size_t zlib_compression_reader::read_some()

in src/native/io/compressed/zlib_compression_reader.cpp [77:144]

• 47 lines of code
• 13 McCabe index (conditional complexity)

size_t zlib_compression_reader::read_some(std::span<char> buffer)
{
	auto to_read = static_cast<uInt>(buffer.size());

	m_zstr.next_out  = const_cast<Bytef *>(reinterpret_cast<const Bytef *>(buffer.data()));
	m_zstr.avail_out = to_read;

	uint64_t actual_read = 0;

	while (true)
	{
		bool last_chunk  = m_processed_bytes == m_uncompressed_input_size;
		auto flush_param = last_chunk ? Z_FINISH : Z_NO_FLUSH;

		auto ret = ::deflate(&m_zstr, flush_param);

		// if the state of compression is invalid, then error out
		if (ret == Z_STREAM_ERROR)
		{
			auto msg = "deflate() failed. ret: " + std::to_string(ret);
			throw errors::user_exception(errors::error_code::io_zlib_reader_deflate_failed, msg);
		}

		// If there's an issue with the buffers and we don't have any input for the deflate available,
		// then read some data and make it available. We'll call deflate again.
		if ((ret == Z_BUF_ERROR) && (m_zstr.avail_in == 0))
		{
			auto input_to_read = m_input_data.capacity();
			auto from_reader   = m_reader->read_some(std::span<char>{m_input_data.data(), input_to_read});

			m_zstr.next_in  = const_cast<Bytef *>(reinterpret_cast<const Bytef *>(m_input_data.data()));
			m_zstr.avail_in = static_cast<uInt>(from_reader);

			m_processed_bytes += from_reader;
			continue;
		}

		actual_read = m_zstr.total_out - m_read_offset;

		if (ret == Z_STREAM_END)
		{
			break;
		}

		// If there was no error and we've read everything
		if (ret == Z_OK && (m_processed_bytes == m_uncompressed_input_size))
		{
			break;
		}

		// If we've read as much as we expected and have no error or need more buffers then return
		if (((ret == Z_OK) || ret == (Z_BUF_ERROR)) && (actual_read == to_read))
		{
			break;
		}

		// Otherwise, if we are in some error state, throw an exception
		if (ret != Z_OK)
		{
			auto msg = "deflate() failed. ret: " + std::to_string(ret);
			throw errors::user_exception(errors::error_code::io_zlib_reader_deflate_failed, msg);
		}
	}

	m_read_offset = m_zstr.total_out;

	return actual_read;
}