Class BitStringPayloadDecoder

pager_lib/pyasn1/codec/ber/decoder.py:165–293

class BitStringPayloadDecoder(AbstractSimplePayloadDecoder):
    protoComponent = univ.BitString(())
    supportConstructedForm = True

    def valueDecoder(self, substrate, asn1Spec,
                     tagSet=None, length=None, state=None,
                     decodeFun=None, substrateFun=None,
                     **options):

        if substrateFun:
            asn1Object = self._createComponent(asn1Spec, tagSet, noValue, **options)

            for chunk in substrateFun(asn1Object, substrate, length, options):
                yield chunk

            return

        if not length:
            raise error.PyAsn1Error('Empty BIT STRING substrate')

        for chunk in isEndOfStream(substrate):
            if isinstance(chunk, SubstrateUnderrunError):
                yield chunk

        if chunk:
            raise error.PyAsn1Error('Empty BIT STRING substrate')

        if tagSet[0].tagFormat == tag.tagFormatSimple:  # XXX what tag to check?

            for trailingBits in readFromStream(substrate, 1, options):
                if isinstance(trailingBits, SubstrateUnderrunError):
                    yield trailingBits

            trailingBits = ord(trailingBits)
            if trailingBits > 7:
                raise error.PyAsn1Error(
                    'Trailing bits overflow %s' % trailingBits
                )

            for chunk in readFromStream(substrate, length - 1, options):
                if isinstance(chunk, SubstrateUnderrunError):
                    yield chunk

            value = self.protoComponent.fromOctetString(
                chunk, internalFormat=True, padding=trailingBits)

            yield self._createComponent(asn1Spec, tagSet, value, **options)

            return

        if not self.supportConstructedForm:
            raise error.PyAsn1Error('Constructed encoding form prohibited '
                                    'at %s' % self.__class__.__name__)

        if LOG:
            LOG('assembling constructed serialization')

        # All inner fragments are of the same type, treat them as octet string