Windows: Docker build starting to work

Signed-off-by: John Howard <jhoward@microsoft.com>

chrootarchive/archive_unix.go

@@ -3,7 +3,17 @@
 package chrootarchive
 
 import (
+	"bytes"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"runtime"
 	"syscall"
+
+	"github.com/docker/docker/pkg/archive"
+	"github.com/docker/docker/pkg/reexec"
 )
 
 func chroot(path string) error {
@@ -12,3 +22,64 @@ func chroot(path string) error {
 	}
 	return syscall.Chdir("/")
 }
+
+// untar is the entry-point for docker-untar on re-exec. This is not used on
+// Windows as it does not support chroot, hence no point sandboxing through
+// chroot and rexec.
+func untar() {
+	runtime.LockOSThread()
+	flag.Parse()
+
+	var options *archive.TarOptions
+
+	//read the options from the pipe "ExtraFiles"
+	if err := json.NewDecoder(os.NewFile(3, "options")).Decode(&options); err != nil {
+		fatal(err)
+	}
+
+	if err := chroot(flag.Arg(0)); err != nil {
+		fatal(err)
+	}
+
+	if err := archive.Unpack(os.Stdin, "/", options); err != nil {
+		fatal(err)
+	}
+	// fully consume stdin in case it is zero padded
+	flush(os.Stdin)
+	os.Exit(0)
+}
+
+func invokeUnpack(decompressedArchive io.ReadCloser, dest string, options *archive.TarOptions) error {
+
+	// We can't pass a potentially large exclude list directly via cmd line
+	// because we easily overrun the kernel's max argument/environment size
+	// when the full image list is passed (e.g. when this is used by
+	// `docker load`). We will marshall the options via a pipe to the
+	// child
+	r, w, err := os.Pipe()
+	if err != nil {
+		return fmt.Errorf("Untar pipe failure: %v", err)
+	}
+
+	cmd := reexec.Command("docker-untar", dest)
+	cmd.Stdin = decompressedArchive
+
+	cmd.ExtraFiles = append(cmd.ExtraFiles, r)
+	output := bytes.NewBuffer(nil)
+	cmd.Stdout = output
+	cmd.Stderr = output
+
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("Untar error on re-exec cmd: %v", err)
+	}
+	//write the options to the pipe for the untar exec to read
+	if err := json.NewEncoder(w).Encode(options); err != nil {
+		return fmt.Errorf("Untar json encode to pipe failed: %v", err)
+	}
+	w.Close()
+
+	if err := cmd.Wait(); err != nil {
+		return fmt.Errorf("Untar re-exec error: %v: output: %s", err, output)
+	}
+	return nil
+}