def _SimpleDecoder(wire_type, decode_value):
  """Return a constructor for a decoder for fields of a particular type.

  Args:
      wire_type:  The field's wire type.
      decode_value:  A function which decodes an individual value, e.g.
        _DecodeVarint()
  """

  def SpecificDecoder(field_number, is_repeated, is_packed, key, new_default,
                      clear_if_default=False):
    if is_packed:
      local_DecodeVarint = _DecodeVarint
      def DecodePackedField(buffer, pos, end, message, field_dict):
        value = field_dict.get(key)
        if value is None:
          value = field_dict.setdefault(key, new_default(message))
        (endpoint, pos) = local_DecodeVarint(buffer, pos)
        endpoint += pos
        if endpoint > end:
          raise _DecodeError('Truncated message.')
        while pos < endpoint:
          (element, pos) = decode_value(buffer, pos)
          value.append(element)
        if pos > endpoint:
          del value[-1]   # Discard corrupt value.
          raise _DecodeError('Packed element was truncated.')
        return pos
      return DecodePackedField
    elif is_repeated:
      tag_bytes = encoder.TagBytes(field_number, wire_type)
      tag_len = len(tag_bytes)
      def DecodeRepeatedField(buffer, pos, end, message, field_dict):
        value = field_dict.get(key)
        if value is None:
          value = field_dict.setdefault(key, new_default(message))
        while 1:
          (element, new_pos) = decode_value(buffer, pos)
          value.append(element)
          # Predict that the next tag is another copy of the same repeated
          # field.
          pos = new_pos + tag_len
          if buffer[new_pos:pos] != tag_bytes or new_pos >= end:
            # Prediction failed.  Return.
            if new_pos > end:
              raise _DecodeError('Truncated message.')
            return new_pos
      return DecodeRepeatedField
    else:
      def DecodeField(buffer, pos, end, message, field_dict):
        (new_value, pos) = decode_value(buffer, pos)
        if pos > end:
          raise _DecodeError('Truncated message.')
        if clear_if_default and not new_value:
          field_dict.pop(key, None)
        else:
          field_dict[key] = new_value
        return pos
      return DecodeField

  return SpecificDecoder
Return a constructor for a decoder for fields of a particular type.

  Args:
      wire_type:  The field's wire type.
      decode_value:  A function which decodes an individual value, e.g.
        _DecodeVarint()
  
deps/protobuf/python/google/protobuf/internal/decoder.py