Class ReversePadField

scapy/fields.py:661–687

Add bytes BEFORE the proxified field so that it starts at the specified alignment from its beginning

class ReversePadField(PadField):
    """Add bytes BEFORE the proxified field so that it starts at the specified
       alignment from its beginning"""

    def original_length(self, pkt):
        # type: (Packet) -> int
        return len(pkt.original)

    def getfield(self,
                 pkt,  # type: Packet
                 s,  # type: bytes
                 ):
        # type: (...) -> Tuple[bytes, Any]
        # We need to get the length that has already been dissected
        padlen = self.padlen(self.original_length(pkt) - len(s), pkt)
        return self.fld.getfield(pkt, s[padlen:])

    def addfield(self,
                 pkt,  # type: Packet
                 s,  # type: bytes
                 val,  # type: Any
                 ):
        # type: (...) -> bytes
        sval = self.fld.addfield(pkt, b"", val)
        return s + struct.pack("%is" % (
            self.padlen(len(s), pkt)
        ), self._padwith) + sval


class TrailerBytes(bytes):