code: async def read_chunk(self, size: int=chunk_size) -> bytes:
          
          if self._at_eof:
              return b''
          if self._length:
              chunk = await self._read_chunk_from_length(size)
          else:
              chunk = await self._read_chunk_from_stream(size)
  
          self._read_bytes += len(chunk)
          if self._read_bytes == self._length:
              self._at_eof = True
          if self._at_eof:
              newline = await self._content.readline()
              assert newline == self._newline, \
                  'reader did not read all the data or it is malformed'
          return chunk
docs: Reads body part content chunk of the specified size.
  
          size: chunk size