Introduce containerd-shim-runhcs-v1 on Windows

Implements the containerd-shim-runhcs-v1 shim on Windows for the runtime
v2 shim API.

Signed-off-by: Justin Terry (VM) <juterry@microsoft.com>

runtime/v2/runhcs/cmdutil.go

@@ -0,0 +1,98 @@
+// +build windows
+
+/*
+   Copyright The containerd 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 runhcs
+
+import (
+	"bytes"
+	"context"
+	"os/exec"
+	"sync"
+	"syscall"
+	"time"
+)
+
+var (
+	bytesBufferPool = sync.Pool{
+		New: func() interface{} {
+			return bytes.NewBuffer(nil)
+		},
+	}
+)
+
+func getBuffer() *bytes.Buffer {
+	return bytesBufferPool.Get().(*bytes.Buffer)
+}
+
+func putBuffer(b *bytes.Buffer) {
+	b.Reset()
+	bytesBufferPool.Put(b)
+}
+
+type processExit struct {
+	pid        uint32
+	exitStatus uint32
+	exitedAt   time.Time
+	exitErr    error
+}
+
+func runCmd(ctx context.Context, c *exec.Cmd) (*processExit, error) {
+	ec, startErr := startCmd(ctx, c)
+	if startErr != nil {
+		return nil, startErr
+	}
+	er, cmdErr := waitCmd(ctx, ec)
+	return er, cmdErr
+}
+
+func startCmd(ctx context.Context, c *exec.Cmd) (<-chan *processExit, error) {
+	if err := c.Start(); err != nil {
+		return nil, err
+	}
+	ec := make(chan *processExit, 1)
+	go func() {
+		defer close(ec)
+
+		var status int
+		eerr := c.Wait()
+		if eerr != nil {
+			status = 255
+			if exitErr, ok := eerr.(*exec.ExitError); ok {
+				if ws, ok := exitErr.Sys().(syscall.WaitStatus); ok {
+					status = ws.ExitStatus()
+				}
+			}
+		}
+		ec <- &processExit{
+			pid:        uint32(c.Process.Pid),
+			exitStatus: uint32(status),
+			exitedAt:   time.Now(),
+			exitErr:    eerr,
+		}
+	}()
+
+	return ec, nil
+}
+
+func waitCmd(ctx context.Context, ec <-chan *processExit) (*processExit, error) {
+	e := <-ec
+	if e.exitStatus != 0 {
+		return e, e.exitErr
+	}
+	return e, nil
+}