[release-v2.1] p2p: Handle peer ID wraparound

When wraparound of the uint64 peer ID counter occurs, take care to never
conflict (sharing a peer ID) with existing peers who are still connected with
the same ID.

While here, continue to skip the zero ID (remote peer IDs always start at one)
so zero can be reserved for local peer usage.

Backport of 54a9b82.

Author: jrick

p2p/peering.go

@@ -144,7 +144,6 @@ type RemotePeer struct {
 // messages with remote peers on the network.
 type LocalPeer struct {
 	mask          atomic.Uint64
-	peerIDCounter atomic.Uint64
 	requireHeight atomic.Int32
 
 	dial DialFunc
@@ -160,8 +159,9 @@ type LocalPeer struct {
 	chainParams    *chaincfg.Params
 	disableRelayTx bool
 
-	rpByID map[uint64]*RemotePeer
-	rpMu   sync.Mutex
+	rpByID      map[uint64]*RemotePeer
+	rpIDCounter uint64
+	rpMu        sync.Mutex
 }
 
 // NewLocalPeer creates a LocalPeer that is externally reachable to remote peers
@@ -257,9 +257,6 @@ func (lp *LocalPeer) ConnectOutbound(ctx context.Context, addr string, reqSvcs w
 
 	log.Debugf("Attempting connection to peer %v", addr)
 
-	// Generate a unique ID for this peer and add the initial connection state.
-	id := lp.peerIDCounter.Add(1)
-
 	tcpAddr, err := net.ResolveTCPAddr("tcp", addr)
 	if err != nil {
 		return nil, err
@@ -269,7 +266,7 @@ func (lp *LocalPeer) ConnectOutbound(ctx context.Context, addr string, reqSvcs w
 	na := addrmgr.NewNetAddressFromIPPort(tcpAddr.IP, uint16(tcpAddr.Port), wire.SFNodeNetwork)
 	na.Timestamp = time.Now()
 
-	rp, err := lp.connectOutbound(ctx, id, addr, na)
+	rp, err := lp.connectOutbound(ctx, addr, na)
 	if err != nil {
 		op := errors.Opf(opf, addr)
 		return nil, errors.E(op, err)
@@ -544,11 +541,11 @@ func (rp *RemotePeer) sendWaitingInventory(ctx context.Context) error {
 	return nil
 }
 
-func handshake(ctx context.Context, lp *LocalPeer, id uint64, na *addrmgr.NetAddress, c net.Conn) (*RemotePeer, error) {
+func handshake(ctx context.Context, lp *LocalPeer, na *addrmgr.NetAddress, c net.Conn) (*RemotePeer, error) {
 	const op errors.Op = "p2p.handshake"
 
 	rp := &RemotePeer{
-		id:               id,
+		id:               0, // Set after handshake completes
 		lp:               lp,
 		ua:               "",
 		services:         0,
@@ -618,9 +615,7 @@ func handshake(ctx context.Context, lp *LocalPeer, id uint64, na *addrmgr.NetAdd
 	return rp, nil
 }
 
-func (lp *LocalPeer) connectOutbound(ctx context.Context, id uint64, addr string,
-	na *addrmgr.NetAddress) (*RemotePeer, error) {
-
+func (lp *LocalPeer) connectOutbound(ctx context.Context, addr string, na *addrmgr.NetAddress) (*RemotePeer, error) {
 	// Mark the connection attempt.
 	lp.amgr.Attempt(na)
 
@@ -636,15 +631,24 @@ func (lp *LocalPeer) connectOutbound(ctx context.Context, id uint64, addr string
 
 	// Handshake with a timeout of 5s.
 	handshakeCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
-	rp, err := handshake(handshakeCtx, lp, id, na, c)
+	rp, err := handshake(handshakeCtx, lp, na, c)
 	cancel()
 	if err != nil {
 		return nil, err
 	}
 
 	// Associate connected rp with local peer.
 	lp.rpMu.Lock()
-	lp.rpByID[rp.id] = rp
+	for {
+		// Generate a unique ID for this peer and add the initial connection state.
+		lp.rpIDCounter++
+		id := lp.rpIDCounter
+		if _, ok := lp.rpByID[id]; !ok && id != 0 {
+			rp.id = id
+			lp.rpByID[id] = rp
+			break
+		}
+	}
 	lp.rpMu.Unlock()
 
 	// The real services of the net address are now known.