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24 lines
830 B
24 lines
830 B
import struct
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def read_chunk(fh, chunk_location):
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"""
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Reads a piece of data given the location of its pointer.
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:param fh: an open file handle to the ND2
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:param chunk_location: a pointer
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:type chunk_location: int
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:rtype: bytes
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"""
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fh.seek(chunk_location)
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# The chunk metadata is always 16 bytes long
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chunk_metadata = fh.read(16)
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header, relative_offset, data_length = struct.unpack("IIQ", chunk_metadata)
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if header != 0xabeceda:
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raise ValueError("The ND2 file seems to be corrupted.")
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# We start at the location of the chunk metadata, skip over the metadata, and then proceed to the
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# start of the actual data field, which is at some arbitrary place after the metadata.
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fh.seek(chunk_location + 16 + relative_offset)
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return fh.read(data_length)
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