Add dial-stdio command

This allows the buildx CLI to act a proxy to the configured instance.
It allows external code to use buildx itself as a driver for connecting
to buildkitd instances.

Instance and node selection should follow the same semantics as as
`buildx build`, including taking into account the `BUILDX_BUILDER` env
var and the `--builder` global flag.

Signed-off-by: Brian Goff <[email protected]>

build/dial.go

@@ -0,0 +1,62 @@
+package build
+
+import (
+	"context"
+	stderrors "errors"
+	"net"
+
+	"github.com/containerd/containerd/platforms"
+	"github.com/docker/buildx/builder"
+	"github.com/docker/buildx/util/progress"
+	v1 "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
+)
+
+func Dial(ctx context.Context, nodes []builder.Node, pw progress.Writer, platform *v1.Platform) (net.Conn, error) {
+	nodes, err := filterAvailableNodes(nodes)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(nodes) == 0 {
+		return nil, errors.New("no nodes available")
+	}
+
+	var pls []v1.Platform
+	if platform != nil {
+		pls = []v1.Platform{*platform}
+	}
+
+	opts := map[string]Options{"default": {Platforms: pls}}
+	resolved, err := resolveDrivers(ctx, nodes, opts, pw)
+	if err != nil {
+		return nil, err
+	}
+
+	var dialError error
+	for _, ls := range resolved {
+		for _, rn := range ls {
+			if platform != nil {
+				p := *platform
+				var found bool
+				for _, pp := range rn.platforms {
+					if platforms.Only(p).Match(pp) {
+						found = true
+						break
+					}
+				}
+				if !found {
+					continue
+				}
+			}
+
+			conn, err := nodes[rn.driverIndex].Driver.Dial(ctx)
+			if err == nil {
+				return conn, nil
+			}
+			dialError = stderrors.Join(err)
+		}
+	}
+
+	return nil, errors.Wrap(dialError, "no nodes available")
+}

commands/dial_stdio.go

@@ -0,0 +1,132 @@
+package commands
+
+import (
+	"io"
+	"net"
+	"os"
+
+	"github.com/containerd/containerd/platforms"
+	"github.com/docker/buildx/build"
+	"github.com/docker/buildx/builder"
+	"github.com/docker/buildx/util/progress"
+	"github.com/docker/cli/cli/command"
+	"github.com/moby/buildkit/util/appcontext"
+	"github.com/moby/buildkit/util/progress/progressui"
+	v1 "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+	"golang.org/x/sync/errgroup"
+)
+
+type stdioOptions struct {
+	builder  string
+	platform string
+	progress string
+}
+
+func runDialStdio(dockerCli command.Cli, opts stdioOptions) error {
+	ctx := appcontext.Context()
+
+	contextPathHash, _ := os.Getwd()
+	b, err := builder.New(dockerCli,
+		builder.WithName(opts.builder),
+		builder.WithContextPathHash(contextPathHash),
+	)
+	if err != nil {
+		return err
+	}
+
+	if err = updateLastActivity(dockerCli, b.NodeGroup); err != nil {
+		return errors.Wrapf(err, "failed to update builder last activity time")
+	}
+	nodes, err := b.LoadNodes(ctx)
+	if err != nil {
+		return err
+	}
+
+	printer, err := progress.NewPrinter(ctx, os.Stderr, progressui.DisplayMode(opts.progress), progress.WithPhase("dial-stdio"), progress.WithDesc("builder: "+b.Name, "builder:"+b.Name))
+	if err != nil {
+		return err
+	}
+
+	var p *v1.Platform
+	if opts.platform != "" {
+		pp, err := platforms.Parse(opts.platform)
+		if err != nil {
+			return errors.Wrapf(err, "invalid platform %q", opts.platform)
+		}
+		p = &pp
+	}
+
+	defer printer.Wait()
+
+	return progress.Wrap("Proxying to builder", printer.Write, func(sub progress.SubLogger) error {
+		var conn net.Conn
+
+		err := sub.Wrap("Dialing builder", func() error {
+			conn, err = build.Dial(ctx, nodes, printer, p)
+			if err != nil {
+				return err
+			}
+			return nil
+		})
+		if err != nil {
+			return err
+		}
+
+		defer conn.Close()
+
+		go func() {
+			<-ctx.Done()
+			closeWrite(conn)
+		}()
+
+		var eg errgroup.Group
+
+		eg.Go(func() error {
+			_, err := io.Copy(conn, os.Stdin)
+			closeWrite(conn)
+			return err
+		})
+		eg.Go(func() error {
+			_, err := io.Copy(os.Stdout, conn)
+			closeRead(conn)
+			return err
+		})
+		return eg.Wait()
+	})
+}
+
+func closeRead(conn net.Conn) error {
+	if c, ok := conn.(interface{ CloseRead() error }); ok {
+		return c.CloseRead()
+	}
+	return conn.Close()
+}
+
+func closeWrite(conn net.Conn) error {
+	if c, ok := conn.(interface{ CloseWrite() error }); ok {
+		return c.CloseWrite()
+	}
+	return conn.Close()
+}
+
+func dialStdioCmd(dockerCli command.Cli, rootOpts *rootOptions) *cobra.Command {
+	opts := stdioOptions{}
+
+	cmd := &cobra.Command{
+		Use:   "dial-stdio",
+		Short: "Dial stdio",
+		Args:  cobra.NoArgs,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			opts.builder = rootOpts.builder
+			return runDialStdio(dockerCli, opts)
+		},
+	}
+
+	flags := cmd.Flags()
+	cmd.Flags()
+	flags.StringVar(&opts.platform, "platform", os.Getenv("DOCKER_DEFAULT_PLATFORM"), "Target platform: this is used for node selection")
+	flags.StringVar(&opts.progress, "progress", "quiet", "Set type of progress output (auto, plain, tty).")
+	return cmd
+}

commands/root.go

@@ -83,6 +83,7 @@ func addCommands(cmd *cobra.Command, dockerCli command.Cli) {
 		buildCmd(dockerCli, opts, nil),
 		bakeCmd(dockerCli, opts),
 		createCmd(dockerCli),
+		dialStdioCmd(dockerCli, opts),
 		rmCmd(dockerCli, opts),
 		lsCmd(dockerCli),
 		useCmd(dockerCli, opts),

docs/reference/buildx.md

@@ -15,6 +15,7 @@ Extended build capabilities with BuildKit
 | [`build`](buildx_build.md)           | Start a build                          |
 | [`create`](buildx_create.md)         | Create a new builder instance          |
 | [`debug`](buildx_debug.md)           | Start debugger (EXPERIMENTAL)          |
+| [`dial-stdio`](buildx_dial-stdio.md) | Dial stdio                             |
 | [`du`](buildx_du.md)                 | Disk usage                             |
 | [`imagetools`](buildx_imagetools.md) | Commands to work on images in registry |
 | [`inspect`](buildx_inspect.md)       | Inspect current builder instance       |

docs/reference/buildx_dial-stdio.md

@@ -0,0 +1,49 @@
+# docker buildx dial-stdio
+
+<!---MARKER_GEN_START-->
+Dial stdio
+
+### Options
+
+| Name         | Type     | Default | Description                                      |
+|:-------------|:---------|:--------|:-------------------------------------------------|
+| `--builder`  | `string` |         | Override the configured builder instance         |
+| `--platform` | `string` |         | Target platform: this is used for node selection |
+| `--progress` | `string` | `quiet` | Set type of progress output (auto, plain, tty).  |
+
+
+<!---MARKER_GEN_END-->
+
+## Description
+
+dial-stdio uses the stdin and stoud streams of the command to proxy to the configured builder instance.
+It is not intended to be used by humans, but rather by other tools that want to interact with the builder instance API.
+
+## Examples
+
+Example go program that uses the dial-stdio command wire up a buildkit client.
+This is for example use only and may not be suitable for production use.
+
+```go
+c1, c2 := net.Pipe()
+cmd := exec.Command("docker", "buildx", "dial-stdio")
+cmd.Stdin = c1
+cmd.Stdout = c2
+
+if err := cmd.Start() {
+    c1.Close()
+    c2.Close()
+    return nil, err
+}
+
+defer cmd.Wait()
+
+go func() {
+    cmd.Wait()
+    c2.Close()
+}()
+
+client.New(ctx, "", client.WithContextDialer(func(ctx context.Context, s string) (net.Conn, error) {
+    return c2, nil
+}))
+```

driver/docker-container/driver.go

@@ -384,13 +384,20 @@ func (d *Driver) Rm(ctx context.Context, force, rmVolume, rmDaemon bool) error {
 	return nil
 }
 
-func (d *Driver) Client(ctx context.Context) (*client.Client, error) {
+func (d *Driver) Dial(ctx context.Context) (net.Conn, error) {
 	_, conn, err := d.exec(ctx, []string{"buildctl", "dial-stdio"})
 	if err != nil {
 		return nil, err
 	}
-
 	conn = demuxConn(conn)
+	return conn, nil
+}
+
+func (d *Driver) Client(ctx context.Context) (*client.Client, error) {
+	conn, err := d.Dial(ctx)
+	if err != nil {
+		return nil, err
+	}
 
 	exp, _, err := detect.Exporter()
 	if err != nil {

driver/docker/driver.go

@@ -57,10 +57,14 @@ func (d *Driver) Rm(ctx context.Context, force, rmVolume, rmDaemon bool) error {
 	return nil
 }
 
+func (d *Driver) Dial(ctx context.Context) (net.Conn, error) {
+	return d.DockerAPI.DialHijack(ctx, "/grpc", "h2c", d.DialMeta)
+}
+
 func (d *Driver) Client(ctx context.Context) (*client.Client, error) {
 	opts := []client.ClientOpt{
 		client.WithContextDialer(func(context.Context, string) (net.Conn, error) {
-			return d.DockerAPI.DialHijack(ctx, "/grpc", "h2c", d.DialMeta)
+			return d.Dial(ctx)
 		}), client.WithSessionDialer(func(ctx context.Context, proto string, meta map[string][]string) (net.Conn, error) {
 			return d.DockerAPI.DialHijack(ctx, "/session", proto, meta)
 		}),

driver/driver.go

@@ -59,6 +59,7 @@ type Driver interface {
 	Version(context.Context) (string, error)
 	Stop(ctx context.Context, force bool) error
 	Rm(ctx context.Context, force, rmVolume, rmDaemon bool) error
+	Dial(ctx context.Context) (net.Conn, error)
 	Client(ctx context.Context) (*client.Client, error)
 	Features(ctx context.Context) map[Feature]bool
 	HostGatewayIP(ctx context.Context) (net.IP, error)

driver/kubernetes/driver.go

@@ -189,7 +189,7 @@ func (d *Driver) Rm(ctx context.Context, force, rmVolume, rmDaemon bool) error {
 	return nil
 }
 
-func (d *Driver) Client(ctx context.Context) (*client.Client, error) {
+func (d *Driver) Dial(ctx context.Context) (net.Conn, error) {
 	restClient := d.clientset.CoreV1().RESTClient()
 	restClientConfig, err := d.KubeClientConfig.ClientConfig()
 	if err != nil {
@@ -208,15 +208,18 @@ func (d *Driver) Client(ctx context.Context) (*client.Client, error) {
 	if err != nil {
 		return nil, err
 	}
+	return conn, nil
+}
 
+func (d *Driver) Client(ctx context.Context) (*client.Client, error) {
 	exp, _, err := detect.Exporter()
 	if err != nil {
 		return nil, err
 	}
 
 	var opts []client.ClientOpt
 	opts = append(opts, client.WithContextDialer(func(context.Context, string) (net.Conn, error) {
-		return conn, nil
+		return d.Dial(ctx)
 	}))
 	if td, ok := exp.(client.TracerDelegate); ok {
 		opts = append(opts, client.WithTracerDelegate(td))