feat(bigtable): add an experimental attempt DirectPath flag

bigtable/bigtable.go

@@ -19,6 +19,7 @@ package bigtable // import "cloud.google.com/go/bigtable"
 import (
 	"context"
 	"errors"
+	"flag"
 	"fmt"
 	"io"
 	"net/url"
@@ -30,6 +31,7 @@ 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"
@@ -40,6 +42,15 @@ import (
 
 const prodAddr = "bigtable.googleapis.com:443"
 
+// Add an experimental flag to control the attempt to directpath.
+// Once e2e tests are finished, this flag will be removed, and client
+// will attempt by default.
+var attemptDirectPath bool
+
+func init() {
+	flag.BoolVar(&attemptDirectPath, "it.attempt-directpath", false, "flag to attempt directpath")
+}
+
 // 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 +90,8 @@ 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()),
+		internaloption.EnableDirectPath(attemptDirectPath))
 	o = append(o, opts...)
 	connPool, err := gtransport.DialPool(ctx, o...)
 	if err != nil {