------------------------------------------------

func (rp *remotePeer) CanRelay() bool {
	data := rp.published.Load()
	return data.relay && data.up
}

// ----------------------------------------------------------------------------

func (rp *remotePeer) RelayFor(destIP byte, data []byte) {
	rp.encryptAndSend(relayStreamID, destIP, data)
}

// ----------------------------------------------------------------------------

func (rp *remotePeer) encryptAndSend(streamID byte, destIP byte, data []byte) {
	routingData := rp.published.Load()
	if routingData.dataCipher == nil || routingData.remoteAddr == zeroAddrPort {
		rp.logf("Not connected (encrypt and send).")
		return
	}

	h := header{
		StreamID: streamID,
		Counter:  atomic.AddUint64(&rp.counter, 1),
		SourceIP: rp.localIP,
		DestIP:   destIP,
	}

	enc := routingData.dataCipher.Encrypt(h, data, rp.encryptBuf)
	rp.conn.WriteTo(enc, routingData.remoteAddr)
}

// ----------------------------------------------------------------------------

// SendAsIs is used when forwarding already-encrypted data from one peer to
// another.
func (rp *remotePeer) SendAsIs(data []byte) {
	routingData := rp.published.Load()
	if routingData.remoteAddr == zeroAddrPort {
		rp.logf("Not connected (send direct).")
		return
	}
	rp.conn.WriteTo(data, routingData.remoteAddr)
}