Russole commented on code in PR #24052: URL: https://github.com/apache/kafka/pull/24052#discussion_r4444271752
########## storage/src/main/java/org/apache/kafka/storage/internals/checkpoint/CheckpointFile.java: ########## @@ -0,0 +1,212 @@ +/* + * 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.storage.internals.checkpoint; + +import org.apache.kafka.common.errors.KafkaStorageException; +import org.apache.kafka.common.utils.Utils; +import org.apache.kafka.storage.internals.log.LogDirFailureChannel; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.io.BufferedReader; +import java.io.BufferedWriter; +import java.io.File; +import java.io.FileNotFoundException; +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.NoSuchFileException; +import java.nio.file.Path; +import java.nio.file.Paths; +import java.util.ArrayList; +import java.util.Collection; +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. + * <pre> + * ========= File beginning ========= + * version: int + * entries-count: int + * entry-as-string-on-each-line + * ========= File end =============== + * </pre> + * 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 <T> entry type. + */ +public class CheckpointFile<T> { + private static final Logger log = LoggerFactory.getLogger(CheckpointFile.class); + + public final File file; + private final int version; + private final EntryFormatter<T> formatter; + private final LogDirFailureChannel logDirFailureChannel; + private final String logDir; + private final Object lock = new Object(); + private final Path absolutePath; + private final Path tempPath; + + public CheckpointFile(File file, + int version, + EntryFormatter<T> formatter, + LogDirFailureChannel logDirFailureChannel, + String logDir) throws IOException { + this.file = file; + this.version = version; + this.formatter = formatter; + this.logDirFailureChannel = logDirFailureChannel; + this.logDir = logDir; + try { + 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<T> entries) { + try { + writeInternal(entries); + } catch (IOException e) { + throw handleFailure("writing to", e); + } + } + + public void writeIfDirExists(Collection<T> entries) { + try { + writeInternal(entries); + } catch (FileNotFoundException | NoSuchFileException e) { + log.warn("Failed to write to checkpoint file {}. This is ok if the topic/partition is being deleted", file.getAbsolutePath(), e); + } catch (IOException e) { + throw handleFailure("writing to", e); + } + } + + public List<T> read() { + try { + synchronized (lock) { + try (BufferedReader reader = Files.newBufferedReader(absolutePath, StandardCharsets.UTF_8)) { + return read(absolutePath.toString(), reader, version, formatter); + } + } + } catch (IOException e) { + throw handleFailure("reading", e); + } + } + + public static <T> void write(BufferedWriter writer, + int version, + EntryFormatter<T> formatter, + Collection<T> entries) throws IOException { + writer.write(Integer.toString(version)); + writer.newLine(); + writer.write(Integer.toString(entries.size())); + writer.newLine(); + for (T entry : entries) { + writer.write(formatter.toString(entry)); + writer.newLine(); + } + } + + public static <T> List<T> read(String location, + BufferedReader reader, + int version, + EntryFormatter<T> formatter) throws IOException { + String line = reader.readLine(); + if (line == null) { + return List.of(); + } + + int readVersion = toInt(location, 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 List.of(); + } + int expectedSize = toInt(location, line); + List<T> entries = new ArrayList<>(expectedSize); + line = reader.readLine(); + while (line != null) { + Optional<T> maybeEntry = formatter.fromString(line); + if (maybeEntry.isEmpty()) { + throw buildMalformedLineException(location, 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 void writeInternal(Collection<T> entries) throws IOException { + synchronized (lock) { + try (FileOutputStream fileOutputStream = new FileOutputStream(tempPath.toFile()); + BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(fileOutputStream, StandardCharsets.UTF_8))) { + write(writer, version, formatter, entries); + writer.flush(); + fileOutputStream.getFD().sync(); + } + Utils.atomicMoveWithFallback(tempPath, absolutePath); + } + } + + private KafkaStorageException handleFailure(String operation, IOException e) { + String msg = "Error while " + operation + " checkpoint file " + file.getAbsolutePath(); + logDirFailureChannel.maybeAddOfflineLogDir(logDir, msg, e); + return new KafkaStorageException(msg, e); + } + + private static int toInt(String location, String line) throws IOException { + try { + return Integer.parseInt(line); + } catch (NumberFormatException e) { + throw buildMalformedLineException(location, line); + } + } + + private static IOException buildMalformedLineException(String location, 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 <T> entry type + */ + public interface EntryFormatter<T> { + String toString(T entry); + + Optional<T> fromString(String value); Review Comment: Good point, updated. -- This is an automated message from the Apache Git Service. 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