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"""StarStruct element class.""" |
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import struct |
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import re |
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from starstruct.element import register, Element |
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from starstruct.modes import Mode |
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from starstruct.bitfield import BitField |
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from starstruct.packedbitfield import PackedBitField |
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@register |
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class ElementBitField(Element): |
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""" |
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The bitfield StarStruct element class. |
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""" |
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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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self.ref = field[2] |
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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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@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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enum element type. |
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The basics have already been validated by the Element factory class, |
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validate that the struct format is a valid numeric value. |
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Signed fields are not allowed, bit manipulation does not work well |
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""" |
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return (len(field) == 3 and |
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isinstance(field[1], str) and |
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re.match(r'\d*[BHILQN]', field[1]) and |
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isinstance(field[2], (BitField, PackedBitField))) |
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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 "enum" 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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# Turn the enum value list into a single number and pack it into the |
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# specified format |
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data = self._struct.pack(self.ref.pack(msg[self.name])) |
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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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# Convert the returned value to the referenced BitField type |
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try: |
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member = self.ref.unpack(ret[0]) |
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except ValueError as e: |
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raise ValueError( |
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'Value: {0} was not valid for {1}\n\twith msg: {2},\n\tbuf: {3}'.format( |
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ret[0], self.ref, msg, buf |
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)).with_traceback(e.__traceback__) |
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return (member, unused) |
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def make(self, msg): |
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"""Return the "transformed" value for this element""" |
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return self.ref.make(msg[self.name]) |
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sprout42 /
StarStruct
