org.apache.kafka.server.common.CheckpointFile Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.kafka.server.common;
import org.apache.kafka.common.utils.Utils;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;
import java.nio.file.FileAlreadyExistsException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
/**
* This class represents a utility to capture a checkpoint in a file. It writes down to the file in the below format.
*
* ========= File beginning =========
* version: int
* entries-count: int
* entry-as-string-on-each-line
* ========= File end ===============
*
* Each entry is represented as a string on each line in the checkpoint file. {@link EntryFormatter} is used
* to convert the entry into a string and vice versa.
*
* @param entry type.
*/
public class CheckpointFile {
private final int version;
private final EntryFormatter formatter;
private final Object lock = new Object();
private final Path absolutePath;
private final Path tempPath;
public CheckpointFile(File file,
int version,
EntryFormatter formatter) throws IOException {
this.version = version;
this.formatter = formatter;
try {
// Create the file if it does not exist.
Files.createFile(file.toPath());
} catch (FileAlreadyExistsException ex) {
// Ignore if file already exists.
}
absolutePath = file.toPath().toAbsolutePath();
tempPath = Paths.get(absolutePath + ".tmp");
}
public void write(Collection entries) throws IOException {
synchronized (lock) {
// write to temp file and then swap with the existing file
try (FileOutputStream fileOutputStream = new FileOutputStream(tempPath.toFile());
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(fileOutputStream, StandardCharsets.UTF_8))) {
CheckpointWriteBuffer checkpointWriteBuffer = new CheckpointWriteBuffer<>(writer, version, formatter);
checkpointWriteBuffer.write(entries);
writer.flush();
fileOutputStream.getFD().sync();
}
Utils.atomicMoveWithFallback(tempPath, absolutePath);
}
}
public List read() throws IOException {
synchronized (lock) {
try (BufferedReader reader = Files.newBufferedReader(absolutePath)) {
CheckpointReadBuffer checkpointBuffer = new CheckpointReadBuffer<>(absolutePath.toString(), reader, version, formatter);
return checkpointBuffer.read();
}
}
}
public static class CheckpointWriteBuffer {
private final BufferedWriter writer;
private final int version;
private final EntryFormatter formatter;
public CheckpointWriteBuffer(BufferedWriter writer,
int version,
EntryFormatter formatter) {
this.writer = writer;
this.version = version;
this.formatter = formatter;
}
public void write(Collection entries) throws IOException {
// Write the version
writer.write(Integer.toString(version));
writer.newLine();
// Write the entries count
writer.write(Integer.toString(entries.size()));
writer.newLine();
// Write each entry on a new line.
for (T entry : entries) {
writer.write(formatter.toString(entry));
writer.newLine();
}
}
}
public static class CheckpointReadBuffer {
private final String location;
private final BufferedReader reader;
private final int version;
private final EntryFormatter formatter;
public CheckpointReadBuffer(String location,
BufferedReader reader,
int version,
EntryFormatter formatter) {
this.location = location;
this.reader = reader;
this.version = version;
this.formatter = formatter;
}
public List read() throws IOException {
String line = reader.readLine();
if (line == null)
return Collections.emptyList();
int readVersion = toInt(line);
if (readVersion != version) {
throw new IOException("Unrecognised version:" + readVersion + ", expected version: " + version
+ " in checkpoint file at: " + location);
}
line = reader.readLine();
if (line == null) {
return Collections.emptyList();
}
int expectedSize = toInt(line);
List entries = new ArrayList<>(expectedSize);
line = reader.readLine();
while (line != null) {
Optional maybeEntry = formatter.fromString(line);
if (!maybeEntry.isPresent()) {
throw buildMalformedLineException(line);
}
entries.add(maybeEntry.get());
line = reader.readLine();
}
if (entries.size() != expectedSize) {
throw new IOException("Expected [" + expectedSize + "] entries in checkpoint file ["
+ location + "], but found only [" + entries.size() + "]");
}
return entries;
}
private int toInt(String line) throws IOException {
try {
return Integer.parseInt(line);
} catch (NumberFormatException e) {
throw buildMalformedLineException(line);
}
}
private IOException buildMalformedLineException(String line) {
return new IOException(String.format("Malformed line in checkpoint file [%s]: %s", location, line));
}
}
/**
* This is used to convert the given entry of type {@code T} into a string and vice versa.
*
* @param entry type
*/
public interface EntryFormatter {
/**
* @param entry entry to be converted into string.
* @return String representation of the given entry.
*/
String toString(T entry);
/**
* @param value string representation of an entry.
* @return entry converted from the given string representation if possible. {@link Optional#empty()} represents
* that the given string representation could not be converted into an entry.
*/
Optional fromString(String value);
}
}