driver: add docker driver

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

driver/docker/factory.go

@@ -0,0 +1,53 @@
+package docker
+
+import (
+	"context"
+
+	"github.com/pkg/errors"
+	"github.com/tonistiigi/buildx/driver"
+)
+
+const prioritySupported = 10
+const priorityUnsupported = 99
+
+func init() {
+	driver.Register(&factory{})
+}
+
+type factory struct {
+}
+
+func (*factory) Name() string {
+	return "docker"
+}
+
+func (*factory) Usage() string {
+	return "docker"
+}
+
+func (*factory) Priority(cfg driver.InitConfig) int {
+	if cfg.DockerAPI == nil {
+		return priorityUnsupported
+	}
+
+	c, err := cfg.DockerAPI.DialHijack(context.TODO(), "/grpc", "h2c", nil)
+	if err != nil {
+		return priorityUnsupported
+	}
+	c.Close()
+
+	return prioritySupported
+}
+
+func (*factory) New(ctx context.Context, cfg driver.InitConfig) (driver.Driver, error) {
+	if cfg.DockerAPI == nil {
+		return nil, errors.Errorf("docker driver requires docker API access")
+	}
+
+	v, err := cfg.DockerAPI.ServerVersion(ctx)
+	if err != nil {
+		return nil, errors.Wrapf(driver.ErrNotConnecting, err.Error())
+	}
+
+	return &Driver{InitConfig: cfg, version: v}, nil
+}