Patches file attributes in ZIP files

modzip.py

#!/usr/bin/python
#
# modifies zip file attributes
# 2015.07.01 darell tan
#

from zipfile import *
import struct
import sys

eocdStruct = '<4s4H2LH'
sizeEndCentDir = struct.calcsize(eocdStruct)

cdStruct = '<4s4B4HL2L5H2L'
sizeCentDir = struct.calcsize(cdStruct)

FILE_ATTRIBUTE_NOT_CONTENT_INDEXED = 0x2000
FILE_ATTRIBUTE_ENCRYPTED = 0x4000

# don't write any changes
_NOOP = False

def main():
	# get EoCD record
	f = open(sys.argv[1], 'r+b')
	f.seek(-sizeEndCentDir, 2)

	data = f.read()
	if data[0:4] == 'PK\005\006' and data[-2:] == '\000\000':
		eocd = struct.unpack(eocdStruct, data)
		cdSizeTotal, cdOffset = eocd[5:7]

		f.seek(cdOffset)
	else:
		# maybe there's a comment?
		# i'm not gonna find it - see zipfile.py for details
		assert False, "can't find end of central directory"

	cdCount = 0
	while cdCount < cdSizeTotal:
		#print "cd @", f.tell()
		centDir = struct.unpack(cdStruct, f.read(sizeCentDir))
		assert centDir[0] == 'PK\001\002'

		createVer, createOs = centDir[1:3]
		nameLen, extraLen, commentLen = centDir[12:15]
		extAttrib = centDir[17]
		name = f.read(nameLen)

		print '%s\t%x' % (name, extAttrib)

		# advance to next central directory
		cdSize = sizeCentDir + nameLen + extraLen + commentLen
		cdCount += cdSize
		f.seek(extraLen + commentLen, 1)
		#print "end cd @", f.tell()

		# make modifications here
		if createOs == 0:
			#print 'modifying ext attrib @', f.tell()
			f.seek(-cdSize + 38, 1)
			assert struct.unpack('<L', f.read(4))[0] == extAttrib

			# overwrite
			extAttrib = extAttrib & ~FILE_ATTRIBUTE_ENCRYPTED
			if not _NOOP:
				f.seek(-4, 1)
				f.write(struct.pack('<L', extAttrib))

			f.seek(cdSize - 38 - 4, 1)

	#print "cd end @ ", f.tell()

	f.close()


if __name__ == '__main__':
	main()