michael@0: /*
michael@0:  * Copyright (C) 2012 Google Inc.
michael@0:  *
michael@0:  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
michael@0:  * use this file except in compliance with the License. You may obtain a copy of
michael@0:  * the License at
michael@0:  *
michael@0:  * http://www.apache.org/licenses/LICENSE-2.0
michael@0:  *
michael@0:  * Unless required by applicable law or agreed to in writing, software
michael@0:  * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
michael@0:  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
michael@0:  * License for the specific language governing permissions and limitations under
michael@0:  * the License.
michael@0:  */
michael@0: 
michael@0: package com.googlecode.eyesfree.braille.selfbraille;
michael@0: 
michael@0: import android.content.ComponentName;
michael@0: import android.content.Context;
michael@0: import android.content.Intent;
michael@0: import android.content.ServiceConnection;
michael@0: import android.content.pm.PackageInfo;
michael@0: import android.content.pm.PackageManager;
michael@0: import android.content.pm.Signature;
michael@0: import android.os.Binder;
michael@0: import android.os.Handler;
michael@0: import android.os.IBinder;
michael@0: import android.os.Message;
michael@0: import android.os.RemoteException;
michael@0: import android.util.Log;
michael@0: 
michael@0: import java.security.MessageDigest;
michael@0: import java.security.NoSuchAlgorithmException;
michael@0: 
michael@0: /**
michael@0:  * Client-side interface to the self brailling interface.
michael@0:  *
michael@0:  * Threading: Instances of this object should be created and shut down
michael@0:  * in a thread with a {@link Looper} associated with it.  Other methods may
michael@0:  * be called on any thread.
michael@0:  */
michael@0: public class SelfBrailleClient {
michael@0:     private static final String LOG_TAG =
michael@0:             SelfBrailleClient.class.getSimpleName();
michael@0:     private static final String ACTION_SELF_BRAILLE_SERVICE =
michael@0:             "com.googlecode.eyesfree.braille.service.ACTION_SELF_BRAILLE_SERVICE";
michael@0:     private static final String BRAILLE_BACK_PACKAGE =
michael@0:             "com.googlecode.eyesfree.brailleback";
michael@0:     private static final Intent mServiceIntent =
michael@0:             new Intent(ACTION_SELF_BRAILLE_SERVICE)
michael@0:             .setPackage(BRAILLE_BACK_PACKAGE);
michael@0:     /**
michael@0:      * SHA-1 hash value of the Eyes-Free release key certificate, used to sign
michael@0:      * BrailleBack.  It was generated from the keystore with:
michael@0:      * $ keytool -exportcert -keystore <keystorefile> -alias android.keystore \
michael@0:      *   > cert
michael@0:      * $ keytool -printcert -file cert
michael@0:      */
michael@0:     // The typecasts are to silence a compiler warning about loss of precision
michael@0:     private static final byte[] EYES_FREE_CERT_SHA1 = new byte[] {
michael@0:         (byte) 0x9B, (byte) 0x42, (byte) 0x4C, (byte) 0x2D,
michael@0:         (byte) 0x27, (byte) 0xAD, (byte) 0x51, (byte) 0xA4,
michael@0:         (byte) 0x2A, (byte) 0x33, (byte) 0x7E, (byte) 0x0B,
michael@0:         (byte) 0xB6, (byte) 0x99, (byte) 0x1C, (byte) 0x76,
michael@0:         (byte) 0xEC, (byte) 0xA4, (byte) 0x44, (byte) 0x61
michael@0:     };
michael@0:     /**
michael@0:      * Delay before the first rebind attempt on bind error or service
michael@0:      * disconnect.
michael@0:      */
michael@0:     private static final int REBIND_DELAY_MILLIS = 500;
michael@0:     private static final int MAX_REBIND_ATTEMPTS = 5;
michael@0: 
michael@0:     private final Binder mIdentity = new Binder();
michael@0:     private final Context mContext;
michael@0:     private final boolean mAllowDebugService;
michael@0:     private final SelfBrailleHandler mHandler = new SelfBrailleHandler();
michael@0:     private boolean mShutdown = false;
michael@0: 
michael@0:     /**
michael@0:      * Written in handler thread, read in any thread calling methods on the
michael@0:      * object.
michael@0:      */
michael@0:     private volatile Connection mConnection;
michael@0:     /** Protected by synchronizing on mHandler. */
michael@0:     private int mNumFailedBinds = 0;
michael@0: 
michael@0:     /**
michael@0:      * Constructs an instance of this class.  {@code context} is used to bind
michael@0:      * to the self braille service.  The current thread must have a Looper
michael@0:      * associated with it.  If {@code allowDebugService} is true, this instance
michael@0:      * will connect to a BrailleBack service without requiring it to be signed
michael@0:      * by the release key used to sign BrailleBack.
michael@0:      */
michael@0:     public SelfBrailleClient(Context context, boolean allowDebugService) {
michael@0:         mContext = context;
michael@0:         mAllowDebugService = allowDebugService;
michael@0:         doBindService();
michael@0:     }
michael@0: 
michael@0:     /**
michael@0:      * Shuts this instance down, deallocating any global resources it is using.
michael@0:      * This method must be called on the same thread that created this object.
michael@0:      */
michael@0:     public void shutdown() {
michael@0:         mShutdown = true;
michael@0:         doUnbindService();
michael@0:     }
michael@0: 
michael@0:     public void write(WriteData writeData) {
michael@0:         writeData.validate();
michael@0:         ISelfBrailleService localService = getSelfBrailleService();
michael@0:         if (localService != null) {
michael@0:             try {
michael@0:                 localService.write(mIdentity, writeData);
michael@0:             } catch (RemoteException ex) {
michael@0:                 Log.e(LOG_TAG, "Self braille write failed", ex);
michael@0:             }
michael@0:         }
michael@0:     }
michael@0: 
michael@0:     private void doBindService() {
michael@0:         Connection localConnection = new Connection();
michael@0:         if (!mContext.bindService(mServiceIntent, localConnection,
michael@0:                 Context.BIND_AUTO_CREATE)) {
michael@0:             Log.e(LOG_TAG, "Failed to bind to service");
michael@0:             mHandler.scheduleRebind();
michael@0:             return;
michael@0:         }
michael@0:         mConnection = localConnection;
michael@0:         Log.i(LOG_TAG, "Bound to self braille service");
michael@0:     }
michael@0: 
michael@0:     private void doUnbindService() {
michael@0:         if (mConnection != null) {
michael@0:             ISelfBrailleService localService = getSelfBrailleService();
michael@0:             if (localService != null) {
michael@0:                 try {
michael@0:                     localService.disconnect(mIdentity);
michael@0:                 } catch (RemoteException ex) {
michael@0:                     // Nothing to do.
michael@0:                 }
michael@0:             }
michael@0:             mContext.unbindService(mConnection);
michael@0:             mConnection = null;
michael@0:         }
michael@0:     }
michael@0: 
michael@0:     private ISelfBrailleService getSelfBrailleService() {
michael@0:         Connection localConnection = mConnection;
michael@0:         if (localConnection != null) {
michael@0:             return localConnection.mService;
michael@0:         }
michael@0:         return null;
michael@0:     }
michael@0: 
michael@0:     private boolean verifyPackage() {
michael@0:         PackageManager pm = mContext.getPackageManager();
michael@0:         PackageInfo pi;
michael@0:         try {
michael@0:             pi = pm.getPackageInfo(BRAILLE_BACK_PACKAGE,
michael@0:                     PackageManager.GET_SIGNATURES);
michael@0:         } catch (PackageManager.NameNotFoundException ex) {
michael@0:             Log.w(LOG_TAG, "Can't verify package " + BRAILLE_BACK_PACKAGE,
michael@0:                     ex);
michael@0:             return false;
michael@0:         }
michael@0:         MessageDigest digest;
michael@0:         try {
michael@0:             digest = MessageDigest.getInstance("SHA-1");
michael@0:         } catch (NoSuchAlgorithmException ex) {
michael@0:             Log.e(LOG_TAG, "SHA-1 not supported", ex);
michael@0:             return false;
michael@0:         }
michael@0:         // Check if any of the certificates match our hash.
michael@0:         for (Signature signature : pi.signatures) {
michael@0:             digest.update(signature.toByteArray());
michael@0:             if (MessageDigest.isEqual(EYES_FREE_CERT_SHA1, digest.digest())) {
michael@0:                 return true;
michael@0:             }
michael@0:             digest.reset();
michael@0:         }
michael@0:         if (mAllowDebugService) {
michael@0:             Log.w(LOG_TAG, String.format(
michael@0:                 "*** %s connected to BrailleBack with invalid (debug?) "
michael@0:                 + "signature ***",
michael@0:                 mContext.getPackageName()));
michael@0:             return true;
michael@0:         }
michael@0:         return false;
michael@0:     }
michael@0:     private class Connection implements ServiceConnection {
michael@0:         // Read in application threads, written in main thread.
michael@0:         private volatile ISelfBrailleService mService;
michael@0: 
michael@0:         @Override
michael@0:         public void onServiceConnected(ComponentName className,
michael@0:                 IBinder binder) {
michael@0:             if (!verifyPackage()) {
michael@0:                 Log.w(LOG_TAG, String.format("Service certificate mismatch "
michael@0:                                 + "for %s, dropping connection",
michael@0:                                 BRAILLE_BACK_PACKAGE));
michael@0:                 mHandler.unbindService();
michael@0:                 return;
michael@0:             }
michael@0:             Log.i(LOG_TAG, "Connected to self braille service");
michael@0:             mService = ISelfBrailleService.Stub.asInterface(binder);
michael@0:             synchronized (mHandler) {
michael@0:                 mNumFailedBinds = 0;
michael@0:             }
michael@0:         }
michael@0: 
michael@0:         @Override
michael@0:         public void onServiceDisconnected(ComponentName className) {
michael@0:             Log.e(LOG_TAG, "Disconnected from self braille service");
michael@0:             mService = null;
michael@0:             // Retry by rebinding.
michael@0:             mHandler.scheduleRebind();
michael@0:         }
michael@0:     }
michael@0: 
michael@0:     private class SelfBrailleHandler extends Handler {
michael@0:         private static final int MSG_REBIND_SERVICE = 1;
michael@0:         private static final int MSG_UNBIND_SERVICE = 2;
michael@0: 
michael@0:         public void scheduleRebind() {
michael@0:             synchronized (this) {
michael@0:                 if (mNumFailedBinds < MAX_REBIND_ATTEMPTS) {
michael@0:                     int delay = REBIND_DELAY_MILLIS << mNumFailedBinds;
michael@0:                     sendEmptyMessageDelayed(MSG_REBIND_SERVICE, delay);
michael@0:                     ++mNumFailedBinds;
michael@0:                 }
michael@0:             }
michael@0:         }
michael@0: 
michael@0:         public void unbindService() {
michael@0:             sendEmptyMessage(MSG_UNBIND_SERVICE);
michael@0:         }
michael@0: 
michael@0:         @Override
michael@0:         public void handleMessage(Message msg) {
michael@0:             switch (msg.what) {
michael@0:                 case MSG_REBIND_SERVICE:
michael@0:                     handleRebindService();
michael@0:                     break;
michael@0:                 case MSG_UNBIND_SERVICE:
michael@0:                     handleUnbindService();
michael@0:                     break;
michael@0:             }
michael@0:         }
michael@0: 
michael@0:         private void handleRebindService() {
michael@0:             if (mShutdown) {
michael@0:                 return;
michael@0:             }
michael@0:             if (mConnection != null) {
michael@0:                 doUnbindService();
michael@0:             }
michael@0:             doBindService();
michael@0:         }
michael@0: 
michael@0:         private void handleUnbindService() {
michael@0:             doUnbindService();
michael@0:         }
michael@0:     }
michael@0: }