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132 lines
4.1 KiB
132 lines
4.1 KiB
import struct
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import array
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import six
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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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if chunk_location is None:
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return None
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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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def read_array(fh, kind, chunk_location):
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kinds = {'double': 'd',
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'int': 'i',
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'float': 'f'}
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if kind not in kinds:
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raise ValueError('You attempted to read an array of an unknown type.')
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raw_data = read_chunk(fh, chunk_location)
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if raw_data is None:
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return None
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return array.array(kinds[kind], raw_data)
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def _parse_unsigned_char(data):
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return struct.unpack("B", data.read(1))[0]
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def _parse_unsigned_int(data):
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return struct.unpack("I", data.read(4))[0]
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def _parse_unsigned_long(data):
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return struct.unpack("Q", data.read(8))[0]
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def _parse_double(data):
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return struct.unpack("d", data.read(8))[0]
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def _parse_string(data):
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value = data.read(2)
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while not value.endswith(six.b("\x00\x00")):
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# the string ends at the first instance of \x00\x00
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value += data.read(2)
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return value.decode("utf16")[:-1].encode("utf8")
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def _parse_char_array(data):
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array_length = struct.unpack("Q", data.read(8))[0]
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return array.array("B", data.read(array_length))
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def _parse_metadata_item(data, cursor_position):
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"""
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Reads hierarchical data, analogous to a Python dict.
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"""
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new_count, length = struct.unpack("<IQ", data.read(12))
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length -= data.tell() - cursor_position
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next_data_length = data.read(length)
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value = read_metadata(next_data_length, new_count)
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# Skip some offsets
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data.read(new_count * 8)
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return value
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def _get_value(data, data_type, cursor_position):
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"""
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ND2s use various codes to indicate different data types, which we translate here.
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"""
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parser = {1: _parse_unsigned_char,
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2: _parse_unsigned_int,
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3: _parse_unsigned_int,
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5: _parse_unsigned_long,
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6: _parse_double,
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8: _parse_string,
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9: _parse_char_array,
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11: _parse_metadata_item}
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return parser[data_type](data) if data_type < 11 else parser[data_type](data, cursor_position)
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def read_metadata(data, count):
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"""
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Iterates over each element some section of the metadata and parses it.
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"""
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if data is None:
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return None
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data = six.BytesIO(data)
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metadata = {}
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for _ in range(count):
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cursor_position = data.tell()
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header = data.read(2)
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if not header:
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# We've reached the end of some hierarchy of data
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break
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if six.PY3:
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header = header.decode("utf8")
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data_type, name_length = map(ord, header)
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name = data.read(name_length * 2).decode("utf16")[:-1].encode("utf8")
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value = _get_value(data, data_type, cursor_position)
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if name not in metadata.keys():
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metadata[name] = value
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else:
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if not isinstance(metadata[name], list):
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# We have encountered this key exactly once before. Since we're seeing it again, we know we
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# need to convert it to a list before proceeding.
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metadata[name] = [metadata[name]]
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# We've encountered this key before so we're guaranteed to be dealing with a list. Thus we append
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# the value to the already-existing list.
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metadata[name].append(value)
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return metadata
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