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274 行
8.7 KiB
274 行
8.7 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 <stdio.h>
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#include "leveldb/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() = default;
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Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum,
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uint64_t initial_offset)
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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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last_record_offset_(0),
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end_of_buffer_offset_(0),
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initial_offset_(initial_offset),
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resyncing_(initial_offset > 0) {}
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Reader::~Reader() { delete[] backing_store_; }
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bool Reader::SkipToInitialBlock() {
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const size_t offset_in_block = initial_offset_ % kBlockSize;
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uint64_t block_start_location = initial_offset_ - offset_in_block;
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// Don't search a block if we'd be in the trailer
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if (offset_in_block > kBlockSize - 6) {
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block_start_location += kBlockSize;
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}
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end_of_buffer_offset_ = block_start_location;
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// Skip to start of first block that can contain the initial record
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if (block_start_location > 0) {
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Status skip_status = file_->Skip(block_start_location);
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if (!skip_status.ok()) {
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ReportDrop(block_start_location, skip_status);
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return false;
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}
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}
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return true;
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}
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bool Reader::ReadRecord(Slice* record, std::string* scratch) {
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if (last_record_offset_ < initial_offset_) {
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if (!SkipToInitialBlock()) {
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return false;
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}
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}
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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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// Record offset of the logical record that we're reading
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// 0 is a dummy value to make compilers happy
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uint64_t prospective_record_offset = 0;
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Slice fragment;
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while (true) {
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const unsigned int record_type = ReadPhysicalRecord(&fragment);
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// ReadPhysicalRecord may have only had an empty trailer remaining in its
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// internal buffer. Calculate the offset of the next physical record now
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// that it has returned, properly accounting for its header size.
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uint64_t physical_record_offset =
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end_of_buffer_offset_ - buffer_.size() - kHeaderSize - fragment.size();
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if (resyncing_) {
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if (record_type == kMiddleType) {
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continue;
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} else if (record_type == kLastType) {
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resyncing_ = false;
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continue;
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} else {
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resyncing_ = false;
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}
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}
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switch (record_type) {
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case kFullType:
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if (in_fragmented_record) {
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// Handle bug in earlier versions of log::Writer where
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// it could emit an empty kFirstType record at the tail end
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// of a block followed by a kFullType or kFirstType record
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// at the beginning of the next block.
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if (!scratch->empty()) {
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ReportCorruption(scratch->size(), "partial record without end(1)");
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}
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}
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prospective_record_offset = physical_record_offset;
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scratch->clear();
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*record = fragment;
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last_record_offset_ = prospective_record_offset;
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return true;
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case kFirstType:
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if (in_fragmented_record) {
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// Handle bug in earlier versions of log::Writer where
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// it could emit an empty kFirstType record at the tail end
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// of a block followed by a kFullType or kFirstType record
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// at the beginning of the next block.
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if (!scratch->empty()) {
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ReportCorruption(scratch->size(), "partial record without end(2)");
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}
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}
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prospective_record_offset = physical_record_offset;
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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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ReportCorruption(fragment.size(),
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"missing start of fragmented record(1)");
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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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ReportCorruption(fragment.size(),
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"missing start of fragmented record(2)");
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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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last_record_offset_ = prospective_record_offset;
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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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// This can be caused by the writer dying immediately after
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// writing a physical record but before completing the next; don't
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// treat it as a corruption, just ignore the entire logical record.
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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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ReportCorruption(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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char buf[40];
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snprintf(buf, sizeof(buf), "unknown record type %u", record_type);
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ReportCorruption(
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(fragment.size() + (in_fragmented_record ? scratch->size() : 0)),
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buf);
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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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}
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return false;
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}
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uint64_t Reader::LastRecordOffset() { return last_record_offset_; }
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void Reader::ReportCorruption(uint64_t bytes, const char* reason) {
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ReportDrop(bytes, Status::Corruption(reason));
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}
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void Reader::ReportDrop(uint64_t bytes, const Status& reason) {
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if (reporter_ != nullptr &&
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end_of_buffer_offset_ - buffer_.size() - bytes >= initial_offset_) {
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reporter_->Corruption(static_cast<size_t>(bytes), 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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end_of_buffer_offset_ += buffer_.size();
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if (!status.ok()) {
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buffer_.clear();
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ReportDrop(kBlockSize, status);
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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 {
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// Note that if buffer_ is non-empty, we have a truncated header at the
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// end of the file, which can be caused by the writer crashing in the
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// middle of writing the header. Instead of considering this an error,
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// just report EOF.
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buffer_.clear();
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return kEof;
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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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size_t drop_size = buffer_.size();
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buffer_.clear();
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if (!eof_) {
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ReportCorruption(drop_size, "bad record length");
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return kBadRecord;
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}
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// If the end of the file has been reached without reading |length| bytes
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// of payload, assume the writer died in the middle of writing the record.
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// Don't report a corruption.
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return kEof;
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}
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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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// Check crc
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if (checksum_) {
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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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size_t drop_size = buffer_.size();
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buffer_.clear();
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ReportCorruption(drop_size, "checksum mismatch");
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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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// Skip physical record that started before initial_offset_
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if (end_of_buffer_offset_ - buffer_.size() - kHeaderSize - length <
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initial_offset_) {
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result->clear();
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return kBadRecord;
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}
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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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} // namespace log
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} // namespace leveldb
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