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86 lines
2.5 KiB
86 lines
2.5 KiB
3 years ago
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# 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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import dns.exception
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import dns.name
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class Parser:
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def __init__(self, wire, current=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):
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return self.end - self.current
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def get_bytes(self, size):
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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=1):
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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):
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return self.get_bytes(self.remaining())
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def get_uint8(self):
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return struct.unpack('!B', self.get_bytes(1))[0]
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def get_uint16(self):
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return struct.unpack('!H', self.get_bytes(2))[0]
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def get_uint32(self):
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return struct.unpack('!I', self.get_bytes(4))[0]
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def get_uint48(self):
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return int.from_bytes(self.get_bytes(6), 'big')
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def get_struct(self, format):
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return struct.unpack(format, self.get_bytes(struct.calcsize(format)))
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def get_name(self, origin=None):
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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):
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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):
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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):
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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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