docs: def encode_bytes(src_buf, dst_file):
      """Encode a buffer length followed by the bytes of the buffer
      itself.
  
      Parameters
      ----------
      src_buf: bytes
          Source bytes to be encoded.  Function asserts that
          0 <= len(src_buf) <= 2**16-1.
      dst_file: file
          File-like object with write method.
  
      Returns
      -------
      int
          Number of bytes written to `dst_file`.
      """
      if not isinstance(src_buf, bytes):
          raise TypeError('src_buf must by bytes.')
  
      len_src_buf = len(src_buf)
      assert 0 <= len_src_buf <= 2**16-1
      num_written_bytes = len_src_buf + 2
  
      len_buf = FIELD_U16.pack(len_src_buf)
      dst_file.write(len_buf)
      dst_file.write(src_buf)
  
      return num_written_bytes