class ExampleStructure(destructify.Structure):
some_number = destructify.IntegerField(default=0x13,
length=4,
byte_order='little',
signed=True)
length = destructify.IntegerField(length=1)
data = destructify.FixedLengthField(length='length')
class PngChunk_IHDR(destructify.Structure):
width = destructify.IntegerField(4, "big")
height = destructify.IntegerField(4, "big")
bit_depth = destructify.IntegerField(1)
color_type = destructify.EnumField(destructify.IntegerField(1), ColorType)
compression_method = destructify.IntegerField(1)
filter_method = destructify.IntegerField(1)
interlace_method = destructify.EnumField(destructify.IntegerField(1), InterlaceMethod)
class PngChunk(destructify.Structure):
length = destructify.IntegerField(4, "big")
chunk_type = destructify.EnumField(destructify.StringField(length=4, encoding="ascii"), enum=ChunkType)
chunk_data = destructify.SwitchField(
cases={
ChunkType.IHDR: destructify.StructureField(PngChunk_IHDR, length='length'),
ChunkType.IEND: destructify.ConstantField(b""),
ChunkType.TEXT: destructify.StructureField(PngChunk_tEXt, length='length'),
ChunkType.PHYS: destructify.StructureField(PngChunk_pHYs, length='length'),
ChunkType.PLTE: destructify.StructureField(PngChunk_PLTE, length='length'),
},
switch="chunk_type",
other=destructify.FixedLengthField("length")
)
crc = destructify.IntegerField(4, "big", override=lambda f, v: calculate_crc(f))
class Meta:
capture_raw = True
checks = [
lambda f: f._context.fields['chunk_data'].length == f.length,
lambda f: calculate_crc(f) == f.crc,
]
class PngChunk_pHYs(destructify.Structure):
pixels_per_unit_x = destructify.IntegerField(4, "big")
pixels_per_unit_y = destructify.IntegerField(4, "big")
unit = destructify.EnumField(destructify.IntegerField(1), PhysUnit)
class PaletteEntry(destructify.Structure):
red = destructify.IntegerField(length=1)
green = destructify.IntegerField(length=1)
blue = destructify.IntegerField(length=1)