py7zlib.py

#!/usr/bin/python -u
#
# Python Bindings for LZMA
#
# Copyright (c) 2004-2015 by Joachim Bauch, mail@joachim-bauch.de
# 7-Zip Copyright (C) 1999-2010 Igor Pavlov
# LZMA SDK Copyright (C) 1999-2010 Igor Pavlov
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
# $Id$
#
"""Read from and write to 7zip format archives.
"""

from array import array
from binascii import unhexlify
from datetime import datetime
import pylzma
from struct import pack, unpack
from zlib import crc32
import zlib
import bz2
import os
import sys
try:
    from io import BytesIO
except ImportError:
    from cStringIO import StringIO as BytesIO
try:
    from functools import reduce
except ImportError:
    # reduce is available in functools starting with Python 2.6
    pass

try:
    from pytz import UTC
except ImportError:
    # pytz is optional, define own "UTC" timestamp
    # reference implementation from Python documentation
    from datetime import timedelta, tzinfo

    ZERO = timedelta(0)

    class UTC(tzinfo):
        """UTC"""

        def utcoffset(self, dt):
            return ZERO

        def tzname(self, dt):
            return "UTC"

        def dst(self, dt):
            return ZERO

        def _call__(self):
            return self

    UTC = UTC()

try:
    unicode
except NameError:
    # Python 3.x
    def unicode(s, encoding):
        return s
else:
    def bytes(s, encoding):
        return s

try:
    long
except NameError:
    # Python 3.x
    long = int

try:
    xrange
except NameError:
    # Python 3.x
    xrange = range

IS_PYTHON3 = sys.version_info[0] == 3

NEED_BYTESWAP = sys.byteorder != 'little'

if array('L').itemsize == 4:
    ARRAY_TYPE_UINT32 = 'L'
else:
    assert array('I').itemsize == 4
    ARRAY_TYPE_UINT32 = 'I'

READ_BLOCKSIZE                   = 16384

MAGIC_7Z                         = unhexlify('377abcaf271c')  # '7z\xbc\xaf\x27\x1c'

PROPERTY_END                     = unhexlify('00')  # '\x00'
PROPERTY_HEADER                  = unhexlify('01')  # '\x01'
PROPERTY_ARCHIVE_PROPERTIES      = unhexlify('02')  # '\x02'
PROPERTY_ADDITIONAL_STREAMS_INFO = unhexlify('03')  # '\x03'
PROPERTY_MAIN_STREAMS_INFO       = unhexlify('04')  # '\x04'
PROPERTY_FILES_INFO              = unhexlify('05')  # '\x05'
PROPERTY_PACK_INFO               = unhexlify('06')  # '\x06'
PROPERTY_UNPACK_INFO             = unhexlify('07')  # '\x07'
PROPERTY_SUBSTREAMS_INFO         = unhexlify('08')  # '\x08'
PROPERTY_SIZE                    = unhexlify('09')  # '\x09'
PROPERTY_CRC                     = unhexlify('0a')  # '\x0a'
PROPERTY_FOLDER                  = unhexlify('0b')  # '\x0b'
PROPERTY_CODERS_UNPACK_SIZE      = unhexlify('0c')  # '\x0c'
PROPERTY_NUM_UNPACK_STREAM       = unhexlify('0d')  # '\x0d'
PROPERTY_EMPTY_STREAM            = unhexlify('0e')  # '\x0e'
PROPERTY_EMPTY_FILE              = unhexlify('0f')  # '\x0f'
PROPERTY_ANTI                    = unhexlify('10')  # '\x10'
PROPERTY_NAME                    = unhexlify('11')  # '\x11'
PROPERTY_CREATION_TIME           = unhexlify('12')  # '\x12'
PROPERTY_LAST_ACCESS_TIME        = unhexlify('13')  # '\x13'
PROPERTY_LAST_WRITE_TIME         = unhexlify('14')  # '\x14'
PROPERTY_ATTRIBUTES              = unhexlify('15')  # '\x15'
PROPERTY_COMMENT                 = unhexlify('16')  # '\x16'
PROPERTY_ENCODED_HEADER          = unhexlify('17')  # '\x17'

COMPRESSION_METHOD_COPY          = unhexlify('00')  # '\x00'
COMPRESSION_METHOD_LZMA          = unhexlify('03')  # '\x03'
COMPRESSION_METHOD_CRYPTO        = unhexlify('06')  # '\x06'
COMPRESSION_METHOD_MISC          = unhexlify('04')  # '\x04'
COMPRESSION_METHOD_MISC_ZIP      = unhexlify('0401')  # '\x04\x01'
COMPRESSION_METHOD_MISC_BZIP     = unhexlify('0402')  # '\x04\x02'
COMPRESSION_METHOD_7Z_AES256_SHA256 = unhexlify('06f10701')  # '\x06\xf1\x07\x01'

# number of seconds between 1601/01/01 and 1970/01/01 (UTC)
# used to adjust 7z FILETIME to Python timestamp
TIMESTAMP_ADJUST                 = -11644473600

def toTimestamp(filetime):
    """Convert 7z FILETIME to Python timestamp."""
    # FILETIME is 100-nanosecond intervals since 1601/01/01 (UTC)
    return (filetime / 10000000.0) + TIMESTAMP_ADJUST

def calculate_crc32(data, value=None, blocksize=1024*1024):
    """Calculate CRC32 of strings with arbitrary lengths."""
    length = len(data)
    pos = blocksize
    if value:
        value = crc32(data[:pos], value)
    else:
        value = crc32(data[:pos])
    while pos < length:
        value = crc32(data[pos:pos+blocksize], value)
        pos += blocksize

    return value & 0xffffffff

class ArchiveError(Exception):
    pass

class FormatError(ArchiveError):
    pass

class EncryptedArchiveError(ArchiveError):
    pass

class UnsupportedCompressionMethodError(ArchiveError):
    pass

class DecryptionError(ArchiveError):
    pass

class NoPasswordGivenError(DecryptionError):
    pass

class WrongPasswordError(DecryptionError):
    pass

class DecompressionError(ArchiveError):
    pass

class ArchiveTimestamp(long):
    """Windows FILETIME timestamp."""
    
    def __repr__(self):
        return '%s(%d)' % (type(self).__name__, self)
    
    def as_datetime(self):
        """Convert FILETIME to Python datetime object."""
        return datetime.fromtimestamp(toTimestamp(self), UTC)

class Base(object):
    """ base class with support for various basic read/write functions """
    
    def _readReal64Bit(self, file):
        res = file.read(8)
        a, b = unpack('<LL', res)
        return b << 32 | a, res
    
    def _read64Bit(self, file):
        b = ord(file.read(1))
        mask = 0x80
        for i in xrange(8):
            if b & mask == 0:
                bytes = array('B', file.read(i))
                bytes.reverse()
                value = (bytes and reduce(lambda x, y: x << 8 | y, bytes)) or 0
                highpart = b & (mask - 1)
                return value + (highpart << (i * 8))
            
            mask >>= 1

    def _readBoolean(self, file, count, checkall=0):
        if checkall:
            alldefined = file.read(1)
            if alldefined != unhexlify('00'):
                return [True] * count
            
        result = []
        b = 0
        mask = 0
        for i in xrange(count):
            if mask == 0:
                b = ord(file.read(1))
                mask = 0x80
            result.append(b & mask != 0)
            mask >>= 1
        
        return result

    def checkcrc(self, crc, data):
        check = calculate_crc32(data)
        return crc == check


class PackInfo(Base):
    """ informations about packed streams """
    
    def __init__(self, file):
        self.packpos = self._read64Bit(file)
        self.numstreams = self._read64Bit(file)
        id = file.read(1)
        if id == PROPERTY_SIZE:
            self.packsizes = [self._read64Bit(file) for x in xrange(self.numstreams)]
            id = file.read(1)
            
            if id == PROPERTY_CRC:
                self.crcs = [self._read64Bit(file) for x in xrange(self.numstreams)]
                id = file.read(1)
            
        if id != PROPERTY_END:
            raise FormatError('end id expected but %s found' % repr(id))

class Folder(Base):
    """ a "Folder" represents a stream of compressed data """
    
    def __init__(self, file):
        numcoders = self._read64Bit(file)
        self.coders = []
        self.digestdefined = False
        totalin = 0
        self.totalout = 0
        for i in xrange(numcoders):
            while True:
                b = ord(file.read(1))
                methodsize = b & 0xf
                issimple = b & 0x10 == 0
                noattributes = b & 0x20 == 0
                last_alternative = b & 0x80 == 0
                c = {}
                c['method'] = file.read(methodsize)
                if not issimple:
                    c['numinstreams'] = self._read64Bit(file)
                    c['numoutstreams'] = self._read64Bit(file)
                else:
                    c['numinstreams'] = 1
                    c['numoutstreams'] = 1
                totalin += c['numinstreams']
                self.totalout += c['numoutstreams']
                if not noattributes:
                    c['properties'] = file.read(self._read64Bit(file))
                self.coders.append(c)
                if last_alternative:
                    break
        
        numbindpairs = self.totalout - 1
        self.bindpairs = []
        for i in xrange(numbindpairs):
            self.bindpairs.append((self._read64Bit(file), self._read64Bit(file), ))
        
        numpackedstreams = totalin - numbindpairs
        self.packed_indexes = []
        if numpackedstreams == 1:
            for i in xrange(totalin):
                if self.findInBindPair(i) < 0:
                    self.packed_indexes.append(i)
        elif numpackedstreams > 1:
            for i in xrange(numpackedstreams):
                self.packed_indexes.append(self._read64Bit(file))

    def getUnpackSize(self):
        if not self.unpacksizes:
            return 0
            
        for i in xrange(len(self.unpacksizes)-1, -1, -1):
            if self.findOutBindPair(i):
                return self.unpacksizes[i]
        
        raise TypeError('not found')

    def findInBindPair(self, index):
        for idx, (a, b) in enumerate(self.bindpairs):
            if a == index:
                return idx
        return -1

    def findOutBindPair(self, index):
        for idx, (a, b) in enumerate(self.bindpairs):
            if b == index:
                return idx
        return -1

    def isEncrypted(self):
        return COMPRESSION_METHOD_7Z_AES256_SHA256 in [x['method'] for x in self.coders]

class Digests(Base):
    """ holds a list of checksums """
    
    def __init__(self, file, count):
        self.defined = self._readBoolean(file, count, checkall=1)
        self.crcs = array(ARRAY_TYPE_UINT32, file.read(4*count))
        if NEED_BYTESWAP:
            self.crcs.byteswap()
    
UnpackDigests = Digests

class UnpackInfo(Base):
    """ combines multiple folders """

    def __init__(self, file):
        id = file.read(1)
        if id != PROPERTY_FOLDER:
            raise FormatError('folder id expected but %s found' % repr(id))
        self.numfolders = self._read64Bit(file)
        self.folders = []
        external = file.read(1)
        if external == unhexlify('00'):
            self.folders = [Folder(file) for x in xrange(self.numfolders)]
        elif external == unhexlify('01'):
            self.datastreamidx = self._read64Bit(file)
        else:
            raise FormatError('0x00 or 0x01 expected but %s found' % repr(external))
        
        id = file.read(1)
        if id != PROPERTY_CODERS_UNPACK_SIZE:
            raise FormatError('coders unpack size id expected but %s found' % repr(id))
        
        for folder in self.folders:
            folder.unpacksizes = [self._read64Bit(file) for x in xrange(folder.totalout)]
            
        id = file.read(1)
        if id == PROPERTY_CRC:
            digests = UnpackDigests(file, self.numfolders)
            for idx, folder in enumerate(self.folders):
                folder.digestdefined = digests.defined[idx]
                folder.crc = digests.crcs[idx]
                
            id = file.read(1)
        
        if id != PROPERTY_END:
            raise FormatError('end id expected but %s found' % repr(id))
            
class SubstreamsInfo(Base):
    """ defines the substreams of a folder """
    
    def __init__(self, file, numfolders, folders):
        self.digests = []
        self.digestsdefined = []
        id = file.read(1)
        if id == PROPERTY_NUM_UNPACK_STREAM:
            self.numunpackstreams = [self._read64Bit(file) for x in xrange(numfolders)]
            id = file.read(1)
        else:
            self.numunpackstreams = [1]*numfolders
        
        if id == PROPERTY_SIZE:
            self.unpacksizes = []
            for i in xrange(len(self.numunpackstreams)):
                sum = 0
                for j in xrange(1, self.numunpackstreams[i]):
                    size = self._read64Bit(file)
                    self.unpacksizes.append(size)
                    sum += size
                self.unpacksizes.append(folders[i].getUnpackSize() - sum)
                
            id = file.read(1)

        numdigests = 0
        numdigeststotal = 0
        for i in xrange(numfolders):
            numsubstreams = self.numunpackstreams[i]
            if numsubstreams != 1 or not folders[i].digestdefined:
                numdigests += numsubstreams
            numdigeststotal += numsubstreams
        
        if id == PROPERTY_CRC:
            digests = Digests(file, numdigests)
            didx = 0
            for i in xrange(numfolders):
                folder = folders[i]
                numsubstreams = self.numunpackstreams[i]
                if numsubstreams == 1 and folder.digestdefined:
                    self.digestsdefined.append(True)
                    self.digests.append(folder.crc)
                else:
                    for j in xrange(numsubstreams):
                        self.digestsdefined.append(digests.defined[didx])
                        self.digests.append(digests.crcs[didx])
                        didx += 1
                            
            id = file.read(1)
            
        if id != PROPERTY_END:
            raise FormatError('end id expected but %r found' % id)

        if not self.digestsdefined:
            self.digestsdefined = [False] * numdigeststotal
            self.digests = [0] * numdigeststotal

class StreamsInfo(Base):
    """ informations about compressed streams """
    
    def __init__(self, file):
        id = file.read(1)
        if id == PROPERTY_PACK_INFO:
            self.packinfo = PackInfo(file)
            id = file.read(1)
        
        if id == PROPERTY_UNPACK_INFO:
            self.unpackinfo = UnpackInfo(file)
            id = file.read(1)
            
        if id == PROPERTY_SUBSTREAMS_INFO:
            self.substreamsinfo = SubstreamsInfo(file, self.unpackinfo.numfolders, self.unpackinfo.folders)
            id = file.read(1)
        
        if id != PROPERTY_END:
            raise FormatError('end id expected but %s found' % repr(id))

class FilesInfo(Base):
    """ holds file properties """
    
    def _readTimes(self, file, files, name):
        defined = self._readBoolean(file, len(files), checkall=1)
        
        # NOTE: the "external" flag is currently ignored, should be 0x00
        external = file.read(1)
        for i in xrange(len(files)):
            if defined[i]:
                files[i][name] = ArchiveTimestamp(self._readReal64Bit(file)[0])
            else:
                files[i][name] = None

    def __init__(self, file):
        self.numfiles = self._read64Bit(file)
        self.files = [{'emptystream': False} for x in xrange(self.numfiles)]
        numemptystreams = 0
        while True:
            typ = self._read64Bit(file)
            if typ > 255:
                raise FormatError('invalid type, must be below 256, is %d' % typ)
                
            typ = pack('B', typ)
            if typ == PROPERTY_END:
                break
                
            size = self._read64Bit(file)
            buffer = BytesIO(file.read(size))
            if typ == PROPERTY_EMPTY_STREAM:
                isempty = self._readBoolean(buffer, self.numfiles)
                list(map(lambda x, y: x.update({'emptystream': y}), self.files, isempty))
                for x in isempty:
                    if x: numemptystreams += 1
                emptyfiles = [False] * numemptystreams
                antifiles = [False] * numemptystreams
            elif typ == PROPERTY_EMPTY_FILE:
                emptyfiles = self._readBoolean(buffer, numemptystreams)
            elif typ == PROPERTY_ANTI:
                antifiles = self._readBoolean(buffer, numemptystreams)
            elif typ == PROPERTY_NAME:
                external = buffer.read(1)
                if external != unhexlify('00'):
                    self.dataindex = self._read64Bit(buffer)
                    # XXX: evaluate external
                    raise NotImplementedError
                    
                for f in self.files:
                    name = ''
                    while True:
                        ch = buffer.read(2)
                        if ch == unhexlify('0000'):
                            f['filename'] = name
                            break
                        name += ch.decode('utf-16')
            elif typ == PROPERTY_CREATION_TIME:
                self._readTimes(buffer, self.files, 'creationtime')
            elif typ == PROPERTY_LAST_ACCESS_TIME:
                self._readTimes(buffer, self.files, 'lastaccesstime')
            elif typ == PROPERTY_LAST_WRITE_TIME:
                self._readTimes(buffer, self.files, 'lastwritetime')
            elif typ == PROPERTY_ATTRIBUTES:
                defined = self._readBoolean(buffer, self.numfiles, checkall=1)
                for idx, f in enumerate(self.files):
                    if defined[idx]:
                        f['attributes'] = unpack('<L', buffer.read(4))[0]
                    else:
                        f['attributes'] = None
            else:
                raise FormatError('invalid type %r' % (typ))
        
class Header(Base):
    """ the archive header """
    
    def __init__(self, file):
        id = file.read(1)
        if id == PROPERTY_ARCHIVE_PROPERTIES:
            self.properties = ArchiveProperties(file)
            id = file.read(1)
        
        if id == PROPERTY_ADDITIONAL_STREAMS_INFO:
            self.additional_streams = StreamsInfo(file)
            id = file.read(1)
        
        if id == PROPERTY_MAIN_STREAMS_INFO:
            self.main_streams = StreamsInfo(file)
            id = file.read(1)
            
        if id == PROPERTY_FILES_INFO:
            self.files = FilesInfo(file)
            id = file.read(1)
            
        if id != PROPERTY_END:
            raise FormatError('end id expected but %s found' % (repr(id)))

class ArchiveFile(Base):
    """ wrapper around a file in the archive """
    
    def __init__(self, info, start, src_start, folder, archive, maxsize=None):
        self.digest = None
        self._archive = archive
        self._file = archive._file
        self._start = start
        self._src_start = src_start
        self._folder = folder
        # maxsize is only valid for solid archives
        self._maxsize = maxsize
        for k, v in info.items():
            setattr(self, k, v)
        self.size = self.uncompressed = self._uncompressed[-1]
        if not hasattr(self, 'filename'):
            # compressed file is stored without a name, generate one
            try:
                basefilename = self._file.name
            except AttributeError:
                # 7z archive file doesn't have a name
                self.filename = 'contents'
            else:
                self.filename = os.path.splitext(os.path.basename(basefilename))[0]
        self.reset()
        self._decoders = {
            COMPRESSION_METHOD_COPY: '_read_copy',
            COMPRESSION_METHOD_LZMA: '_read_lzma',
            COMPRESSION_METHOD_MISC_ZIP: '_read_zip',
            COMPRESSION_METHOD_MISC_BZIP: '_read_bzip',
            COMPRESSION_METHOD_7Z_AES256_SHA256: '_read_7z_aes256_sha256',
        }

    def _is_encrypted(self):
        return self._folder.isEncrypted()

    def reset(self):
        self.pos = 0
    
    def read(self):
        if not self._folder.coders:
            raise TypeError("file has no coder informations")
        
        data = None
        level = 0
        for coder in self._folder.coders:
            method = coder['method']
            decoder = None
            while method and decoder is None:
                decoder = self._decoders.get(method, None)
                method = method[:-1]
            
            if decoder is None:
                raise UnsupportedCompressionMethodError(repr(coder['method']))
            
            data = getattr(self, decoder)(coder, data, level)
            level += 1
        
        return data
    
    def _read_copy(self, coder, input, level):
        size = self._uncompressed[level]
        if not input:
            self._file.seek(self._src_start)
            input = self._file.read(size)
        return input[self._start:self._start+size]
    
    def _read_from_decompressor(self, coder, decompressor, input, level, checkremaining=False, with_cache=False):
        size = self._uncompressed[level]
        data = ''
        idx = 0
        cnt = 0
        properties = coder.get('properties', None)
        if properties:
            decompressor.decompress(properties)
        total = self.compressed
        if not input and total is None:
            remaining = self._start+size
            out = BytesIO()
            cache = getattr(self._folder, '_decompress_cache', None)
            if cache is not None:
                data, pos, decompressor = cache
                out.write(data)
                remaining -= len(data)
                self._file.seek(pos)
            else:
                self._file.seek(self._src_start)
            checkremaining = checkremaining and not self._folder.solid
            while remaining > 0:
                data = self._file.read(READ_BLOCKSIZE)
                if checkremaining or (with_cache and len(data) < READ_BLOCKSIZE):
                    tmp = decompressor.decompress(data, remaining)
                else:
                    tmp = decompressor.decompress(data)
                if not tmp and not data:
                    raise DecompressionError('end of stream while decompressing')
                out.write(tmp)
                remaining -= len(tmp)
            
            data = out.getvalue()
            if with_cache and self._folder.solid:
                # don't decompress start of solid archive for next file
                # TODO: limit size of cached data
                self._folder._decompress_cache = (data, self._file.tell(), decompressor)
        else:
            if not input:
                self._file.seek(self._src_start)
                input = self._file.read(total)
            if checkremaining:
                data = decompressor.decompress(input, self._start+size)
            else:
                data = decompressor.decompress(input)
        return data[self._start:self._start+size]
    
    def _read_lzma(self, coder, input, level):
        size = self._uncompressed[level]
        dec = pylzma.decompressobj(maxlength=self._start+size)
        try:
            return self._read_from_decompressor(coder, dec, input, level, checkremaining=True, with_cache=True)
        except ValueError:
            if self._is_encrypted():
                raise WrongPasswordError('invalid password')
            
            raise
        
    def _read_zip(self, coder, input, level):
        dec = zlib.decompressobj(-15)
        return self._read_from_decompressor(coder, dec, input, level, checkremaining=True)
        
    def _read_bzip(self, coder, input, level):
        dec = bz2.BZ2Decompressor()
        return self._read_from_decompressor(coder, dec, input, level)
    
    def _read_7z_aes256_sha256(self, coder, input, level):
        if not self._archive.password:
            raise NoPasswordGivenError()
        
        # TODO: this needs some sanity checks
        firstbyte = coder['properties'][0]
        if not IS_PYTHON3:
            firstbyte = ord(firstbyte)
        numcyclespower = firstbyte & 0x3f
        if firstbyte & 0xc0 != 0:
            saltsize = (firstbyte >> 7) & 1
            ivsize = (firstbyte >> 6) & 1
            
            secondbyte = coder['properties'][1]
            if not IS_PYTHON3:
                secondbyte = ord(secondbyte)
            saltsize += (secondbyte >> 4)
            ivsize += (secondbyte & 0x0f)
            
            assert len(coder['properties']) == 2+saltsize+ivsize
            salt = coder['properties'][2:2+saltsize]
            iv = coder['properties'][2+saltsize:2+saltsize+ivsize]
            assert len(salt) == saltsize
            assert len(iv) == ivsize
            assert numcyclespower <= 24
            if ivsize < 16:
                iv += bytes('\x00'*(16-ivsize), 'ascii')
        else:
            salt = iv = bytes('', 'ascii')
        
        password = self._archive.password.encode('utf-16-le')
        key = pylzma.calculate_key(password, numcyclespower, salt=salt)
        cipher = pylzma.AESDecrypt(key, iv=iv)
        if not input:
            self._file.seek(self._src_start)
            uncompressed_size = self._uncompressed[level]
            if uncompressed_size & 0x0f:
                # we need a multiple of 16 bytes
                uncompressed_size += 16 - (uncompressed_size & 0x0f)
            input = self._file.read(uncompressed_size)
        result = cipher.decrypt(input)
        return result
    
    def checkcrc(self):
        if self.digest is None:
            return True
            
        self.reset()
        data = self.read()
        return super(ArchiveFile, self).checkcrc(self.digest, data)
        

class Archive7z(Base):
    """ the archive itself """
    
    def __init__(self, file, password=None):
        self._file = file
        self.password = password
        self.header = file.read(len(MAGIC_7Z))
        if self.header != MAGIC_7Z:
            raise FormatError('not a 7z file')
        self.version = unpack('BB', file.read(2))

        self.startheadercrc = unpack('<L', file.read(4))[0]
        self.nextheaderofs, data = self._readReal64Bit(file)
        crc = calculate_crc32(data)
        self.nextheadersize, data = self._readReal64Bit(file)
        crc = calculate_crc32(data, crc)
        data = file.read(4)
        self.nextheadercrc = unpack('<L', data)[0]
        crc = calculate_crc32(data, crc)
        if crc != self.startheadercrc:
            raise FormatError('invalid header data')
        self.afterheader = file.tell()
        
        file.seek(self.nextheaderofs, 1)
        buffer = BytesIO(file.read(self.nextheadersize))
        if not self.checkcrc(self.nextheadercrc, buffer.getvalue()):
            raise FormatError('invalid header data')
        
        while True:
            id = buffer.read(1)
            if not id or id == PROPERTY_HEADER:
                break
                
            if id != PROPERTY_ENCODED_HEADER:
                raise TypeError('Unknown field: %r' % (id))
            
            streams = StreamsInfo(buffer)
            file.seek(self.afterheader + 0)
            data = bytes('', 'ascii')
            src_start = self.afterheader
            for folder in streams.unpackinfo.folders:
                if folder.isEncrypted() and not password:
                    raise NoPasswordGivenError()

                src_start += streams.packinfo.packpos
                uncompressed = folder.unpacksizes
                if not isinstance(uncompressed, (list, tuple)):
                    uncompressed = [uncompressed] * len(folder.coders)
                info = {
                    'compressed': streams.packinfo.packsizes[0],
                    '_uncompressed': uncompressed,
                }
                tmp = ArchiveFile(info, 0, src_start, folder, self)
                folderdata = tmp.read()
                src_start += uncompressed[-1]

                if folder.digestdefined:
                    if not self.checkcrc(folder.crc, folderdata):
                        raise FormatError('invalid block data')

                data += folderdata

            buffer = BytesIO(data)
        
        self.files = []
        self.files_map = {}
        if not id:
            # empty archive
            self.solid = False
            self.numfiles = 0
            self.filenames = []
            return
        
        self.header = Header(buffer)
        files = self.header.files
        folders = self.header.main_streams.unpackinfo.folders
        packinfo = self.header.main_streams.packinfo
        subinfo = self.header.main_streams.substreamsinfo
        packsizes = packinfo.packsizes
        self.solid = packinfo.numstreams == 1
        if hasattr(subinfo, 'unpacksizes'):
            unpacksizes = subinfo.unpacksizes
        else:
            unpacksizes = [x.unpacksizes for x in folders]
        
        fidx = 0
        obidx = 0
        streamidx = 0
        src_pos = self.afterheader
        pos = 0
        folder_pos = src_pos
        maxsize = (self.solid and packinfo.packsizes[0]) or None
        for info in files.files:
            if info['emptystream']:
                continue
            
            folder = folders[fidx]
            if streamidx == 0:
                folder.solid = subinfo.numunpackstreams[fidx] > 1

            maxsize = (folder.solid and packinfo.packsizes[fidx]) or None
            uncompressed = unpacksizes[obidx]
            if not isinstance(uncompressed, (list, tuple)):
                uncompressed = [uncompressed] * len(folder.coders)
            if pos > 0:
                # file is part of solid archive
                info['compressed'] = None
            elif fidx < len(packsizes):
                # file is compressed
                info['compressed'] = packsizes[fidx]
            else:
                # file is not compressed
                info['compressed'] = uncompressed
            info['_uncompressed'] = uncompressed
            file = ArchiveFile(info, pos, src_pos, folder, self, maxsize=maxsize)
            if subinfo.digestsdefined[obidx]:
                file.digest = subinfo.digests[obidx]
            self.files.append(file)
            if folder.solid:
                pos += unpacksizes[obidx]
            else:
                src_pos += info['compressed']
            obidx += 1
            streamidx += 1
            if streamidx >= subinfo.numunpackstreams[fidx]:
                pos = 0
                folder_pos += packinfo.packsizes[fidx]
                src_pos = folder_pos
                fidx += 1
                streamidx = 0
        
        self.numfiles = len(self.files)
        self.filenames = list(map(lambda x: x.filename, self.files))
        self.files_map.update([(x.filename, x) for x in self.files])
        
    # interface like TarFile
        
    def getmember(self, name):
        if isinstance(name, (int, long)):
            try:
                return self.files[name]
            except IndexError:
                return None

        return self.files_map.get(name, None)
        
    def getmembers(self):
        return self.files
        
    def getnames(self):
        return self.filenames

    def list(self, verbose=True, file=sys.stdout):
        file.write('total %d files in %sarchive\n' % (self.numfiles, (self.solid and 'solid ') or ''))
        if not verbose:
            file.write('\n'.join(self.filenames) + '\n')
            return
            
        for f in self.files:
            extra = (f.compressed and '%10d ' % (f.compressed)) or ' '
            file.write('%10d%s%.8x %s\n' % (f.size, extra, f.digest, f.filename))
            
if __name__ == '__main__':
    f = Archive7z(open('test.7z', 'rb'))
    #f = Archive7z(open('pylzma.7z', 'rb'))
    f.list()