1 /*
2  * Copyright (C) 2011 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package android.content.pm;
18 
19 import android.compat.annotation.UnsupportedAppUsage;
20 import android.os.Binder;
21 import android.os.Build;
22 import android.os.IBinder;
23 import android.os.Parcel;
24 import android.os.Parcelable;
25 import android.os.RemoteException;
26 import android.util.Log;
27 
28 import java.util.ArrayList;
29 import java.util.List;
30 
31 /**
32  * Transfer a large list of Parcelable objects across an IPC.  Splits into
33  * multiple transactions if needed.
34  *
35  * Caveat: for efficiency and security, all elements must be the same concrete type.
36  * In order to avoid writing the class name of each object, we must ensure that
37  * each object is the same type, or else unparceling then reparceling the data may yield
38  * a different result if the class name encoded in the Parcelable is a Base type.
39  * See b/17671747.
40  *
41  * @hide
42  */
43 abstract class BaseParceledListSlice<T> implements Parcelable {
44     private static String TAG = "ParceledListSlice";
45     private static boolean DEBUG = false;
46 
47     /*
48      * TODO get this number from somewhere else. For now set it to a quarter of
49      * the 1MB limit.
50      */
51     private static final int MAX_IPC_SIZE = IBinder.getSuggestedMaxIpcSizeBytes();
52 
53     private final List<T> mList;
54 
55     private int mInlineCountLimit = Integer.MAX_VALUE;
56 
BaseParceledListSlice(List<T> list)57     public BaseParceledListSlice(List<T> list) {
58         mList = list;
59     }
60 
61     @SuppressWarnings("unchecked")
BaseParceledListSlice(Parcel p, ClassLoader loader)62     BaseParceledListSlice(Parcel p, ClassLoader loader) {
63         final int N = p.readInt();
64         mList = new ArrayList<T>(N);
65         if (DEBUG) Log.d(TAG, "Retrieving " + N + " items");
66         if (N <= 0) {
67             return;
68         }
69 
70         Parcelable.Creator<?> creator = readParcelableCreator(p, loader);
71         Class<?> listElementClass = null;
72 
73         int i = 0;
74         while (i < N) {
75             if (p.readInt() == 0) {
76                 break;
77             }
78             listElementClass = readVerifyAndAddElement(creator, p, loader, listElementClass);
79             if (DEBUG) Log.d(TAG, "Read inline #" + i + ": " + mList.get(mList.size()-1));
80             i++;
81         }
82         if (i >= N) {
83             return;
84         }
85         final IBinder retriever = p.readStrongBinder();
86         while (i < N) {
87             if (DEBUG) Log.d(TAG, "Reading more @" + i + " of " + N + ": retriever=" + retriever);
88             Parcel data = Parcel.obtain();
89             Parcel reply = Parcel.obtain();
90             data.writeInt(i);
91             try {
92                 retriever.transact(IBinder.FIRST_CALL_TRANSACTION, data, reply, 0);
93             } catch (RemoteException e) {
94                 Log.w(TAG, "Failure retrieving array; only received " + i + " of " + N, e);
95                 return;
96             }
97             while (i < N && reply.readInt() != 0) {
98                 listElementClass = readVerifyAndAddElement(creator, reply, loader,
99                         listElementClass);
100                 if (DEBUG) Log.d(TAG, "Read extra #" + i + ": " + mList.get(mList.size()-1));
101                 i++;
102             }
103             reply.recycle();
104             data.recycle();
105         }
106     }
107 
readVerifyAndAddElement(Parcelable.Creator<?> creator, Parcel p, ClassLoader loader, Class<?> listElementClass)108     private Class<?> readVerifyAndAddElement(Parcelable.Creator<?> creator, Parcel p,
109             ClassLoader loader, Class<?> listElementClass) {
110         final T parcelable = readCreator(creator, p, loader);
111         if (listElementClass == null) {
112             listElementClass = parcelable.getClass();
113         } else {
114             verifySameType(listElementClass, parcelable.getClass());
115         }
116         mList.add(parcelable);
117         return listElementClass;
118     }
119 
readCreator(Parcelable.Creator<?> creator, Parcel p, ClassLoader loader)120     private T readCreator(Parcelable.Creator<?> creator, Parcel p, ClassLoader loader) {
121         if (creator instanceof Parcelable.ClassLoaderCreator<?>) {
122             Parcelable.ClassLoaderCreator<?> classLoaderCreator =
123                     (Parcelable.ClassLoaderCreator<?>) creator;
124             return (T) classLoaderCreator.createFromParcel(p, loader);
125         }
126         return (T) creator.createFromParcel(p);
127     }
128 
verifySameType(final Class<?> expected, final Class<?> actual)129     private static void verifySameType(final Class<?> expected, final Class<?> actual) {
130         if (!actual.equals(expected)) {
131             throw new IllegalArgumentException("Can't unparcel type "
132                     + (actual == null ? null : actual.getName()) + " in list of type "
133                     + (expected == null ? null : expected.getName()));
134         }
135     }
136 
137     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
getList()138     public List<T> getList() {
139         return mList;
140     }
141 
142     /**
143      * Set a limit on the maximum number of entries in the array that will be included
144      * inline in the initial parcelling of this object.
145      */
setInlineCountLimit(int maxCount)146     public void setInlineCountLimit(int maxCount) {
147         mInlineCountLimit = maxCount;
148     }
149 
150     /**
151      * Write this to another Parcel. Note that this discards the internal Parcel
152      * and should not be used anymore. This is so we can pass this to a Binder
153      * where we won't have a chance to call recycle on this.
154      */
155     @Override
writeToParcel(Parcel dest, int flags)156     public void writeToParcel(Parcel dest, int flags) {
157         final int N = mList.size();
158         final int callFlags = flags;
159         dest.writeInt(N);
160         if (DEBUG) Log.d(TAG, "Writing " + N + " items");
161         if (N > 0) {
162             final Class<?> listElementClass = mList.get(0).getClass();
163             writeParcelableCreator(mList.get(0), dest);
164             int i = 0;
165             while (i < N && i < mInlineCountLimit && dest.dataSize() < MAX_IPC_SIZE) {
166                 dest.writeInt(1);
167 
168                 final T parcelable = mList.get(i);
169                 verifySameType(listElementClass, parcelable.getClass());
170                 writeElement(parcelable, dest, callFlags);
171 
172                 if (DEBUG) Log.d(TAG, "Wrote inline #" + i + ": " + mList.get(i));
173                 i++;
174             }
175             if (i < N) {
176                 dest.writeInt(0);
177                 Binder retriever = new Binder() {
178                     @Override
179                     protected boolean onTransact(int code, Parcel data, Parcel reply, int flags)
180                             throws RemoteException {
181                         if (code != FIRST_CALL_TRANSACTION) {
182                             return super.onTransact(code, data, reply, flags);
183                         }
184                         int i = data.readInt();
185                         if (DEBUG) Log.d(TAG, "Writing more @" + i + " of " + N);
186                         while (i < N && reply.dataSize() < MAX_IPC_SIZE) {
187                             reply.writeInt(1);
188 
189                             final T parcelable = mList.get(i);
190                             verifySameType(listElementClass, parcelable.getClass());
191                             writeElement(parcelable, reply, callFlags);
192 
193                             if (DEBUG) Log.d(TAG, "Wrote extra #" + i + ": " + mList.get(i));
194                             i++;
195                         }
196                         if (i < N) {
197                             if (DEBUG) Log.d(TAG, "Breaking @" + i + " of " + N);
198                             reply.writeInt(0);
199                         }
200                         return true;
201                     }
202                 };
203                 if (DEBUG) Log.d(TAG, "Breaking @" + i + " of " + N + ": retriever=" + retriever);
204                 dest.writeStrongBinder(retriever);
205             }
206         }
207     }
208 
writeElement(T parcelable, Parcel reply, int callFlags)209     protected abstract void writeElement(T parcelable, Parcel reply, int callFlags);
210 
211     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
writeParcelableCreator(T parcelable, Parcel dest)212     protected abstract void writeParcelableCreator(T parcelable, Parcel dest);
213 
readParcelableCreator(Parcel from, ClassLoader loader)214     protected abstract Parcelable.Creator<?> readParcelableCreator(Parcel from, ClassLoader loader);
215 }
216