xarextract.py

#! /usr/bin/python -u
from collections import namedtuple
import xml.etree.cElementTree as ET
import io,zlib,sys,struct,os
from tempfile import mkdtemp, mkstemp
from subprocess import Popen, PIPE

def decode_xar_header(header_bytes):
	header_fmt = '>4sHHQQI'
	XARHeader = namedtuple('XARHeader', 'magic size version toc_length_compressed toc_length_uncompressed chksum_alg')
	header = XARHeader._make(struct.unpack_from(header_fmt, header_bytes))
	if header.magic != 'xar!':
		raise Exception('Wrong magic %s'%header.magic)
	return header

def extract_toc(header, xar):
	toc = zlib.decompress(xar.read(header.toc_length_compressed))
	if header.toc_length_uncompressed != len(toc):
		raise Exception('Wrong toc length')
	return toc

def extract_xar(xar):
	with open(xar, mode='rb') as f:
		try:
			header = decode_xar_header(f.read(28))
			toc = extract_toc(header, f)
			tree = ET.fromstring(toc)
			for e in ET.ElementPath.findall(tree, "toc/file"):
				if e.find('name').text == 'Payload':
					data = e.find('data')
					length = long(data.find('length').text)
					size = long(data.find('size').text)
					payload_offset = long(data.find('offset').text)
			sys.stderr.write('%s: Payload at offset %d, %d (%d) bytes long\n'%(xar, payload_offset, length, size))
			f.seek(payload_offset, os.SEEK_CUR)
			tempdir = mkdtemp(prefix=os.path.basename(xar))
			p = Popen(['cpio', '-i', '--quiet'], stdin=PIPE, stdout=PIPE, stderr=PIPE, cwd=tempdir)
			d = zlib.decompressobj(-zlib.MAX_WBITS)
			gzip_header = f.read(10)
			data = f.read(length)
			io = p.communicate(input=d.decompress(data))
			if io[1] == '':
				print tempdir
			else:
				print "Error: %s"%io[1]
		finally:
			f.close()

def main(argv):
	if argv[1] == '-x':
		extract_xar(argv[2])
	else:
		with io.open(sys.argv[1], mode='rb') as f:
			try:
				if len(argv) > 1:
					offsets = argv[2:]
				for e in offsets:
					extract_xar(f, e)
			finally:
				f.close()

sys.exit(main(sys.argv))