new driver: kubernetes

Tested with `kind` and GKE.

Note: "nodes" shown in `docker buildx ls` are unrelated to Kubernetes "nodes".
Probably buildx should come up with an alternative term.

Usage:

  $ kind create cluster
  $ export KUBECONFIG="$(kind get kubeconfig-path --name="kind")"

  $ docker buildx create --driver kubernetes --driver-opt replicas=3 --use
  $ docker buildx build -t foo --load .

`--load` loads the image into the local Docker.

Driver opts:

  - `image=IMAGE` - Sets the container image to be used for running buildkit.
  - `namespace=NS` - Sets the Kubernetes namespace. Defaults to the current namespace.
  - `replicas=N` - Sets the number of `Pod` replicas. Defaults to 1.
  - `rootless=(true|false)` - Run the container as a non-root user without `securityContext.privileged`. Defaults to false.
  - `loadbalance=(sticky|random)` - Load-balancing strategy. If set to "sticky", the pod is chosen using the hash of the context path. Defaults to "sticky"

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

vendor/k8s.io/client-go/tools/remotecommand/v4.go

@@ -0,0 +1,119 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package remotecommand
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strconv"
+	"sync"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/util/remotecommand"
+	"k8s.io/client-go/util/exec"
+)
+
+// streamProtocolV4 implements version 4 of the streaming protocol for attach
+// and exec. This version adds support for exit codes on the error stream through
+// the use of metav1.Status instead of plain text messages.
+type streamProtocolV4 struct {
+	*streamProtocolV3
+}
+
+var _ streamProtocolHandler = &streamProtocolV4{}
+
+func newStreamProtocolV4(options StreamOptions) streamProtocolHandler {
+	return &streamProtocolV4{
+		streamProtocolV3: newStreamProtocolV3(options).(*streamProtocolV3),
+	}
+}
+
+func (p *streamProtocolV4) createStreams(conn streamCreator) error {
+	return p.streamProtocolV3.createStreams(conn)
+}
+
+func (p *streamProtocolV4) handleResizes() {
+	p.streamProtocolV3.handleResizes()
+}
+
+func (p *streamProtocolV4) stream(conn streamCreator) error {
+	if err := p.createStreams(conn); err != nil {
+		return err
+	}
+
+	// now that all the streams have been created, proceed with reading & copying
+
+	errorChan := watchErrorStream(p.errorStream, &errorDecoderV4{})
+
+	p.handleResizes()
+
+	p.copyStdin()
+
+	var wg sync.WaitGroup
+	p.copyStdout(&wg)
+	p.copyStderr(&wg)
+
+	// we're waiting for stdout/stderr to finish copying
+	wg.Wait()
+
+	// waits for errorStream to finish reading with an error or nil
+	return <-errorChan
+}
+
+// errorDecoderV4 interprets the json-marshaled metav1.Status on the error channel
+// and creates an exec.ExitError from it.
+type errorDecoderV4 struct{}
+
+func (d *errorDecoderV4) decode(message []byte) error {
+	status := metav1.Status{}
+	err := json.Unmarshal(message, &status)
+	if err != nil {
+		return fmt.Errorf("error stream protocol error: %v in %q", err, string(message))
+	}
+	switch status.Status {
+	case metav1.StatusSuccess:
+		return nil
+	case metav1.StatusFailure:
+		if status.Reason == remotecommand.NonZeroExitCodeReason {
+			if status.Details == nil {
+				return errors.New("error stream protocol error: details must be set")
+			}
+			for i := range status.Details.Causes {
+				c := &status.Details.Causes[i]
+				if c.Type != remotecommand.ExitCodeCauseType {
+					continue
+				}
+
+				rc, err := strconv.ParseUint(c.Message, 10, 8)
+				if err != nil {
+					return fmt.Errorf("error stream protocol error: invalid exit code value %q", c.Message)
+				}
+				return exec.CodeExitError{
+					Err:  fmt.Errorf("command terminated with exit code %d", rc),
+					Code: int(rc),
+				}
+			}
+
+			return fmt.Errorf("error stream protocol error: no %s cause given", remotecommand.ExitCodeCauseType)
+		}
+	default:
+		return errors.New("error stream protocol error: unknown error")
+	}
+
+	return fmt.Errorf(status.Message)
+}