p2p: adjust max non-persistent peer score (#8137)

Guarantee persistent peers have the highest connecting priority. 
The peerStore.Ranked returns an arbitrary order of peers with the same scores.

internal/p2p/peermanager.go

@@ -42,7 +42,8 @@ const (
 type PeerScore uint8
 
 const (
-	PeerScorePersistent PeerScore = math.MaxUint8 // persistent peers
+	PeerScorePersistent       PeerScore = math.MaxUint8 // persistent peers
+	MaxPeerScoreNotPersistent PeerScore = PeerScorePersistent - 1
 )
 
 // PeerUpdate is a peer update event sent via PeerUpdates.
@@ -1283,6 +1284,9 @@ func (p *peerInfo) Score() PeerScore {
 	}
 
 	score := p.MutableScore
+	if score > int64(MaxPeerScoreNotPersistent) {
+		score = int64(MaxPeerScoreNotPersistent)
+	}
 
 	for _, addr := range p.AddressInfo {
 		// DialFailures is reset when dials succeed, so this
@@ -1294,10 +1298,6 @@ func (p *peerInfo) Score() PeerScore {
 		return 0
 	}
 
-	if score >= math.MaxUint8 {
-		return PeerScore(math.MaxUint8)
-	}
-
 	return PeerScore(score)
 }
 

internal/p2p/peermanager_scoring_test.go

@@ -80,4 +80,20 @@ func TestPeerScoring(t *testing.T) {
 			time.Millisecond,
 			"startAt=%d score=%d", start, peerManager.Scores()[id])
 	})
+	t.Run("TestNonPersistantPeerUpperBound", func(t *testing.T) {
+		start := int64(peerManager.Scores()[id] + 1)
+
+		for i := start; i <= int64(PeerScorePersistent); i++ {
+			peerManager.processPeerEvent(ctx, PeerUpdate{
+				NodeID: id,
+				Status: PeerStatusGood,
+			})
+
+			if i == int64(PeerScorePersistent) {
+				require.EqualValues(t, MaxPeerScoreNotPersistent, peerManager.Scores()[id])
+			} else {
+				require.EqualValues(t, i, peerManager.Scores()[id])
+			}
+		}
+	})
 }