[aggregator] Prevent tcp client panic on nil placement (#3139)

src/aggregator/client/tcp_client.go

@@ -21,6 +21,7 @@
 package client
 
 import (
+	"errors"
 	"fmt"
 	"math"
 	"time"
@@ -39,7 +40,11 @@ import (
 	xerrors "github.com/m3db/m3/src/x/errors"
 )
 
-var _ AdminClient = (*TCPClient)(nil)
+var (
+	_ AdminClient = (*TCPClient)(nil)
+
+	errNilPlacement = errors.New("placement is nil")
+)
 
 // TCPClient sends metrics to M3 Aggregator via over custom TCP protocol.
 type TCPClient struct {
@@ -229,6 +234,9 @@ func (c *TCPClient) ActivePlacement() (placement.Placement, int, error) {
 		return nil, 0, err
 	}
 	defer onStagedPlacementDoneFn()
+	if stagedPlacement == nil {
+		return nil, 0, errNilPlacement
+	}
 
 	placement, onPlacementDoneFn, err := stagedPlacement.ActivePlacement()
 	if err != nil {
@@ -247,6 +255,9 @@ func (c *TCPClient) ActivePlacementVersion() (int, error) {
 		return 0, err
 	}
 	defer onStagedPlacementDoneFn()
+	if stagedPlacement == nil {
+		return 0, errNilPlacement
+	}
 
 	return stagedPlacement.Version(), nil
 }
@@ -274,6 +285,10 @@ func (c *TCPClient) write(
 	if err != nil {
 		return err
 	}
+	if stagedPlacement == nil {
+		onStagedPlacementDoneFn()
+		return errNilPlacement
+	}
 	placement, onPlacementDoneFn, err := stagedPlacement.ActivePlacement()
 	if err != nil {
 		onStagedPlacementDoneFn()

src/aggregator/client/tcp_client_test.go

@@ -241,6 +241,31 @@ func TestTCPClientWriteUntimedMetricActiveStagedPlacementError(t *testing.T) {
 	}
 }
 
+func TestTCPClientWriteUntimedMetricActiveStagedPlacementNil(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+
+	watcher := placement.NewMockStagedPlacementWatcher(ctrl)
+	watcher.EXPECT().ActiveStagedPlacement().
+		Return(nil, func() {}, nil).
+		MinTimes(1)
+	c := mustNewTestTCPClient(t, testOptions())
+	c.placementWatcher = watcher
+
+	for _, input := range []unaggregated.MetricUnion{testCounter, testBatchTimer, testGauge} {
+		var err error
+		switch input.Type {
+		case metric.CounterType:
+			err = c.WriteUntimedCounter(input.Counter(), testStagedMetadatas)
+		case metric.TimerType:
+			err = c.WriteUntimedBatchTimer(input.BatchTimer(), testStagedMetadatas)
+		case metric.GaugeType:
+			err = c.WriteUntimedGauge(input.Gauge(), testStagedMetadatas)
+		}
+		require.Equal(t, errNilPlacement, err)
+	}
+}
+
 func TestTCPClientWriteUntimedMetricActivePlacementError(t *testing.T) {
 	ctrl := gomock.NewController(t)
 	defer ctrl.Finish()