diff options
Diffstat (limited to 'db/log_reader.cc')
| -rw-r--r-- | db/log_reader.cc | 259 |
1 files changed, 259 insertions, 0 deletions
diff --git a/db/log_reader.cc b/db/log_reader.cc new file mode 100644 index 0000000..b35f115 --- /dev/null +++ b/db/log_reader.cc @@ -0,0 +1,259 @@ +// Copyright (c) 2011 The LevelDB Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. See the AUTHORS file for names of contributors. + +#include "db/log_reader.h" + +#include <stdio.h> +#include "leveldb/env.h" +#include "util/coding.h" +#include "util/crc32c.h" + +namespace leveldb { +namespace log { + +Reader::Reporter::~Reporter() { +} + +Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum, + uint64_t initial_offset) + : file_(file), + reporter_(reporter), + checksum_(checksum), + backing_store_(new char[kBlockSize]), + buffer_(), + eof_(false), + last_record_offset_(0), + end_of_buffer_offset_(0), + initial_offset_(initial_offset) { +} + +Reader::~Reader() { + delete[] backing_store_; +} + +bool Reader::SkipToInitialBlock() { + size_t offset_in_block = initial_offset_ % kBlockSize; + uint64_t block_start_location = initial_offset_ - offset_in_block; + + // Don't search a block if we'd be in the trailer + if (offset_in_block > kBlockSize - 6) { + offset_in_block = 0; + block_start_location += kBlockSize; + } + + end_of_buffer_offset_ = block_start_location; + + // Skip to start of first block that can contain the initial record + if (block_start_location > 0) { + Status skip_status = file_->Skip(block_start_location); + if (!skip_status.ok()) { + ReportDrop(block_start_location, skip_status); + return false; + } + } + + return true; +} + +bool Reader::ReadRecord(Slice* record, std::string* scratch) { + if (last_record_offset_ < initial_offset_) { + if (!SkipToInitialBlock()) { + return false; + } + } + + scratch->clear(); + record->clear(); + bool in_fragmented_record = false; + // Record offset of the logical record that we're reading + // 0 is a dummy value to make compilers happy + uint64_t prospective_record_offset = 0; + + Slice fragment; + while (true) { + uint64_t physical_record_offset = end_of_buffer_offset_ - buffer_.size(); + const unsigned int record_type = ReadPhysicalRecord(&fragment); + switch (record_type) { + case kFullType: + if (in_fragmented_record) { + // Handle bug in earlier versions of log::Writer where + // it could emit an empty kFirstType record at the tail end + // of a block followed by a kFullType or kFirstType record + // at the beginning of the next block. + if (scratch->empty()) { + in_fragmented_record = false; + } else { + ReportCorruption(scratch->size(), "partial record without end(1)"); + } + } + prospective_record_offset = physical_record_offset; + scratch->clear(); + *record = fragment; + last_record_offset_ = prospective_record_offset; + return true; + + case kFirstType: + if (in_fragmented_record) { + // Handle bug in earlier versions of log::Writer where + // it could emit an empty kFirstType record at the tail end + // of a block followed by a kFullType or kFirstType record + // at the beginning of the next block. + if (scratch->empty()) { + in_fragmented_record = false; + } else { + ReportCorruption(scratch->size(), "partial record without end(2)"); + } + } + prospective_record_offset = physical_record_offset; + scratch->assign(fragment.data(), fragment.size()); + in_fragmented_record = true; + break; + + case kMiddleType: + if (!in_fragmented_record) { + ReportCorruption(fragment.size(), + "missing start of fragmented record(1)"); + } else { + scratch->append(fragment.data(), fragment.size()); + } + break; + + case kLastType: + if (!in_fragmented_record) { + ReportCorruption(fragment.size(), + "missing start of fragmented record(2)"); + } else { + scratch->append(fragment.data(), fragment.size()); + *record = Slice(*scratch); + last_record_offset_ = prospective_record_offset; + return true; + } + break; + + case kEof: + if (in_fragmented_record) { + ReportCorruption(scratch->size(), "partial record without end(3)"); + scratch->clear(); + } + return false; + + case kBadRecord: + if (in_fragmented_record) { + ReportCorruption(scratch->size(), "error in middle of record"); + in_fragmented_record = false; + scratch->clear(); + } + break; + + default: { + char buf[40]; + snprintf(buf, sizeof(buf), "unknown record type %u", record_type); + ReportCorruption( + (fragment.size() + (in_fragmented_record ? scratch->size() : 0)), + buf); + in_fragmented_record = false; + scratch->clear(); + break; + } + } + } + return false; +} + +uint64_t Reader::LastRecordOffset() { + return last_record_offset_; +} + +void Reader::ReportCorruption(size_t bytes, const char* reason) { + ReportDrop(bytes, Status::Corruption(reason)); +} + +void Reader::ReportDrop(size_t bytes, const Status& reason) { + if (reporter_ != NULL && + end_of_buffer_offset_ - buffer_.size() - bytes >= initial_offset_) { + reporter_->Corruption(bytes, reason); + } +} + +unsigned int Reader::ReadPhysicalRecord(Slice* result) { + while (true) { + if (buffer_.size() < kHeaderSize) { + if (!eof_) { + // Last read was a full read, so this is a trailer to skip + buffer_.clear(); + Status status = file_->Read(kBlockSize, &buffer_, backing_store_); + end_of_buffer_offset_ += buffer_.size(); + if (!status.ok()) { + buffer_.clear(); + ReportDrop(kBlockSize, status); + eof_ = true; + return kEof; + } else if (buffer_.size() < kBlockSize) { + eof_ = true; + } + continue; + } else if (buffer_.size() == 0) { + // End of file + return kEof; + } else { + size_t drop_size = buffer_.size(); + buffer_.clear(); + ReportCorruption(drop_size, "truncated record at end of file"); + return kEof; + } + } + + // Parse the header + const char* header = buffer_.data(); + const uint32_t a = static_cast<uint32_t>(header[4]) & 0xff; + const uint32_t b = static_cast<uint32_t>(header[5]) & 0xff; + const unsigned int type = header[6]; + const uint32_t length = a | (b << 8); + if (kHeaderSize + length > buffer_.size()) { + size_t drop_size = buffer_.size(); + buffer_.clear(); + ReportCorruption(drop_size, "bad record length"); + return kBadRecord; + } + + if (type == kZeroType && length == 0) { + // Skip zero length record without reporting any drops since + // such records are produced by the mmap based writing code in + // env_posix.cc that preallocates file regions. + buffer_.clear(); + return kBadRecord; + } + + // Check crc + if (checksum_) { + uint32_t expected_crc = crc32c::Unmask(DecodeFixed32(header)); + uint32_t actual_crc = crc32c::Value(header + 6, 1 + length); + if (actual_crc != expected_crc) { + // Drop the rest of the buffer since "length" itself may have + // been corrupted and if we trust it, we could find some + // fragment of a real log record that just happens to look + // like a valid log record. + size_t drop_size = buffer_.size(); + buffer_.clear(); + ReportCorruption(drop_size, "checksum mismatch"); + return kBadRecord; + } + } + + buffer_.remove_prefix(kHeaderSize + length); + + // Skip physical record that started before initial_offset_ + if (end_of_buffer_offset_ - buffer_.size() - kHeaderSize - length < + initial_offset_) { + result->clear(); + return kBadRecord; + } + + *result = Slice(header + kHeaderSize, length); + return type; + } +} + +} // namespace log +} // namespace leveldb |