Windows: Work around Windows BS/DEL behavior

In Windows containers in TP5, DEL is interpreted as the delete key, but
Linux generally interprets it as backspace. This prevents backspace from
working when using a Linux terminal or the native console terminal
emulation in Windows.

To work around this, translate DEL to BS in Windows containers stdin when
TTY is enabled. Do this only for builds that do not have the fix in
Windows itself.

Signed-off-by: John Starks <jostarks@microsoft.com>

libcontainerd/client_windows.go

@@ -291,6 +291,9 @@ func (clnt *client) AddProcess(containerID, processFriendlyName string, procToAd
 		return err
 	}
 
+	// TEMP: Work around Windows BS/DEL behavior.
+	iopipe.Stdin = fixStdinBackspaceBehavior(iopipe.Stdin, procToAdd.Terminal)
+
 	// Convert io.ReadClosers to io.Readers
 	if stdout != nil {
 		iopipe.Stdout = openReaderFromPipe(stdout)

libcontainerd/container_windows.go

@@ -102,6 +102,9 @@ func (ctr *container) start() error {
 	}
 	ctr.startedAt = time.Now()
 
+	// TEMP: Work around Windows BS/DEL behavior.
+	iopipe.Stdin = fixStdinBackspaceBehavior(iopipe.Stdin, ctr.ociSpec.Process.Terminal)
+
 	// Convert io.ReadClosers to io.Readers
 	if stdout != nil {
 		iopipe.Stdout = openReaderFromPipe(stdout)

libcontainerd/process_windows.go

@@ -2,6 +2,8 @@ package libcontainerd
 
 import (
 	"io"
+
+	"github.com/docker/docker/pkg/system"
 )
 
 // process keeps the state for both main container process and exec process.
@@ -25,3 +27,33 @@ func openReaderFromPipe(p io.ReadCloser) io.Reader {
 	}()
 	return r
 }
+
+// fixStdinBackspaceBehavior works around a bug in Windows before build 14350
+// where it interpreted DEL as VK_DELETE instead of as VK_BACK. This replaces
+// DEL with BS to work around this.
+func fixStdinBackspaceBehavior(w io.WriteCloser, tty bool) io.WriteCloser {
+	if !tty || system.GetOSVersion().Build >= 14350 {
+		return w
+	}
+	return &delToBsWriter{w}
+}
+
+type delToBsWriter struct {
+	io.WriteCloser
+}
+
+func (w *delToBsWriter) Write(b []byte) (int, error) {
+	const (
+		backspace = 0x8
+		del       = 0x7f
+	)
+	bc := make([]byte, len(b))
+	for i, c := range b {
+		if c == del {
+			bc[i] = backspace
+		} else {
+			bc[i] = c
+		}
+	}
+	return w.WriteCloser.Write(bc)
+}