cpython/Lib/tarfile.py

#!/usr/bin/env python
# -*- coding: iso-8859-1 -*-
#-------------------------------------------------------------------
# tarfile.py
#-------------------------------------------------------------------
# Copyright (C) 2002 Lars Gust<73>bel <lars@gustaebel.de>
# All rights reserved.
#
# Permission  is  hereby granted,  free  of charge,  to  any person
# obtaining a  copy of  this software  and associated documentation
# files  (the  "Software"),  to   deal  in  the  Software   without
# restriction,  including  without limitation  the  rights to  use,
# copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies  of  the  Software,  and to  permit  persons  to  whom the
# Software  is  furnished  to  do  so,  subject  to  the  following
# conditions:
#
# The above copyright  notice and this  permission notice shall  be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS  IS", WITHOUT WARRANTY OF ANY  KIND,
# EXPRESS OR IMPLIED, INCLUDING  BUT NOT LIMITED TO  THE WARRANTIES
# OF  MERCHANTABILITY,  FITNESS   FOR  A  PARTICULAR   PURPOSE  AND
# NONINFRINGEMENT.  IN  NO  EVENT SHALL  THE  AUTHORS  OR COPYRIGHT
# HOLDERS  BE LIABLE  FOR ANY  CLAIM, DAMAGES  OR OTHER  LIABILITY,
# WHETHER  IN AN  ACTION OF  CONTRACT, TORT  OR OTHERWISE,  ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
# OTHER DEALINGS IN THE SOFTWARE.
#
"""Read from and write to tar format archives.
"""

__version__ = "$Revision$"
# $Source$

version     = "0.8.0"
__author__  = "Lars Gust<73>bel (lars@gustaebel.de)"
__date__    = "$Date$"
__cvsid__   = "$Id$"
__credits__ = "Gustavo Niemeyer, Niels Gust<73>bel, Richard Townsend."

#---------
# Imports
#---------
import sys
import os
import shutil
import stat
import errno
import time
import struct

if sys.platform == 'mac':
    # This module needs work for MacOS9, especially in the area of pathname
    # handling. In many places it is assumed a simple substitution of / by the
    # local os.path.sep is good enough to convert pathnames, but this does not
    # work with the mac rooted:path:name versus :nonrooted:path:name syntax
    raise ImportError, "tarfile does not work for platform==mac"

try:
    import grp, pwd
except ImportError:
    grp = pwd = None

# from tarfile import *
__all__ = ["TarFile", "TarInfo", "is_tarfile", "TarError"]

#---------------------------------------------------------
# tar constants
#---------------------------------------------------------
NUL        = "\0"               # the null character
BLOCKSIZE  = 512                # length of processing blocks
RECORDSIZE = BLOCKSIZE * 20     # length of records
MAGIC      = "ustar"            # magic tar string
VERSION    = "00"               # version number

LENGTH_NAME    = 100            # maximum length of a filename
LENGTH_LINK    = 100            # maximum length of a linkname
LENGTH_PREFIX  = 155            # maximum length of the prefix field
MAXSIZE_MEMBER = 077777777777L  # maximum size of a file (11 octal digits)

REGTYPE  = "0"                  # regular file
AREGTYPE = "\0"                 # regular file
LNKTYPE  = "1"                  # link (inside tarfile)
SYMTYPE  = "2"                  # symbolic link
CHRTYPE  = "3"                  # character special device
BLKTYPE  = "4"                  # block special device
DIRTYPE  = "5"                  # directory
FIFOTYPE = "6"                  # fifo special device
CONTTYPE = "7"                  # contiguous file

GNUTYPE_LONGNAME = "L"          # GNU tar extension for longnames
GNUTYPE_LONGLINK = "K"          # GNU tar extension for longlink
GNUTYPE_SPARSE   = "S"          # GNU tar extension for sparse file

#---------------------------------------------------------
# tarfile constants
#---------------------------------------------------------
SUPPORTED_TYPES = (REGTYPE, AREGTYPE, LNKTYPE,  # file types that tarfile
                   SYMTYPE, DIRTYPE, FIFOTYPE,  # can cope with.
                   CONTTYPE, CHRTYPE, BLKTYPE,
                   GNUTYPE_LONGNAME, GNUTYPE_LONGLINK,
                   GNUTYPE_SPARSE)

REGULAR_TYPES = (REGTYPE, AREGTYPE,             # file types that somehow
                 CONTTYPE, GNUTYPE_SPARSE)      # represent regular files

#---------------------------------------------------------
# Bits used in the mode field, values in octal.
#---------------------------------------------------------
S_IFLNK = 0120000        # symbolic link
S_IFREG = 0100000        # regular file
S_IFBLK = 0060000        # block device
S_IFDIR = 0040000        # directory
S_IFCHR = 0020000        # character device
S_IFIFO = 0010000        # fifo

TSUID   = 04000          # set UID on execution
TSGID   = 02000          # set GID on execution
TSVTX   = 01000          # reserved

TUREAD  = 0400           # read by owner
TUWRITE = 0200           # write by owner
TUEXEC  = 0100           # execute/search by owner
TGREAD  = 0040           # read by group
TGWRITE = 0020           # write by group
TGEXEC  = 0010           # execute/search by group
TOREAD  = 0004           # read by other
TOWRITE = 0002           # write by other
TOEXEC  = 0001           # execute/search by other

#---------------------------------------------------------
# Some useful functions
#---------------------------------------------------------

def stn(s, length):
    """Convert a python string to a null-terminated string buffer.
    """
    return s[:length] + (length - len(s)) * NUL

def nti(s):
    """Convert a number field to a python number.
    """
    # There are two possible encodings for a number field, see
    # itn() below.
    if s[0] != chr(0200):
        n = int(s.rstrip(NUL + " ") or "0", 8)
    else:
        n = 0L
        for i in xrange(len(s) - 1):
            n <<= 8
            n += ord(s[i + 1])
    return n

def itn(n, digits=8, posix=False):
    """Convert a python number to a number field.
    """
    # POSIX 1003.1-1988 requires numbers to be encoded as a string of
    # octal digits followed by a null-byte, this allows values up to
    # (8**(digits-1))-1. GNU tar allows storing numbers greater than
    # that if necessary. A leading 0200 byte indicates this particular
    # encoding, the following digits-1 bytes are a big-endian
    # representation. This allows values up to (256**(digits-1))-1.
    if 0 <= n < 8 ** (digits - 1):
        s = "%0*o" % (digits - 1, n) + NUL
    else:
        if posix:
            raise ValueError("overflow in number field")

        if n < 0:
            # XXX We mimic GNU tar's behaviour with negative numbers,
            # this could raise OverflowError.
            n = struct.unpack("L", struct.pack("l", n))[0]

        s = ""
        for i in xrange(digits - 1):
            s = chr(n & 0377) + s
            n >>= 8
        s = chr(0200) + s
    return s

def calc_chksums(buf):
    """Calculate the checksum for a member's header by summing up all
       characters except for the chksum field which is treated as if
       it was filled with spaces. According to the GNU tar sources,
       some tars (Sun and NeXT) calculate chksum with signed char,
       which will be different if there are chars in the buffer with
       the high bit set. So we calculate two checksums, unsigned and
       signed.
    """
    unsigned_chksum = 256 + sum(struct.unpack("148B", buf[:148]) + struct.unpack("356B", buf[156:512]))
    signed_chksum = 256 + sum(struct.unpack("148b", buf[:148]) + struct.unpack("356b", buf[156:512]))
    return unsigned_chksum, signed_chksum

def copyfileobj(src, dst, length=None):
    """Copy length bytes from fileobj src to fileobj dst.
       If length is None, copy the entire content.
    """
    if length == 0:
        return
    if length is None:
        shutil.copyfileobj(src, dst)
        return

    BUFSIZE = 16 * 1024
    blocks, remainder = divmod(length, BUFSIZE)
    for b in xrange(blocks):
        buf = src.read(BUFSIZE)
        if len(buf) < BUFSIZE:
            raise IOError("end of file reached")
        dst.write(buf)

    if remainder != 0:
        buf = src.read(remainder)
        if len(buf) < remainder:
            raise IOError("end of file reached")
        dst.write(buf)
    return

filemode_table = (
    ((S_IFLNK,      "l"),
     (S_IFREG,      "-"),
     (S_IFBLK,      "b"),
     (S_IFDIR,      "d"),
     (S_IFCHR,      "c"),
     (S_IFIFO,      "p")),

    ((TUREAD,       "r"),),
    ((TUWRITE,      "w"),),
    ((TUEXEC|TSUID, "s"),
     (TSUID,        "S"),
     (TUEXEC,       "x")),

    ((TGREAD,       "r"),),
    ((TGWRITE,      "w"),),
    ((TGEXEC|TSGID, "s"),
     (TSGID,        "S"),
     (TGEXEC,       "x")),

    ((TOREAD,       "r"),),
    ((TOWRITE,      "w"),),
    ((TOEXEC|TSVTX, "t"),
     (TSVTX,        "T"),
     (TOEXEC,       "x"))
)

def filemode(mode):
    """Convert a file's mode to a string of the form
       -rwxrwxrwx.
       Used by TarFile.list()
    """
    perm = []
    for table in filemode_table:
        for bit, char in table:
            if mode & bit == bit:
                perm.append(char)
                break
        else:
            perm.append("-")
    return "".join(perm)

if os.sep != "/":
    normpath = lambda path: os.path.normpath(path).replace(os.sep, "/")
else:
    normpath = os.path.normpath

class TarError(Exception):
    """Base exception."""
    pass
class ExtractError(TarError):
    """General exception for extract errors."""
    pass
class ReadError(TarError):
    """Exception for unreadble tar archives."""
    pass
class CompressionError(TarError):
    """Exception for unavailable compression methods."""
    pass
class StreamError(TarError):
    """Exception for unsupported operations on stream-like TarFiles."""
    pass

#---------------------------
# internal stream interface
#---------------------------
class _LowLevelFile:
    """Low-level file object. Supports reading and writing.
       It is used instead of a regular file object for streaming
       access.
    """

    def __init__(self, name, mode):
        mode = {
            "r": os.O_RDONLY,
            "w": os.O_WRONLY | os.O_CREAT | os.O_TRUNC,
        }[mode]
        if hasattr(os, "O_BINARY"):
            mode |= os.O_BINARY
        self.fd = os.open(name, mode)

    def close(self):
        os.close(self.fd)

    def read(self, size):
        return os.read(self.fd, size)

    def write(self, s):
        os.write(self.fd, s)

class _Stream:
    """Class that serves as an adapter between TarFile and
       a stream-like object.  The stream-like object only
       needs to have a read() or write() method and is accessed
       blockwise.  Use of gzip or bzip2 compression is possible.
       A stream-like object could be for example: sys.stdin,
       sys.stdout, a socket, a tape device etc.

       _Stream is intended to be used only internally.
    """

    def __init__(self, name, mode, comptype, fileobj, bufsize):
        """Construct a _Stream object.
        """
        self._extfileobj = True
        if fileobj is None:
            fileobj = _LowLevelFile(name, mode)
            self._extfileobj = False

        if comptype == '*':
            # Enable transparent compression detection for the
            # stream interface
            fileobj = _StreamProxy(fileobj)
            comptype = fileobj.getcomptype()

        self.name     = name or ""
        self.mode     = mode
        self.comptype = comptype
        self.fileobj  = fileobj
        self.bufsize  = bufsize
        self.buf      = ""
        self.pos      = 0L
        self.closed   = False

        if comptype == "gz":
            try:
                import zlib
            except ImportError:
                raise CompressionError("zlib module is not available")
            self.zlib = zlib
            self.crc = zlib.crc32("")
            if mode == "r":
                self._init_read_gz()
            else:
                self._init_write_gz()

        if comptype == "bz2":
            try:
                import bz2
            except ImportError:
                raise CompressionError("bz2 module is not available")
            if mode == "r":
                self.dbuf = ""
                self.cmp = bz2.BZ2Decompressor()
            else:
                self.cmp = bz2.BZ2Compressor()

    def __del__(self):
        if hasattr(self, "closed") and not self.closed:
            self.close()

    def _init_write_gz(self):
        """Initialize for writing with gzip compression.
        """
        self.cmp = self.zlib.compressobj(9, self.zlib.DEFLATED,
                                            -self.zlib.MAX_WBITS,
                                            self.zlib.DEF_MEM_LEVEL,
                                            0)
        timestamp = struct.pack("<L", long(time.time()))
        self.__write("\037\213\010\010%s\002\377" % timestamp)
        if self.name.endswith(".gz"):
            self.name = self.name[:-3]
        self.__write(self.name + NUL)

    def write(self, s):
        """Write string s to the stream.
        """
        if self.comptype == "gz":
            self.crc = self.zlib.crc32(s, self.crc)
        self.pos += len(s)
        if self.comptype != "tar":
            s = self.cmp.compress(s)
        self.__write(s)

    def __write(self, s):
        """Write string s to the stream if a whole new block
           is ready to be written.
        """
        self.buf += s
        while len(self.buf) > self.bufsize:
            self.fileobj.write(self.buf[:self.bufsize])
            self.buf = self.buf[self.bufsize:]

    def close(self):
        """Close the _Stream object. No operation should be
           done on it afterwards.
        """
        if self.closed:
            return

        if self.mode == "w" and self.comptype != "tar":
            self.buf += self.cmp.flush()

        if self.mode == "w" and self.buf:
            self.fileobj.write(self.buf)
            self.buf = ""
            if self.comptype == "gz":
                # The native zlib crc is an unsigned 32-bit integer, but
                # the Python wrapper implicitly casts that to a signed C
                # long.  So, on a 32-bit box self.crc may "look negative",
                # while the same crc on a 64-bit box may "look positive".
                # To avoid irksome warnings from the `struct` module, force
                # it to look positive on all boxes.
                self.fileobj.write(struct.pack("<L", self.crc & 0xffffffffL))
                self.fileobj.write(struct.pack("<L", self.pos & 0xffffFFFFL))

        if not self._extfileobj:
            self.fileobj.close()

        self.closed = True

    def _init_read_gz(self):
        """Initialize for reading a gzip compressed fileobj.
        """
        self.cmp = self.zlib.decompressobj(-self.zlib.MAX_WBITS)
        self.dbuf = ""

        # taken from gzip.GzipFile with some alterations
        if self.__read(2) != "\037\213":
            raise ReadError("not a gzip file")
        if self.__read(1) != "\010":
            raise CompressionError("unsupported compression method")

        flag = ord(self.__read(1))
        self.__read(6)

        if flag & 4:
            xlen = ord(self.__read(1)) + 256 * ord(self.__read(1))
            self.read(xlen)
        if flag & 8:
            while True:
                s = self.__read(1)
                if not s or s == NUL:
                    break
        if flag & 16:
            while True:
                s = self.__read(1)
                if not s or s == NUL:
                    break
        if flag & 2:
            self.__read(2)

    def tell(self):
        """Return the stream's file pointer position.
        """
        return self.pos

    def seek(self, pos=0):
        """Set the stream's file pointer to pos. Negative seeking
           is forbidden.
        """
        if pos - self.pos >= 0:
            blocks, remainder = divmod(pos - self.pos, self.bufsize)
            for i in xrange(blocks):
                self.read(self.bufsize)
            self.read(remainder)
        else:
            raise StreamError("seeking backwards is not allowed")
        return self.pos

    def read(self, size=None):
        """Return the next size number of bytes from the stream.
           If size is not defined, return all bytes of the stream
           up to EOF.
        """
        if size is None:
            t = []
            while True:
                buf = self._read(self.bufsize)
                if not buf:
                    break
                t.append(buf)
            buf = "".join(t)
        else:
            buf = self._read(size)
        self.pos += len(buf)
        return buf

    def _read(self, size):
        """Return size bytes from the stream.
        """
        if self.comptype == "tar":
            return self.__read(size)

        c = len(self.dbuf)
        t = [self.dbuf]
        while c < size:
            buf = self.__read(self.bufsize)
            if not buf:
                break
            buf = self.cmp.decompress(buf)
            t.append(buf)
            c += len(buf)
        t = "".join(t)
        self.dbuf = t[size:]
        return t[:size]

    def __read(self, size):
        """Return size bytes from stream. If internal buffer is empty,
           read another block from the stream.
        """
        c = len(self.buf)
        t = [self.buf]
        while c < size:
            buf = self.fileobj.read(self.bufsize)
            if not buf:
                break
            t.append(buf)
            c += len(buf)
        t = "".join(t)
        self.buf = t[size:]
        return t[:size]
# class _Stream

class _StreamProxy(object):
    """Small proxy class that enables transparent compression
       detection for the Stream interface (mode 'r|*').
    """

    def __init__(self, fileobj):
        self.fileobj = fileobj
        self.buf = self.fileobj.read(BLOCKSIZE)

    def read(self, size):
        self.read = self.fileobj.read
        return self.buf

    def getcomptype(self):
        if self.buf.startswith("\037\213\010"):
            return "gz"
        if self.buf.startswith("BZh91"):
            return "bz2"
        return "tar"

    def close(self):
        self.fileobj.close()
# class StreamProxy

class _BZ2Proxy(object):
    """Small proxy class that enables external file object
       support for "r:bz2" and "w:bz2" modes. This is actually
       a workaround for a limitation in bz2 module's BZ2File
       class which (unlike gzip.GzipFile) has no support for
       a file object argument.
    """

    blocksize = 16 * 1024

    def __init__(self, fileobj, mode):
        self.fileobj = fileobj
        self.mode = mode
        self.init()

    def init(self):
        import bz2
        self.pos = 0
        if self.mode == "r":
            self.bz2obj = bz2.BZ2Decompressor()
            self.fileobj.seek(0)
            self.buf = ""
        else:
            self.bz2obj = bz2.BZ2Compressor()

    def read(self, size):
        b = [self.buf]
        x = len(self.buf)
        while x < size:
            try:
                raw = self.fileobj.read(self.blocksize)
                data = self.bz2obj.decompress(raw)
                b.append(data)
            except EOFError:
                break
            x += len(data)
        self.buf = "".join(b)

        buf = self.buf[:size]
        self.buf = self.buf[size:]
        self.pos += len(buf)
        return buf

    def seek(self, pos):
        if pos < self.pos:
            self.init()
        self.read(pos - self.pos)

    def tell(self):
        return self.pos

    def write(self, data):
        self.pos += len(data)
        raw = self.bz2obj.compress(data)
        self.fileobj.write(raw)

    def close(self):
        if self.mode == "w":
            raw = self.bz2obj.flush()
            self.fileobj.write(raw)
        self.fileobj.close()
# class _BZ2Proxy

#------------------------
# Extraction file object
#------------------------
class ExFileObject(object):
    """File-like object for reading an archive member.
       Is returned by TarFile.extractfile(). Support for
       sparse files included.
    """

    def __init__(self, tarfile, tarinfo):
        self.fileobj = tarfile.fileobj
        self.name    = tarinfo.name
        self.mode    = "r"
        self.closed  = False
        self.offset  = tarinfo.offset_data
        self.size    = tarinfo.size
        self.pos     = 0L
        self.linebuffer = ""
        if tarinfo.issparse():
            self.sparse = tarinfo.sparse
            self.read = self._readsparse
        else:
            self.read = self._readnormal

    def __read(self, size):
        """Overloadable read method.
        """
        return self.fileobj.read(size)

    def readline(self, size=-1):
        """Read a line with approx. size. If size is negative,
           read a whole line. readline() and read() must not
           be mixed up (!).
        """
        if size < 0:
            size = sys.maxint

        nl = self.linebuffer.find("\n")
        if nl >= 0:
            nl = min(nl, size)
        else:
            size -= len(self.linebuffer)
            while (nl < 0 and size > 0):
                buf = self.read(min(size, 100))
                if not buf:
                    break
                self.linebuffer += buf
                size -= len(buf)
                nl = self.linebuffer.find("\n")
            if nl == -1:
                s = self.linebuffer
                self.linebuffer = ""
                return s
        buf = self.linebuffer[:nl]
        self.linebuffer = self.linebuffer[nl + 1:]
        while buf[-1:] == "\r":
            buf = buf[:-1]
        return buf + "\n"

    def readlines(self):
        """Return a list with all (following) lines.
        """
        result = []
        while True:
            line = self.readline()
            if not line: break
            result.append(line)
        return result

    def _readnormal(self, size=None):
        """Read operation for regular files.
        """
        if self.closed:
            raise ValueError("file is closed")
        self.fileobj.seek(self.offset + self.pos)
        bytesleft = self.size - self.pos
        if size is None:
            bytestoread = bytesleft
        else:
            bytestoread = min(size, bytesleft)
        self.pos += bytestoread
        return self.__read(bytestoread)

    def _readsparse(self, size=None):
        """Read operation for sparse files.
        """
        if self.closed:
            raise ValueError("file is closed")

        if size is None:
            size = self.size - self.pos

        data = []
        while size > 0:
            buf = self._readsparsesection(size)
            if not buf:
                break
            size -= len(buf)
            data.append(buf)
        return "".join(data)

    def _readsparsesection(self, size):
        """Read a single section of a sparse file.
        """
        section = self.sparse.find(self.pos)

        if section is None:
            return ""

        toread = min(size, section.offset + section.size - self.pos)
        if isinstance(section, _data):
            realpos = section.realpos + self.pos - section.offset
            self.pos += toread
            self.fileobj.seek(self.offset + realpos)
            return self.__read(toread)
        else:
            self.pos += toread
            return NUL * toread

    def tell(self):
        """Return the current file position.
        """
        return self.pos

    def seek(self, pos, whence=0):
        """Seek to a position in the file.
        """
        self.linebuffer = ""
        if whence == 0:
            self.pos = min(max(pos, 0), self.size)
        if whence == 1:
            if pos < 0:
                self.pos = max(self.pos + pos, 0)
            else:
                self.pos = min(self.pos + pos, self.size)
        if whence == 2:
            self.pos = max(min(self.size + pos, self.size), 0)

    def close(self):
        """Close the file object.
        """
        self.closed = True

    def __iter__(self):
        """Get an iterator over the file object.
        """
        if self.closed:
            raise ValueError("I/O operation on closed file")
        return self

    def next(self):
        """Get the next item from the file iterator.
        """
        result = self.readline()
        if not result:
            raise StopIteration
        return result

#class ExFileObject

#------------------
# Exported Classes
#------------------
class TarInfo(object):
    """Informational class which holds the details about an
       archive member given by a tar header block.
       TarInfo objects are returned by TarFile.getmember(),
       TarFile.getmembers() and TarFile.gettarinfo() and are
       usually created internally.
    """

    def __init__(self, name=""):
        """Construct a TarInfo object. name is the optional name
           of the member.
        """

        self.name = name        # member name (dirnames must end with '/')
        self.mode = 0666        # file permissions
        self.uid = 0            # user id
        self.gid = 0            # group id
        self.size = 0           # file size
        self.mtime = 0          # modification time
        self.chksum = 0         # header checksum
        self.type = REGTYPE     # member type
        self.linkname = ""      # link name
        self.uname = "user"     # user name
        self.gname = "group"    # group name
        self.devmajor = 0       # device major number
        self.devminor = 0       # device minor number
        self.prefix = ""        # prefix to filename or information
                                # about sparse files

        self.offset = 0         # the tar header starts here
        self.offset_data = 0    # the file's data starts here

    def __repr__(self):
        return "<%s %r at %#x>" % (self.__class__.__name__,self.name,id(self))

    @classmethod
    def frombuf(cls, buf):
        """Construct a TarInfo object from a 512 byte string buffer.
        """
        if len(buf) != BLOCKSIZE:
            raise ValueError("truncated header")
        if buf.count(NUL) == BLOCKSIZE:
            raise ValueError("empty header")

        tarinfo = cls()
        tarinfo.buf = buf
        tarinfo.name = buf[0:100].rstrip(NUL)
        tarinfo.mode = nti(buf[100:108])
        tarinfo.uid = nti(buf[108:116])
        tarinfo.gid = nti(buf[116:124])
        tarinfo.size = nti(buf[124:136])
        tarinfo.mtime = nti(buf[136:148])
        tarinfo.chksum = nti(buf[148:156])
        tarinfo.type = buf[156:157]
        tarinfo.linkname = buf[157:257].rstrip(NUL)
        tarinfo.uname = buf[265:297].rstrip(NUL)
        tarinfo.gname = buf[297:329].rstrip(NUL)
        tarinfo.devmajor = nti(buf[329:337])
        tarinfo.devminor = nti(buf[337:345])
        tarinfo.prefix = buf[345:500]

        if tarinfo.chksum not in calc_chksums(buf):
            raise ValueError("invalid header")
        return tarinfo

    def tobuf(self, posix=False):
        """Return a tar header block as a 512 byte string.
        """
        parts = [
            stn(self.name, 100),
            itn(self.mode & 07777, 8, posix),
            itn(self.uid, 8, posix),
            itn(self.gid, 8, posix),
            itn(self.size, 12, posix),
            itn(self.mtime, 12, posix),
            "        ", # checksum field
            self.type,
            stn(self.linkname, 100),
            stn(MAGIC, 6),
            stn(VERSION, 2),
            stn(self.uname, 32),
            stn(self.gname, 32),
            itn(self.devmajor, 8, posix),
            itn(self.devminor, 8, posix),
            stn(self.prefix, 155)
        ]

        buf = struct.pack("%ds" % BLOCKSIZE, "".join(parts))
        chksum = calc_chksums(buf)[0]
        buf = buf[:148] + "%06o\0" % chksum + buf[155:]
        self.buf = buf
        return buf

    def isreg(self):
        return self.type in REGULAR_TYPES
    def isfile(self):
        return self.isreg()
    def isdir(self):
        return self.type == DIRTYPE
    def issym(self):
        return self.type == SYMTYPE
    def islnk(self):
        return self.type == LNKTYPE
    def ischr(self):
        return self.type == CHRTYPE
    def isblk(self):
        return self.type == BLKTYPE
    def isfifo(self):
        return self.type == FIFOTYPE
    def issparse(self):
        return self.type == GNUTYPE_SPARSE
    def isdev(self):
        return self.type in (CHRTYPE, BLKTYPE, FIFOTYPE)
# class TarInfo

class TarFile(object):
    """The TarFile Class provides an interface to tar archives.
    """

    debug = 0                   # May be set from 0 (no msgs) to 3 (all msgs)

    dereference = False         # If true, add content of linked file to the
                                # tar file, else the link.

    ignore_zeros = False        # If true, skips empty or invalid blocks and
                                # continues processing.

    errorlevel = 0              # If 0, fatal errors only appear in debug
                                # messages (if debug >= 0). If > 0, errors
                                # are passed to the caller as exceptions.

    posix = False               # If True, generates POSIX.1-1990-compliant
                                # archives (no GNU extensions!)

    fileobject = ExFileObject

    def __init__(self, name=None, mode="r", fileobj=None):
        """Open an (uncompressed) tar archive `name'. `mode' is either 'r' to
           read from an existing archive, 'a' to append data to an existing
           file or 'w' to create a new file overwriting an existing one. `mode'
           defaults to 'r'.
           If `fileobj' is given, it is used for reading or writing data. If it
           can be determined, `mode' is overridden by `fileobj's mode.
           `fileobj' is not closed, when TarFile is closed.
        """
        self.name = name

        if len(mode) > 1 or mode not in "raw":
            raise ValueError("mode must be 'r', 'a' or 'w'")
        self._mode = mode
        self.mode = {"r": "rb", "a": "r+b", "w": "wb"}[mode]

        if not fileobj:
            fileobj = file(self.name, self.mode)
            self._extfileobj = False
        else:
            if self.name is None and hasattr(fileobj, "name"):
                self.name = fileobj.name
            if hasattr(fileobj, "mode"):
                self.mode = fileobj.mode
            self._extfileobj = True
        self.fileobj = fileobj

        # Init datastructures
        self.closed = False
        self.members = []       # list of members as TarInfo objects
        self._loaded = False    # flag if all members have been read
        self.offset = 0L        # current position in the archive file
        self.inodes = {}        # dictionary caching the inodes of
                                # archive members already added

        if self._mode == "r":
            self.firstmember = None
            self.firstmember = self.next()

        if self._mode == "a":
            # Move to the end of the archive,
            # before the first empty block.
            self.firstmember = None
            while True:
                try:
                    tarinfo = self.next()
                except ReadError:
                    self.fileobj.seek(0)
                    break
                if tarinfo is None:
                    self.fileobj.seek(- BLOCKSIZE, 1)
                    break

        if self._mode in "aw":
            self._loaded = True

    #--------------------------------------------------------------------------
    # Below are the classmethods which act as alternate constructors to the
    # TarFile class. The open() method is the only one that is needed for
    # public use; it is the "super"-constructor and is able to select an
    # adequate "sub"-constructor for a particular compression using the mapping
    # from OPEN_METH.
    #
    # This concept allows one to subclass TarFile without losing the comfort of
    # the super-constructor. A sub-constructor is registered and made available
    # by adding it to the mapping in OPEN_METH.

    @classmethod
    def open(cls, name=None, mode="r", fileobj=None, bufsize=20*512):
        """Open a tar archive for reading, writing or appending. Return
           an appropriate TarFile class.

           mode:
           'r' or 'r:*' open for reading with transparent compression
           'r:'         open for reading exclusively uncompressed
           'r:gz'       open for reading with gzip compression
           'r:bz2'      open for reading with bzip2 compression
           'a' or 'a:'  open for appending
           'w' or 'w:'  open for writing without compression
           'w:gz'       open for writing with gzip compression
           'w:bz2'      open for writing with bzip2 compression

           'r|*'        open a stream of tar blocks with transparent compression
           'r|'         open an uncompressed stream of tar blocks for reading
           'r|gz'       open a gzip compressed stream of tar blocks
           'r|bz2'      open a bzip2 compressed stream of tar blocks
           'w|'         open an uncompressed stream for writing
           'w|gz'       open a gzip compressed stream for writing
           'w|bz2'      open a bzip2 compressed stream for writing
        """

        if not name and not fileobj:
            raise ValueError("nothing to open")

        if mode in ("r", "r:*"):
            # Find out which *open() is appropriate for opening the file.
            for comptype in cls.OPEN_METH:
                func = getattr(cls, cls.OPEN_METH[comptype])
                try:
                    return func(name, "r", fileobj)
                except (ReadError, CompressionError):
                    continue
            raise ReadError("file could not be opened successfully")

        elif ":" in mode:
            filemode, comptype = mode.split(":", 1)
            filemode = filemode or "r"
            comptype = comptype or "tar"

            # Select the *open() function according to
            # given compression.
            if comptype in cls.OPEN_METH:
                func = getattr(cls, cls.OPEN_METH[comptype])
            else:
                raise CompressionError("unknown compression type %r" % comptype)
            return func(name, filemode, fileobj)

        elif "|" in mode:
            filemode, comptype = mode.split("|", 1)
            filemode = filemode or "r"
            comptype = comptype or "tar"

            if filemode not in "rw":
                raise ValueError("mode must be 'r' or 'w'")

            t = cls(name, filemode,
                    _Stream(name, filemode, comptype, fileobj, bufsize))
            t._extfileobj = False
            return t

        elif mode in "aw":
            return cls.taropen(name, mode, fileobj)

        raise ValueError("undiscernible mode")

    @classmethod
    def taropen(cls, name, mode="r", fileobj=None):
        """Open uncompressed tar archive name for reading or writing.
        """
        if len(mode) > 1 or mode not in "raw":
            raise ValueError("mode must be 'r', 'a' or 'w'")
        return cls(name, mode, fileobj)

    @classmethod
    def gzopen(cls, name, mode="r", fileobj=None, compresslevel=9):
        """Open gzip compressed tar archive name for reading or writing.
           Appending is not allowed.
        """
        if len(mode) > 1 or mode not in "rw":
            raise ValueError("mode must be 'r' or 'w'")

        try:
            import gzip
            gzip.GzipFile
        except (ImportError, AttributeError):
            raise CompressionError("gzip module is not available")

        pre, ext = os.path.splitext(name)
        pre = os.path.basename(pre)
        if ext == ".tgz":
            ext = ".tar"
        if ext == ".gz":
            ext = ""
        tarname = pre + ext

        if fileobj is None:
            fileobj = file(name, mode + "b")

        if mode != "r":
            name = tarname

        try:
            t = cls.taropen(tarname, mode,
                gzip.GzipFile(name, mode, compresslevel, fileobj)
            )
        except IOError:
            raise ReadError("not a gzip file")
        t._extfileobj = False
        return t

    @classmethod
    def bz2open(cls, name, mode="r", fileobj=None, compresslevel=9):
        """Open bzip2 compressed tar archive name for reading or writing.
           Appending is not allowed.
        """
        if len(mode) > 1 or mode not in "rw":
            raise ValueError("mode must be 'r' or 'w'.")

        try:
            import bz2
        except ImportError:
            raise CompressionError("bz2 module is not available")

        pre, ext = os.path.splitext(name)
        pre = os.path.basename(pre)
        if ext == ".tbz2":
            ext = ".tar"
        if ext == ".bz2":
            ext = ""
        tarname = pre + ext

        if fileobj is not None:
            fileobj = _BZ2Proxy(fileobj, mode)
        else:
            fileobj = bz2.BZ2File(name, mode, compresslevel=compresslevel)

        try:
            t = cls.taropen(tarname, mode, fileobj)
        except IOError:
            raise ReadError("not a bzip2 file")
        t._extfileobj = False
        return t

    # All *open() methods are registered here.
    OPEN_METH = {
        "tar": "taropen",   # uncompressed tar
        "gz":  "gzopen",    # gzip compressed tar
        "bz2": "bz2open"    # bzip2 compressed tar
    }

    #--------------------------------------------------------------------------
    # The public methods which TarFile provides:

    def close(self):
        """Close the TarFile. In write-mode, two finishing zero blocks are
           appended to the archive.
        """
        if self.closed:
            return

        if self._mode in "aw":
            self.fileobj.write(NUL * (BLOCKSIZE * 2))
            self.offset += (BLOCKSIZE * 2)
            # fill up the end with zero-blocks
            # (like option -b20 for tar does)
            blocks, remainder = divmod(self.offset, RECORDSIZE)
            if remainder > 0:
                self.fileobj.write(NUL * (RECORDSIZE - remainder))

        if not self._extfileobj:
            self.fileobj.close()
        self.closed = True

    def getmember(self, name):
        """Return a TarInfo object for member `name'. If `name' can not be
           found in the archive, KeyError is raised. If a member occurs more
           than once in the archive, its last occurence is assumed to be the
           most up-to-date version.
        """
        tarinfo = self._getmember(name)
        if tarinfo is None:
            raise KeyError("filename %r not found" % name)
        return tarinfo

    def getmembers(self):
        """Return the members of the archive as a list of TarInfo objects. The
           list has the same order as the members in the archive.
        """
        self._check()
        if not self._loaded:    # if we want to obtain a list of
            self._load()        # all members, we first have to
                                # scan the whole archive.
        return self.members

    def getnames(self):
        """Return the members of the archive as a list of their names. It has
           the same order as the list returned by getmembers().
        """
        return [tarinfo.name for tarinfo in self.getmembers()]

    def gettarinfo(self, name=None, arcname=None, fileobj=None):
        """Create a TarInfo object for either the file `name' or the file
           object `fileobj' (using os.fstat on its file descriptor). You can
           modify some of the TarInfo's attributes before you add it using
           addfile(). If given, `arcname' specifies an alternative name for the
           file in the archive.
        """
        self._check("aw")

        # When fileobj is given, replace name by
        # fileobj's real name.
        if fileobj is not None:
            name = fileobj.name

        # Building the name of the member in the archive.
        # Backward slashes are converted to forward slashes,
        # Absolute paths are turned to relative paths.
        if arcname is None:
            arcname = name
        arcname = normpath(arcname)
        drv, arcname = os.path.splitdrive(arcname)
        while arcname[0:1] == "/":
            arcname = arcname[1:]

        # Now, fill the TarInfo object with
        # information specific for the file.
        tarinfo = TarInfo()

        # Use os.stat or os.lstat, depending on platform
        # and if symlinks shall be resolved.
        if fileobj is None:
            if hasattr(os, "lstat") and not self.dereference:
                statres = os.lstat(name)
            else:
                statres = os.stat(name)
        else:
            statres = os.fstat(fileobj.fileno())
        linkname = ""

        stmd = statres.st_mode
        if stat.S_ISREG(stmd):
            inode = (statres.st_ino, statres.st_dev)
            if not self.dereference and \
                    statres.st_nlink > 1 and inode in self.inodes:
                # Is it a hardlink to an already
                # archived file?
                type = LNKTYPE
                linkname = self.inodes[inode]
            else:
                # The inode is added only if its valid.
                # For win32 it is always 0.
                type = REGTYPE
                if inode[0]:
                    self.inodes[inode] = arcname
        elif stat.S_ISDIR(stmd):
            type = DIRTYPE
            if arcname[-1:] != "/":
                arcname += "/"
        elif stat.S_ISFIFO(stmd):
            type = FIFOTYPE
        elif stat.S_ISLNK(stmd):
            type = SYMTYPE
            linkname = os.readlink(name)
        elif stat.S_ISCHR(stmd):
            type = CHRTYPE
        elif stat.S_ISBLK(stmd):
            type = BLKTYPE
        else:
            return None

        # Fill the TarInfo object with all
        # information we can get.
        tarinfo.name = arcname
        tarinfo.mode = stmd
        tarinfo.uid = statres.st_uid
        tarinfo.gid = statres.st_gid
        if stat.S_ISREG(stmd):
            tarinfo.size = statres.st_size
        else:
            tarinfo.size = 0L
        tarinfo.mtime = statres.st_mtime
        tarinfo.type = type
        tarinfo.linkname = linkname
        if pwd:
            try:
                tarinfo.uname = pwd.getpwuid(tarinfo.uid)[0]
            except KeyError:
                pass
        if grp:
            try:
                tarinfo.gname = grp.getgrgid(tarinfo.gid)[0]
            except KeyError:
                pass

        if type in (CHRTYPE, BLKTYPE):
            if hasattr(os, "major") and hasattr(os, "minor"):
                tarinfo.devmajor = os.major(statres.st_rdev)
                tarinfo.devminor = os.minor(statres.st_rdev)
        return tarinfo

    def list(self, verbose=True):
        """Print a table of contents to sys.stdout. If `verbose' is False, only
           the names of the members are printed. If it is True, an `ls -l'-like
           output is produced.
        """
        self._check()

        for tarinfo in self:
            if verbose:
                print filemode(tarinfo.mode),
                print "%s/%s" % (tarinfo.uname or tarinfo.uid,
                                 tarinfo.gname or tarinfo.gid),
                if tarinfo.ischr() or tarinfo.isblk():
                    print "%10s" % ("%d,%d" \
                                    % (tarinfo.devmajor, tarinfo.devminor)),
                else:
                    print "%10d" % tarinfo.size,
                print "%d-%02d-%02d %02d:%02d:%02d" \
                      % time.localtime(tarinfo.mtime)[:6],

            print tarinfo.name,

            if verbose:
                if tarinfo.issym():
                    print "->", tarinfo.linkname,
                if tarinfo.islnk():
                    print "link to", tarinfo.linkname,
            print

    def add(self, name, arcname=None, recursive=True):
        """Add the file `name' to the archive. `name' may be any type of file
           (directory, fifo, symbolic link, etc.). If given, `arcname'
           specifies an alternative name for the file in the archive.
           Directories are added recursively by default. This can be avoided by
           setting `recursive' to False.
        """
        self._check("aw")

        if arcname is None:
            arcname = name

        # Skip if somebody tries to archive the archive...
        if self.name is not None \
            and os.path.abspath(name) == os.path.abspath(self.name):
            self._dbg(2, "tarfile: Skipped %r" % name)
            return

        # Special case: The user wants to add the current
        # working directory.
        if name == ".":
            if recursive:
                if arcname == ".":
                    arcname = ""
                for f in os.listdir("."):
                    self.add(f, os.path.join(arcname, f))
            return

        self._dbg(1, name)

        # Create a TarInfo object from the file.
        tarinfo = self.gettarinfo(name, arcname)

        if tarinfo is None:
            self._dbg(1, "tarfile: Unsupported type %r" % name)
            return

        # Append the tar header and data to the archive.
        if tarinfo.isreg():
            f = file(name, "rb")
            self.addfile(tarinfo, f)
            f.close()

        elif tarinfo.isdir():
            self.addfile(tarinfo)
            if recursive:
                for f in os.listdir(name):
                    self.add(os.path.join(name, f), os.path.join(arcname, f))

        else:
            self.addfile(tarinfo)

    def addfile(self, tarinfo, fileobj=None):
        """Add the TarInfo object `tarinfo' to the archive. If `fileobj' is
           given, tarinfo.size bytes are read from it and added to the archive.
           You can create TarInfo objects using gettarinfo().
           On Windows platforms, `fileobj' should always be opened with mode
           'rb' to avoid irritation about the file size.
        """
        self._check("aw")

        tarinfo.name = normpath(tarinfo.name)
        if tarinfo.isdir():
            # directories should end with '/'
            tarinfo.name += "/"

        if tarinfo.linkname:
            tarinfo.linkname = normpath(tarinfo.linkname)

        if tarinfo.size > MAXSIZE_MEMBER:
            if self.posix:
                raise ValueError("file is too large (>= 8 GB)")
            else:
                self._dbg(2, "tarfile: Created GNU tar largefile header")


        if len(tarinfo.linkname) > LENGTH_LINK:
            if self.posix:
                raise ValueError("linkname is too long (>%d)" % (LENGTH_LINK))
            else:
                self._create_gnulong(tarinfo.linkname, GNUTYPE_LONGLINK)
                tarinfo.linkname = tarinfo.linkname[:LENGTH_LINK -1]
                self._dbg(2, "tarfile: Created GNU tar extension LONGLINK")

        if len(tarinfo.name) > LENGTH_NAME:
            if self.posix:
                prefix = tarinfo.name[:LENGTH_PREFIX + 1]
                while prefix and prefix[-1] != "/":
                    prefix = prefix[:-1]

                name = tarinfo.name[len(prefix):]
                prefix = prefix[:-1]

                if not prefix or len(name) > LENGTH_NAME:
                    raise ValueError("name is too long (>%d)" % (LENGTH_NAME))

                tarinfo.name   = name
                tarinfo.prefix = prefix
            else:
                self._create_gnulong(tarinfo.name, GNUTYPE_LONGNAME)
                tarinfo.name = tarinfo.name[:LENGTH_NAME - 1]
                self._dbg(2, "tarfile: Created GNU tar extension LONGNAME")

        self.fileobj.write(tarinfo.tobuf(self.posix))
        self.offset += BLOCKSIZE

        # If there's data to follow, append it.
        if fileobj is not None:
            copyfileobj(fileobj, self.fileobj, tarinfo.size)
            blocks, remainder = divmod(tarinfo.size, BLOCKSIZE)
            if remainder > 0:
                self.fileobj.write(NUL * (BLOCKSIZE - remainder))
                blocks += 1
            self.offset += blocks * BLOCKSIZE

        self.members.append(tarinfo)

    def extractall(self, path=".", members=None):
        """Extract all members from the archive to the current working
           directory and set owner, modification time and permissions on
           directories afterwards. `path' specifies a different directory
           to extract to. `members' is optional and must be a subset of the
           list returned by getmembers().
        """
        directories = []

        if members is None:
            members = self

        for tarinfo in members:
            if tarinfo.isdir():
                # Extract directory with a safe mode, so that
                # all files below can be extracted as well.
                try:
                    os.makedirs(os.path.join(path, tarinfo.name), 0777)
                except EnvironmentError:
                    pass
                directories.append(tarinfo)
            else:
                self.extract(tarinfo, path)

        # Reverse sort directories.
        directories.sort(lambda a, b: cmp(a.name, b.name))
        directories.reverse()

        # Set correct owner, mtime and filemode on directories.
        for tarinfo in directories:
            path = os.path.join(path, tarinfo.name)
            try:
                self.chown(tarinfo, path)
                self.utime(tarinfo, path)
                self.chmod(tarinfo, path)
            except ExtractError, e:
                if self.errorlevel > 1:
                    raise
                else:
                    self._dbg(1, "tarfile: %s" % e)

    def extract(self, member, path=""):
        """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 TarInfo object. You can
           specify a different directory using `path'.
        """
        self._check("r")

        if isinstance(member, TarInfo):
            tarinfo = member
        else:
            tarinfo = self.getmember(member)

        # Prepare the link target for makelink().
        if tarinfo.islnk():
            tarinfo._link_target = os.path.join(path, tarinfo.linkname)

        try:
            self._extract_member(tarinfo, os.path.join(path, tarinfo.name))
        except EnvironmentError, e:
            if self.errorlevel > 0:
                raise
            else:
                if e.filename is None:
                    self._dbg(1, "tarfile: %s" % e.strerror)
                else:
                    self._dbg(1, "tarfile: %s %r" % (e.strerror, e.filename))
        except ExtractError, e:
            if self.errorlevel > 1:
                raise
            else:
                self._dbg(1, "tarfile: %s" % e)

    def extractfile(self, member):
        """Extract a member from the archive as a file object. `member' may be
           a filename or a TarInfo object. If `member' is a regular file, a
           file-like object is returned. If `member' is a link, a file-like
           object is constructed from the link's target. If `member' is none of
           the above, None is returned.
           The file-like object is read-only and provides the following
           methods: read(), readline(), readlines(), seek() and tell()
        """
        self._check("r")

        if isinstance(member, TarInfo):
            tarinfo = member
        else:
            tarinfo = self.getmember(member)

        if tarinfo.isreg():
            return self.fileobject(self, tarinfo)

        elif tarinfo.type not in SUPPORTED_TYPES:
            # If a member's type is unknown, it is treated as a
            # regular file.
            return self.fileobject(self, tarinfo)

        elif tarinfo.islnk() or tarinfo.issym():
            if isinstance(self.fileobj, _Stream):
                # A small but ugly workaround for the case that someone tries
                # to extract a (sym)link as a file-object from a non-seekable
                # stream of tar blocks.
                raise StreamError("cannot extract (sym)link as file object")
            else:
                # A (sym)link's file object is its target's file object.
                return self.extractfile(self._getmember(tarinfo.linkname,
                                                        tarinfo))
        else:
            # If there's no data associated with the member (directory, chrdev,
            # blkdev, etc.), return None instead of a file object.
            return None

    def _extract_member(self, tarinfo, targetpath):
        """Extract the TarInfo object tarinfo to a physical
           file called targetpath.
        """
        # Fetch the TarInfo object for the given name
        # and build the destination pathname, replacing
        # forward slashes to platform specific separators.
        if targetpath[-1:] == "/":
            targetpath = targetpath[:-1]
        targetpath = os.path.normpath(targetpath)

        # Create all upper directories.
        upperdirs = os.path.dirname(targetpath)
        if upperdirs and not os.path.exists(upperdirs):
            ti = TarInfo()
            ti.name  = upperdirs
            ti.type  = DIRTYPE
            ti.mode  = 0777
            ti.mtime = tarinfo.mtime
            ti.uid   = tarinfo.uid
            ti.gid   = tarinfo.gid
            ti.uname = tarinfo.uname
            ti.gname = tarinfo.gname
            try:
                self._extract_member(ti, ti.name)
            except:
                pass

        if tarinfo.islnk() or tarinfo.issym():
            self._dbg(1, "%s -> %s" % (tarinfo.name, tarinfo.linkname))
        else:
            self._dbg(1, tarinfo.name)

        if tarinfo.isreg():
            self.makefile(tarinfo, targetpath)
        elif tarinfo.isdir():
            self.makedir(tarinfo, targetpath)
        elif tarinfo.isfifo():
            self.makefifo(tarinfo, targetpath)
        elif tarinfo.ischr() or tarinfo.isblk():
            self.makedev(tarinfo, targetpath)
        elif tarinfo.islnk() or tarinfo.issym():
            self.makelink(tarinfo, targetpath)
        elif tarinfo.type not in SUPPORTED_TYPES:
            self.makeunknown(tarinfo, targetpath)
        else:
            self.makefile(tarinfo, targetpath)

        self.chown(tarinfo, targetpath)
        if not tarinfo.issym():
            self.chmod(tarinfo, targetpath)
            self.utime(tarinfo, targetpath)

    #--------------------------------------------------------------------------
    # Below are the different file methods. They are called via
    # _extract_member() when extract() is called. They can be replaced in a
    # subclass to implement other functionality.

    def makedir(self, tarinfo, targetpath):
        """Make a directory called targetpath.
        """
        try:
            os.mkdir(targetpath)
        except EnvironmentError, e:
            if e.errno != errno.EEXIST:
                raise

    def makefile(self, tarinfo, targetpath):
        """Make a file called targetpath.
        """
        source = self.extractfile(tarinfo)
        target = file(targetpath, "wb")
        copyfileobj(source, target)
        source.close()
        target.close()

    def makeunknown(self, tarinfo, targetpath):
        """Make a file from a TarInfo object with an unknown type
           at targetpath.
        """
        self.makefile(tarinfo, targetpath)
        self._dbg(1, "tarfile: Unknown file type %r, " \
                     "extracted as regular file." % tarinfo.type)

    def makefifo(self, tarinfo, targetpath):
        """Make a fifo called targetpath.
        """
        if hasattr(os, "mkfifo"):
            os.mkfifo(targetpath)
        else:
            raise ExtractError("fifo not supported by system")

    def makedev(self, tarinfo, targetpath):
        """Make a character or block device called targetpath.
        """
        if not hasattr(os, "mknod") or not hasattr(os, "makedev"):
            raise ExtractError("special devices not supported by system")

        mode = tarinfo.mode
        if tarinfo.isblk():
            mode |= stat.S_IFBLK
        else:
            mode |= stat.S_IFCHR

        os.mknod(targetpath, mode,
                 os.makedev(tarinfo.devmajor, tarinfo.devminor))

    def makelink(self, tarinfo, targetpath):
        """Make a (symbolic) link called targetpath. If it cannot be created
          (platform limitation), we try to make a copy of the referenced file
          instead of a link.
        """
        linkpath = tarinfo.linkname
        try:
            if tarinfo.issym():
                os.symlink(linkpath, targetpath)
            else:
                # See extract().
                os.link(tarinfo._link_target, targetpath)
        except AttributeError:
            if tarinfo.issym():
                linkpath = os.path.join(os.path.dirname(tarinfo.name),
                                        linkpath)
                linkpath = normpath(linkpath)

            try:
                self._extract_member(self.getmember(linkpath), targetpath)
            except (EnvironmentError, KeyError), e:
                linkpath = os.path.normpath(linkpath)
                try:
                    shutil.copy2(linkpath, targetpath)
                except EnvironmentError, e:
                    raise IOError("link could not be created")

    def chown(self, tarinfo, targetpath):
        """Set owner of targetpath according to tarinfo.
        """
        if pwd and hasattr(os, "geteuid") and os.geteuid() == 0:
            # We have to be root to do so.
            try:
                g = grp.getgrnam(tarinfo.gname)[2]
            except KeyError:
                try:
                    g = grp.getgrgid(tarinfo.gid)[2]
                except KeyError:
                    g = os.getgid()
            try:
                u = pwd.getpwnam(tarinfo.uname)[2]
            except KeyError:
                try:
                    u = pwd.getpwuid(tarinfo.uid)[2]
                except KeyError:
                    u = os.getuid()
            try:
                if tarinfo.issym() and hasattr(os, "lchown"):
                    os.lchown(targetpath, u, g)
                else:
                    if sys.platform != "os2emx":
                        os.chown(targetpath, u, g)
            except EnvironmentError, e:
                raise ExtractError("could not change owner")

    def chmod(self, tarinfo, targetpath):
        """Set file permissions of targetpath according to tarinfo.
        """
        if hasattr(os, 'chmod'):
            try:
                os.chmod(targetpath, tarinfo.mode)
            except EnvironmentError, e:
                raise ExtractError("could not change mode")

    def utime(self, tarinfo, targetpath):
        """Set modification time of targetpath according to tarinfo.
        """
        if not hasattr(os, 'utime'):
            return
        if sys.platform == "win32" and tarinfo.isdir():
            # According to msdn.microsoft.com, it is an error (EACCES)
            # to use utime() on directories.
            return
        try:
            os.utime(targetpath, (tarinfo.mtime, tarinfo.mtime))
        except EnvironmentError, e:
            raise ExtractError("could not change modification time")

    #--------------------------------------------------------------------------
    def next(self):
        """Return the next member of the archive as a TarInfo object, when
           TarFile is opened for reading. Return None if there is no more
           available.
        """
        self._check("ra")
        if self.firstmember is not None:
            m = self.firstmember
            self.firstmember = None
            return m

        # Read the next block.
        self.fileobj.seek(self.offset)
        while True:
            buf = self.fileobj.read(BLOCKSIZE)
            if not buf:
                return None

            try:
                tarinfo = TarInfo.frombuf(buf)

                # Set the TarInfo object's offset to the current position of the
                # TarFile and set self.offset to the position where the data blocks
                # should begin.
                tarinfo.offset = self.offset
                self.offset += BLOCKSIZE

                tarinfo = self.proc_member(tarinfo)

            except ValueError, e:
                if self.ignore_zeros:
                    self._dbg(2, "0x%X: empty or invalid block: %s" %
                              (self.offset, e))
                    self.offset += BLOCKSIZE
                    continue
                else:
                    if self.offset == 0:
                        raise ReadError("empty, unreadable or compressed "
                                        "file: %s" % e)
                    return None
            break

        # Some old tar programs represent a directory as a regular
        # file with a trailing slash.
        if tarinfo.isreg() and tarinfo.name.endswith("/"):
            tarinfo.type = DIRTYPE

        # The prefix field is used for filenames > 100 in
        # the POSIX standard.
        # name = prefix + '/' + name
        tarinfo.name = normpath(os.path.join(tarinfo.prefix.rstrip(NUL),
                                             tarinfo.name))

        # Directory names should have a '/' at the end.
        if tarinfo.isdir():
            tarinfo.name += "/"

        self.members.append(tarinfo)
        return tarinfo

    #--------------------------------------------------------------------------
    # The following are methods that are called depending on the type of a
    # member. The entry point is proc_member() which is called with a TarInfo
    # object created from the header block from the current offset. The
    # proc_member() method can be overridden in a subclass to add custom
    # proc_*() methods. A proc_*() method MUST implement the following
    # operations:
    # 1. Set tarinfo.offset_data to the position where the data blocks begin,
    #    if there is data that follows.
    # 2. Set self.offset to the position where the next member's header will
    #    begin.
    # 3. Return tarinfo or another valid TarInfo object.
    def proc_member(self, tarinfo):
        """Choose the right processing method for tarinfo depending
           on its type and call it.
        """
        if tarinfo.type in (GNUTYPE_LONGNAME, GNUTYPE_LONGLINK):
            return self.proc_gnulong(tarinfo)
        elif tarinfo.type == GNUTYPE_SPARSE:
            return self.proc_sparse(tarinfo)
        else:
            return self.proc_builtin(tarinfo)

    def proc_builtin(self, tarinfo):
        """Process a builtin type member or an unknown member
           which will be treated as a regular file.
        """
        tarinfo.offset_data = self.offset
        if tarinfo.isreg() or tarinfo.type not in SUPPORTED_TYPES:
            # Skip the following data blocks.
            self.offset += self._block(tarinfo.size)
        return tarinfo

    def proc_gnulong(self, tarinfo):
        """Process the blocks that hold a GNU longname
           or longlink member.
        """
        buf = ""
        count = tarinfo.size
        while count > 0:
            block = self.fileobj.read(BLOCKSIZE)
            buf += block
            self.offset += BLOCKSIZE
            count -= BLOCKSIZE

        # Fetch the next header and process it.
        b = self.fileobj.read(BLOCKSIZE)
        t = TarInfo.frombuf(b)
        t.offset = self.offset
        self.offset += BLOCKSIZE
        next = self.proc_member(t)

        # Patch the TarInfo object from the next header with
        # the longname information.
        next.offset = tarinfo.offset
        if tarinfo.type == GNUTYPE_LONGNAME:
            next.name = buf.rstrip(NUL)
        elif tarinfo.type == GNUTYPE_LONGLINK:
            next.linkname = buf.rstrip(NUL)

        return next

    def proc_sparse(self, tarinfo):
        """Process a GNU sparse header plus extra headers.
        """
        buf = tarinfo.buf
        sp = _ringbuffer()
        pos = 386
        lastpos = 0L
        realpos = 0L
        # There are 4 possible sparse structs in the
        # first header.
        for i in xrange(4):
            try:
                offset = nti(buf[pos:pos + 12])
                numbytes = nti(buf[pos + 12:pos + 24])
            except ValueError:
                break
            if offset > lastpos:
                sp.append(_hole(lastpos, offset - lastpos))
            sp.append(_data(offset, numbytes, realpos))
            realpos += numbytes
            lastpos = offset + numbytes
            pos += 24

        isextended = ord(buf[482])
        origsize = nti(buf[483:495])

        # If the isextended flag is given,
        # there are extra headers to process.
        while isextended == 1:
            buf = self.fileobj.read(BLOCKSIZE)
            self.offset += BLOCKSIZE
            pos = 0
            for i in xrange(21):
                try:
                    offset = nti(buf[pos:pos + 12])
                    numbytes = nti(buf[pos + 12:pos + 24])
                except ValueError:
                    break
                if offset > lastpos:
                    sp.append(_hole(lastpos, offset - lastpos))
                sp.append(_data(offset, numbytes, realpos))
                realpos += numbytes
                lastpos = offset + numbytes
                pos += 24
            isextended = ord(buf[504])

        if lastpos < origsize:
            sp.append(_hole(lastpos, origsize - lastpos))

        tarinfo.sparse = sp

        tarinfo.offset_data = self.offset
        self.offset += self._block(tarinfo.size)
        tarinfo.size = origsize

        # Clear the prefix field so that it is not used
        # as a pathname in next().
        tarinfo.prefix = ""

        return tarinfo

    #--------------------------------------------------------------------------
    # Little helper methods:

    def _block(self, count):
        """Round up a byte count by BLOCKSIZE and return it,
           e.g. _block(834) => 1024.
        """
        blocks, remainder = divmod(count, BLOCKSIZE)
        if remainder:
            blocks += 1
        return blocks * BLOCKSIZE

    def _getmember(self, name, tarinfo=None):
        """Find an archive member by name from bottom to top.
           If tarinfo is given, it is used as the starting point.
        """
        # Ensure that all members have been loaded.
        members = self.getmembers()

        if tarinfo is None:
            end = len(members)
        else:
            end = members.index(tarinfo)

        for i in xrange(end - 1, -1, -1):
            if name == members[i].name:
                return members[i]

    def _load(self):
        """Read through the entire archive file and look for readable
           members.
        """
        while True:
            tarinfo = self.next()
            if tarinfo is None:
                break
        self._loaded = True

    def _check(self, mode=None):
        """Check if TarFile is still open, and if the operation's mode
           corresponds to TarFile's mode.
        """
        if self.closed:
            raise IOError("%s is closed" % self.__class__.__name__)
        if mode is not None and self._mode not in mode:
            raise IOError("bad operation for mode %r" % self._mode)

    def __iter__(self):
        """Provide an iterator object.
        """
        if self._loaded:
            return iter(self.members)
        else:
            return TarIter(self)

    def _create_gnulong(self, name, type):
        """Write a GNU longname/longlink member to the TarFile.
           It consists of an extended tar header, with the length
           of the longname as size, followed by data blocks,
           which contain the longname as a null terminated string.
        """
        name += NUL

        tarinfo = TarInfo()
        tarinfo.name = "././@LongLink"
        tarinfo.type = type
        tarinfo.mode = 0
        tarinfo.size = len(name)

        # write extended header
        self.fileobj.write(tarinfo.tobuf())
        self.offset += BLOCKSIZE
        # write name blocks
        self.fileobj.write(name)
        blocks, remainder = divmod(tarinfo.size, BLOCKSIZE)
        if remainder > 0:
            self.fileobj.write(NUL * (BLOCKSIZE - remainder))
            blocks += 1
        self.offset += blocks * BLOCKSIZE

    def _dbg(self, level, msg):
        """Write debugging output to sys.stderr.
        """
        if level <= self.debug:
            print >> sys.stderr, msg
# class TarFile

class TarIter:
    """Iterator Class.

       for tarinfo in TarFile(...):
           suite...
    """

    def __init__(self, tarfile):
        """Construct a TarIter object.
        """
        self.tarfile = tarfile
        self.index = 0
    def __iter__(self):
        """Return iterator object.
        """
        return self
    def next(self):
        """Return the next item using TarFile's next() method.
           When all members have been read, set TarFile as _loaded.
        """
        # Fix for SF #1100429: Under rare circumstances it can
        # happen that getmembers() is called during iteration,
        # which will cause TarIter to stop prematurely.
        if not self.tarfile._loaded:
            tarinfo = self.tarfile.next()
            if not tarinfo:
                self.tarfile._loaded = True
                raise StopIteration
        else:
            try:
                tarinfo = self.tarfile.members[self.index]
            except IndexError:
                raise StopIteration
        self.index += 1
        return tarinfo

# Helper classes for sparse file support
class _section:
    """Base class for _data and _hole.
    """
    def __init__(self, offset, size):
        self.offset = offset
        self.size = size
    def __contains__(self, offset):
        return self.offset <= offset < self.offset + self.size

class _data(_section):
    """Represent a data section in a sparse file.
    """
    def __init__(self, offset, size, realpos):
        _section.__init__(self, offset, size)
        self.realpos = realpos

class _hole(_section):
    """Represent a hole section in a sparse file.
    """
    pass

class _ringbuffer(list):
    """Ringbuffer class which increases performance
       over a regular list.
    """
    def __init__(self):
        self.idx = 0
    def find(self, offset):
        idx = self.idx
        while True:
            item = self[idx]
            if offset in item:
                break
            idx += 1
            if idx == len(self):
                idx = 0
            if idx == self.idx:
                # End of File
                return None
        self.idx = idx
        return item

#---------------------------------------------
# zipfile compatible TarFile class
#---------------------------------------------
TAR_PLAIN = 0           # zipfile.ZIP_STORED
TAR_GZIPPED = 8         # zipfile.ZIP_DEFLATED
class TarFileCompat:
    """TarFile class compatible with standard module zipfile's
       ZipFile class.
    """
    def __init__(self, file, mode="r", compression=TAR_PLAIN):
        if compression == TAR_PLAIN:
            self.tarfile = TarFile.taropen(file, mode)
        elif compression == TAR_GZIPPED:
            self.tarfile = TarFile.gzopen(file, mode)
        else:
            raise ValueError("unknown compression constant")
        if mode[0:1] == "r":
            members = self.tarfile.getmembers()
            for m in members:
                m.filename = m.name
                m.file_size = m.size
                m.date_time = time.gmtime(m.mtime)[:6]
    def namelist(self):
        return map(lambda m: m.name, self.infolist())
    def infolist(self):
        return filter(lambda m: m.type in REGULAR_TYPES,
                      self.tarfile.getmembers())
    def printdir(self):
        self.tarfile.list()
    def testzip(self):
        return
    def getinfo(self, name):
        return self.tarfile.getmember(name)
    def read(self, name):
        return self.tarfile.extractfile(self.tarfile.getmember(name)).read()
    def write(self, filename, arcname=None, compress_type=None):
        self.tarfile.add(filename, arcname)
    def writestr(self, zinfo, bytes):
        try:
            from cStringIO import StringIO
        except ImportError:
            from StringIO import StringIO
        import calendar
        zinfo.name = zinfo.filename
        zinfo.size = zinfo.file_size
        zinfo.mtime = calendar.timegm(zinfo.date_time)
        self.tarfile.addfile(zinfo, StringIO(bytes))
    def close(self):
        self.tarfile.close()
#class TarFileCompat

#--------------------
# exported functions
#--------------------
def is_tarfile(name):
    """Return True if name points to a tar archive that we
       are able to handle, else return False.
    """
    try:
        t = open(name)
        t.close()
        return True
    except TarError:
        return False

open = TarFile.open