Add ability to get selected candidate pair stats

It is useful to have stats from just the selected pair as a lightweight
option where a lot of agents are running, for example, an SFU.

agent_stats.go

@@ -54,6 +54,56 @@ func (a *Agent) GetCandidatePairsStats() []CandidatePairStats {
 	return res
 }
 
+// GetSelectedCandidatePairStats returns a candidate pair stats for selected candidate pair.
+// Returns false if there is no selected pair
+func (a *Agent) GetSelectedCandidatePairStats() (CandidatePairStats, bool) {
+	isAvailable := false
+	var res CandidatePairStats
+	err := a.loop.Run(a.loop, func(_ context.Context) {
+		sp := a.getSelectedPair()
+		if sp == nil {
+			return
+		}
+
+		isAvailable = true
+		res = CandidatePairStats{
+			Timestamp:         time.Now(),
+			LocalCandidateID:  sp.Local.ID(),
+			RemoteCandidateID: sp.Remote.ID(),
+			State:             sp.state,
+			Nominated:         sp.nominated,
+			// PacketsSent uint32
+			// PacketsReceived uint32
+			// BytesSent uint64
+			// BytesReceived uint64
+			// LastPacketSentTimestamp time.Time
+			// LastPacketReceivedTimestamp time.Time
+			// FirstRequestTimestamp time.Time
+			// LastRequestTimestamp time.Time
+			// LastResponseTimestamp time.Time
+			TotalRoundTripTime:   sp.TotalRoundTripTime(),
+			CurrentRoundTripTime: sp.CurrentRoundTripTime(),
+			// AvailableOutgoingBitrate float64
+			// AvailableIncomingBitrate float64
+			// CircuitBreakerTriggerCount uint32
+			// RequestsReceived uint64
+			// RequestsSent uint64
+			ResponsesReceived: sp.ResponsesReceived(),
+			// ResponsesSent uint64
+			// RetransmissionsReceived uint64
+			// RetransmissionsSent uint64
+			// ConsentRequestsSent uint64
+			// ConsentExpiredTimestamp time.Time
+		}
+	})
+	if err != nil {
+		a.log.Errorf("Failed to get selected candidate pair stats: %v", err)
+		return CandidatePairStats{}, false
+	}
+
+	return res, isAvailable
+}
+
 // GetLocalCandidatesStats returns a list of local candidates stats
 func (a *Agent) GetLocalCandidatesStats() []CandidateStats {
 	var res []CandidateStats

agent_test.go

@@ -635,7 +635,7 @@ func TestInvalidGather(t *testing.T) {
 	})
 }
 
-func TestCandidatePairStats(t *testing.T) {
+func TestCandidatePairsStats(t *testing.T) {
 	defer test.CheckRoutines(t)()
 
 	// Avoid deadlocks?
@@ -789,6 +789,89 @@ func TestCandidatePairStats(t *testing.T) {
 	}
 }
 
+func TestSelectedCandidatePairStats(t *testing.T) {
+	defer test.CheckRoutines(t)()
+
+	// Avoid deadlocks?
+	defer test.TimeOut(1 * time.Second).Stop()
+
+	a, err := NewAgent(&AgentConfig{})
+	if err != nil {
+		t.Fatalf("Failed to create agent: %s", err)
+	}
+	defer func() {
+		require.NoError(t, a.Close())
+	}()
+
+	hostConfig := &CandidateHostConfig{
+		Network:   "udp",
+		Address:   "192.168.1.1",
+		Port:      19216,
+		Component: 1,
+	}
+	hostLocal, err := NewCandidateHost(hostConfig)
+	if err != nil {
+		t.Fatalf("Failed to construct local host candidate: %s", err)
+	}
+
+	srflxConfig := &CandidateServerReflexiveConfig{
+		Network:   "udp",
+		Address:   "10.10.10.2",
+		Port:      19218,
+		Component: 1,
+		RelAddr:   "4.3.2.1",
+		RelPort:   43212,
+	}
+	srflxRemote, err := NewCandidateServerReflexive(srflxConfig)
+	if err != nil {
+		t.Fatalf("Failed to construct remote srflx candidate: %s", err)
+	}
+
+	// no selected pair, should return not available
+	stats, ok := a.GetSelectedCandidatePairStats()
+	require.False(t, ok)
+
+	// add pair and populate some RTT stats
+	p := a.findPair(hostLocal, srflxRemote)
+	if p == nil {
+		a.addPair(hostLocal, srflxRemote)
+		p = a.findPair(hostLocal, srflxRemote)
+	}
+	for i := 0; i < 10; i++ {
+		p.UpdateRoundTripTime(time.Duration(i+1) * time.Second)
+	}
+
+	// set the pair as selected
+	a.setSelectedPair(p)
+
+	stats, ok = a.GetSelectedCandidatePairStats()
+	require.True(t, ok)
+
+	if stats.LocalCandidateID != hostLocal.ID() {
+		t.Fatal("invalid local candidate id")
+	}
+	if stats.RemoteCandidateID != srflxRemote.ID() {
+		t.Fatal("invalid remote candidate id")
+	}
+
+	expectedCurrentRoundTripTime := time.Duration(10) * time.Second
+	if stats.CurrentRoundTripTime != expectedCurrentRoundTripTime.Seconds() {
+		t.Fatalf("expected current round trip time to be %f, it is %f instead",
+			expectedCurrentRoundTripTime.Seconds(), stats.CurrentRoundTripTime)
+	}
+
+	expectedTotalRoundTripTime := time.Duration(55) * time.Second
+	if stats.TotalRoundTripTime != expectedTotalRoundTripTime.Seconds() {
+		t.Fatalf("expected total round trip time to be %f, it is %f instead",
+			expectedTotalRoundTripTime.Seconds(), stats.TotalRoundTripTime)
+	}
+
+	if stats.ResponsesReceived != 10 {
+		t.Fatalf("expected responses received to be 10, it is %d instead",
+			stats.ResponsesReceived)
+	}
+}
+
 func TestLocalCandidateStats(t *testing.T) {
 	defer test.CheckRoutines(t)()