Class Parser

dns/wire.py:11–98

Helper class for parsing DNS wire format.

class Parser:
    """Helper class for parsing DNS wire format."""

    def __init__(self, wire: bytes, current: int = 0):
        """Initialize a Parser

        *wire*, a ``bytes`` contains the data to be parsed, and possibly other data.
        Typically it is the whole message or a slice of it.

        *current*, an `int`, the offset within *wire* where parsing should begin.
        """
        self.wire = wire
        self.current = 0
        self.end = len(self.wire)
        if current:
            self.seek(current)
        self.furthest = current

    def remaining(self) -> int:
        return self.end - self.current

    def get_bytes(self, size: int) -> bytes:
        assert size >= 0
        if size > self.remaining():
            raise dns.exception.FormError
        output = self.wire[self.current : self.current + size]
        self.current += size
        self.furthest = max(self.furthest, self.current)
        return output

    def get_counted_bytes(self, length_size: int = 1) -> bytes:
        length = int.from_bytes(self.get_bytes(length_size), "big")
        return self.get_bytes(length)

    def get_remaining(self) -> bytes:
        return self.get_bytes(self.remaining())

    def get_uint8(self) -> int:
        return struct.unpack("!B", self.get_bytes(1))[0]

    def get_uint16(self) -> int:
        return struct.unpack("!H", self.get_bytes(2))[0]

    def get_uint32(self) -> int:
        return struct.unpack("!I", self.get_bytes(4))[0]

    def get_uint48(self) -> int:
        return int.from_bytes(self.get_bytes(6), "big")

    def get_struct(self, format: str) -> Tuple:
        return struct.unpack(format, self.get_bytes(struct.calcsize(format)))

    def get_name(self, origin: Optional["dns.name.Name"] = None) -> "dns.name.Name":
        name = dns.name.from_wire_parser(self)
        if origin:
            name = name.relativize(origin)
        return name