import zlib
import struct
def parse(input):
"""Parses the header information from an SWF file."""
if hasattr(input, 'read'):
input.seek(0)
else:
input = open(input, 'rb')
def read_ui8(c):
return struct.unpack('<B', c)[0]
def read_ui16(c):
return struct.unpack('<H', c)[0]
def read_ui32(c):
return struct.unpack('<I', c)[0]
header = {}
# Read the 3-byte signature field
signature = ''.join(struct.unpack('<3c', input.read(3)))
if signature not in ('FWS', 'CWS'):
raise ValueError('Invalid SWF signature: %s' % signature)
# Compression
header['compressed'] = signature.startswith('C')
# Version
header['version'] = read_ui8(input.read(1))
# File size (stored as a 32-bit integer)
header['size'] = read_ui32(input.read(4))
# Payload
buffer = input.read(header['size'])
if header['compressed']:
# Unpack the zlib compression
buffer = zlib.decompress(buffer)
# Containing rectangle (struct RECT)
# The number of bits used to store the each of the RECT values are
# stored in first five bits of the first byte.
nbits = read_ui8(buffer[0]) >> 3
current_byte, buffer = read_ui8(buffer[0]), buffer[1:]
bit_cursor = 5
for item in 'xmin', 'xmax', 'ymin', 'ymax':
value = 0
for value_bit in range(nbits-1, -1, -1): # == reversed(range(nbits))
if (current_byte << bit_cursor) & 0x80:
value |= 1 << value_bit
# Advance the bit cursor to the next bit
bit_cursor += 1
if bit_cursor > 7:
# We've exhausted the current byte, consume the next one
# from the buffer.
current_byte, buffer = read_ui8(buffer[0]), buffer[1:]
bit_cursor = 0
# Convert value from TWIPS to a pixel value
header[item] = value / 20
header['width'] = header['xmax'] - header['xmin']
header['height'] = header['ymax'] - header['ymin']
header['frames'] = read_ui16(buffer[0:2])
header['fps'] = read_ui16(buffer[2:4])
input.close()
return header
def main():
import sys
if len(sys.argv) < 2:
print 'Usage: %s [SWF file]' % sys.argv[0]
sys.exit(1)
header = parse(sys.argv[1])
print 'SWF header'
print '----------'
print 'Version: %s' % header['version']
print 'Compression: %s' % header['compressed']
print 'Dimensions: %s x %s' % (header['width'], header['height'])
print 'Bounding box: (%s, %s, %s, %s)' % (header['xmin'], header['xmax'], header['ymin'], header['ymax'])
print 'Frames: %s' % header['frames']
print 'FPS: %s' % header['fps']
