gnmi/client: add bdp flag

Setting this flag to false will disable BDP and dynamic windows
 for the grpc connection that the client uses.
This is a workaround for grpc/grpc-go#5358
 which affects clients with high-latency.

Change-Id: Id43097bd32df6801fbbc0011886589a06d883903

gnmi/client.go

@@ -64,6 +64,7 @@ type Config struct {
 	Username     string
 	TLS          bool
 	Compression  string
+	BDP          bool
 	DialOptions  []grpc.DialOption
 	Token        string
 	GRPCMetadata map[string]string
@@ -164,6 +165,23 @@ func (a *accessTokenCred) RequireTransportSecurity() bool { return true }
 func DialContext(ctx context.Context, cfg *Config) (pb.GNMIClient, error) {
 	opts := append([]grpc.DialOption(nil), cfg.DialOptions...)
 
+	if !cfg.BDP {
+		// By default, the client and server will dynamically adjust the connection's
+		// window size using the Bandwidth Delay Product (BDP).
+		// See: https://grpc.io/blog/grpc-go-perf-improvements/
+		// The default values for InitialWindowSize and InitialConnWindowSize are 65535.
+		// If values less than 65535 are used, then BDP and dynamic windows are enabled.
+		// Here, we disable the BDP and dynamic windows by setting these values >= 65535.
+		// We set these values to (1 << 20) * 16 as this is the largest window size that
+		// the BDP estimator could ever use.
+		// See: https://github.com/grpc/grpc-go/blob/master/internal/transport/bdp_estimator.go
+		const maxWindowSize int32 = (1 << 20) * 16
+		opts = append(opts,
+			grpc.WithInitialWindowSize(maxWindowSize),
+			grpc.WithInitialConnWindowSize(maxWindowSize),
+		)
+	}
+
 	switch cfg.Compression {
 	case "":
 	case "gzip":

gnmi/client/client.go

@@ -60,6 +60,8 @@ func Main() {
 	flag.StringVar(&cfg.Compression, "compression", "", "Compression method. "+
 		`Supported options: "" and "gzip"`)
 	flag.BoolVar(&cfg.TLS, "tls", false, "Enable TLS")
+	flag.BoolVar(&cfg.BDP, "bdp", true,
+		"Enable Bandwidth Delay Product (BDP) estimation and dynamic flow control window")
 
 	subscribeOptions := &gnmi.SubscribeOptions{}
 	flag.StringVar(&subscribeOptions.Prefix, "prefix", "", "Subscribe prefix path")