server: populate WireLength on stats.InPayload for unary RPCs

Fixes #2692 which was incompletely fixed by #2711.

Also adds a basic unit test which provides scaffolding for further testing of
the stats logic.

server.go

@@ -971,10 +971,11 @@ func (s *Server) processUnaryRPC(t transport.ServerTransport, stream *transport.
 		}
 		if sh != nil {
 			sh.HandleRPC(stream.Context(), &stats.InPayload{
-				RecvTime: time.Now(),
-				Payload:  v,
-				Data:     d,
-				Length:   len(d),
+				RecvTime:   time.Now(),
+				Payload:    v,
+				WireLength: payInfo.wireLength,
+				Data:       d,
+				Length:     len(d),
 			})
 		}
 		if binlog != nil {

test/stats_test.go

@@ -0,0 +1,112 @@
+/*
+ *
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package test
+
+import (
+	"context"
+	"net"
+	"testing"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/health"
+	"google.golang.org/grpc/health/grpc_health_v1"
+	"google.golang.org/grpc/stats"
+)
+
+// TestStatsHandlerRPCWireLength ensure that the WireLength fields of stats.RPCStats
+// information carries sane values.
+func (s) TestStatsHandlerRPCWireLength(t *testing.T) {
+	lis, err := net.Listen("tcp", "localhost:0")
+	if err != nil {
+		t.Fatalf("failed to create listener: %v", err)
+	}
+	sh := statsHandler{
+		handleRPC: func(_ context.Context, rpcStats stats.RPCStats) {
+			switch s := rpcStats.(type) {
+			case *stats.InPayload:
+				if len(s.Data) > 0 && s.WireLength == 0 {
+					t.Errorf("WireLength cannot be zero for a non-zero InPayload: %+v", s)
+				}
+			case *stats.OutPayload:
+				if len(s.Data) > 0 && s.WireLength == 0 {
+					t.Errorf("WireLength cannot be zero for a non-zero OutPayload: %+v", s)
+				}
+			}
+		},
+	}
+	server := grpc.NewServer(
+		grpc.StatsHandler(&sh),
+	)
+	healthServer := health.NewServer()
+	grpc_health_v1.RegisterHealthServer(server, healthServer)
+
+	defer server.Stop()
+	go server.Serve(lis)
+	c, err := grpc.Dial(lis.Addr().String(),
+		grpc.WithStatsHandler(&sh),
+		grpc.WithInsecure())
+	if err != nil {
+		t.Fatalf("Failed to listen: %v", err)
+	}
+	defer c.Close()
+	if !c.WaitForStateChange(context.TODO(), connectivity.Ready) {
+		t.Fatal()
+	}
+	const service = "foo"
+	healthServer.SetServingStatus(service, grpc_health_v1.HealthCheckResponse_SERVING)
+	hc := grpc_health_v1.NewHealthClient(c)
+	req := &grpc_health_v1.HealthCheckRequest{
+		Service: service,
+	}
+	if _, err := hc.Check(context.TODO(), req); err != nil {
+		t.Fatalf("failed to check health: %v", err)
+	}
+	w, err := hc.Watch(context.TODO(), req)
+	if err != nil {
+		t.Fatalf("failed to watch: %v", err)
+	}
+	if _, err := w.Recv(); err != nil {
+		t.Fatalf("failed to receive a health update: %v", err)
+	}
+}
+
+// statsHandler implements stats.Handler and allows clients to mock the HandleRPC method.
+type statsHandler struct {
+	handleRPC func(ctx context.Context, rpcStats stats.RPCStats)
+}
+
+var _ stats.Handler = (*statsHandler)(nil)
+
+func (s *statsHandler) HandleConn(context.Context, stats.ConnStats) {
+}
+
+func (s *statsHandler) TagConn(ctx context.Context, _ *stats.ConnTagInfo) context.Context {
+	return ctx
+}
+
+func (s *statsHandler) HandleRPC(ctx context.Context, rpcStats stats.RPCStats) {
+	if s.handleRPC != nil {
+		s.handleRPC(ctx, rpcStats)
+	}
+}
+
+func (s *statsHandler) TagRPC(ctx context.Context, _ *stats.RPCTagInfo) context.Context {
+	return ctx
+}