protect one peer per topic

beacon-chain/p2p/gossip_peer_controller.go

@@ -303,33 +303,31 @@ func (g *GossipPeerDialer) peersForTopic(topic string, targetCount int) []*enode
 	return newPeers
 }
 
-// SoleProviderPeers returns peer IDs that are the sole provider for at least one topic.
-// A peer is considered a sole provider if it's the only connected peer for a topic (listPeers returns only this peer)
-//
-// These peers should be protected from pruning since losing them would mean
-// losing connectivity to that topic entirely.
-func (g *GossipPeerDialer) SoleProviderPeers() []peer.ID {
+// ProtectedPeers returns peer IDs that should be protected from pruning.
+// For each topic, one connected peer is marked as protected to ensure
+// we maintain connectivity to all subscribed topics.
+func (g *GossipPeerDialer) ProtectedPeers() []peer.ID {
 	if g.topicsProvider == nil {
 		return nil
 	}
 
 	topics := g.topicsProvider()
-	soleProviders := make(map[peer.ID]struct{})
+	protectedPeers := make(map[peer.ID]struct{})
 
 	for topic := range topics {
 		connectedPeers := g.listPeers(topic)
 
-		// Skip if no peers or more than one connected peer
-		if len(connectedPeers) != 1 {
+		// Skip if no peers connected
+		if len(connectedPeers) == 0 {
 			continue
 		}
 
-		// This peer is the sole known provider
-		soleProviders[connectedPeers[0]] = struct{}{}
+		// Protect the first peer for this topic
+		protectedPeers[connectedPeers[0]] = struct{}{}
 	}
 
-	result := make([]peer.ID, 0, len(soleProviders))
-	for pid := range soleProviders {
+	result := make([]peer.ID, 0, len(protectedPeers))
+	for pid := range protectedPeers {
 		result = append(result, pid)
 	}
 	return result

beacon-chain/p2p/gossip_peer_controller_test.go

@@ -442,7 +442,7 @@ func TestGossipPeerDialer_selectPeersForTopics(t *testing.T) {
 	}
 }
 
-func TestGossipPeerDialer_SoleProviderPeers(t *testing.T) {
+func TestGossipPeerDialer_ProtectedPeers(t *testing.T) {
 	peerA := peer.ID("peerA")
 	peerB := peer.ID("peerB")
 	peerC := peer.ID("peerC")
@@ -472,10 +472,10 @@ func TestGossipPeerDialer_SoleProviderPeers(t *testing.T) {
 			expected:       []peer.ID{},
 		},
 		{
-			name:           "multiple peers for all topics",
+			name:           "multiple peers for all topics protects first peer from each",
 			topicsProvider: func() map[string]int { return map[string]int{"topic/a": 2, "topic/b": 2} },
 			connectedPeers: map[string][]peer.ID{"topic/a": {peerA, peerB}, "topic/b": {peerB, peerC}},
-			expected:       []peer.ID{},
+			expected:       []peer.ID{peerA, peerB},
 		},
 		{
 			name:           "single peer for one topic",
@@ -484,22 +484,22 @@ func TestGossipPeerDialer_SoleProviderPeers(t *testing.T) {
 			expected:       []peer.ID{peerA},
 		},
 		{
-			name:           "same peer is sole provider for multiple topics",
+			name:           "same peer is first for multiple topics",
 			topicsProvider: func() map[string]int { return map[string]int{"topic/a": 1, "topic/b": 1} },
 			connectedPeers: map[string][]peer.ID{"topic/a": {peerA}, "topic/b": {peerA}},
 			expected:       []peer.ID{peerA},
 		},
 		{
-			name:           "different sole providers for different topics",
+			name:           "different first peers for different topics",
 			topicsProvider: func() map[string]int { return map[string]int{"topic/a": 1, "topic/b": 1} },
 			connectedPeers: map[string][]peer.ID{"topic/a": {peerA}, "topic/b": {peerB}},
 			expected:       []peer.ID{peerA, peerB},
 		},
 		{
-			name:           "mix of single and multiple peers",
+			name:           "protects first peer from each topic",
 			topicsProvider: func() map[string]int { return map[string]int{"topic/a": 1, "topic/b": 2, "topic/c": 1} },
 			connectedPeers: map[string][]peer.ID{"topic/a": {peerA}, "topic/b": {peerB, peerC}, "topic/c": {peerC}},
-			expected:       []peer.ID{peerA, peerC},
+			expected:       []peer.ID{peerA, peerB, peerC},
 		},
 	}
 
@@ -514,7 +514,7 @@ func TestGossipPeerDialer_SoleProviderPeers(t *testing.T) {
 				listPeers:      listPeers,
 			}
 
-			got := dialer.SoleProviderPeers()
+			got := dialer.ProtectedPeers()
 
 			if tt.expected == nil {
 				require.Nil(t, got)

beacon-chain/p2p/gossipcrawler/interface.go

@@ -33,5 +33,5 @@ type SubnetTopicsProvider func() map[string]int
 type GossipDialer interface {
 	Start(provider SubnetTopicsProvider) error
 	DialPeersForTopicBlocking(ctx context.Context, topic string, nPeers int) error
-	SoleProviderPeers() []peer.ID
+	ProtectedPeers() []peer.ID
 }

beacon-chain/sync/subscriber.go

@@ -248,9 +248,8 @@ func (s *Service) filterNeededPeers(pids []peer.ID) []peer.ID {
 	dialer := s.cfg.p2p.GossipDialer()
 
 	if dialer != nil {
-		// Protect peers that are the sole provider for any gossip topic.
-		// These peers should not be pruned since we have no alternative.
-		for _, pid := range dialer.SoleProviderPeers() {
+		// ask the dialer for peers that should be protected from pruning.
+		for _, pid := range dialer.ProtectedPeers() {
 			peerMap[pid] = true
 		}
 	}