| // 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) { |
| // This can be caused by the writer dying immediately after |
| // writing a physical record but before completing the next; don't |
| // treat it as a corruption, just ignore the entire logical record. |
| 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(uint64_t bytes, const char* reason) { |
| ReportDrop(bytes, Status::Corruption(reason)); |
| } |
| |
| void Reader::ReportDrop(uint64_t bytes, const Status& reason) { |
| if (reporter_ != NULL && |
| end_of_buffer_offset_ - buffer_.size() - bytes >= initial_offset_) { |
| reporter_->Corruption(static_cast<size_t>(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 { |
| // Note that if buffer_ is non-empty, we have a truncated header at the |
| // end of the file, which can be caused by the writer crashing in the |
| // middle of writing the header. Instead of considering this an error, |
| // just report EOF. |
| buffer_.clear(); |
| 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(); |
| if (!eof_) { |
| ReportCorruption(drop_size, "bad record length"); |
| return kBadRecord; |
| } |
| // If the end of the file has been reached without reading |length| bytes |
| // of payload, assume the writer died in the middle of writing the record. |
| // Don't report a corruption. |
| return kEof; |
| } |
| |
| 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 |