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178 行
5.0 KiB
178 行
5.0 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include "db/log_reader.h"
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#include <stdint.h>
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#include "include/env.h"
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#include "util/coding.h"
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#include "util/crc32c.h"
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namespace leveldb {
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namespace log {
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Reader::Reporter::~Reporter() {
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}
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Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum)
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: file_(file),
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reporter_(reporter),
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checksum_(checksum),
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backing_store_(new char[kBlockSize]),
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buffer_(),
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eof_(false) {
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}
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Reader::~Reader() {
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delete[] backing_store_;
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}
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bool Reader::ReadRecord(Slice* record, std::string* scratch) {
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scratch->clear();
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record->clear();
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bool in_fragmented_record = false;
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Slice fragment;
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while (true) {
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switch (ReadPhysicalRecord(&fragment)) {
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case kFullType:
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if (in_fragmented_record) {
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ReportDrop(scratch->size(), "partial record without end");
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}
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scratch->clear();
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*record = fragment;
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return true;
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case kFirstType:
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if (in_fragmented_record) {
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ReportDrop(scratch->size(), "partial record without end");
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}
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scratch->assign(fragment.data(), fragment.size());
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in_fragmented_record = true;
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break;
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case kMiddleType:
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if (!in_fragmented_record) {
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ReportDrop(fragment.size(), "missing start of fragmented record");
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} else {
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scratch->append(fragment.data(), fragment.size());
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}
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break;
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case kLastType:
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if (!in_fragmented_record) {
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ReportDrop(fragment.size(), "missing start of fragmented record");
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} else {
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scratch->append(fragment.data(), fragment.size());
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*record = Slice(*scratch);
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return true;
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}
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break;
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case kEof:
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if (in_fragmented_record) {
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ReportDrop(scratch->size(), "partial record without end");
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scratch->clear();
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}
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return false;
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case kBadRecord:
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if (in_fragmented_record) {
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ReportDrop(scratch->size(), "error in middle of record");
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in_fragmented_record = false;
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scratch->clear();
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}
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break;
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default:
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ReportDrop(
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(fragment.size() + (in_fragmented_record ? scratch->size() : 0)),
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"unknown record type");
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in_fragmented_record = false;
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scratch->clear();
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break;
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}
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}
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return false;
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}
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void Reader::ReportDrop(size_t bytes, const char* reason) {
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if (reporter_ != NULL) {
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reporter_->Corruption(bytes, Status::Corruption(reason));
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}
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}
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unsigned int Reader::ReadPhysicalRecord(Slice* result) {
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while (true) {
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if (buffer_.size() <= kHeaderSize) {
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if (!eof_) {
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// Last read was a full read, so this is a trailer to skip
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buffer_.clear();
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Status status = file_->Read(kBlockSize, &buffer_, backing_store_);
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if (!status.ok()) {
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if (reporter_ != NULL) {
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reporter_->Corruption(kBlockSize, status);
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}
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buffer_.clear();
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eof_ = true;
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return kEof;
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} else if (buffer_.size() < kBlockSize) {
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eof_ = true;
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}
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continue;
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} else if (buffer_.size() == 0) {
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// End of file
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return kEof;
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} else if (buffer_.size() < kHeaderSize) {
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ReportDrop(buffer_.size(), "truncated record at end of file");
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buffer_.clear();
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return kEof;
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} else {
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// We have a trailing zero-length record. Fall through and check it.
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}
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}
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// Parse the header
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const char* header = buffer_.data();
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const uint32_t a = static_cast<uint32_t>(header[4]) & 0xff;
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const uint32_t b = static_cast<uint32_t>(header[5]) & 0xff;
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const unsigned int type = header[6];
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const uint32_t length = a | (b << 8);
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if (kHeaderSize + length > buffer_.size()) {
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ReportDrop(buffer_.size(), "bad record length");
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buffer_.clear();
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return kBadRecord;
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}
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// Check crc
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if (checksum_) {
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if (type == kZeroType && length == 0) {
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// Skip zero length record without reporting any drops since
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// such records are produced by the mmap based writing code in
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// env_posix.cc that preallocates file regions.
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buffer_.clear();
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return kBadRecord;
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}
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uint32_t expected_crc = crc32c::Unmask(DecodeFixed32(header));
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uint32_t actual_crc = crc32c::Value(header + 6, 1 + length);
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if (actual_crc != expected_crc) {
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// Drop the rest of the buffer since "length" itself may have
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// been corrupted and if we trust it, we could find some
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// fragment of a real log record that just happens to look
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// like a valid log record.
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ReportDrop(buffer_.size(), "checksum mismatch");
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buffer_.clear();
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return kBadRecord;
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}
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}
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buffer_.remove_prefix(kHeaderSize + length);
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*result = Slice(header + kHeaderSize, length);
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return type;
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}
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}
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}
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}
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