def ConvertFromWireFormat(self, value, container=None):
    try:
      return unicode(value[2], "utf8")
    except UnicodeError:
      raise rdfvalue.DecodeError("Unicode decoding error")
Internally strings are utf8 encoded.
dataset/ETHPy150Open google/grr/grr/lib/rdfvalues/structs.py/ProtoString.ConvertFromWireFormat