Empty InputStream for Android Porcess with "su"

Question

I have Android 7 device with root (it works)

I want to execute root commands via OutputStream and get messages about results via InputStream.

    private void getSu() {
    if (mProcess != null) return;

    try {
        mProcess = Runtime.getRuntime().exec("su");
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private void getStdOut() {
    if (mStdOut != null) return;
    getSu();

    mStdOut = new DataOutputStream(mProcess.getOutputStream());
}

private void getStdIn() {
    if (mStdIn != null) return;
    getSu();

    mStdIn = new BufferedReader(new InputStreamReader(mProcess.getInputStream()));
}

After that I'm trying to execute "mount" command and read results of this command.

getSu();
getStdOut();
getStdIn();

String[] mountLine = getMount(mStdOut, mStdIn, "/system");



  private String[] getMount(@NonNull DataOutputStream stdOut, @NonNull BufferedReader stdIn, String string) {
    String[] res=null;
    try {

        stdOut.writeBytes("mount");
        stdOut.writeBytes("\n");

        String str;
        while ((str=stdIn.readLine()) != null) {
            if (str.contains(string)) {
                res = str.split(" ");
                break;
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    return res;
}

This code was working on Android 6 before. But on Android 7 I get InputSream full of \u0000

I tried to execute this command via adb shell and I got nice results. Why do I get InputSream full of \u0000?

Answer 1

Android 7+ needs:

stdOut.flush();

After writeBytes()