/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * 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 android.os;

import android.util.Slog;

import com.android.internal.util.FastPrintWriter;

import java.io.BufferedInputStream;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;

Helper for implementing Binder.onShellCommand. 
@hide
/**
 * Helper for implementing {@link Binder#onShellCommand Binder.onShellCommand}.
 * @hide
 */
public abstract class ShellCommand {
    static final String TAG = "ShellCommand";
    static final boolean DEBUG = false;

    private Binder mTarget;
    private FileDescriptor mIn;
    private FileDescriptor mOut;
    private FileDescriptor mErr;
    private String[] mArgs;
    private ShellCallback mShellCallback;
    private ResultReceiver mResultReceiver;

    private String mCmd;
    private int mArgPos;
    private String mCurArgData;

    private FileInputStream mFileIn;
    private FileOutputStream mFileOut;
    private FileOutputStream mFileErr;

    private FastPrintWriter mOutPrintWriter;
    private FastPrintWriter mErrPrintWriter;
    private InputStream mInputStream;

    public void init(Binder target, FileDescriptor in, FileDescriptor out, FileDescriptor err,
            String[] args, ShellCallback callback, int firstArgPos) {
        mTarget = target;
        mIn = in;
        mOut = out;
        mErr = err;
        mArgs = args;
        mShellCallback = callback;
        mResultReceiver = null;
        mCmd = null;
        mArgPos = firstArgPos;
        mCurArgData = null;
        mFileIn = null;
        mFileOut = null;
        mFileErr = null;
        mOutPrintWriter = null;
        mErrPrintWriter = null;
        mInputStream = null;
    }

    public int exec(Binder target, FileDescriptor in, FileDescriptor out, FileDescriptor err,
            String[] args, ShellCallback callback, ResultReceiver resultReceiver) {
        String cmd;
        int start;
        if (args != null && args.length > 0) {
            cmd = args[0];
            start = 1;
        } else {
            cmd = null;
            start = 0;
        }
        init(target, in, out, err, args, callback, start);
        mCmd = cmd;
        mResultReceiver = resultReceiver;

        if (DEBUG) {
            RuntimeException here = new RuntimeException("here");
            here.fillInStackTrace();
            Slog.d(TAG, "Starting command " + mCmd + " on " + mTarget, here);
            Slog.d(TAG, "Calling uid=" + Binder.getCallingUid()
                    + " pid=" + Binder.getCallingPid() + " ShellCallback=" + getShellCallback());
        }
        int res = -1;
        try {
            res = onCommand(mCmd);
            if (DEBUG) Slog.d(TAG, "Executed command " + mCmd + " on " + mTarget);
        } catch (SecurityException e) {
            PrintWriter eout = getErrPrintWriter();
            eout.println("Security exception: " + e.getMessage());
            eout.println();
            e.printStackTrace(eout);
        } catch (Throwable e) {
            // Unlike usual calls, in this case if an exception gets thrown
            // back to us we want to print it back in to the dump data, since
            // that is where the caller expects all interesting information to
            // go.
            PrintWriter eout = getErrPrintWriter();
            eout.println();
            eout.println("Exception occurred while executing:");
            e.printStackTrace(eout);
        } finally {
            if (DEBUG) Slog.d(TAG, "Flushing output streams on " + mTarget);
            if (mOutPrintWriter != null) {
                mOutPrintWriter.flush();
            }
            if (mErrPrintWriter != null) {
                mErrPrintWriter.flush();
            }
            if (DEBUG) Slog.d(TAG, "Sending command result on " + mTarget);
            if (mResultReceiver != null) {
                mResultReceiver.send(res, null);
            }
        }
        if (DEBUG) Slog.d(TAG, "Finished command " + mCmd + " on " + mTarget);
        return res;
    }

    
Adopt the ResultReceiver that was given to this shell command from it, taking
it over.  Primarily used to dispatch to another shell command.  Once called,
this shell command will no longer return its own result when done.
/**
     * Adopt the ResultReceiver that was given to this shell command from it, taking
     * it over.  Primarily used to dispatch to another shell command.  Once called,
     * this shell command will no longer return its own result when done.
     */
    public ResultReceiver adoptResultReceiver() {
        ResultReceiver rr = mResultReceiver;
        mResultReceiver = null;
        return rr;
    }

    
Return the raw FileDescriptor for the output stream.
/**
     * Return the raw FileDescriptor for the output stream.
     */
    public FileDescriptor getOutFileDescriptor() {
        return mOut;
    }

    
Return direct raw access (not buffered) to the command's output data stream.
/**
     * Return direct raw access (not buffered) to the command's output data stream.
     */
    public OutputStream getRawOutputStream() {
        if (mFileOut == null) {
            mFileOut = new FileOutputStream(mOut);
        }
        return mFileOut;
    }

    
Return a PrintWriter for formatting output to getRawOutputStream(). /**
     * Return a PrintWriter for formatting output to {@link #getRawOutputStream()}.
     */
    public PrintWriter getOutPrintWriter() {
        if (mOutPrintWriter == null) {
            mOutPrintWriter = new FastPrintWriter(getRawOutputStream());
        }
        return mOutPrintWriter;
    }

    
Return the raw FileDescriptor for the error stream.
/**
     * Return the raw FileDescriptor for the error stream.
     */
    public FileDescriptor getErrFileDescriptor() {
        return mErr;
    }

    
Return direct raw access (not buffered) to the command's error output data stream.
/**
     * Return direct raw access (not buffered) to the command's error output data stream.
     */
    public OutputStream getRawErrorStream() {
        if (mFileErr == null) {
            mFileErr = new FileOutputStream(mErr);
        }
        return mFileErr;
    }

    
Return a PrintWriter for formatting output to getRawErrorStream(). /**
     * Return a PrintWriter for formatting output to {@link #getRawErrorStream()}.
     */
    public PrintWriter getErrPrintWriter() {
        if (mErr == null) {
            return getOutPrintWriter();
        }
        if (mErrPrintWriter == null) {
            mErrPrintWriter = new FastPrintWriter(getRawErrorStream());
        }
        return mErrPrintWriter;
    }

    
Return the raw FileDescriptor for the input stream.
/**
     * Return the raw FileDescriptor for the input stream.
     */
    public FileDescriptor getInFileDescriptor() {
        return mIn;
    }

    
Return direct raw access (not buffered) to the command's input data stream.
/**
     * Return direct raw access (not buffered) to the command's input data stream.
     */
    public InputStream getRawInputStream() {
        if (mFileIn == null) {
            mFileIn = new FileInputStream(mIn);
        }
        return mFileIn;
    }

    
Return buffered access to the command's getRawInputStream(). /**
     * Return buffered access to the command's {@link #getRawInputStream()}.
     */
    public InputStream getBufferedInputStream() {
        if (mInputStream == null) {
            mInputStream = new BufferedInputStream(getRawInputStream());
        }
        return mInputStream;
    }

    
Helper for just system services to ask the shell to open an output file.
@hide
/**
     * Helper for just system services to ask the shell to open an output file.
     * @hide
     */
    public ParcelFileDescriptor openFileForSystem(String path, String mode) {
        if (DEBUG) Slog.d(TAG, "openFileForSystem: " + path + " mode=" + mode);
        try {
            ParcelFileDescriptor pfd = getShellCallback().openFile(path,
                    "u:r:system_server:s0", mode);
            if (pfd != null) {
                if (DEBUG) Slog.d(TAG, "Got file: " + pfd);
                return pfd;
            }
        } catch (RuntimeException e) {
            if (DEBUG) Slog.d(TAG, "Failure opening file: " + e.getMessage());
            getErrPrintWriter().println("Failure opening file: " + e.getMessage());
        }
        if (DEBUG) Slog.d(TAG, "Error: Unable to open file: " + path);
        getErrPrintWriter().println("Error: Unable to open file: " + path);
        getErrPrintWriter().println("Consider using a file under /data/local/tmp/");
        return null;
    }

    
Return the next option on the command line -- that is an argument that
starts with '-'.  If the next argument is not an option, null is returned.
/**
     * Return the next option on the command line -- that is an argument that
     * starts with '-'.  If the next argument is not an option, null is returned.
     */
    public String getNextOption() {
        if (mCurArgData != null) {
            String prev = mArgs[mArgPos - 1];
            throw new IllegalArgumentException("No argument expected after \"" + prev + "\"");
        }
        if (mArgPos >= mArgs.length) {
            return null;
        }
        String arg = mArgs[mArgPos];
        if (!arg.startsWith("-")) {
            return null;
        }
        mArgPos++;
        if (arg.equals("--")) {
            return null;
        }
        if (arg.length() > 1 && arg.charAt(1) != '-') {
            if (arg.length() > 2) {
                mCurArgData = arg.substring(2);
                return arg.substring(0, 2);
            } else {
                mCurArgData = null;
                return arg;
            }
        }
        mCurArgData = null;
        return arg;
    }

    
Return the next argument on the command line, whatever it is; if there are
no arguments left, return null.
/**
     * Return the next argument on the command line, whatever it is; if there are
     * no arguments left, return null.
     */
    public String getNextArg() {
        if (mCurArgData != null) {
            String arg = mCurArgData;
            mCurArgData = null;
            return arg;
        } else if (mArgPos < mArgs.length) {
            return mArgs[mArgPos++];
        } else {
            return null;
        }
    }

    public String peekNextArg() {
        if (mCurArgData != null) {
            return mCurArgData;
        } else if (mArgPos < mArgs.length) {
            return mArgs[mArgPos];
        } else {
            return null;
        }
    }

    
Return the next argument on the command line, whatever it is; if there are
no arguments left, throws an IllegalArgumentException to report this to the user.
/**
     * Return the next argument on the command line, whatever it is; if there are
     * no arguments left, throws an IllegalArgumentException to report this to the user.
     */
    public String getNextArgRequired() {
        String arg = getNextArg();
        if (arg == null) {
            String prev = mArgs[mArgPos - 1];
            throw new IllegalArgumentException("Argument expected after \"" + prev + "\"");
        }
        return arg;
    }

    
Return the ShellCallback for communicating back with the calling shell. /**
     * Return the {@link ShellCallback} for communicating back with the calling shell.
     */
    public ShellCallback getShellCallback() {
        return mShellCallback;
    }

    public int handleDefaultCommands(String cmd) {
        if ("dump".equals(cmd)) {
            String[] newArgs = new String[mArgs.length-1];
            System.arraycopy(mArgs, 1, newArgs, 0, mArgs.length-1);
            mTarget.doDump(mOut, getOutPrintWriter(), newArgs);
            return 0;
        } else if (cmd == null || "help".equals(cmd) || "-h".equals(cmd)) {
            onHelp();
        } else {
            getOutPrintWriter().println("Unknown command: " + cmd);
        }
        return -1;
    }

    
Implement parsing and execution of a command. If it isn't a command you understand, call handleDefaultCommands(String) and return its result as a last resort. Use getNextOption(), getNextArg(), and getNextArgRequired() to process additional command line arguments. Command output can be written to getOutPrintWriter() and errors to getErrPrintWriter(). 
Note that no permission checking has been done before entering this function,
so you need to be sure to do your own security verification for any commands you
are executing.  The easiest way to do this is to have the ShellCommand contain
only a reference to your service's aidl interface, and do all of your command
implementations on top of that -- that way you can rely entirely on your executing security
code behind that interface.
Params:
cmd – The first command line argument representing the name of the command to execute.
Returns:
Return the command result; generally 0 or positive indicates success and
negative values indicate error./**
     * Implement parsing and execution of a command.  If it isn't a command you understand,
     * call {@link #handleDefaultCommands(String)} and return its result as a last resort.
     * Use {@link #getNextOption()}, {@link #getNextArg()}, and {@link #getNextArgRequired()}
     * to process additional command line arguments.  Command output can be written to
     * {@link #getOutPrintWriter()} and errors to {@link #getErrPrintWriter()}.
     *
     * <p class="caution">Note that no permission checking has been done before entering this function,
     * so you need to be sure to do your own security verification for any commands you
     * are executing.  The easiest way to do this is to have the ShellCommand contain
     * only a reference to your service's aidl interface, and do all of your command
     * implementations on top of that -- that way you can rely entirely on your executing security
     * code behind that interface.</p>
     *
     * @param cmd The first command line argument representing the name of the command to execute.
     * @return Return the command result; generally 0 or positive indicates success and
     * negative values indicate error.
     */
    public abstract int onCommand(String cmd);

    
Implement this to print help text about your command to getOutPrintWriter(). /**
     * Implement this to print help text about your command to {@link #getOutPrintWriter()}.
     */
    public abstract void onHelp();
}