Python zip file working on remote files over http

zipfileremote.py

"""
Read ZIP files over sliceable objects. This is a modified version
of the original python zipfile implementation.

The main use case is to provide an efficient way to read
even large zip files over remote sites allowing for RANGE
queries.

This work has been ispired by the pinch project
  https://github.com/peterhellberg/pinch
"""
import struct, os, sys, shutil
import binascii, cStringIO
import io
import re
import string

try:
    import zlib  # We may need its compression method
    crc32 = zlib.crc32
except ImportError:
    zlib = None
    crc32 = binascii.crc32

__all__ = ["BadZipfile", "error", "ZIP_STORED", "ZIP_DEFLATED", "is_zipfile",
           "ZipInfo", "ZipFile", "LargeZipFile"]


class BadZipfile(Exception):
    pass


class LargeZipFile(Exception):
    """
    Raised when writing a zipfile, the zipfile requires ZIP64 extensions
    and those extensions are disabled.
    """

error = BadZipfile      # The exception raised by this module

ZIP64_LIMIT = (1 << 31) - 1
ZIP_FILECOUNT_LIMIT = (1 << 16) - 1
ZIP_MAX_COMMENT = (1 << 16) - 1

# constants for Zip file compression methods
ZIP_STORED = 0
ZIP_DEFLATED = 8
# Other ZIP compression methods not supported

# Below are some formats and associated data for reading/writing headers using
# the struct module. The names and structures of headers/records are those used
# in the PKWARE description of the ZIP file format:
#     http://www.pkware.com/documents/casestudies/APPNOTE.TXT
# (URL valid as of January 2008)

# The "end of central directory" structure, magic number, size, and indices
# (section V.I in the format document)
structEndArchive = "<4s4H2LH"
stringEndArchive = "PK\005\006"
sizeEndCentDir = struct.calcsize(structEndArchive)

_ECD_SIGNATURE = 0
_ECD_DISK_NUMBER = 1
_ECD_DISK_START = 2
_ECD_ENTRIES_THIS_DISK = 3
_ECD_ENTRIES_TOTAL = 4
_ECD_SIZE = 5
_ECD_OFFSET = 6
_ECD_COMMENT_SIZE = 7
# These last two indices are not part of the structure as defined in the
# spec, but they are used internally by this module as a convenience
_ECD_COMMENT = 8
_ECD_LOCATION = 9
_ECD_CHUNK = 10

# The "central directory" structure, magic number, size, and indices
# of entries in the structure (section V.F in the format document)
structCentralDir = "<4s4B4HL2L5H2L"
stringCentralDir = "PK\001\002"
sizeCentralDir = struct.calcsize(structCentralDir)

# indexes of entries in the central directory structure
_CD_SIGNATURE = 0
_CD_CREATE_VERSION = 1
_CD_CREATE_SYSTEM = 2
_CD_EXTRACT_VERSION = 3
_CD_EXTRACT_SYSTEM = 4
_CD_FLAG_BITS = 5
_CD_COMPRESS_TYPE = 6
_CD_TIME = 7
_CD_DATE = 8
_CD_CRC = 9
_CD_COMPRESSED_SIZE = 10
_CD_UNCOMPRESSED_SIZE = 11
_CD_FILENAME_LENGTH = 12
_CD_EXTRA_FIELD_LENGTH = 13
_CD_COMMENT_LENGTH = 14
_CD_DISK_NUMBER_START = 15
_CD_INTERNAL_FILE_ATTRIBUTES = 16
_CD_EXTERNAL_FILE_ATTRIBUTES = 17
_CD_LOCAL_HEADER_OFFSET = 18

# The "local file header" structure, magic number, size, and indices
# (section V.A in the format document)
structFileHeader = "<4s2B4HL2L2H"
stringFileHeader = "PK\003\004"
sizeFileHeader = struct.calcsize(structFileHeader)

_FH_SIGNATURE = 0
_FH_EXTRACT_VERSION = 1
_FH_EXTRACT_SYSTEM = 2
_FH_GENERAL_PURPOSE_FLAG_BITS = 3
_FH_COMPRESSION_METHOD = 4
_FH_LAST_MOD_TIME = 5
_FH_LAST_MOD_DATE = 6
_FH_CRC = 7
_FH_COMPRESSED_SIZE = 8
_FH_UNCOMPRESSED_SIZE = 9
_FH_FILENAME_LENGTH = 10
_FH_EXTRA_FIELD_LENGTH = 11

# The "Zip64 end of central directory locator" structure, magic number, and size
structEndArchive64Locator = "<4sLQL"
stringEndArchive64Locator = "PK\x06\x07"
sizeEndCentDir64Locator = struct.calcsize(structEndArchive64Locator)

# The "Zip64 end of central directory" record, magic number, size, and indices
# (section V.G in the format document)
structEndArchive64 = "<4sQ2H2L4Q"
stringEndArchive64 = "PK\x06\x06"
sizeEndCentDir64 = struct.calcsize(structEndArchive64)

_CD64_SIGNATURE = 0
_CD64_DIRECTORY_RECSIZE = 1
_CD64_CREATE_VERSION = 2
_CD64_EXTRACT_VERSION = 3
_CD64_DISK_NUMBER = 4
_CD64_DISK_NUMBER_START = 5
_CD64_NUMBER_ENTRIES_THIS_DISK = 6
_CD64_NUMBER_ENTRIES_TOTAL = 7
_CD64_DIRECTORY_SIZE = 8
_CD64_OFFSET_START_CENTDIR = 9

def _check_zipfile(fp):
    try:
        if _EndRecData(fp):
            return True         # file has correct magic number
    except IOError:
        pass
    return False

def is_zipfile(filename):
    """Quickly see if a file is a ZIP file by checking the magic number.

    The filename argument may be a file or file-like object too.
    """
    result = False
    try:
        if hasattr(filename, "read"):
            result = _check_zipfile(fp=filename)
        else:
            with open(filename, "rb") as fp:
                result = _check_zipfile(fp)
    except IOError:
        pass
    return result

def _EndRecData64(fpin, offset, endrec):
    """
    Read the ZIP64 end-of-archive records and use that to update endrec
    """

    data = fpin[offset - sizeEndCentDir64Locator:]

    if len(data) != sizeEndCentDir64Locator:
        return endrec
    sig, diskno, reloff, disks = struct.unpack(structEndArchive64Locator, data)
    if sig != stringEndArchive64Locator:
        return endrec

    if diskno != 0 or disks != 1:
        raise BadZipfile("zipfiles that span multiple disks are not supported")

    # Assume no 'zip64 extensible data'
    data = fpin[offset - sizeEndCentDir64Locator - sizeEndCentDir64:]

    if len(data) != sizeEndCentDir64:
        return endrec
    sig, sz, create_version, read_version, disk_num, disk_dir, \
            dircount, dircount2, dirsize, diroffset = \
            struct.unpack(structEndArchive64, data)
    if sig != stringEndArchive64:
        return endrec

    # Update the original endrec using data from the ZIP64 record
    endrec[_ECD_SIGNATURE] = sig
    endrec[_ECD_DISK_NUMBER] = disk_num
    endrec[_ECD_DISK_START] = disk_dir
    endrec[_ECD_ENTRIES_THIS_DISK] = dircount
    endrec[_ECD_ENTRIES_TOTAL] = dircount2
    endrec[_ECD_SIZE] = dirsize
    endrec[_ECD_OFFSET] = diroffset
    return endrec


def _EndRecData(fpin):
    """Return data from the "End of Central Directory" record, or None.

    The data is a list of the nine items in the ZIP "End of central dir"
    record followed by a tenth item, the file seek offset of this record."""

    # Determine file size
    filesize = len(fpin)

    # this should include the eocd and eventually the comment
    lastChunkOffset = filesize - (1 << 16) - sizeEndCentDir
    lastChunk = fpin[lastChunkOffset:filesize]

    # Check to see if this is ZIP file with no archive comment (the
    # "end of central directory" structure should be the last item in the
    # file if this is the case).
    data = lastChunk[-sizeEndCentDir:]

    if (len(data) == sizeEndCentDir and
        data[0:4] == stringEndArchive and
        data[-2:] == b"\000\000"):
        # the signature is correct and there's no comment, unpack structure
        endrec = struct.unpack(structEndArchive, data)
        endrec=list(endrec)

        # Append a blank comment and record start offset
        endrec.append("")
        endrec.append(filesize - sizeEndCentDir)
        endrec.append( (lastChunk, lastChunkOffset, filesize) )

        # Try to read the "Zip64 end of central directory" structure
        return _EndRecData64(lastChunk, -sizeEndCentDir, endrec)

    # Either this is not a ZIP file, or it is a ZIP file with an archive
    # comment.  Search the end of the file for the "end of central directory"
    # record signature. The comment is the last item in the ZIP file and may be
    # up to 64K long.  It is assumed that the "end of central directory" magic
    # number does not appear in the comment.
    maxCommentStart = max(filesize - (1 << 16) - sizeEndCentDir, 0)

    data = lastChunk[:]
    start = data.rfind(stringEndArchive)
    if start >= 0:
        # found the magic number; attempt to unpack and interpret
        recData = data[start:start+sizeEndCentDir]
        if len(recData) != sizeEndCentDir:
            # Zip file is corrupted.
            return None
        endrec = list(struct.unpack(structEndArchive, recData))
        commentSize = endrec[_ECD_COMMENT_SIZE] #as claimed by the zip file
        comment = data[start+sizeEndCentDir:start+sizeEndCentDir+commentSize]
        endrec.append(comment)
        endrec.append(maxCommentStart + start)
        endrec.append( (lastChunk, lastChunkOffset, filesize) )

        # Try to read the "Zip64 end of central directory" structure
        return _EndRecData64(lastChunk, maxCommentStart + start - filesize,
                             endrec)

    # Unable to find a valid end of central directory structure
    return None


class ZipInfo (object):
    """Class with attributes describing each file in the ZIP archive."""

    __slots__ = (
            'orig_filename',
            'filename',
            'date_time',
            'compress_type',
            'comment',
            'extra',
            'create_system',
            'create_version',
            'extract_version',
            'reserved',
            'flag_bits',
            'volume',
            'internal_attr',
            'external_attr',
            'header_offset',
            'CRC',
            'compress_size',
            'file_size',
            '_raw_time',
        )

    def __init__(self, filename="NoName", date_time=(1980,1,1,0,0,0)):
        self.orig_filename = filename   # Original file name in archive

        # Terminate the file name at the first null byte.  Null bytes in file
        # names are used as tricks by viruses in archives.
        null_byte = filename.find(chr(0))
        if null_byte >= 0:
            filename = filename[0:null_byte]
        # This is used to ensure paths in generated ZIP files always use
        # forward slashes as the directory separator, as required by the
        # ZIP format specification.
        if os.sep != "/" and os.sep in filename:
            filename = filename.replace(os.sep, "/")

        self.filename = filename        # Normalized file name
        self.date_time = date_time      # year, month, day, hour, min, sec

        if date_time[0] < 1980:
            raise ValueError('ZIP does not support timestamps before 1980')

        # Standard values:
        self.compress_type = ZIP_STORED # Type of compression for the file
        self.comment = ""               # Comment for each file
        self.extra = ""                 # ZIP extra data
        if sys.platform == 'win32':
            self.create_system = 0          # System which created ZIP archive
        else:
            # Assume everything else is unix-y
            self.create_system = 3          # System which created ZIP archive
        self.create_version = 20        # Version which created ZIP archive
        self.extract_version = 20       # Version needed to extract archive
        self.reserved = 0               # Must be zero
        self.flag_bits = 0              # ZIP flag bits
        self.volume = 0                 # Volume number of file header
        self.internal_attr = 0          # Internal attributes
        self.external_attr = 0          # External file attributes
        # Other attributes are set by class ZipFile:
        # header_offset         Byte offset to the file header
        # CRC                   CRC-32 of the uncompressed file
        # compress_size         Size of the compressed file
        # file_size             Size of the uncompressed file

    def FileHeader(self, zip64=None):
        """Return the per-file header as a string."""
        dt = self.date_time
        dosdate = (dt[0] - 1980) << 9 | dt[1] << 5 | dt[2]
        dostime = dt[3] << 11 | dt[4] << 5 | (dt[5] // 2)
        if self.flag_bits & 0x08:
            # Set these to zero because we write them after the file data
            CRC = compress_size = file_size = 0
        else:
            CRC = self.CRC
            compress_size = self.compress_size
            file_size = self.file_size

        extra = self.extra

        if zip64 is None:
            zip64 = file_size > ZIP64_LIMIT or compress_size > ZIP64_LIMIT
        if zip64:
            fmt = '<HHQQ'
            extra = extra + struct.pack(fmt,
                    1, struct.calcsize(fmt)-4, file_size, compress_size)
        if file_size > ZIP64_LIMIT or compress_size > ZIP64_LIMIT:
            if not zip64:
                raise LargeZipFile("Filesize would require ZIP64 extensions")
            # File is larger than what fits into a 4 byte integer,
            # fall back to the ZIP64 extension
            file_size = 0xffffffff
            compress_size = 0xffffffff
            self.extract_version = max(45, self.extract_version)
            self.create_version = max(45, self.extract_version)

        filename, flag_bits = self._encodeFilenameFlags()
        header = struct.pack(structFileHeader, stringFileHeader,
                 self.extract_version, self.reserved, flag_bits,
                 self.compress_type, dostime, dosdate, CRC,
                 compress_size, file_size,
                 len(filename), len(extra))
        return header + filename + extra

    def _encodeFilenameFlags(self):
        if isinstance(self.filename, unicode):
            try:
                return self.filename.encode('ascii'), self.flag_bits
            except UnicodeEncodeError:
                return self.filename.encode('utf-8'), self.flag_bits | 0x800
        else:
            return self.filename, self.flag_bits

    def _decodeFilename(self):
        if self.flag_bits & 0x800:
            return self.filename.decode('utf-8')
        else:
            return self.filename

    def _decodeExtra(self):
        # Try to decode the extra field.
        extra = self.extra
        unpack = struct.unpack
        while len(extra) >= 4:
            tp, ln = unpack('<HH', extra[:4])
            if tp == 1:
                if ln >= 24:
                    counts = unpack('<QQQ', extra[4:28])
                elif ln == 16:
                    counts = unpack('<QQ', extra[4:20])
                elif ln == 8:
                    counts = unpack('<Q', extra[4:12])
                elif ln == 0:
                    counts = ()
                else:
                    raise RuntimeError, "Corrupt extra field %s"%(ln,)

                idx = 0

                # ZIP64 extension (large files and/or large archives)
                if self.file_size in (0xffffffffffffffffL, 0xffffffffL):
                    self.file_size = counts[idx]
                    idx += 1

                if self.compress_size == 0xFFFFFFFFL:
                    self.compress_size = counts[idx]
                    idx += 1

                if self.header_offset == 0xffffffffL:
                    old = self.header_offset
                    self.header_offset = counts[idx]
                    idx+=1

            extra = extra[ln+4:]


class _ZipDecrypter:
    """Class to handle decryption of files stored within a ZIP archive.

    ZIP supports a password-based form of encryption. Even though known
    plaintext attacks have been found against it, it is still useful
    to be able to get data out of such a file.

    Usage:
        zd = _ZipDecrypter(mypwd)
        plain_char = zd(cypher_char)
        plain_text = map(zd, cypher_text)
    """

    def _GenerateCRCTable():
        """Generate a CRC-32 table.

        ZIP encryption uses the CRC32 one-byte primitive for scrambling some
        internal keys. We noticed that a direct implementation is faster than
        relying on binascii.crc32().
        """
        poly = 0xedb88320
        table = [0] * 256
        for i in range(256):
            crc = i
            for j in range(8):
                if crc & 1:
                    crc = ((crc >> 1) & 0x7FFFFFFF) ^ poly
                else:
                    crc = ((crc >> 1) & 0x7FFFFFFF)
            table[i] = crc
        return table
    crctable = _GenerateCRCTable()

    def _crc32(self, ch, crc):
        """Compute the CRC32 primitive on one byte."""
        return ((crc >> 8) & 0xffffff) ^ self.crctable[(crc ^ ord(ch)) & 0xff]

    def __init__(self, pwd):
        self.key0 = 305419896
        self.key1 = 591751049
        self.key2 = 878082192
        for p in pwd:
            self._UpdateKeys(p)

    def _UpdateKeys(self, c):
        self.key0 = self._crc32(c, self.key0)
        self.key1 = (self.key1 + (self.key0 & 255)) & 4294967295
        self.key1 = (self.key1 * 134775813 + 1) & 4294967295
        self.key2 = self._crc32(chr((self.key1 >> 24) & 255), self.key2)

    def __call__(self, c):
        """Decrypt a single character."""
        c = ord(c)
        k = self.key2 | 2
        c = c ^ (((k * (k^1)) >> 8) & 255)
        c = chr(c)
        self._UpdateKeys(c)
        return c


compressor_names = {
    0: 'store',
    1: 'shrink',
    2: 'reduce',
    3: 'reduce',
    4: 'reduce',
    5: 'reduce',
    6: 'implode',
    7: 'tokenize',
    8: 'deflate',
    9: 'deflate64',
    10: 'implode',
    12: 'bzip2',
    14: 'lzma',
    18: 'terse',
    19: 'lz77',
    97: 'wavpack',
    98: 'ppmd',
}


class ZipExtFile(io.BufferedIOBase):
    """File-like object for reading an archive member.
       Is returned by ZipFile.open().
    """

    # Max size supported by decompressor.
    MAX_N = 1 << 31 - 1

    # Read from compressed files in 4k blocks.
    MIN_READ_SIZE = 4096

    # Search for universal newlines or line chunks.
    PATTERN = re.compile(r'^(?P<chunk>[^\r\n]+)|(?P<newline>\n|\r\n?)')

    def __init__(self, fileobj, mode, zipinfo, decrypter=None,
            close_fileobj=False):
        self._fileobj = fileobj
        self._decrypter = decrypter
        self._close_fileobj = close_fileobj

        self._compress_type = zipinfo.compress_type
        self._compress_size = zipinfo.compress_size
        self._compress_left = zipinfo.compress_size

        if self._compress_type == ZIP_DEFLATED:
            self._decompressor = zlib.decompressobj(-15)
        elif self._compress_type != ZIP_STORED:
            descr = compressor_names.get(self._compress_type)
            if descr:
                raise NotImplementedError("compression type %d (%s)" % (self._compress_type, descr))
            else:
                raise NotImplementedError("compression type %d" % (self._compress_type,))
        self._unconsumed = ''

        self._readbuffer = ''
        self._offset = 0

        self._universal = 'U' in mode
        self.newlines = None

        # Adjust read size for encrypted files since the first 12 bytes
        # are for the encryption/password information.
        if self._decrypter is not None:
            self._compress_left -= 12

        self.mode = mode
        self.name = zipinfo.filename

        if hasattr(zipinfo, 'CRC'):
            self._expected_crc = zipinfo.CRC
            self._running_crc = crc32(b'') & 0xffffffff
        else:
            self._expected_crc = None

    def readline(self, limit=-1):
        """Read and return a line from the stream.

        If limit is specified, at most limit bytes will be read.
        """

        if not self._universal and limit < 0:
            # Shortcut common case - newline found in buffer.
            i = self._readbuffer.find('\n', self._offset) + 1
            if i > 0:
                line = self._readbuffer[self._offset: i]
                self._offset = i
                return line

        if not self._universal:
            return io.BufferedIOBase.readline(self, limit)

        line = ''
        while limit < 0 or len(line) < limit:
            readahead = self.peek(2)
            if readahead == '':
                return line

            #
            # Search for universal newlines or line chunks.
            #
            # The pattern returns either a line chunk or a newline, but not
            # both. Combined with peek(2), we are assured that the sequence
            # '\r\n' is always retrieved completely and never split into
            # separate newlines - '\r', '\n' due to coincidental readaheads.
            #
            match = self.PATTERN.search(readahead)
            newline = match.group('newline')
            if newline is not None:
                if self.newlines is None:
                    self.newlines = []
                if newline not in self.newlines:
                    self.newlines.append(newline)
                self._offset += len(newline)
                return line + '\n'

            chunk = match.group('chunk')
            if limit >= 0:
                chunk = chunk[: limit - len(line)]

            self._offset += len(chunk)
            line += chunk

        return line

    def peek(self, n=1):
        """Returns buffered bytes without advancing the position."""
        if n > len(self._readbuffer) - self._offset:
            chunk = self.read(n)
            if len(chunk) > self._offset:
                self._readbuffer = chunk + self._readbuffer[self._offset:]
                self._offset = 0
            else:
                self._offset -= len(chunk)

        # Return up to 512 bytes to reduce allocation overhead for tight loops.
        return self._readbuffer[self._offset: self._offset + 512]

    def readable(self):
        return True

    def read(self, n=-1):
        """Read and return up to n bytes.
        If the argument is omitted, None, or negative, data is read and returned until EOF is reached..
        """
        buf = ''
        if n is None:
            n = -1
        while True:
            if n < 0:
                data = self.read1(n)
            elif n > len(buf):
                data = self.read1(n - len(buf))
            else:
                return buf
            if len(data) == 0:
                return buf
            buf += data

    def _update_crc(self, newdata, eof):
        # Update the CRC using the given data.
        if self._expected_crc is None:
            # No need to compute the CRC if we don't have a reference value
            return
        self._running_crc = crc32(newdata, self._running_crc) & 0xffffffff
        # Check the CRC if we're at the end of the file
        if eof and self._running_crc != self._expected_crc:
            raise BadZipfile("Bad CRC-32 for file %r" % self.name)

    def read1(self, n):
        """Read up to n bytes with at most one read() system call."""

        # Simplify algorithm (branching) by transforming negative n to large n.
        if n < 0 or n is None:
            n = self.MAX_N

        # Bytes available in read buffer.
        len_readbuffer = len(self._readbuffer) - self._offset

        # Read from file.
        if self._compress_left > 0 and n > len_readbuffer + len(self._unconsumed):
            nbytes = n - len_readbuffer - len(self._unconsumed)
            nbytes = max(nbytes, self.MIN_READ_SIZE)
            nbytes = min(nbytes, self._compress_left)

            data = self._fileobj.read(nbytes)
            self._compress_left -= len(data)

            if data and self._decrypter is not None:
                data = ''.join(map(self._decrypter, data))

            if self._compress_type == ZIP_STORED:
                self._update_crc(data, eof=(self._compress_left==0))
                self._readbuffer = self._readbuffer[self._offset:] + data
                self._offset = 0
            else:
                # Prepare deflated bytes for decompression.
                self._unconsumed += data

        # Handle unconsumed data.
        if (len(self._unconsumed) > 0 and n > len_readbuffer and
            self._compress_type == ZIP_DEFLATED):
            data = self._decompressor.decompress(
                self._unconsumed,
                max(n - len_readbuffer, self.MIN_READ_SIZE)
            )

            self._unconsumed = self._decompressor.unconsumed_tail
            eof = len(self._unconsumed) == 0 and self._compress_left == 0
            if eof:
                data += self._decompressor.flush()

            self._update_crc(data, eof=eof)
            self._readbuffer = self._readbuffer[self._offset:] + data
            self._offset = 0

        # Read from buffer.
        data = self._readbuffer[self._offset: self._offset + n]
        self._offset += len(data)
        return data

    def close(self):
        try :
            if self._close_fileobj:
                self._fileobj.close()
        finally:
            super(ZipExtFile, self).close()


class ZipFile(object):
    """ Class to read zip files using sliceable objects (with length).

    z = ZipFile(sliceable)

    sliceable: an object that allows fetching data by range

    """

    def __init__(self, sliceable):
        """Open the ZIP file with mode read "r", write "w" or append "a"."""

        self.debug = 0  # Level of printing: 0 through 3
        self.NameToInfo = {}    # Find file info given name
        self.filelist = []      # List of ZipInfo instances for archive
        self.pwd = None
        self._comment = ''

        self.fp = sliceable
        self._RealGetContents()

    def attach(self, sliceable):
        self.fp = sliceable

    def detach(self):
        self.fp = None

    def _RealGetContents(self):
        """Read in the table of contents for the ZIP file."""
        fp = self.fp
        try:
            endrec = _EndRecData(fp)
        except IOError:
            raise BadZipfile("File is not a zip file")
        if not endrec:
            raise BadZipfile, "File is not a zip file"
        if self.debug > 1:
            print endrec
        size_cd = endrec[_ECD_SIZE]             # bytes in central directory
        offset_cd = endrec[_ECD_OFFSET]         # offset of central directory
        self._comment = endrec[_ECD_COMMENT]    # archive comment

        # "concat" is zero, unless zip was concatenated to another file
        concat = endrec[_ECD_LOCATION] - size_cd - offset_cd
        if endrec[_ECD_SIGNATURE] == stringEndArchive64:
            # If Zip64 extension structures are present, account for them
            concat -= (sizeEndCentDir64 + sizeEndCentDir64Locator)

        if self.debug > 2:
            inferred = concat + offset_cd
            print "given, inferred, offset", offset_cd, inferred, concat
        # self.start_dir:  Position of start of central directory
        self.start_dir = offset_cd + concat

        # check to see if data is already on last chunk, so to avoid
        # a useless roundtrip!
        (lastChunk, lastChunkOffset, filesize) = endrec[_ECD_CHUNK]

        if self.start_dir >= lastChunkOffset:
            data = lastChunk[self.start_dir - lastChunkOffset:self.start_dir+size_cd]
        else:
            data = fp[self.start_dir:self.start_dir+size_cd]

        fp = cStringIO.StringIO(data)
        total = 0
        while total < size_cd:
            centdir = fp.read(sizeCentralDir)
            if len(centdir) != sizeCentralDir:
                raise BadZipfile("Truncated central directory")
            centdir = struct.unpack(structCentralDir, centdir)
            if centdir[_CD_SIGNATURE] != stringCentralDir:
                raise BadZipfile("Bad magic number for central directory")
            if self.debug > 2:
                print centdir
            filename = fp.read(centdir[_CD_FILENAME_LENGTH])
            # Create ZipInfo instance to store file information
            x = ZipInfo(filename)            
            x.extra = fp.read(centdir[_CD_EXTRA_FIELD_LENGTH])
            x.comment = fp.read(centdir[_CD_COMMENT_LENGTH])
            x.header_offset = centdir[_CD_LOCAL_HEADER_OFFSET]
            (x.create_version, x.create_system, x.extract_version, x.reserved,
                x.flag_bits, x.compress_type, t, d,
                x.CRC, x.compress_size, x.file_size) = centdir[1:12]
            x.volume, x.internal_attr, x.external_attr = centdir[15:18]
            # Convert date/time code to (year, month, day, hour, min, sec)
            x._raw_time = t
            x.date_time = ( (d>>9)+1980, (d>>5)&0xF, d&0x1F,
                                     t>>11, (t>>5)&0x3F, (t&0x1F) * 2 )

            x._decodeExtra()
            x.header_offset = x.header_offset + concat
            x.filename = x._decodeFilename()
            self.filelist.append(x)
            self.NameToInfo[x.filename] = x

            # update total bytes read from central directory
            total = (total + sizeCentralDir + centdir[_CD_FILENAME_LENGTH]
                     + centdir[_CD_EXTRA_FIELD_LENGTH]
                     + centdir[_CD_COMMENT_LENGTH])

            if self.debug > 2:
                print "total", total


    def namelist(self):
        """Return a list of file names in the archive."""
        l = []
        for data in self.filelist:
            l.append(data.filename)
        return l

    def infolist(self):
        """Return a list of class ZipInfo instances for files in the
        archive."""
        return self.filelist

    def printdir(self):
        """Print a table of contents for the zip file."""
        print "%-46s %19s %12s" % ("File Name", "Modified    ", "Size")
        for zinfo in self.filelist:
            date = "%d-%02d-%02d %02d:%02d:%02d" % zinfo.date_time[:6]
            print "%-46s %s %12d" % (zinfo.filename, date, zinfo.file_size)

    def testzip(self):
        """Read all the files and check the CRC."""
        chunk_size = 2 ** 20
        for zinfo in self.filelist:
            try:
                # Read by chunks, to avoid an OverflowError or a
                # MemoryError with very large embedded files.
                with self.open(zinfo.filename, "r") as f:
                    while f.read(chunk_size):     # Check CRC-32
                        pass
            except BadZipfile:
                return zinfo.filename

    def getinfo(self, name):
        """Return the instance of ZipInfo given 'name'."""
        info = self.NameToInfo.get(name)
        if info is None:
            raise KeyError(
                'There is no item named %r in the archive' % name)

        return info

    @property
    def comment(self):
        """The comment text associated with the ZIP file."""
        return self._comment

    def read(self, name, pwd=None):
        """Return file bytes (as a string) for name."""
        return self.open(name, "r", pwd).read()

    def open(self, name, mode="r", pwd=None):
        """Return file-like object for 'name'."""
        if mode not in ("r", "U", "rU"):
            raise RuntimeError, 'open() requires mode "r", "U", or "rU"'
        if not self.fp:
            raise RuntimeError, \
                  "ZIP archive is not attached to any sliceable object"


        # Make sure we have an info object
        if isinstance(name, ZipInfo):
            # 'name' is already an info object
            zinfo = name
        else:
            # Get info object for name
            zinfo = self.getinfo(name)

        start = zinfo.header_offset
        
        # we add some byte to accomodate files with mismatching extra length header
        max_extra_field_len_allowed = len(zinfo.extra) + 128
        end = start + sizeFileHeader + len(zinfo.orig_filename) + max_extra_field_len_allowed + zinfo.compress_size
        compressed = self.fp[start:end]
        
        zef_file = cStringIO.StringIO(compressed)
        # Skip the file header:
        fheader = zef_file.read(sizeFileHeader)
        if len(fheader) != sizeFileHeader:
            raise BadZipfile("Truncated file header")
        fheader = struct.unpack(structFileHeader, fheader)
        if fheader[_FH_SIGNATURE] != stringFileHeader:
            raise BadZipfile("Bad magic number for file header")

        fname = zef_file.read(fheader[_FH_FILENAME_LENGTH])
        if fheader[_FH_EXTRA_FIELD_LENGTH]:
            if fheader[_FH_EXTRA_FIELD_LENGTH] > max_extra_field_len_allowed:
                raise BadZipfile("Extra field length mismatch, expected between %d to %d, is %d" % (len(zinfo.extra), max_extra_field_len_allowed, fheader[_FH_EXTRA_FIELD_LENGTH]))
            zef_file.read(fheader[_FH_EXTRA_FIELD_LENGTH])

        if fname != zinfo.orig_filename:
            raise BadZipfile, \
                    'File name in directory "%s" and header "%s" differ.' % (
                        zinfo.orig_filename, fname)

        # check for encrypted flag & handle password
        is_encrypted = zinfo.flag_bits & 0x1
        zd = None
        if is_encrypted:
            if not pwd:
                pwd = self.pwd
            if not pwd:
                raise RuntimeError, "File %s is encrypted, " \
                    "password required for extraction" % name

            zd = _ZipDecrypter(pwd)
            # The first 12 bytes in the cypher stream is an encryption header
            #  used to strengthen the algorithm. The first 11 bytes are
            #  completely random, while the 12th contains the MSB of the CRC,
            #  or the MSB of the file time depending on the header type
            #  and is used to check the correctness of the password.
            bytes = zef_file.read(12)
            h = map(zd, bytes[0:12])
            if zinfo.flag_bits & 0x8:
                # compare against the file type from extended local headers
                check_byte = (zinfo._raw_time >> 8) & 0xff
            else:
                # compare against the CRC otherwise
                check_byte = (zinfo.CRC >> 24) & 0xff
            if ord(h[11]) != check_byte:
                raise RuntimeError("Bad password for file", name)

        return ZipExtFile(zef_file, mode, zinfo, zd,
                close_fileobj=False)


    def extract(self, member, path=None, pwd=None):
        """Extract a member from the archive to the current working directory,
           using its full name. Its file information is extracted as accurately
           as possible. `member' may be a filename or a ZipInfo object. You can
           specify a different directory using `path'.
        """
        if not isinstance(member, ZipInfo):
            member = self.getinfo(member)

        if path is None:
            path = os.getcwd()

        return self._extract_member(member, path, pwd)

    def extractall(self, path=None, members=None, pwd=None):
        """Extract all members from the archive to the current working
           directory. `path' specifies a different directory to extract to.
           `members' is optional and must be a subset of the list returned
           by namelist().
        """
        if members is None:
            members = self.namelist()

        for zipinfo in members:
            self.extract(zipinfo, path, pwd)

    def _extract_member(self, member, targetpath, pwd):
        """Extract the ZipInfo object 'member' to a physical
           file on the path targetpath.
        """
        # build the destination pathname, replacing
        # forward slashes to platform specific separators.
        arcname = member.filename.replace('/', os.path.sep)

        if os.path.altsep:
            arcname = arcname.replace(os.path.altsep, os.path.sep)
        # interpret absolute pathname as relative, remove drive letter or
        # UNC path, redundant separators, "." and ".." components.
        arcname = os.path.splitdrive(arcname)[1]
        arcname = os.path.sep.join(x for x in arcname.split(os.path.sep)
                    if x not in ('', os.path.curdir, os.path.pardir))
        if os.path.sep == '\\':
            # filter illegal characters on Windows
            illegal = ':<>|"?*'
            if isinstance(arcname, unicode):
                table = {ord(c): ord('_') for c in illegal}
            else:
                table = string.maketrans(illegal, '_' * len(illegal))
            arcname = arcname.translate(table)
            # remove trailing dots
            arcname = (x.rstrip('.') for x in arcname.split(os.path.sep))
            arcname = os.path.sep.join(x for x in arcname if x)

        targetpath = os.path.join(targetpath, arcname)
        targetpath = os.path.normpath(targetpath)

        # Create all upper directories if necessary.
        upperdirs = os.path.dirname(targetpath)
        if upperdirs and not os.path.exists(upperdirs):
            os.makedirs(upperdirs)

        if member.filename[-1] == '/':
            if not os.path.isdir(targetpath):
                os.mkdir(targetpath)
            return targetpath

        with self.open(member, pwd=pwd) as source, \
             file(targetpath, "wb") as target:
            shutil.copyfileobj(source, target)

        return targetpath


def main(args=None):
    import mmap
    import textwrap
    USAGE=textwrap.dedent("""\
        Usage:
            zipfile.py -l zipfile.zip        # Show listing of a zipfile
            zipfile.py -t zipfile.zip        # Test if a zipfile is valid
            zipfile.py -e zipfile.zip target # Extract zipfile into target dir
            zipfile.py -c zipfile.zip src ... # Create zipfile from sources
        """)
    if args is None:
        args = sys.argv[1:]

    if not args or args[0] not in ('-l', '-c', '-e', '-t'):
        print USAGE
        sys.exit(1)

    if args[0] == '-l':
        if len(args) != 2:
            print USAGE
            sys.exit(1)
        with open(args[1], 'r+b') as f:
            mm = mmap.mmap(f.fileno(), 0)
            zf = ZipFile(mm)
            zf.printdir()

    elif args[0] == '-t':
        if len(args) != 2:
            print USAGE
            sys.exit(1)
        with open(args[1], 'r+b') as f:
            mm = mmap.mmap(f.fileno(), 0)
            zf = ZipFile(mm)
            badfile = zf.testzip()
        if badfile:
            print("The following enclosed file is corrupted: {!r}".format(badfile))
        print "Done testing"

    elif args[0] == '-e':
        if len(args) != 3:
            print USAGE
            sys.exit(1)
        with open(args[1], 'r+b') as f:
            mm = mmap.mmap(f.fileno(), 0)
            zf = ZipFile(mm)
            zf.extractall(args[2])

    elif args[0] == '-c':
        if len(args) < 3:
            print USAGE
            sys.exit(1)

        def addToZip(zf, path, zippath):
            if os.path.isfile(path):
                zf.write(path, zippath, ZIP_DEFLATED)
            elif os.path.isdir(path):
                if zippath:
                    zf.write(path, zippath)
                for nm in os.listdir(path):
                    addToZip(zf,
                            os.path.join(path, nm), os.path.join(zippath, nm))
            # else: ignore

        with ZipFile(args[1], 'w', allowZip64=True) as zf:
            for path in args[2:]:
                zippath = os.path.basename(path)
                if not zippath:
                    zippath = os.path.basename(os.path.dirname(path))
                if zippath in ('', os.curdir, os.pardir):
                    zippath = ''
                addToZip(zf, path, zippath)

if __name__ == "__main__":
    main()