fix(p2p/session): return err if peer tracker is empty

Author: vgonkivs

p2p/exchange.go

@@ -292,9 +292,13 @@ func (ex *Exchange[H]) GetRangeByHeight(
 			attribute.Int64("to", int64(to)),
 		))
 	defer span.End()
-	session := newSession[H](
+	session, err := newSession[H](
 		ex.ctx, ex.host, ex.peerTracker, ex.protocolID, ex.Params.RequestTimeout, ex.metrics, withValidation(from),
 	)
+	// TODO(@vgonkivs): decide what to do with this error. Maybe we should fall into "discovery mode" and try to collect peers???
+	if err != nil {
+		return nil, err
+	}
 	defer session.close()
 	// we request the next header height that we don't have: `fromHead`+1
 	amount := to - (from.Height() + 1)

p2p/peer_tracker.go

@@ -16,11 +16,12 @@ import (
 )
 
 type peerTracker struct {
-	host       host.Host
-	connGater  *conngater.BasicConnectionGater
-	metrics    *exchangeMetrics
 	protocolID protocol.ID
-	peerLk     sync.RWMutex
+
+	host      host.Host
+	connGater *conngater.BasicConnectionGater
+
+	peerLk sync.RWMutex
 	// trackedPeers contains active peers that we can request to.
 	// we cache the peer once they disconnect,
 	// so we can guarantee that peerQueue will only contain active peers
@@ -30,6 +31,8 @@ type peerTracker struct {
 	// good peers during garbage collection
 	pidstore PeerIDStore
 
+	metrics *exchangeMetrics
+
 	ctx    context.Context
 	cancel context.CancelFunc
 	// done is used to gracefully stop the peerTracker.
@@ -135,11 +138,13 @@ func (p *peerTracker) track() {
 			if network.NotConnected == ev.Connectedness {
 				p.disconnected(ev.Peer)
 			}
-		case subscription := <-identifySub.Out():
-			ev := subscription.(event.EvtPeerIdentificationCompleted)
-			p.connected(ev.Peer)
-		case subscription := <-protocolSub.Out():
-			ev := subscription.(event.EvtPeerProtocolsUpdated)
+		case identSubscription := <-identifySub.Out():
+			ev := identSubscription.(event.EvtPeerIdentificationCompleted)
+			if slices.Contains(ev.Protocols, p.protocolID) {
+				p.connected(ev.Peer)
+			}
+		case protocolSubscription := <-protocolSub.Out():
+			ev := protocolSubscription.(event.EvtPeerProtocolsUpdated)
 			if slices.Contains(ev.Removed, p.protocolID) {
 				p.disconnected(ev.Peer)
 				break
@@ -173,15 +178,6 @@ func (p *peerTracker) connected(pID libpeer.ID) {
 		return
 	}
 
-	// check that peer supports our protocol id.
-	protocol, err := p.host.Peerstore().SupportsProtocols(pID, p.protocolID)
-	if err != nil {
-		return
-	}
-	if !slices.Contains(protocol, p.protocolID) {
-		return
-	}
-
 	for _, c := range p.host.Network().ConnsToPeer(pID) {
 		// check if connection is short-termed and skip this peer
 		if c.Stat().Limited {

p2p/session.go

@@ -60,23 +60,28 @@ func newSession[H header.Header[H]](
 	requestTimeout time.Duration,
 	metrics *exchangeMetrics,
 	options ...option[H],
-) *session[H] {
+) (*session[H], error) {
 	ctx, cancel := context.WithCancel(ctx)
 	ses := &session[H]{
 		ctx:            ctx,
 		cancel:         cancel,
 		protocolID:     protocolID,
 		host:           h,
-		queue:          newPeerQueue(ctx, peerTracker.peers()),
 		peerTracker:    peerTracker,
 		requestTimeout: requestTimeout,
 		metrics:        metrics,
 	}
 
+	peers := peerTracker.peers()
+	if len(peers) == 0 {
+		return nil, errors.New("empty peer tracker")
+	}
+	ses.queue = newPeerQueue(ctx, peers)
+
 	for _, opt := range options {
 		opt(ses)
 	}
-	return ses
+	return ses, nil
 }
 
 // getRangeByHeight requests headers from different peers.

p2p/session_test.go

@@ -6,6 +6,8 @@ import (
 	"time"
 
 	"github.com/libp2p/go-libp2p/core/peer"
+	blankhost "github.com/libp2p/go-libp2p/p2p/host/blank"
+	swarm "github.com/libp2p/go-libp2p/p2p/net/swarm/testing"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
@@ -25,34 +27,44 @@ func Test_PrepareRequests(t *testing.T) {
 func Test_Validate(t *testing.T) {
 	suite := headertest.NewTestSuite(t)
 	head := suite.Head()
-	ses := newSession(
+	peerId := peer.ID("test")
+	pT := &peerTracker{trackedPeers: make(map[peer.ID]struct{})}
+	pT.trackedPeers[peerId] = struct{}{}
+	pT.host = blankhost.NewBlankHost(swarm.GenSwarm(t))
+	ses, err := newSession(
 		context.Background(),
 		nil,
-		&peerTracker{trackedPeers: make(map[peer.ID]struct{})},
+		pT,
 		"", time.Second, nil,
 		withValidation(head),
 	)
 
+	require.NoError(t, err)
 	headers := suite.GenDummyHeaders(5)
-	err := ses.verify(headers)
+	err = ses.verify(headers)
 	assert.NoError(t, err)
 }
 
 // Test_ValidateFails ensures that non-adjacent range will return an error.
 func Test_ValidateFails(t *testing.T) {
 	suite := headertest.NewTestSuite(t)
 	head := suite.Head()
-	ses := newSession(
+
+	peerId := peer.ID("test")
+	pT := &peerTracker{trackedPeers: make(map[peer.ID]struct{})}
+	pT.trackedPeers[peerId] = struct{}{}
+	pT.host = blankhost.NewBlankHost(swarm.GenSwarm(t))
+	ses, err := newSession(
 		context.Background(),
-		nil,
-		&peerTracker{trackedPeers: make(map[peer.ID]struct{})},
+		blankhost.NewBlankHost(swarm.GenSwarm(t)),
+		pT,
 		"", time.Second, nil,
 		withValidation(head),
 	)
-
+	require.NoError(t, err)
 	headers := suite.GenDummyHeaders(5)
 	// break adjacency
 	headers[2] = headers[4]
-	err := ses.verify(headers)
+	err = ses.verify(headers)
 	assert.Error(t, err)
 }