Method TestReads

cpp/src/arrow/io/buffered_test.cc:953–988

  }

  void TestReads() {
    std::default_random_engine gen(/*seed*/ 42);
    std::uniform_int_distribution<int64_t> read_len_dist(1, 80);

    int64_t pos = 0;
    const int64_t size = static_cast<int64_t>(data_.size());
    while (pos < size) {
      const int64_t read_len = read_len_dist(gen);
      ASSERT_OK_AND_ASSIGN(auto buf, buffered_->Read(read_len));
      AssertBufferEqual(*buf, std::string_view(data_).substr(pos, read_len));
      pos += buf->size();
    }

    // EOF was reached
    ASSERT_EQ(pos, size);

    // Number of reads should not be excessive given the buffer size
    int64_t max_reads = (size + buffer_size_ - 1) / buffer_size_;
    EXPECT_LE(tracked_->num_reads(), max_reads);
    const auto& read_ranges = tracked_->get_read_ranges();
    pos = 0;
    for (size_t i = 0; i < read_ranges.size(); ++i) {
      const auto cur = read_ranges[i];
      ASSERT_EQ(cur.offset, pos);
      // Never read less than buffer size bytes, except perhaps if fewer bytes remain
      ASSERT_GE(cur.length, std::min(buffer_size_, size - pos));
      // Bump actual position in the file
      pos += std::min(cur.length, size - pos);
    }

    // Further reads return an empty buffer
    ASSERT_OK_AND_ASSIGN(auto buf, buffered_->Read(buffer_size_ - 1));
    AssertBufferEqual(*buf, "");
    ASSERT_OK_AND_ASSIGN(buf, buffered_->Read(buffer_size_ + 1));
    AssertBufferEqual(*buf, "");
  }

 protected:
  std::string data_;