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/apimachinery/pkg/util/httpstream/spdy/upgrade.go

@@ -0,0 +1,107 @@
+/*
+Copyright 2015 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 spdy
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"strings"
+	"sync/atomic"
+
+	"k8s.io/apimachinery/pkg/util/httpstream"
+	"k8s.io/apimachinery/pkg/util/runtime"
+)
+
+const HeaderSpdy31 = "SPDY/3.1"
+
+// responseUpgrader knows how to upgrade HTTP responses. It
+// implements the httpstream.ResponseUpgrader interface.
+type responseUpgrader struct {
+}
+
+// connWrapper is used to wrap a hijacked connection and its bufio.Reader. All
+// calls will be handled directly by the underlying net.Conn with the exception
+// of Read and Close calls, which will consider data in the bufio.Reader. This
+// ensures that data already inside the used bufio.Reader instance is also
+// read.
+type connWrapper struct {
+	net.Conn
+	closed    int32
+	bufReader *bufio.Reader
+}
+
+func (w *connWrapper) Read(b []byte) (n int, err error) {
+	if atomic.LoadInt32(&w.closed) == 1 {
+		return 0, io.EOF
+	}
+	return w.bufReader.Read(b)
+}
+
+func (w *connWrapper) Close() error {
+	err := w.Conn.Close()
+	atomic.StoreInt32(&w.closed, 1)
+	return err
+}
+
+// NewResponseUpgrader returns a new httpstream.ResponseUpgrader that is
+// capable of upgrading HTTP responses using SPDY/3.1 via the
+// spdystream package.
+func NewResponseUpgrader() httpstream.ResponseUpgrader {
+	return responseUpgrader{}
+}
+
+// UpgradeResponse upgrades an HTTP response to one that supports multiplexed
+// streams. newStreamHandler will be called synchronously whenever the
+// other end of the upgraded connection creates a new stream.
+func (u responseUpgrader) UpgradeResponse(w http.ResponseWriter, req *http.Request, newStreamHandler httpstream.NewStreamHandler) httpstream.Connection {
+	connectionHeader := strings.ToLower(req.Header.Get(httpstream.HeaderConnection))
+	upgradeHeader := strings.ToLower(req.Header.Get(httpstream.HeaderUpgrade))
+	if !strings.Contains(connectionHeader, strings.ToLower(httpstream.HeaderUpgrade)) || !strings.Contains(upgradeHeader, strings.ToLower(HeaderSpdy31)) {
+		w.WriteHeader(http.StatusBadRequest)
+		fmt.Fprintf(w, "unable to upgrade: missing upgrade headers in request: %#v", req.Header)
+		return nil
+	}
+
+	hijacker, ok := w.(http.Hijacker)
+	if !ok {
+		w.WriteHeader(http.StatusInternalServerError)
+		fmt.Fprintf(w, "unable to upgrade: unable to hijack response")
+		return nil
+	}
+
+	w.Header().Add(httpstream.HeaderConnection, httpstream.HeaderUpgrade)
+	w.Header().Add(httpstream.HeaderUpgrade, HeaderSpdy31)
+	w.WriteHeader(http.StatusSwitchingProtocols)
+
+	conn, bufrw, err := hijacker.Hijack()
+	if err != nil {
+		runtime.HandleError(fmt.Errorf("unable to upgrade: error hijacking response: %v", err))
+		return nil
+	}
+
+	connWithBuf := &connWrapper{Conn: conn, bufReader: bufrw.Reader}
+	spdyConn, err := NewServerConnection(connWithBuf, newStreamHandler)
+	if err != nil {
+		runtime.HandleError(fmt.Errorf("unable to upgrade: error creating SPDY server connection: %v", err))
+		return nil
+	}
+
+	return spdyConn
+}