gossip tracer implementation

gossip_tracer.go

 package pubsub
 
 import (
+	"math/rand"
+	"sync"
+	"time"
+
 	"github.com/libp2p/go-libp2p-core/peer"
 	"github.com/libp2p/go-libp2p-core/protocol"
 )
@@ -9,12 +13,15 @@ import (
 // peers who don't follow up on IWANT requests after an IHAVE advertisement.
 // The tracking of promises is probabilistic to avoid using too much memory.
 type gossipTracer struct {
-	msgID MsgIdFunction
+	sync.Mutex
+	msgID    MsgIdFunction
+	promises map[string]map[peer.ID]time.Time
 }
 
 func newGossipTracer() *gossipTracer {
 	return &gossipTracer{
-		msgID: DefaultMsgIdFn,
+		msgID:    DefaultMsgIdFn,
+		promises: make(map[string]map[peer.ID]time.Time),
 	}
 }
 
@@ -26,27 +33,94 @@ func (gt *gossipTracer) Start(gs *GossipSubRouter) {
 	gt.msgID = gs.p.msgID
 }
 
+// track a promise to deliver a message from a list of msgIDs we are requesting
 func (gt *gossipTracer) AddPromise(p peer.ID, msgIDs []string) {
 	if gt == nil {
 		return
 	}
 
-	// TODO
+	idx := rand.Intn(len(msgIDs))
+	mid := msgIDs[idx]
+
+	gt.Lock()
+	defer gt.Unlock()
+
+	peers, ok := gt.promises[mid]
+	if !ok {
+		peers = make(map[peer.ID]time.Time)
+		gt.promises[mid] = peers
+	}
+
+	_, ok = peers[p]
+	if !ok {
+		peers[p] = time.Now().Add(GossipSubIWantFollowupTime)
+	}
 }
 
+// returns the number of broken promises for each peer who didn't follow up
+// on an IWANT request.
 func (gt *gossipTracer) GetBrokenPromises() map[peer.ID]int {
-	// TODO
-	return nil
+	if gt == nil {
+		return nil
+	}
+
+	gt.Lock()
+	defer gt.Unlock()
+
+	var res map[peer.ID]int
+	now := time.Now()
+
+	for mid, peers := range gt.promises {
+		for p, expire := range peers {
+			if expire.Before(now) {
+				if res == nil {
+					res = make(map[peer.ID]int)
+				}
+				res[p]++
+
+				delete(peers, p)
+			}
+		}
+		if len(peers) == 0 {
+			delete(gt.promises, mid)
+		}
+	}
+
+	return res
 }
 
 var _ internalTracer = (*gossipTracer)(nil)
 
 func (gt *gossipTracer) DeliverMessage(msg *Message) {
-	// TODO
+	// someone delivered a message, stop tracking promises for it
+	mid := gt.msgID(msg.Message)
+
+	gt.Lock()
+	defer gt.Unlock()
+
+	delete(gt.promises, mid)
 }
 
 func (gt *gossipTracer) RejectMessage(msg *Message, reason string) {
-	// TODO
+	// A message got rejected, so we can stop tracking promises and let the score penalty apply
+	// from invalid message delivery.
+	// We do take exception and apply promise penalty regardless in the following cases, where
+	// the peer delivered an obviously invalid message.
+	switch reason {
+	case rejectMissingSignature:
+		return
+	case rejectInvalidSignature:
+		return
+	case rejectSelfOrigin:
+		return
+	}
+
+	mid := gt.msgID(msg.Message)
+
+	gt.Lock()
+	defer gt.Unlock()
+
+	delete(gt.promises, mid)
 }
 
 func (gt *gossipTracer) AddPeer(p peer.ID, proto protocol.ID) {}

gossipsub.go

@@ -87,6 +87,11 @@ var (
 
 	// Maximum number of IHAVE messages to accept from a peer within a heartbeat.
 	GossipSubMaxIHaveMessages = 10
+
+	// Time to wait for a message requested through IWANT following an IHAVE advertisement.
+	// If the message is not received within this window, a broken promise is declared and
+	// the router may apply bahavioural penalties.
+	GossipSubIWantFollowupTime = 3 * time.Second
 )
 
 // NewGossipSub returns a new PubSub object using GossipSubRouter as the router.
@@ -1291,6 +1296,7 @@ func (gs *GossipSubRouter) clearIHaveCounters() {
 
 func (gs *GossipSubRouter) applyIwantPenalties() {
 	for p, count := range gs.gossipTracer.GetBrokenPromises() {
+		log.Infof("peer %s didn't follow up in %d IWANT requests; adding penalty", p, count)
 		gs.score.AddPenalty(p, count)
 	}
 }