2 * Copyright (c) 2024 PANTHEON.tech, s.r.o. and others. All rights reserved.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
16 package io.atomix.storage.journal;
18 import static com.google.common.base.Verify.verify;
19 import static java.util.Objects.requireNonNull;
21 import io.netty.buffer.ByteBuf;
22 import io.netty.buffer.Unpooled;
23 import java.util.zip.CRC32;
24 import org.eclipse.jdt.annotation.Nullable;
25 import org.slf4j.Logger;
26 import org.slf4j.LoggerFactory;
28 final class JournalSegmentReader {
29 private static final Logger LOG = LoggerFactory.getLogger(JournalSegmentReader.class);
31 private final JournalSegment segment;
32 private final FileReader fileReader;
33 private final int maxSegmentSize;
34 private final int maxEntrySize;
38 JournalSegmentReader(final JournalSegment segment, final FileReader fileReader, final int maxEntrySize) {
39 this.segment = requireNonNull(segment);
40 this.fileReader = requireNonNull(fileReader);
41 maxSegmentSize = segment.descriptor().maxSegmentSize();
42 this.maxEntrySize = maxEntrySize;
46 * Return the current position.
48 * @return current position.
55 * Set the file position.
57 * @param position new position
59 void setPosition(final int position) {
60 verify(position >= JournalSegmentDescriptor.BYTES && position < maxSegmentSize,
61 "Invalid position %s", position);
62 this.position = position;
63 fileReader.invalidateCache();
67 * Invalidate any cache that is present, so that the next read is coherent with the backing file.
69 void invalidateCache() {
70 fileReader.invalidateCache();
74 * Reads the next binary data block
76 * @param index entry index
77 * @return The binary data, or {@code null}
79 @Nullable ByteBuf readBytes(final long index) {
80 // Check if there is enough in the buffer remaining
81 final int remaining = maxSegmentSize - position - SegmentEntry.HEADER_BYTES;
83 // Not enough space in the segment, there can never be another entry
87 // Calculate maximum entry length not exceeding file size nor maxEntrySize
88 final var maxLength = Math.min(remaining, maxEntrySize);
89 final var buffer = fileReader.read(position, maxLength + SegmentEntry.HEADER_BYTES);
91 // Read the entry length
92 final var length = buffer.getInt(0);
93 if (length < 1 || length > maxLength) {
94 // Invalid length, make sure next read re-tries
99 // Read the entry checksum
100 final int checksum = buffer.getInt(Integer.BYTES);
102 // Slice off the entry's bytes
103 final var entryBuffer = buffer.slice(SegmentEntry.HEADER_BYTES, length);
104 // Compute the checksum for the entry bytes.
105 final var crc32 = new CRC32();
106 crc32.update(entryBuffer);
108 // If the stored checksum does not equal the computed checksum, do not proceed further
109 final var computed = (int) crc32.getValue();
110 if (checksum != computed) {
111 LOG.warn("Expected checksum {}, computed {}", Integer.toHexString(checksum), Integer.toHexString(computed));
117 position += SegmentEntry.HEADER_BYTES + length;
120 entryBuffer.rewind();
121 return Unpooled.buffer(length).writeBytes(entryBuffer);
128 segment.closeReader(this);