'Makes sure that the received data represents a valid number.
Checks if C{self._remainingData} represents a number smaller or
equal to C{self.MAX_LENGTH}.
@raise NetstringParseError: if C{self._remainingData} is no
number or is too big (checked by L{_extractLength}).'

def _checkPartialLengthSpecification(self):

    partialLengthMatch = self._LENGTH_PREFIX.match(self._remainingData)
    if (not partialLengthMatch):
        raise NetstringParseError(self._MISSING_LENGTH)
    lengthSpecification = partialLengthMatch.group(1)
    self._extractLength(lengthSpecification)
