bool Reader::ReadRecord()

in db/log_reader.cc [59:164]

• 85 lines of code
• 19 McCabe index (conditional complexity)

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;
}