107 lines
3.1 KiB
Python
Executable File
107 lines
3.1 KiB
Python
Executable File
import struct
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import zlib
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def parse(input):
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"""Parses the header information from an SWF file."""
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if hasattr(input, 'read'):
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input.seek(0)
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else:
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input = open(input, 'rb')
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def read_ui8(c):
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return struct.unpack('<B', c)[0]
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def read_ui16(c):
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return struct.unpack('<H', c)[0]
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def read_ui32(c):
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return struct.unpack('<I', c)[0]
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header = {}
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# Read the 3-byte signature field
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signature = ''.join(struct.unpack('<3c', input.read(3)))
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if signature not in ('FWS', 'CWS'):
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raise ValueError('Invalid SWF signature: %s' % signature)
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# Compression
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header['compressed'] = signature.startswith('C')
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# Version
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header['version'] = read_ui8(input.read(1))
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# File size (stored as a 32-bit integer)
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header['size'] = read_ui32(input.read(4))
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# Payload
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buffer = input.read(header['size'])
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if header['compressed']:
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# Unpack the zlib compression
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buffer = zlib.decompress(buffer)
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# Containing rectangle (struct RECT)
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# The number of bits used to store the each of the RECT values are
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# stored in first five bits of the first byte.
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nbits = read_ui8(buffer[0]) >> 3
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current_byte, buffer = read_ui8(buffer[0]), buffer[1:]
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bit_cursor = 5
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for item in 'xmin', 'xmax', 'ymin', 'ymax':
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value = 0
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for value_bit in range(nbits - 1, -1, -1): # == reversed(range(nbits))
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if (current_byte << bit_cursor) & 0x80:
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value |= 1 << value_bit
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# Advance the bit cursor to the next bit
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bit_cursor += 1
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if bit_cursor > 7:
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# We've exhausted the current byte, consume the next one
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# from the buffer.
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current_byte, buffer = read_ui8(buffer[0]), buffer[1:]
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bit_cursor = 0
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# Convert value from TWIPS to a pixel value
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header[item] = value / 20
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header['width'] = header['xmax'] - header['xmin']
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header['height'] = header['ymax'] - header['ymin']
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# Appendix A of the SWF specification states the following about the FPS
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# field:
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#
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# [FPS] is supposed to be stored as a 16-bit integer, but the first
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# byte (or last depending on how you look at it) is completely ignored.
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#
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# We handle this by parsing the value as UI16 and taking only the first
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# byte as the value.
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header['fps'] = read_ui16(buffer[0:2]) >> 8
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header['frames'] = read_ui16(buffer[2:4])
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input.close()
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return header
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def main():
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import sys
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if len(sys.argv) < 2:
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print 'Usage: %s [SWF file]' % sys.argv[0]
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sys.exit(1)
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header = parse(sys.argv[1])
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print 'SWF header'
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print '----------'
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print 'Version: %s' % header['version']
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print 'Compression: %s' % header['compressed']
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print 'Dimensions: %s x %s' % (header['width'], header['height'])
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print 'Bounding box: (%s, %s, %s, %s)' % (header['xmin'], header['xmax'], header['ymin'], header['ymax'])
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print 'Frames: %s' % header['frames']
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print 'FPS: %s' % header['fps']
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if __name__ == '__main__':
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main()
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