feat(bigtable): attempt DirectPath by default

bigtable/bigtable.go

@@ -30,6 +30,7 @@ import (
 	"github.com/golang/protobuf/proto"
 	gax "github.com/googleapis/gax-go/v2"
 	"google.golang.org/api/option"
+  "google.golang.org/api/option/internaloption"
 	gtransport "google.golang.org/api/transport/grpc"
 	btpb "google.golang.org/genproto/googleapis/bigtable/v2"
 	"google.golang.org/grpc"
@@ -38,8 +39,10 @@ import (
 	"google.golang.org/grpc/status"
 )
 
-const prodAddr = "bigtable.googleapis.com:443"
-
+const (
+  prodAddr = "bigtable.googleapis.com:443"
+  attemptDirectPath = true
+)
 // Client is a client for reading and writing data to tables in an instance.
 //
 // A Client is safe to use concurrently, except for its Close method.
@@ -79,7 +82,9 @@ func NewClientWithConfig(ctx context.Context, project, instance string, config C
 		option.WithGRPCDialOption(grpc.WithDefaultCallOptions(grpc.MaxCallSendMsgSize(1<<28), grpc.MaxCallRecvMsgSize(1<<28))),
 		// TODO(grpc/grpc-go#1388) using connection pool without WithBlock
 		// can cause RPCs to fail randomly. We can delete this after the issue is fixed.
-		option.WithGRPCDialOption(grpc.WithBlock()))
+		option.WithGRPCDialOption(grpc.WithBlock()),
+    // Attempt DirectPath by default
+    internaloption.EnableDirectPath(attemptDirectPath))
 	o = append(o, opts...)
 	connPool, err := gtransport.DialPool(ctx, o...)
 	if err != nil {