fix(grpc): Ping should check health response status

grpc_client.go

@@ -126,9 +126,14 @@ func (c *GRPCClient) Dispense(name string) (interface{}, error) {
 // ClientProtocol impl.
 func (c *GRPCClient) Ping() error {
 	client := grpc_health_v1.NewHealthClient(c.Conn)
-	_, err := client.Check(context.Background(), &grpc_health_v1.HealthCheckRequest{
+	resp, err := client.Check(context.Background(), &grpc_health_v1.HealthCheckRequest{
 		Service: GRPCServiceName,
 	})
-
-	return err
+	if err != nil {
+		return err
+	}
+	if resp.Status != grpc_health_v1.HealthCheckResponse_SERVING {
+		return fmt.Errorf("plugin %q is not healthy: status=%v", GRPCServiceName, resp.Status)
+	}
+	return nil
 }

grpc_client_ping_test.go

@@ -0,0 +1,47 @@
+package plugin
+
+import (
+	"context"
+	"net"
+	"testing"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+	grpc_health_v1 "google.golang.org/grpc/health/grpc_health_v1"
+)
+
+type notServingHealthServer struct {
+	grpc_health_v1.UnimplementedHealthServer
+}
+
+func (h *notServingHealthServer) Check(ctx context.Context, in *grpc_health_v1.HealthCheckRequest) (*grpc_health_v1.HealthCheckResponse, error) {
+	return &grpc_health_v1.HealthCheckResponse{
+		Status: grpc_health_v1.HealthCheckResponse_NOT_SERVING,
+	}, nil
+}
+
+func TestGRPC_Ping_ChecksServingStatus(t *testing.T) {
+	lis, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	server := grpc.NewServer()
+	grpc_health_v1.RegisterHealthServer(server, &notServingHealthServer{})
+
+	go server.Serve(lis)
+	defer server.Stop()
+
+	conn, err := grpc.Dial(lis.Addr().String(), grpc.WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	defer conn.Close()
+
+	client := &GRPCClient{Conn: conn}
+
+	err = client.Ping()
+	if err == nil {
+		t.Fatal("expected Ping() to fail when health check returns NOT_SERVING")
+	}
+}