remote: ensure that client connection is not established twice

Because remote driver implements Info() by calling
Client() internally, two instances on Client are created
backed by separate TCP connection. This hack avoids it
and improves performance.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

driver/remote/driver.go

@@ -7,6 +7,7 @@ import (
 	"net"
 	"os"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/docker/buildx/driver"
@@ -14,6 +15,7 @@ import (
 	"github.com/docker/buildx/util/progress"
 	"github.com/moby/buildkit/client"
 	"github.com/moby/buildkit/client/connhelper"
+	"github.com/moby/buildkit/util/tracing/delegated"
 	"github.com/pkg/errors"
 )
 
@@ -25,6 +27,11 @@ type Driver struct {
 	// https://github.com/docker/docs/blob/main/content/build/drivers/remote.md
 	*tlsOpts
 	defaultLoad bool
+
+	// remote driver caches the client because its Bootstap/Info methods reuse it internally
+	clientOnce sync.Once
+	client     *client.Client
+	err        error
 }
 
 type tlsOpts struct {
@@ -78,12 +85,18 @@ func (d *Driver) Rm(ctx context.Context, force, rmVolume, rmDaemon bool) error {
 }
 
 func (d *Driver) Client(ctx context.Context, opts ...client.ClientOpt) (*client.Client, error) {
-	opts = append([]client.ClientOpt{
-		client.WithContextDialer(func(ctx context.Context, _ string) (net.Conn, error) {
-			return d.Dial(ctx)
-		}),
-	}, opts...)
-	return client.New(ctx, "", opts...)
+	d.clientOnce.Do(func() {
+		opts = append([]client.ClientOpt{
+			client.WithContextDialer(func(ctx context.Context, _ string) (net.Conn, error) {
+				return d.Dial(ctx)
+			}),
+			client.WithTracerDelegate(delegated.DefaultExporter),
+		}, opts...)
+		c, err := client.New(ctx, "", opts...)
+		d.client = c
+		d.err = err
+	})
+	return d.client, d.err
 }
 
 func (d *Driver) Dial(ctx context.Context) (net.Conn, error) {