62 lines
2.0 KiB
Python
62 lines
2.0 KiB
Python
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# Copyright 2021 The Android Open Source Project
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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#
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import struct
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class PackedStruct(object):
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"""Class representing a C style packed structure
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Derived classes need to provide a dictionary with key will be the attributes and the values are
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the format characters for each field. e.g.
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class Foo(PackedStruct):
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_FIELDS = {
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x: 'I',
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name: '64s',
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}
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In this case Foo.x will represent an "unsigned int" C value, while Foo.name will be a "char[64]"
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C value
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"""
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def __init__(self, *args, **kwargs):
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self._fmt = '<' + ''.join(fmt for fmt in self._FIELDS.values())
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for name in self._FIELDS:
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setattr(self, name, None)
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for name, val in zip(self._FIELDS.keys(), args):
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setattr(self, name, val)
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for name, val in kwargs.items():
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setattr(self, name, val)
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def __repr__(self):
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return '{} {{\n'.format(self.__class__.__name__) + ',\n'.join(
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' {!r}: {!r}'.format(k, getattr(self, k)) for k in self._FIELDS) + '\n}'
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def __str__(self):
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return struct.pack(self._fmt, *(getattr(self, x) for x in self._FIELDS))
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def __bytes__(self):
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return struct.pack(self._fmt, *(getattr(self, x) for x in self._FIELDS))
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def __len__(self):
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return struct.calcsize(self._fmt)
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@classmethod
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def from_bytes(cls, data):
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fmt_str = '<' + ''.join(fmt for fmt in cls._FIELDS.values())
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return cls(*struct.unpack(fmt_str, data))
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