90 lines
2.8 KiB
Python
90 lines
2.8 KiB
Python
# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
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import contextlib
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import struct
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from typing import Iterator, Optional, Tuple
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import dns.exception
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import dns.name
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class Parser:
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def __init__(self, wire: bytes, current: int = 0):
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self.wire = wire
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self.current = 0
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self.end = len(self.wire)
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if current:
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self.seek(current)
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self.furthest = current
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def remaining(self) -> int:
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return self.end - self.current
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def get_bytes(self, size: int) -> bytes:
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assert size >= 0
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if size > self.remaining():
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raise dns.exception.FormError
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output = self.wire[self.current : self.current + size]
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self.current += size
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self.furthest = max(self.furthest, self.current)
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return output
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def get_counted_bytes(self, length_size: int = 1) -> bytes:
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length = int.from_bytes(self.get_bytes(length_size), "big")
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return self.get_bytes(length)
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def get_remaining(self) -> bytes:
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return self.get_bytes(self.remaining())
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def get_uint8(self) -> int:
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return struct.unpack("!B", self.get_bytes(1))[0]
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def get_uint16(self) -> int:
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return struct.unpack("!H", self.get_bytes(2))[0]
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def get_uint32(self) -> int:
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return struct.unpack("!I", self.get_bytes(4))[0]
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def get_uint48(self) -> int:
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return int.from_bytes(self.get_bytes(6), "big")
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def get_struct(self, format: str) -> Tuple:
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return struct.unpack(format, self.get_bytes(struct.calcsize(format)))
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def get_name(self, origin: Optional["dns.name.Name"] = None) -> "dns.name.Name":
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name = dns.name.from_wire_parser(self)
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if origin:
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name = name.relativize(origin)
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return name
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def seek(self, where: int) -> None:
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# Note that seeking to the end is OK! (If you try to read
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# after such a seek, you'll get an exception as expected.)
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if where < 0 or where > self.end:
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raise dns.exception.FormError
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self.current = where
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@contextlib.contextmanager
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def restrict_to(self, size: int) -> Iterator:
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assert size >= 0
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if size > self.remaining():
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raise dns.exception.FormError
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saved_end = self.end
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try:
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self.end = self.current + size
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yield
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# We make this check here and not in the finally as we
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# don't want to raise if we're already raising for some
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# other reason.
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if self.current != self.end:
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raise dns.exception.FormError
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finally:
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self.end = saved_end
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@contextlib.contextmanager
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def restore_furthest(self) -> Iterator:
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try:
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yield None
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finally:
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self.current = self.furthest
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