Class ASN1F_optional

scapy/asn1fields.py:643–684

ASN.1 field that is optional.

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class ASN1F_optional(ASN1F_element):
    """
    ASN.1 field that is optional.
    """
    def __init__(self, field):
        # type: (ASN1F_field[Any, Any]) -> None
        field.flexible_tag = False
        self._field = field

    def __getattr__(self, attr):
        # type: (str) -> Optional[Any]
        return getattr(self._field, attr)

    def m2i(self, pkt, s):
        # type: (ASN1_Packet, bytes) -> Tuple[Any, bytes]
        try:
            return self._field.m2i(pkt, s)
        except (ASN1_Error, ASN1F_badsequence, BER_Decoding_Error):
            # ASN1_Error may be raised by ASN1F_CHOICE
            return None, s

    def dissect(self, pkt, s):
        # type: (ASN1_Packet, bytes) -> bytes
        try:
            return self._field.dissect(pkt, s)
        except (ASN1_Error, ASN1F_badsequence, BER_Decoding_Error):
            self._field.set_val(pkt, None)
            return s

    def build(self, pkt):
        # type: (ASN1_Packet) -> bytes
        if self._field.is_empty(pkt):
            return b""
        return self._field.build(pkt)

    def any2i(self, pkt, x):
        # type: (ASN1_Packet, Any) -> Any
        return self._field.any2i(pkt, x)

    def i2repr(self, pkt, x):
        # type: (ASN1_Packet, Any) -> str
        return self._field.i2repr(pkt, x)


class ASN1F_omit(ASN1F_field[None, None]):