tarfile_stream.py

#-------------------------------------------------------------------
# tarfile.py
#-------------------------------------------------------------------
# Copyright (C) 2002 Lars Gustaebel <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__  = "0.10.0"
__author__  = "Lars Gust\u00e4bel (lars@gustaebel.de)"
__credits__ = "Gustavo Niemeyer, Niels Gust\u00e4bel, Richard Townsend."

#---------
# Imports
#---------
from builtins import open as bltn_open
import contextlib
import sys
import os
import io
import shutil
import stat
import time
import struct
import copy
import re

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

# os.symlink on Windows prior to 6.0 raises NotImplementedError
symlink_exception = (AttributeError, NotImplementedError)
try:
    # OSError (winerror=1314) will be raised if the caller does not hold the
    # SeCreateSymbolicLinkPrivilege privilege
    symlink_exception += (OSError,)
except NameError:
    pass

# from tarfile import *
__all__ = ["TarFile", "TarInfo", "is_tarfile", "TarError", "ReadError",
           "CompressionError", "StreamError", "ExtractError", "HeaderError",
           "ENCODING", "USTAR_FORMAT", "GNU_FORMAT", "PAX_FORMAT",
           "DEFAULT_FORMAT", "open"]

#---------------------------------------------------------
# tar constants
#---------------------------------------------------------
NUL = b"\0"                     # the null character
BLOCKSIZE = 512                 # length of processing blocks
RECORDSIZE = BLOCKSIZE * 20     # length of records
GNU_MAGIC = b"ustar  \0"        # magic gnu tar string
POSIX_MAGIC = b"ustar\x0000"    # magic posix tar string

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

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

GNUTYPE_LONGNAME = b"L"         # GNU tar longname
GNUTYPE_LONGLINK = b"K"         # GNU tar longlink
GNUTYPE_SPARSE = b"S"           # GNU tar sparse file

XHDTYPE = b"x"                  # POSIX.1-2001 extended header
XGLTYPE = b"g"                  # POSIX.1-2001 global header
SOLARIS_XHDTYPE = b"X"          # Solaris extended header

USTAR_FORMAT = 0                # POSIX.1-1988 (ustar) format
GNU_FORMAT = 1                  # GNU tar format
PAX_FORMAT = 2                  # POSIX.1-2001 (pax) format
DEFAULT_FORMAT = PAX_FORMAT

#---------------------------------------------------------
# tarfile constants
#---------------------------------------------------------
# File types that tarfile supports:
SUPPORTED_TYPES = (REGTYPE, AREGTYPE, LNKTYPE,
                   SYMTYPE, DIRTYPE, FIFOTYPE,
                   CONTTYPE, CHRTYPE, BLKTYPE,
                   GNUTYPE_LONGNAME, GNUTYPE_LONGLINK,
                   GNUTYPE_SPARSE)

# File types that will be treated as a regular file.
REGULAR_TYPES = (REGTYPE, AREGTYPE,
                 CONTTYPE, GNUTYPE_SPARSE)

# File types that are part of the GNU tar format.
GNU_TYPES = (GNUTYPE_LONGNAME, GNUTYPE_LONGLINK,
             GNUTYPE_SPARSE)

# Fields from a pax header that override a TarInfo attribute.
PAX_FIELDS = ("path", "linkpath", "size", "mtime",
              "uid", "gid", "uname", "gname")

# Fields from a pax header that are affected by hdrcharset.
PAX_NAME_FIELDS = {"path", "linkpath", "uname", "gname"}

# Fields in a pax header that are numbers, all other fields
# are treated as strings.
PAX_NUMBER_FIELDS = {
    "atime": float,
    "ctime": float,
    "mtime": float,
    "uid": int,
    "gid": int,
    "size": int
}

#---------------------------------------------------------
# initialization
#---------------------------------------------------------
if os.name == "nt":
    ENCODING = "utf-8"
else:
    ENCODING = sys.getfilesystemencoding()

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

def stn(s, length, encoding, errors):
    """Convert a string to a null-terminated bytes object.
    """
    s = s.encode(encoding, errors)
    return s[:length] + (length - len(s)) * NUL

def nts(s, encoding, errors):
    """Convert a null-terminated bytes object to a string.
    """
    p = s.find(b"\0")
    if p != -1:
        s = s[:p]
    return s.decode(encoding, errors)

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] in (0o200, 0o377):
        n = 0
        for i in range(len(s) - 1):
            n <<= 8
            n += s[i + 1]
        if s[0] == 0o377:
            n = -(256 ** (len(s) - 1) - n)
    else:
        try:
            s = nts(s, "ascii", "strict")
            n = int(s.strip() or "0", 8)
        except ValueError:
            raise InvalidHeaderError("invalid header")
    return n

def itn(n, digits=8, format=DEFAULT_FORMAT):
    """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 0o200 or 0o377 byte indicate this
    # particular encoding, the following digits-1 bytes are a big-endian
    # base-256 representation. This allows values up to (256**(digits-1))-1.
    # A 0o200 byte indicates a positive number, a 0o377 byte a negative
    # number.
    n = int(n)
    if 0 <= n < 8 ** (digits - 1):
        s = bytes("%0*o" % (digits - 1, n), "ascii") + NUL
    elif format == GNU_FORMAT and -256 ** (digits - 1) <= n < 256 ** (digits - 1):
        if n >= 0:
            s = bytearray([0o200])
        else:
            s = bytearray([0o377])
            n = 256 ** digits + n

        for i in range(digits - 1):
            s.insert(1, n & 0o377)
            n >>= 8
    else:
        raise ValueError("overflow in number field")

    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_from("148B8x356B", buf))
    signed_chksum = 256 + sum(struct.unpack_from("148b8x356b", buf))
    return unsigned_chksum, signed_chksum

def _copyfileobj(fsrc, length=16*1024):
    """yield data from file-like object fsrc"""
    while True:
        buf = fsrc.read(length)
        if not buf:
            break
        yield buf

def copyfileobj(src, dst, length=None, exception=OSError, bufsize=None):
    """Copy length bytes from fileobj src to fileobj dst.
       If length is None, copy the entire content.
    """
    bufsize = bufsize or 16 * 1024
    if length == 0:
        return
    if length is None:
        yield from _copyfileobj(src, bufsize)
        return

    blocks, remainder = divmod(length, bufsize)
    for b in range(blocks):
        buf = src.read(bufsize)
        if len(buf) < bufsize:
            raise exception("unexpected end of data")
        yield buf

    if remainder != 0:
        buf = src.read(remainder)
        if len(buf) < remainder:
            raise exception("unexpected end of data")
        yield buf
    return

def filemode(mode):
    """Deprecated in this location; use stat.filemode."""
    import warnings
    warnings.warn("deprecated in favor of stat.filemode",
                  DeprecationWarning, 2)
    return stat.filemode(mode)

def _safe_print(s):
    encoding = getattr(sys.stdout, 'encoding', None)
    if encoding is not None:
        s = s.encode(encoding, 'backslashreplace').decode(encoding)
    print(s, end=' ')


class TarError(Exception):
    """Base exception."""
    pass
class ExtractError(TarError):
    """General exception for extract errors."""
    pass
class ReadError(TarError):
    """Exception for unreadable tar archives."""
    pass
class CompressionError(TarError):
    """Exception for unavailable compression methods."""
    pass
class StreamError(TarError):
    """Exception for unsupported operations on stream-like TarFiles."""
    pass
class HeaderError(TarError):
    """Base exception for header errors."""
    pass
class EmptyHeaderError(HeaderError):
    """Exception for empty headers."""
    pass
class TruncatedHeaderError(HeaderError):
    """Exception for truncated headers."""
    pass
class EOFHeaderError(HeaderError):
    """Exception for end of file headers."""
    pass
class InvalidHeaderError(HeaderError):
    """Exception for invalid headers."""
    pass
class SubsequentHeaderError(HeaderError):
    """Exception for missing and invalid extended headers."""
    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]
        with contextlib.suppress(AttributeError):
            mode |= os.O_BINARY
        self.fd = os.open(name, mode, 0o666)

    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 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      = b""
        self.pos      = 0
        self.closed   = False

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

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

            elif comptype == "xz":
                try:
                    import lzma
                except ImportError:
                    raise CompressionError("lzma module is not available")
                if mode == "r":
                    self.dbuf = b""
                    self.cmp = lzma.LZMADecompressor()
                    self.exception = lzma.LZMAError
                else:
                    self.cmp = lzma.LZMACompressor()

            elif comptype != "tar":
                raise CompressionError("unknown compression type %r" % comptype)

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

    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", int(time.time()))
        yield from self.__write(b"\037\213\010\010" + timestamp + b"\002\377")
        if self.name.endswith(".gz"):
            self.name = self.name[:-3]
        # RFC1952 says we must use ISO-8859-1 for the FNAME field.
        yield from self.__write(self.name.encode("iso-8859-1", "replace") + 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)
        yield from self.__write(s)

    # malloc hell
    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:
            yield self.buf[:self.bufsize]
            self.buf = self.buf[self.bufsize:]

    def close(self):
        self.closed = True

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

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

        if self.mode == "w" and self.buf:
            yield self.buf
            self.buf = b""
            if self.comptype == "gz":
                yield struct.pack("<L", self.crc)
                yield struct.pack("<L", self.pos & 0xffffFFFF)

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

        # taken from gzip.GzipFile with some alterations
        if self.__read(2) != b"\037\213":
            raise ReadError("not a gzip file")
        if self.__read(1) != b"\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 range(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 = b"".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
            try:
                buf = self.cmp.decompress(buf)
            except self.exception:
                raise ReadError("invalid compressed data")
            t.append(buf)
            c += len(buf)
        t = b"".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 = b"".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(b"\x1f\x8b\x08"):
            return "gz"
        elif self.buf[0:3] == b"BZh" and self.buf[4:10] == b"1AY&SY":
            return "bz2"
        elif self.buf.startswith((b"\x5d\x00\x00\x80", b"\xfd7zXZ")):
            return "xz"
        else:
            return "tar"

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

#------------------------
# Extraction file object
#------------------------
class _FileInFile(object):
    """A thin wrapper around an existing file object that
       provides a part of its data as an individual file
       object.
    """

    def __init__(self, fileobj, offset, size, blockinfo=None):
        self.fileobj = fileobj
        self.offset = offset
        self.size = size
        self.position = 0
        self.name = getattr(fileobj, "name", None)
        self.closed = False

        if blockinfo is None:
            blockinfo = [(0, size)]

        # Construct a map with data and zero blocks.
        self.map_index = 0
        self.map = []
        lastpos = 0
        realpos = self.offset
        for offset, size in blockinfo:
            if offset > lastpos:
                self.map.append((False, lastpos, offset, None))
            self.map.append((True, offset, offset + size, realpos))
            realpos += size
            lastpos = offset + size
        if lastpos < self.size:
            self.map.append((False, lastpos, self.size, None))

    def flush(self):
        pass

    def readable(self):
        return True

    def writable(self):
        return False

    def seekable(self):
        return self.fileobj.seekable()

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

    def seek(self, position, whence=io.SEEK_SET):
        """Seek to a position in the file.
        """
        if whence == io.SEEK_SET:
            self.position = min(max(position, 0), self.size)
        elif whence == io.SEEK_CUR:
            if position < 0:
                self.position = max(self.position + position, 0)
            else:
                self.position = min(self.position + position, self.size)
        elif whence == io.SEEK_END:
            self.position = max(min(self.size + position, self.size), 0)
        else:
            raise ValueError("Invalid argument")
        return self.position

    def read(self, size=None):
        """Read data from the file.
        """
        if size is None:
            size = self.size - self.position
        else:
            size = min(size, self.size - self.position)

        buf = b""
        while size > 0:
            while True:
                data, start, stop, offset = self.map[self.map_index]
                if start <= self.position < stop:
                    break
                else:
                    self.map_index += 1
                    if self.map_index == len(self.map):
                        self.map_index = 0
            length = min(size, stop - self.position)
            if data:
                self.fileobj.seek(offset + (self.position - start))
                b = self.fileobj.read(length)
                if len(b) != length:
                    raise ReadError("unexpected end of data")
                buf += b
            else:
                buf += NUL * length
            size -= length
            self.position += length
        return buf

    def readinto(self, b):
        buf = self.read(len(b))
        b[:len(buf)] = buf
        return len(buf)

    def close(self):
        self.closed = True
#class _FileInFile

class ExFileObject(io.BufferedReader):

    def __init__(self, tarfile, tarinfo):
        fileobj = _FileInFile(tarfile.fileobj, tarinfo.offset_data,
                tarinfo.size, tarinfo.sparse)
        super().__init__(fileobj)
#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.
    """

    __slots__ = ("name", "mode", "uid", "gid", "size", "mtime",
                 "chksum", "type", "linkname", "uname", "gname",
                 "devmajor", "devminor",
                 "offset", "offset_data", "pax_headers", "sparse",
                 "tarfile", "_sparse_structs", "_link_target")

    def __init__(self, name=""):
        """Construct a TarInfo object. name is the optional name
           of the member.
        """
        self.name = name        # member name
        self.mode = 0o644       # 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 name
        self.gname = ""         # group name
        self.devmajor = 0       # device major number
        self.devminor = 0       # device minor number

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

        self.sparse = None      # sparse member information
        self.pax_headers = {}   # pax header information

    # In pax headers the "name" and "linkname" field are called
    # "path" and "linkpath".
    @property
    def path(self):
        return self.name

    @path.setter
    def path(self, name):
        self.name = name

    @property
    def linkpath(self):
        return self.linkname

    @linkpath.setter
    def linkpath(self, linkname):
        self.linkname = linkname

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

    def get_info(self):
        """Return the TarInfo's attributes as a dictionary.
        """
        info = {
            "name":     self.name,
            "mode":     self.mode & 0o7777,
            "uid":      self.uid,
            "gid":      self.gid,
            "size":     self.size,
            "mtime":    self.mtime,
            "chksum":   self.chksum,
            "type":     self.type,
            "linkname": self.linkname,
            "uname":    self.uname,
            "gname":    self.gname,
            "devmajor": self.devmajor,
            "devminor": self.devminor
        }

        if info["type"] == DIRTYPE and not info["name"].endswith("/"):
            info["name"] += "/"

        return info

    def tobuf(self, format=DEFAULT_FORMAT, encoding=ENCODING, errors="surrogateescape"):
        """Return a tar header as a string of 512 byte blocks.
        """
        info = self.get_info()

        if format == USTAR_FORMAT:
            return self.create_ustar_header(info, encoding, errors)
        elif format == GNU_FORMAT:
            return self.create_gnu_header(info, encoding, errors)
        elif format == PAX_FORMAT:
            return self.create_pax_header(info, encoding)
        else:
            raise ValueError("invalid format")

    def create_ustar_header(self, info, encoding, errors):
        """Return the object as a ustar header block.
        """
        info["magic"] = POSIX_MAGIC

        if len(info["linkname"].encode(encoding, errors)) > LENGTH_LINK:
            raise ValueError("linkname is too long")

        if len(info["name"].encode(encoding, errors)) > LENGTH_NAME:
            info["prefix"], info["name"] = self._posix_split_name(info["name"], encoding, errors)

        return self._create_header(info, USTAR_FORMAT, encoding, errors)

    def create_gnu_header(self, info, encoding, errors):
        """Return the object as a GNU header block sequence.
        """
        info["magic"] = GNU_MAGIC

        buf = b""
        if len(info["linkname"].encode(encoding, errors)) > LENGTH_LINK:
            buf += self._create_gnu_long_header(info["linkname"], GNUTYPE_LONGLINK, encoding, errors)

        if len(info["name"].encode(encoding, errors)) > LENGTH_NAME:
            buf += self._create_gnu_long_header(info["name"], GNUTYPE_LONGNAME, encoding, errors)

        return buf + self._create_header(info, GNU_FORMAT, encoding, errors)

    def create_pax_header(self, info, encoding):
        """Return the object as a ustar header block. If it cannot be
           represented this way, prepend a pax extended header sequence
           with supplement information.
        """
        info["magic"] = POSIX_MAGIC
        pax_headers = self.pax_headers.copy()

        # Test string fields for values that exceed the field length or cannot
        # be represented in ASCII encoding.
        for name, hname, length in (
                ("name", "path", LENGTH_NAME), ("linkname", "linkpath", LENGTH_LINK),
                ("uname", "uname", 32), ("gname", "gname", 32)):

            if hname in pax_headers:
                # The pax header has priority.
                continue

            # Try to encode the string as ASCII.
            try:
                info[name].encode("ascii", "strict")
            except UnicodeEncodeError:
                pax_headers[hname] = info[name]
                continue

            if len(info[name]) > length:
                pax_headers[hname] = info[name]

        # Test number fields for values that exceed the field limit or values
        # that like to be stored as float.
        for name, digits in (("uid", 8), ("gid", 8), ("size", 12), ("mtime", 12)):
            if name in pax_headers:
                # The pax header has priority. Avoid overflow.
                info[name] = 0
                continue

            val = info[name]
            if not 0 <= val < 8 ** (digits - 1) or isinstance(val, float):
                pax_headers[name] = str(val)
                info[name] = 0

        # Create a pax extended header if necessary.
        if pax_headers:
            buf = self._create_pax_generic_header(pax_headers, XHDTYPE, encoding)
        else:
            buf = b""

        return buf + self._create_header(info, USTAR_FORMAT, "ascii", "replace")

    @classmethod
    def create_pax_global_header(cls, pax_headers):
        """Return the object as a pax global header block sequence.
        """
        return cls._create_pax_generic_header(pax_headers, XGLTYPE, "utf-8")

    def _posix_split_name(self, name, encoding, errors):
        """Split a name longer than 100 chars into a prefix
           and a name part.
        """
        components = name.split("/")
        for i in range(1, len(components)):
            prefix = "/".join(components[:i])
            name = "/".join(components[i:])
            if len(prefix.encode(encoding, errors)) <= LENGTH_PREFIX and \
                    len(name.encode(encoding, errors)) <= LENGTH_NAME:
                break
        else:
            raise ValueError("name is too long")

        return prefix, name

    @staticmethod
    def _create_header(info, format, encoding, errors):
        """Return a header block. info is a dictionary with file
           information, format must be one of the *_FORMAT constants.
        """
        parts = [
            stn(info.get("name", ""), 100, encoding, errors),
            itn(info.get("mode", 0) & 0o7777, 8, format),
            itn(info.get("uid", 0), 8, format),
            itn(info.get("gid", 0), 8, format),
            itn(info.get("size", 0), 12, format),
            itn(info.get("mtime", 0), 12, format),
            b"        ", # checksum field
            info.get("type", REGTYPE),
            stn(info.get("linkname", ""), 100, encoding, errors),
            info.get("magic", POSIX_MAGIC),
            stn(info.get("uname", ""), 32, encoding, errors),
            stn(info.get("gname", ""), 32, encoding, errors),
            itn(info.get("devmajor", 0), 8, format),
            itn(info.get("devminor", 0), 8, format),
            stn(info.get("prefix", ""), 155, encoding, errors)
        ]

        buf = struct.pack("%ds" % BLOCKSIZE, b"".join(parts))
        chksum = calc_chksums(buf[-BLOCKSIZE:])[0]
        buf = buf[:-364] + bytes("%06o\0" % chksum, "ascii") + buf[-357:]
        return buf

    @staticmethod
    def _create_payload(payload):
        """Return the string payload filled with zero bytes
           up to the next 512 byte border.
        """
        blocks, remainder = divmod(len(payload), BLOCKSIZE)
        if remainder > 0:
            payload += (BLOCKSIZE - remainder) * NUL
        return payload

    @classmethod
    def _create_gnu_long_header(cls, name, type, encoding, errors):
        """Return a GNUTYPE_LONGNAME or GNUTYPE_LONGLINK sequence
           for name.
        """
        name = name.encode(encoding, errors) + NUL

        info = {}
        info["name"] = "././@LongLink"
        info["type"] = type
        info["size"] = len(name)
        info["magic"] = GNU_MAGIC

        # create extended header + name blocks.
        return cls._create_header(info, USTAR_FORMAT, encoding, errors) + \
                cls._create_payload(name)

    @classmethod
    def _create_pax_generic_header(cls, pax_headers, type, encoding):
        """Return a POSIX.1-2008 extended or global header sequence
           that contains a list of keyword, value pairs. The values
           must be strings.
        """
        # Check if one of the fields contains surrogate characters and thereby
        # forces hdrcharset=BINARY, see _proc_pax() for more information.
        binary = False
        for keyword, value in pax_headers.items():
            try:
                value.encode("utf-8", "strict")
            except UnicodeEncodeError:
                binary = True
                break

        records = b""
        if binary:
            # Put the hdrcharset field at the beginning of the header.
            records += b"21 hdrcharset=BINARY\n"

        for keyword, value in pax_headers.items():
            keyword = keyword.encode("utf-8")
            if binary:
                # Try to restore the original byte representation of `value'.
                # Needless to say, that the encoding must match the string.
                value = value.encode(encoding, "surrogateescape")
            else:
                value = value.encode("utf-8")

            l = len(keyword) + len(value) + 3   # ' ' + '=' + '\n'
            n = p = 0
            while True:
                n = l + len(str(p))
                if n == p:
                    break
                p = n
            records += bytes(str(p), "ascii") + b" " + keyword + b"=" + value + b"\n"

        # We use a hardcoded "././@PaxHeader" name like star does
        # instead of the one that POSIX recommends.
        info = {}
        info["name"] = "././@PaxHeader"
        info["type"] = type
        info["size"] = len(records)
        info["magic"] = POSIX_MAGIC

        # Create pax header + record blocks.
        return cls._create_header(info, USTAR_FORMAT, "ascii", "replace") + \
                cls._create_payload(records)

    @classmethod
    def frombuf(cls, buf, encoding, errors):
        """Construct a TarInfo object from a 512 byte bytes object.
        """
        if len(buf) == 0:
            raise EmptyHeaderError("empty header")
        if len(buf) != BLOCKSIZE:
            raise TruncatedHeaderError("truncated header")
        if buf.count(NUL) == BLOCKSIZE:
            raise EOFHeaderError("end of file header")

        chksum = nti(buf[148:156])
        if chksum not in calc_chksums(buf):
            raise InvalidHeaderError("bad checksum")

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

        # Old V7 tar format represents a directory as a regular
        # file with a trailing slash.
        if obj.type == AREGTYPE and obj.name.endswith("/"):
            obj.type = DIRTYPE

        # The old GNU sparse format occupies some of the unused
        # space in the buffer for up to 4 sparse structures.
        # Save them for later processing in _proc_sparse().
        if obj.type == GNUTYPE_SPARSE:
            pos = 386
            structs = []
            for i in range(4):
                try:
                    offset = nti(buf[pos:pos + 12])
                    numbytes = nti(buf[pos + 12:pos + 24])
                except ValueError:
                    break
                structs.append((offset, numbytes))
                pos += 24
            isextended = bool(buf[482])
            origsize = nti(buf[483:495])
            obj._sparse_structs = (structs, isextended, origsize)

        # Remove redundant slashes from directories.
        if obj.isdir():
            obj.name = obj.name.rstrip("/")

        # Reconstruct a ustar longname.
        if prefix and obj.type not in GNU_TYPES:
            obj.name = prefix + "/" + obj.name
        return obj

    @classmethod
    def fromtarfile(cls, tarfile):
        """Return the next TarInfo object from TarFile object
           tarfile.
        """
        buf = tarfile.fileobj.read(BLOCKSIZE)
        obj = cls.frombuf(buf, tarfile.encoding, tarfile.errors)
        obj.offset = tarfile.fileobj.tell() - BLOCKSIZE
        return obj._proc_member(tarfile)

    #--------------------------------------------------------------------------
    # The following are methods that are called depending on the type of a
    # member. The entry point is _proc_member() which can be overridden in a
    # subclass to add custom _proc_*() methods. A _proc_*() method MUST
    # implement the following
    # operations:
    # 1. Set self.offset_data to the position where the data blocks begin,
    #    if there is data that follows.
    # 2. Set tarfile.offset to the position where the next member's header will
    #    begin.
    # 3. Return self or another valid TarInfo object.
    def _proc_member(self, tarfile):
        """Choose the right processing method depending on
           the type and call it.
        """
        if self.type in (GNUTYPE_LONGNAME, GNUTYPE_LONGLINK):
            return self._proc_gnulong(tarfile)
        elif self.type == GNUTYPE_SPARSE:
            return self._proc_sparse(tarfile)
        elif self.type in (XHDTYPE, XGLTYPE, SOLARIS_XHDTYPE):
            return self._proc_pax(tarfile)
        else:
            return self._proc_builtin(tarfile)

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

        # Patch the TarInfo object with saved global
        # header information.
        self._apply_pax_info(tarfile.pax_headers, tarfile.encoding, tarfile.errors)

        return self

    def _proc_gnulong(self, tarfile):
        """Process the blocks that hold a GNU longname
           or longlink member.
        """
        buf = tarfile.fileobj.read(self._block(self.size))

        # Fetch the next header and process it.
        try:
            next = self.fromtarfile(tarfile)
        except HeaderError:
            raise SubsequentHeaderError("missing or bad subsequent header")

        # Patch the TarInfo object from the next header with
        # the longname information.
        next.offset = self.offset
        if self.type == GNUTYPE_LONGNAME:
            next.name = nts(buf, tarfile.encoding, tarfile.errors)
        elif self.type == GNUTYPE_LONGLINK:
            next.linkname = nts(buf, tarfile.encoding, tarfile.errors)

        return next

    def _proc_sparse(self, tarfile):
        """Process a GNU sparse header plus extra headers.
        """
        # We already collected some sparse structures in frombuf().
        structs, isextended, origsize = self._sparse_structs
        del self._sparse_structs

        # Collect sparse structures from extended header blocks.
        while isextended:
            buf = tarfile.fileobj.read(BLOCKSIZE)
            pos = 0
            for i in range(21):
                try:
                    offset = nti(buf[pos:pos + 12])
                    numbytes = nti(buf[pos + 12:pos + 24])
                except ValueError:
                    break
                if offset and numbytes:
                    structs.append((offset, numbytes))
                pos += 24
            isextended = bool(buf[504])
        self.sparse = structs

        self.offset_data = tarfile.fileobj.tell()
        tarfile.offset = self.offset_data + self._block(self.size)
        self.size = origsize
        return self

    def _proc_pax(self, tarfile):
        """Process an extended or global header as described in
           POSIX.1-2008.
        """
        # Read the header information.
        buf = tarfile.fileobj.read(self._block(self.size))

        # A pax header stores supplemental information for either
        # the following file (extended) or all following files
        # (global).
        if self.type == XGLTYPE:
            pax_headers = tarfile.pax_headers
        else:
            pax_headers = tarfile.pax_headers.copy()

        # Check if the pax header contains a hdrcharset field. This tells us
        # the encoding of the path, linkpath, uname and gname fields. Normally,
        # these fields are UTF-8 encoded but since POSIX.1-2008 tar
        # implementations are allowed to store them as raw binary strings if
        # the translation to UTF-8 fails.
        match = re.search(br"\d+ hdrcharset=([^\n]+)\n", buf)
        if match is not None:
            pax_headers["hdrcharset"] = match.group(1).decode("utf-8")

        # For the time being, we don't care about anything other than "BINARY".
        # The only other value that is currently allowed by the standard is
        # "ISO-IR 10646 2000 UTF-8" in other words UTF-8.
        hdrcharset = pax_headers.get("hdrcharset")
        if hdrcharset == "BINARY":
            encoding = tarfile.encoding
        else:
            encoding = "utf-8"

        # Parse pax header information. A record looks like that:
        # "%d %s=%s\n" % (length, keyword, value). length is the size
        # of the complete record including the length field itself and
        # the newline. keyword and value are both UTF-8 encoded strings.
        regex = re.compile(br"(\d+) ([^=]+)=")
        pos = 0
        while True:
            match = regex.match(buf, pos)
            if not match:
                break

            length, keyword = match.groups()
            length = int(length)
            value = buf[match.end(2) + 1:match.start(1) + length - 1]

            # Normally, we could just use "utf-8" as the encoding and "strict"
            # as the error handler, but we better not take the risk. For
            # example, GNU tar <= 1.23 is known to store filenames it cannot
            # translate to UTF-8 as raw strings (unfortunately without a
            # hdrcharset=BINARY header).
            # We first try the strict standard encoding, and if that fails we
            # fall back on the user's encoding and error handler.
            keyword = self._decode_pax_field(keyword, "utf-8", "utf-8",
                    tarfile.errors)
            if keyword in PAX_NAME_FIELDS:
                value = self._decode_pax_field(value, encoding, tarfile.encoding,
                        tarfile.errors)
            else:
                value = self._decode_pax_field(value, "utf-8", "utf-8",
                        tarfile.errors)

            pax_headers[keyword] = value
            pos += length

        # Fetch the next header.
        try:
            next = self.fromtarfile(tarfile)
        except HeaderError:
            raise SubsequentHeaderError("missing or bad subsequent header")

        # Process GNU sparse information.
        if "GNU.sparse.map" in pax_headers:
            # GNU extended sparse format version 0.1.
            self._proc_gnusparse_01(next, pax_headers)

        elif "GNU.sparse.size" in pax_headers:
            # GNU extended sparse format version 0.0.
            self._proc_gnusparse_00(next, pax_headers, buf)

        elif pax_headers.get("GNU.sparse.major") == "1" and pax_headers.get("GNU.sparse.minor") == "0":
            # GNU extended sparse format version 1.0.
            self._proc_gnusparse_10(next, pax_headers, tarfile)

        if self.type in (XHDTYPE, SOLARIS_XHDTYPE):
            # Patch the TarInfo object with the extended header info.
            next._apply_pax_info(pax_headers, tarfile.encoding, tarfile.errors)
            next.offset = self.offset

            if "size" in pax_headers:
                # If the extended header replaces the size field,
                # we need to recalculate the offset where the next
                # header starts.
                offset = next.offset_data
                if next.isreg() or next.type not in SUPPORTED_TYPES:
                    offset += next._block(next.size)
                tarfile.offset = offset

        return next

    def _proc_gnusparse_00(self, next, pax_headers, buf):
        """Process a GNU tar extended sparse header, version 0.0.
        """
        offsets = []
        for match in re.finditer(br"\d+ GNU.sparse.offset=(\d+)\n", buf):
            offsets.append(int(match.group(1)))
        numbytes = []
        for match in re.finditer(br"\d+ GNU.sparse.numbytes=(\d+)\n", buf):
            numbytes.append(int(match.group(1)))
        next.sparse = list(zip(offsets, numbytes))

    def _proc_gnusparse_01(self, next, pax_headers):
        """Process a GNU tar extended sparse header, version 0.1.
        """
        sparse = [int(x) for x in pax_headers["GNU.sparse.map"].split(",")]
        next.sparse = list(zip(sparse[::2], sparse[1::2]))

    def _proc_gnusparse_10(self, next, pax_headers, tarfile):
        """Process a GNU tar extended sparse header, version 1.0.
        """
        fields = None
        sparse = []
        buf = tarfile.fileobj.read(BLOCKSIZE)
        fields, buf = buf.split(b"\n", 1)
        fields = int(fields)
        while len(sparse) < fields * 2:
            if b"\n" not in buf:
                buf += tarfile.fileobj.read(BLOCKSIZE)
            number, buf = buf.split(b"\n", 1)
            sparse.append(int(number))
        next.offset_data = tarfile.fileobj.tell()
        next.sparse = list(zip(sparse[::2], sparse[1::2]))

    def _apply_pax_info(self, pax_headers, encoding, errors):
        """Replace fields with supplemental information from a previous
           pax extended or global header.
        """
        for keyword, value in pax_headers.items():
            if keyword == "GNU.sparse.name":
                setattr(self, "path", value)
            elif keyword == "GNU.sparse.size":
                setattr(self, "size", int(value))
            elif keyword == "GNU.sparse.realsize":
                setattr(self, "size", int(value))
            elif keyword in PAX_FIELDS:
                if keyword in PAX_NUMBER_FIELDS:
                    try:
                        value = PAX_NUMBER_FIELDS[keyword](value)
                    except ValueError:
                        value = 0
                if keyword == "path":
                    value = value.rstrip("/")
                setattr(self, keyword, value)

        self.pax_headers = pax_headers.copy()

    def _decode_pax_field(self, value, encoding, fallback_encoding, fallback_errors):
        """Decode a single field from a pax record.
        """
        try:
            return value.decode(encoding, "strict")
        except UnicodeDecodeError:
            return value.decode(fallback_encoding, fallback_errors)

    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 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.sparse is not None
    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 = 1              # If 0, fatal errors only appear in debug
                                # messages (if debug >= 0). If > 0, errors
                                # are passed to the caller as exceptions.

    format = DEFAULT_FORMAT     # The format to use when creating an archive.

    encoding = ENCODING         # Encoding for 8-bit character strings.

    errors = None               # Error handler for unicode conversion.

    tarinfo = TarInfo           # The default TarInfo class to use.

    fileobject = ExFileObject   # The file-object for extractfile().

    def __init__(self, name=None, mode="r", fileobj=None, format=None,
            tarinfo=None, dereference=None, ignore_zeros=None, encoding=None,
            errors="surrogateescape", pax_headers=None, debug=None,
            errorlevel=None, copybufsize=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.
        """
        modes = {"r": "rb", "a": "r+b", "w": "wb", "x": "xb"}
        if mode not in modes:
            raise ValueError("mode must be 'r', 'a', 'w' or 'x'")
        self.mode = mode
        self._mode = modes[mode]

        if not fileobj:
            if self.mode == "a" and not os.path.exists(name):
                # Create nonexistent files in append mode.
                self.mode = "w"
                self._mode = "wb"
            fileobj = bltn_open(name, self._mode)
            self._extfileobj = False
        else:
            if (name is None and hasattr(fileobj, "name") and
                isinstance(fileobj.name, (str, bytes))):
                name = fileobj.name
            if hasattr(fileobj, "mode"):
                self._mode = fileobj.mode
            self._extfileobj = True
        self.name = os.path.abspath(name) if name else None
        self.fileobj = fileobj

        # Init attributes.
        if format is not None:
            self.format = format
        if tarinfo is not None:
            self.tarinfo = tarinfo
        if dereference is not None:
            self.dereference = dereference
        if ignore_zeros is not None:
            self.ignore_zeros = ignore_zeros
        if encoding is not None:
            self.encoding = encoding
        self.errors = errors

        if pax_headers is not None and self.format == PAX_FORMAT:
            self.pax_headers = pax_headers
        else:
            self.pax_headers = {}

        if debug is not None:
            self.debug = debug
        if errorlevel is not None:
            self.errorlevel = errorlevel

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

        try:
            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.
                while True:
                    self.fileobj.seek(self.offset)
                    try:
                        tarinfo = self.tarinfo.fromtarfile(self)
                        self.members.append(tarinfo)
                    except EOFHeaderError:
                        self.fileobj.seek(self.offset)
                        break
                    except HeaderError as e:
                        raise ReadError(str(e))

            if self.mode in ("a", "w", "x"):
                self._loaded = True

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

    #--------------------------------------------------------------------------
    # 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=RECORDSIZE, **kwargs):
        """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
           'r:xz'       open for reading with lzma compression
           'a' or 'a:'  open for appending, creating the file if necessary
           'w' or 'w:'  open for writing without compression
           'w:gz'       open for writing with gzip compression
           'w:bz2'      open for writing with bzip2 compression
           'w:xz'       open for writing with lzma compression

           'x' or 'x:'  create a tarfile exclusively without compression, raise
                        an exception if the file is already created
           'x:gz'       create a gzip compressed tarfile, raise an exception
                        if the file is already created
           'x:bz2'      create a bzip2 compressed tarfile, raise an exception
                        if the file is already created
           'x:xz'       create an lzma compressed tarfile, raise an exception
                        if the file is already created

           '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
           'r|xz'       open an lzma 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
           'w|xz'       open an lzma compressed stream for writing
        """

        if mode in ("r", "r:*"):
            # Find out which *open() is appropriate for opening the file.
            def not_compressed(comptype):
                return cls.OPEN_METH[comptype] == 'taropen'
            for comptype in sorted(cls.OPEN_METH, key=not_compressed):
                func = getattr(cls, cls.OPEN_METH[comptype])
                if fileobj is not None:
                    saved_pos = fileobj.tell()
                try:
                    return func(name, "r", fileobj, **kwargs)
                except (ReadError, CompressionError):
                    if fileobj is not None:
                        fileobj.seek(saved_pos)
                    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, **kwargs)

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

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

            stream = _Stream(name, filemode, comptype, fileobj, bufsize)
            try:
                t = cls(name, filemode, stream, **kwargs)
            except:
                stream.close()
                raise
            t._extfileobj = False
            return t

        elif mode in ("a", "w", "x"):
            return cls.taropen(name, mode, fileobj, **kwargs)

        raise ValueError("undiscernible mode")

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

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

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

        try:
            fileobj = gzip.GzipFile(name, mode + "b", compresslevel, fileobj)
        except OSError:
            if fileobj is not None and mode == 'r':
                raise ReadError("not a gzip file")
            raise

        try:
            t = cls.taropen(name, mode, fileobj, **kwargs)
        except OSError:
            fileobj.close()
            if mode == 'r':
                raise ReadError("not a gzip file")
            raise
        except:
            fileobj.close()
            raise
        t._extfileobj = False
        return t

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

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

        fileobj = bz2.BZ2File(fileobj or name, mode,
                              compresslevel=compresslevel)

        try:
            t = cls.taropen(name, mode, fileobj, **kwargs)
        except (OSError, EOFError):
            fileobj.close()
            if mode == 'r':
                raise ReadError("not a bzip2 file")
            raise
        except:
            fileobj.close()
            raise
        t._extfileobj = False
        return t

    @classmethod
    def xzopen(cls, name, mode="r", fileobj=None, preset=None, **kwargs):
        """Open lzma compressed tar archive name for reading or writing.
           Appending is not allowed.
        """
        if mode not in ("r", "w", "x"):
            raise ValueError("mode must be 'r', 'w' or 'x'")

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

        fileobj = lzma.LZMAFile(fileobj or name, mode, preset=preset)

        try:
            t = cls.taropen(name, mode, fileobj, **kwargs)
        except (lzma.LZMAError, EOFError):
            fileobj.close()
            if mode == 'r':
                raise ReadError("not an lzma file")
            raise
        except:
            fileobj.close()
            raise
        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
        "xz":  "xzopen"     # lzma compressed tar
    }

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

    def close(self):
        if self.closed:
            return

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

    def header(self):
        if self.pax_headers:
            buf = self.tarinfo.create_pax_global_header(self.pax_headers.copy())
            self.offset += len(buf)
            yield buf

    def footer(self):
        """In write-mode, yield two finishing zero blocks."""
        if self.closed:
            return

        if self.mode in ("a", "w", "x"):
            yield 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:
                yield NUL * (RECORDSIZE - remainder)

        self.close()

    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 occurrence 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 from the result of os.stat or equivalent
           on an existing file. The file is either named by `name', or
           specified as a file object `fileobj' with a file descriptor. If
           given, `arcname' specifies an alternative name for the file in the
           archive, otherwise, the name is taken from the 'name' attribute of
           'fileobj', or the 'name' argument. The name should be a text
           string.
        """
        self._check("awx")

        # 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
        drv, arcname = os.path.splitdrive(arcname)
        arcname = arcname.replace(os.sep, "/")
        arcname = arcname.lstrip("/")

        # Now, fill the TarInfo object with
        # information specific for the file.
        tarinfo = self.tarinfo()
        tarinfo.tarfile = self  # Not needed

        # 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 and arcname != self.inodes[inode]:
                # 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
        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

        tarinfo.name = arcname
        tarinfo.mode = stmd
        if type == REGTYPE:
            tarinfo.size = statres.st_size
        else:
            tarinfo.size = 0
        tarinfo.mtime = statres.st_mtime
        tarinfo.type = type
        tarinfo.linkname = linkname

        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, *, members=None):
        """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. `members' is optional and must be a subset of the
           list returned by getmembers().
        """
        self._check()

        if members is None:
            members = self
        for tarinfo in members:
            if verbose:
                _safe_print(stat.filemode(tarinfo.mode))
                _safe_print("%s/%s" % (tarinfo.uname or tarinfo.uid,
                                       tarinfo.gname or tarinfo.gid))
                if tarinfo.ischr() or tarinfo.isblk():
                    _safe_print("%10s" %
                            ("%d,%d" % (tarinfo.devmajor, tarinfo.devminor)))
                else:
                    _safe_print("%10d" % tarinfo.size)
                _safe_print("%d-%02d-%02d %02d:%02d:%02d" \
                            % time.localtime(tarinfo.mtime)[:6])

            _safe_print(tarinfo.name + ("/" if tarinfo.isdir() else ""))

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

    def add(self, name, arcname=None, recursive=True, *, filter=None):
        """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. `filter' is a function
           that expects a TarInfo object argument and returns the changed
           TarInfo object, if it returns None the TarInfo object will be
           excluded from the archive.
        """
        self._check("awx")

        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) == self.name:
            self._dbg(2, "tarfile: Skipped %r" % name)
            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

        # Change or exclude the TarInfo object.
        if filter is not None:
            tarinfo = filter(tarinfo)
            if tarinfo is None:
                self._dbg(2, "tarfile: Excluded %r" % name)
                return

        # Append the tar header and data to the archive.
        if tarinfo.isreg():
            try:
                with bltn_open(name, "rb") as f:
                    yield from self.addfile(tarinfo, f)
            except OSError:
                return

        elif tarinfo.isdir():
            yield from self.addfile(tarinfo)
            if recursive:
                try:
                    for f in sorted(os.listdir(name)):
                        yield from self.add(os.path.join(name, f), os.path.join(arcname, f), recursive, filter=filter)
                except OSError:
                    return

        else:
            yield from self.addfile(tarinfo)

    def addfile(self, tarinfo, fileobj=None):
        """Add the TarInfo object `tarinfo' to the archive. If `fileobj' is
           given, it should be a binary file, and tarinfo.size bytes are read
           from it and added to the archive. You can create TarInfo objects
           directly, or by using gettarinfo().
        """
        self._check("awx")

        tarinfo = copy.copy(tarinfo)

        buf = tarinfo.tobuf(self.format, self.encoding, self.errors)
        yield buf
        self.offset += len(buf)
        bufsize=self.copybufsize
        # If there's data to follow, append it.
        if fileobj is not None:
            yield from copyfileobj(fileobj, tarinfo.size, bufsize=bufsize)
            blocks, remainder = divmod(tarinfo.size, BLOCKSIZE)
            if remainder > 0:
                yield NUL * (BLOCKSIZE - remainder)
                blocks += 1
            self.offset += blocks * BLOCKSIZE

        self.members.append(tarinfo)

    def extractall(self, path=".", members=None, *, numeric_owner=False):
        """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(). If `numeric_owner` is True, only
           the numbers for user/group names are used and not the names.
        """
        directories = []

        if members is None:
            members = self

        for tarinfo in members:
            if tarinfo.isdir():
                # Extract directories with a safe mode.
                directories.append(tarinfo)
                tarinfo = copy.copy(tarinfo)
                tarinfo.mode = 0o700
            # Do not set_attrs directories, as we will do that further down
            self.extract(tarinfo, path, set_attrs=not tarinfo.isdir(),
                         numeric_owner=numeric_owner)

        # Reverse sort directories.
        directories.sort(key=lambda a: a.name)
        directories.reverse()

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

    def extract(self, member, path="", set_attrs=True, *, numeric_owner=False):
        """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'. File attributes (owner,
           mtime, mode) are set unless `set_attrs' is False. If `numeric_owner`
           is True, only the numbers for user/group names are used and not
           the names.
        """
        self._check("r")

        if isinstance(member, str):
            tarinfo = self.getmember(member)
        else:
            tarinfo = 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),
                                 set_attrs=set_attrs,
                                 numeric_owner=numeric_owner)
        except OSError as 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 as 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 or a
           link, an io.BufferedReader object is returned. Otherwise, None is
           returned.
        """
        self._check("r")

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

        if tarinfo.isreg() or tarinfo.type not in SUPPORTED_TYPES:
            # Members with unknown types are treated as regular files.
            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._find_link_target(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, set_attrs=True,
                        numeric_owner=False):
        """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.
        targetpath = targetpath.rstrip("/")
        targetpath = targetpath.replace("/", os.sep)

        # Create all upper directories.
        upperdirs = os.path.dirname(targetpath)
        if upperdirs and not os.path.exists(upperdirs):
            # Create directories that are not part of the archive with
            # default permissions.
            os.makedirs(upperdirs)

        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)

        if set_attrs:
            self.chown(tarinfo, targetpath, numeric_owner)
            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:
            # Use a safe mode for the directory, the real mode is set
            # later in _extract_member().
            os.mkdir(targetpath, 0o700)
        except FileExistsError:
            pass

    def makefile(self, tarinfo, targetpath):
        """Make a file called targetpath.
        """
        source = self.fileobj
        source.seek(tarinfo.offset_data)
        bufsize = self.copybufsize
        with bltn_open(targetpath, "wb") as target:
            if tarinfo.sparse is not None:
                for offset, size in tarinfo.sparse:
                    target.seek(offset)
                    copyfileobj(source, target, size, ReadError, bufsize)
                target.seek(tarinfo.size)
                target.truncate()
            else:
                copyfileobj(source, target, tarinfo.size, ReadError, bufsize)

    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.
        """
        try:
            # For systems that support symbolic and hard links.
            if tarinfo.issym():
                os.symlink(tarinfo.linkname, targetpath)
            else:
                # See extract().
                if os.path.exists(tarinfo._link_target):
                    os.link(tarinfo._link_target, targetpath)
                else:
                    self._extract_member(self._find_link_target(tarinfo),
                                         targetpath)
        except symlink_exception:
            try:
                self._extract_member(self._find_link_target(tarinfo),
                                     targetpath)
            except KeyError:
                raise ExtractError("unable to resolve link inside archive")

    def chown(self, tarinfo, targetpath, numeric_owner):
        """Set owner of targetpath according to tarinfo. If numeric_owner
           is True, use .gid/.uid instead of .gname/.uname. If numeric_owner
           is False, fall back to .gid/.uid when the search based on name
           fails.
        """
        if hasattr(os, "geteuid") and os.geteuid() == 0:
            # We have to be root to do so.
            g = tarinfo.gid
            u = tarinfo.uid
            if not numeric_owner:
                try:
                    if grp:
                        g = grp.getgrnam(tarinfo.gname)[2]
                except KeyError:
                    pass
                try:
                    if pwd:
                        u = pwd.getpwnam(tarinfo.uname)[2]
                except KeyError:
                    pass
            try:
                if tarinfo.issym() and hasattr(os, "lchown"):
                    os.lchown(targetpath, u, g)
                else:
                    os.chown(targetpath, u, g)
            except OSError:
                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 OSError:
                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
        try:
            os.utime(targetpath, (tarinfo.mtime, tarinfo.mtime))
        except OSError:
            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

        # Advance the file pointer.
        if self.offset != self.fileobj.tell():
            self.fileobj.seek(self.offset - 1)
            if not self.fileobj.read(1):
                raise ReadError("unexpected end of data")

        # Read the next block.
        tarinfo = None
        while True:
            try:
                tarinfo = self.tarinfo.fromtarfile(self)
            except EOFHeaderError as e:
                if self.ignore_zeros:
                    self._dbg(2, "0x%X: %s" % (self.offset, e))
                    self.offset += BLOCKSIZE
                    continue
            except InvalidHeaderError as e:
                if self.ignore_zeros:
                    self._dbg(2, "0x%X: %s" % (self.offset, e))
                    self.offset += BLOCKSIZE
                    continue
                elif self.offset == 0:
                    raise ReadError(str(e))
            except EmptyHeaderError:
                if self.offset == 0:
                    raise ReadError("empty file")
            except TruncatedHeaderError as e:
                if self.offset == 0:
                    raise ReadError(str(e))
            except SubsequentHeaderError as e:
                raise ReadError(str(e))
            break

        if tarinfo is not None:
            self.members.append(tarinfo)
        else:
            self._loaded = True

        return tarinfo

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

    def _getmember(self, name, tarinfo=None, normalize=False):
        """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()

        # Limit the member search list up to tarinfo.
        if tarinfo is not None:
            members = members[:members.index(tarinfo)]

        if normalize:
            name = os.path.normpath(name)

        for member in reversed(members):
            if normalize:
                member_name = os.path.normpath(member.name)
            else:
                member_name = member.name

            if name == member_name:
                return member

    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 OSError("%s is closed" % self.__class__.__name__)
        if mode is not None and self.mode not in mode:
            raise OSError("bad operation for mode %r" % self.mode)

    def _find_link_target(self, tarinfo):
        """Find the target member of a symlink or hardlink member in the
           archive.
        """
        if tarinfo.issym():
            # Always search the entire archive.
            linkname = "/".join(filter(None, (os.path.dirname(tarinfo.name), tarinfo.linkname)))
            limit = None
        else:
            # Search the archive before the link, because a hard link is
            # just a reference to an already archived file.
            linkname = tarinfo.linkname
            limit = tarinfo

        member = self._getmember(linkname, tarinfo=limit, normalize=True)
        if member is None:
            raise KeyError("linkname %r not found" % linkname)
        return member

    def __iter__(self):
        """Provide an iterator object.
        """
        if self._loaded:
            yield from self.members
            return

        # Yield items using TarFile's next() method.
        # When all members have been read, set TarFile as _loaded.
        index = 0
        # Fix for SF #1100429: Under rare circumstances it can
        # happen that getmembers() is called during iteration,
        # which will have already exhausted the next() method.
        if self.firstmember is not None:
            tarinfo = self.next()
            index += 1
            yield tarinfo

        while True:
            if index < len(self.members):
                tarinfo = self.members[index]
            elif not self._loaded:
                tarinfo = self.next()
                if not tarinfo:
                    self._loaded = True
                    return
            else:
                return
            index += 1
            yield tarinfo

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

#--------------------
# 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