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"""StarStruct element class.""" |
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import struct |
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import re |
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import enum |
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from starstruct.element import register, Element |
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from starstruct.modes import Mode |
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@register |
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class ElementNum(Element): |
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""" |
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A StarStruct element class for number fields. |
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""" |
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# pylint: disable=too-many-instance-attributes |
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def __init__(self, field, mode=Mode.Native, alignment=1): |
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"""Initialize a StarStruct element object.""" |
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# All of the type checks have already been performed by the class |
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# factory |
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self.name = field[0] |
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# The ref attribute is required for all elements, but the base element |
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# type does not have one |
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self.ref = None |
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self._mode = mode |
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self._alignment = alignment |
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# Validate that the format specifiers are valid struct formats, this |
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# doesn't have to be done now because the format will be checked when |
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# any struct functions are called, but it's better to inform the user of |
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# any errors earlier. |
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# The easiest way to perform this check is to create a "Struct" class |
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# instance, this will also increase the efficiency of all struct related |
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# functions called. |
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self.format = mode.value + field[1] |
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self._struct = struct.Struct(self.format) |
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# for numeric elements we should also keep track of how many numeric |
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# fields and what the size of those fields are required to create this |
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# element. |
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self._bytes = struct.calcsize(self.format[-1]) |
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self._signed = self.format[-1] in 'bhilq' |
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@staticmethod |
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def valid(field): |
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""" |
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Validation function to determine if a field tuple represents a valid |
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base element type. |
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The basics have already been validated by the Element factory class, |
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validate the specific struct format now. |
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""" |
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return len(field) == 2 \ |
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and isinstance(field[1], str) \ |
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and re.match(r'\d*[bBhHiIlLqQ]', field[1]) |
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def validate(self, msg): |
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""" |
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Ensure that the supplied message contains the required information for |
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this element object to operate. |
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The "number" element requires no further validation. |
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""" |
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pass |
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def update(self, mode=None, alignment=None): |
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"""change the mode of the struct format""" |
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if alignment: |
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self._alignment = alignment |
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if mode: |
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self._mode = mode |
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self.format = mode.value + self.format[1:] |
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# recreate the struct with the new format |
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self._struct = struct.Struct(self.format) |
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def pack(self, msg): |
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"""Pack the provided values into the supplied buffer.""" |
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# Take a single numeric value and convert it into the necessary list |
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# of values required by the specified format. |
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val = msg[self.name] |
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# This should be a number, but handle cases where it's an enum |
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if isinstance(val, enum.Enum): |
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val = val.value |
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# If the value supplied is not already a bytes object, convert it now. |
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if isinstance(val, (bytes, bytearray)): |
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val_list = val |
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else: |
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val_list = val.to_bytes(struct.calcsize(self.format), |
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byteorder=self._mode.to_byteorder(), |
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signed=self._signed) |
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# join the byte list into the expected number of values to pack the |
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# specified struct format. |
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val = [int.from_bytes(val_list[i:i + self._bytes], # pylint: disable=no-member |
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byteorder=self._mode.to_byteorder(), |
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signed=self._signed) |
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for i in range(0, len(val_list), self._bytes)] |
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data = self._struct.pack(*val) |
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# If the data does not meet the alignment, add some padding |
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missing_bytes = len(data) % self._alignment |
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if missing_bytes: |
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data += b'\x00' * missing_bytes |
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return data |
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def unpack(self, msg, buf): |
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"""Unpack data from the supplied buffer using the initialized format.""" |
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ret = self._struct.unpack_from(buf, 0) |
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# Remember to remove any alignment-based padding |
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extra_bytes = self._alignment - 1 - (struct.calcsize(self.format) % |
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self._alignment) |
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unused = buf[struct.calcsize(self.format) + extra_bytes:] |
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# merge the unpacked data into a byte array |
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data = [v.to_bytes(self._bytes, byteorder=self._mode.to_byteorder(), |
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signed=self._signed) for v in ret] |
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# Join the returned list of numbers into a single value |
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val = int.from_bytes(b''.join(data), # pylint: disable=no-member |
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byteorder=self._mode.to_byteorder(), |
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signed=self._signed) |
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return (val, unused) |
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def make(self, msg): |
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"""Return the expected "made" value""" |
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val = msg[self.name] |
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# This should be a number, but handle cases where it's an enum |
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if isinstance(val, enum.Enum): |
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val = val.value |
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elif isinstance(val, list): |
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# It's unlikely but possible that this could be a list of numbers, |
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# or a list of bytes |
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if all(isinstance(v, bytes) for v in val): |
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# To turn this into a single number, merge the bytes, later the |
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# bytes will be converted into a single number. |
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data = b''.join(val) |
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elif all(isinstance(v, int) for v in val): |
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# To turn this into a single number, convert the numbers into |
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# bytes, and merge the bytes, later the bytes will be converted |
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# into a single number. |
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data = [v.to_bytes(self._bytes, |
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byteorder=self._mode.to_byteorder(), |
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signed=self._signed) for v in val] |
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else: |
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error = 'Invalid value for numerical element: {}' |
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raise TypeError(error.format(val)) |
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elif isinstance(val, bytes): |
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# If the value supplied is a bytes object, convert it to a number |
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data = val |
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elif isinstance(val, int): |
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return val |
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else: |
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error = 'Invalid value for numerical element: {}' |
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raise TypeError(error.format(val)) |
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return int.from_bytes(data, # pylint: disable=no-member |
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byteorder=self._mode.to_byteorder(), |
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signed=self._signed) |
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sprout42 /
StarStruct
Generally, there is nothing wrong with usage of
*or**arguments. For readability of the code base, we suggest to not over-use these language constructs though.For more information, we can recommend this blog post from Ned Batchelder including its comments which also touches this aspect.