Complete remote driver

This patch completes the work started in creating a remote driver:

- Renames the env driver to the remote driver (an alternative suggestion
  that should be more user-friendly)
- Adds support for TLS to encrypt connections with buildkitd
- Fixes outstanding review comments
- Reworks the buildx create command endpoint construction to be clearer
  and include better support for this new driver.

Signed-off-by: Justin Chadwell <me@jedevc.com>

driver/remote/driver.go

@@ -0,0 +1,80 @@
+package remote
+
+import (
+	"context"
+
+	"github.com/docker/buildx/driver"
+	"github.com/docker/buildx/util/progress"
+	"github.com/moby/buildkit/client"
+	"github.com/pkg/errors"
+)
+
+type Driver struct {
+	factory driver.Factory
+	driver.InitConfig
+	*tlsOpts
+}
+
+type tlsOpts struct {
+	serverName string
+	caCert     string
+	cert       string
+	key        string
+}
+
+func (d *Driver) Bootstrap(ctx context.Context, l progress.Logger) error {
+	return nil
+}
+
+func (d *Driver) Info(ctx context.Context) (*driver.Info, error) {
+	c, err := d.Client(ctx)
+	if err != nil {
+		return nil, errors.Wrapf(driver.ErrNotConnecting, err.Error())
+	}
+
+	if _, err := c.ListWorkers(ctx); err != nil {
+		return nil, errors.Wrapf(driver.ErrNotConnecting, err.Error())
+	}
+
+	return &driver.Info{
+		Status: driver.Running,
+	}, nil
+}
+
+func (d *Driver) Stop(ctx context.Context, force bool) error {
+	return nil
+}
+
+func (d *Driver) Rm(ctx context.Context, force, rmVolume, rmDaemon bool) error {
+	return nil
+}
+
+func (d *Driver) Client(ctx context.Context) (*client.Client, error) {
+	opts := []client.ClientOpt{}
+	if d.tlsOpts != nil {
+		opts = append(opts, client.WithCredentials(d.tlsOpts.serverName, d.tlsOpts.caCert, d.tlsOpts.cert, d.tlsOpts.key))
+	}
+
+	return client.New(ctx, d.InitConfig.EndpointAddr, opts...)
+}
+
+func (d *Driver) Features() map[driver.Feature]bool {
+	return map[driver.Feature]bool{
+		driver.OCIExporter:    true,
+		driver.DockerExporter: false,
+		driver.CacheExport:    true,
+		driver.MultiPlatform:  true,
+	}
+}
+
+func (d *Driver) Factory() driver.Factory {
+	return d.factory
+}
+
+func (d *Driver) IsMobyDriver() bool {
+	return false
+}
+
+func (d *Driver) Config() driver.InitConfig {
+	return d.InitConfig
+}

driver/remote/factory.go

@@ -0,0 +1,115 @@
+package remote
+
+import (
+	"context"
+	"net/url"
+	"path/filepath"
+	"regexp"
+	"strings"
+
+	"github.com/docker/buildx/driver"
+	dockerclient "github.com/docker/docker/client"
+	"github.com/pkg/errors"
+)
+
+const prioritySupported = 20
+const priorityUnsupported = 90
+
+var schemeRegexp = regexp.MustCompile("^(tcp|unix)://")
+
+func init() {
+	driver.Register(&factory{})
+}
+
+type factory struct {
+}
+
+func (*factory) Name() string {
+	return "remote"
+}
+
+func (*factory) Usage() string {
+	return "remote"
+}
+
+func (*factory) Priority(ctx context.Context, endpoint string, api dockerclient.APIClient) int {
+	if schemeRegexp.MatchString(endpoint) {
+		return prioritySupported
+	}
+	return priorityUnsupported
+}
+
+func (f *factory) New(ctx context.Context, cfg driver.InitConfig) (driver.Driver, error) {
+	if len(cfg.Files) > 0 {
+		return nil, errors.Errorf("setting config file is not supported for remote driver")
+	}
+	if len(cfg.BuildkitFlags) > 0 {
+		return nil, errors.Errorf("setting buildkit flags is not supported for remote driver")
+	}
+
+	d := &Driver{
+		factory:    f,
+		InitConfig: cfg,
+	}
+
+	tls := &tlsOpts{}
+	tlsEnabled := false
+	for k, v := range cfg.DriverOpts {
+		switch k {
+		case "servername":
+			tls.serverName = v
+			tlsEnabled = true
+		case "cacert":
+			if !filepath.IsAbs(v) {
+				return nil, errors.Errorf("non-absolute path '%s' provided for %s", v, k)
+			}
+			tls.caCert = v
+			tlsEnabled = true
+		case "cert":
+			if !filepath.IsAbs(v) {
+				return nil, errors.Errorf("non-absolute path '%s' provided for %s", v, k)
+			}
+			tls.cert = v
+			tlsEnabled = true
+		case "key":
+			if !filepath.IsAbs(v) {
+				return nil, errors.Errorf("non-absolute path '%s' provided for %s", v, k)
+			}
+			tls.key = v
+			tlsEnabled = true
+		default:
+			return nil, errors.Errorf("invalid driver option %s for remote driver", k)
+		}
+	}
+
+	if tlsEnabled {
+		if tls.serverName == "" {
+			// guess servername as hostname of target address
+			uri, err := url.Parse(cfg.EndpointAddr)
+			if err != nil {
+				return nil, err
+			}
+			tls.serverName = uri.Hostname()
+		}
+		missing := []string{}
+		if tls.caCert == "" {
+			missing = append(missing, "cacert")
+		}
+		if tls.cert == "" {
+			missing = append(missing, "cert")
+		}
+		if tls.key == "" {
+			missing = append(missing, "key")
+		}
+		if len(missing) > 0 {
+			return nil, errors.Errorf("tls enabled, but missing keys %s", strings.Join(missing, ", "))
+		}
+		d.tlsOpts = tls
+	}
+
+	return d, nil
+}
+
+func (f *factory) AllowsInstances() bool {
+	return true
+}