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/*
* Copyright (C) 2017 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.content.pm;
import android.os.Parcel;
import android.util.Log;
import java.util.ArrayList;
import java.util.HashMap;
/**
* Helper classes to read from and write to Parcel with pooled strings.
*
* @hide
*/
public class PackageParserCacheHelper {
private PackageParserCacheHelper() {
}
private static final String TAG = "PackageParserCacheHelper";
private static final boolean DEBUG = false;
/**
* Parcel read helper with a string pool.
*/
public static class ReadHelper extends Parcel.ReadWriteHelper {
private final ArrayList<String> mStrings = new ArrayList<>();
private final Parcel mParcel;
public ReadHelper(Parcel p) {
mParcel = p;
}
/**
* Prepare to read from a parcel, and install itself as a read-write helper.
*
* (We don't do it in the constructor to avoid calling methods before the constructor
* finishes.)
*/
public void startAndInstall() {
mStrings.clear();
final int poolPosition = mParcel.readInt();
final int startPosition = mParcel.dataPosition();
// The pool is at the end of the parcel.
mParcel.setDataPosition(poolPosition);
mParcel.readStringList(mStrings);
// Then move back.
mParcel.setDataPosition(startPosition);
if (DEBUG) {
Log.i(TAG, "Read " + mStrings.size() + " strings");
for (int i = 0; i < mStrings.size(); i++) {
Log.i(TAG, " " + i + ": \"" + mStrings.get(i) + "\"");
}
}
mParcel.setReadWriteHelper(this);
}
/**
* Read an string index from a parcel, and returns the corresponding string from the pool.
*/
@Override
public String readString(Parcel p) {
return mStrings.get(p.readInt());
}
}
/**
* Parcel write helper with a string pool.
*/
public static class WriteHelper extends Parcel.ReadWriteHelper {
private final ArrayList<String> mStrings = new ArrayList<>();
private final HashMap<String, Integer> mIndexes = new HashMap<>();
private final Parcel mParcel;
private final int mStartPos;
/**
* Constructor. Prepare a parcel, and install it self as a read-write helper.
*/
public WriteHelper(Parcel p) {
mParcel = p;
mStartPos = p.dataPosition();
mParcel.writeInt(0); // We come back later here and write the pool position.
mParcel.setReadWriteHelper(this);
}
/**
* Instead of writing a string directly to a parcel, this method adds it to the pool,
* and write the index in the pool to the parcel.
*/
@Override
public void writeString(Parcel p, String s) {
final Integer cur = mIndexes.get(s);
if (cur != null) {
// String already in the pool. Just write the index.
p.writeInt(cur); // Already in the pool.
if (DEBUG) {
Log.i(TAG, "Duplicate '" + s + "' at " + cur);
}
} else {
// Not in the pool. Add to the pool, and write the index.
final int index = mStrings.size();
mIndexes.put(s, index);
mStrings.add(s);
if (DEBUG) {
Log.i(TAG, "New '" + s + "' at " + index);
}
p.writeInt(index);
}
}
/**
* Closes a parcel by appending the string pool at the end and updating the pool offset,
* which it assumes is at the first byte. It also uninstalls itself as a read-write helper.
*/
public void finishAndUninstall() {
// Uninstall first, so that writeStringList() uses the native writeString.
mParcel.setReadWriteHelper(null);
final int poolPosition = mParcel.dataPosition();
mParcel.writeStringList(mStrings);
mParcel.setDataPosition(mStartPos);
mParcel.writeInt(poolPosition);
// Move back to the end.
mParcel.setDataPosition(mParcel.dataSize());
if (DEBUG) {
Log.i(TAG, "Wrote " + mStrings.size() + " strings");
}
}
}
}
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