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/*
* Copyright (C) 2022 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 com.android.server.net;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.util.AtomicFile;
import android.util.SystemConfigFileCommitEventLogger;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
/**
* A simple integer backed by an on-disk {@link AtomicFile}. Not thread-safe.
*/
public class PersistentInt {
private final String mPath;
private final AtomicFile mFile;
/**
* Constructs a new {@code PersistentInt}. The counter is set to 0 if the file does not exist.
* Before returning, the constructor checks that the file is readable and writable. This
* indicates that in the future {@link #get} and {@link #set} are likely to succeed,
* though other events (data corruption, other code deleting the file, etc.) may cause these
* calls to fail in the future.
*
* @param path the path of the file to use.
* @param logger the logger
* @throws IOException the counter could not be read or written
*/
public PersistentInt(@NonNull String path, @Nullable SystemConfigFileCommitEventLogger logger)
throws IOException {
mPath = path;
mFile = new AtomicFile(new File(path), logger);
checkReadWrite();
}
private void checkReadWrite() throws IOException {
int value;
try {
value = get();
} catch (FileNotFoundException e) {
// Counter does not exist. Attempt to initialize to 0.
// Note that we cannot tell here if the file does not exist or if opening it failed,
// because in Java both of those throw FileNotFoundException.
value = 0;
}
set(value);
get();
// No exceptions? Good.
}
/**
* Gets the current value.
*
* @return the current value of the counter.
* @throws IOException if reading the value failed.
*/
public int get() throws IOException {
try (FileInputStream fin = mFile.openRead();
DataInputStream din = new DataInputStream(fin)) {
return din.readInt();
}
}
/**
* Sets the current value.
* @param value the value to set
* @throws IOException if writing the value failed.
*/
public void set(int value) throws IOException {
FileOutputStream fout = null;
try {
fout = mFile.startWrite();
DataOutputStream dout = new DataOutputStream(fout);
dout.writeInt(value);
mFile.finishWrite(fout);
} catch (IOException e) {
if (fout != null) {
mFile.failWrite(fout);
}
throw e;
}
}
public String getPath() {
return mPath;
}
}
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