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/*
* Copyright (C) 2024 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.utils;
import android.annotation.NonNull;
import android.annotation.Nullable;
import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
/**
* Bits and pieces copied from hidden API of android.os.FileUtils.
*
* @hide
*/
public class FileUtils {
/**
* Read a text file into a String, optionally limiting the length.
*
* @param file to read (will not seek, so things like /proc files are OK)
* @param max length (positive for head, negative of tail, 0 for no limit)
* @param ellipsis to add of the file was truncated (can be null)
* @return the contents of the file, possibly truncated
* @throws IOException if something goes wrong reading the file
* @hide
*/
public static @Nullable String readTextFile(@Nullable File file, @Nullable int max,
@Nullable String ellipsis) throws IOException {
InputStream input = new FileInputStream(file);
// wrapping a BufferedInputStream around it because when reading /proc with unbuffered
// input stream, bytes read not equal to buffer size is not necessarily the correct
// indication for EOF; but it is true for BufferedInputStream due to its implementation.
BufferedInputStream bis = new BufferedInputStream(input);
try {
long size = file.length();
if (max > 0 || (size > 0 && max == 0)) { // "head" mode: read the first N bytes
if (size > 0 && (max == 0 || size < max)) max = (int) size;
byte[] data = new byte[max + 1];
int length = bis.read(data);
if (length <= 0) return "";
if (length <= max) return new String(data, 0, length);
if (ellipsis == null) return new String(data, 0, max);
return new String(data, 0, max) + ellipsis;
} else if (max < 0) { // "tail" mode: keep the last N
int len;
boolean rolled = false;
byte[] last = null;
byte[] data = null;
do {
if (last != null) rolled = true;
byte[] tmp = last;
last = data;
data = tmp;
if (data == null) data = new byte[-max];
len = bis.read(data);
} while (len == data.length);
if (last == null && len <= 0) return "";
if (last == null) return new String(data, 0, len);
if (len > 0) {
rolled = true;
System.arraycopy(last, len, last, 0, last.length - len);
System.arraycopy(data, 0, last, last.length - len, len);
}
if (ellipsis == null || !rolled) return new String(last);
return ellipsis + new String(last);
} else { // "cat" mode: size unknown, read it all in streaming fashion
ByteArrayOutputStream contents = new ByteArrayOutputStream();
int len;
byte[] data = new byte[1024];
do {
len = bis.read(data);
if (len > 0) contents.write(data, 0, len);
} while (len == data.length);
return contents.toString();
}
} finally {
bis.close();
input.close();
}
}
/**
* Perform an fsync on the given FileOutputStream. The stream at this
* point must be flushed but not yet closed.
*
* @hide
*/
public static boolean sync(FileOutputStream stream) {
try {
if (stream != null) {
stream.getFD().sync();
}
return true;
} catch (IOException e) {
}
return false;
}
/**
* List the files in the directory or return empty file.
*
* @hide
*/
public static @NonNull File[] listFilesOrEmpty(@Nullable File dir) {
return (dir != null) ? ArrayUtils.defeatNullable(dir.listFiles())
: ArrayUtils.EMPTY_FILE;
}
}
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