cpython/Lib/tarfile.py at 3.6 · python/cpython · GitHub

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#!/usr/bin/env python3
#-------------------------------------------------------------------
# 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     = "0.9.0"
__author__  = "Lars Gust\u00e4bel (lars@gustaebel.de)"
__date__    = "$Date: 2011-02-25 17:42:01 +0200 (Fri, 25 Feb 2011) $"
__cvsid__   = "$Id: tarfile.py 88586 2011-02-25 15:42:01Z marc-andre.lemburg $"
__credits__ = "Gustavo Niemeyer, Niels Gust\u00e4bel, Richard Townsend."

#---------
# Imports
#---------
from builtins import open as bltn_open
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 = GNU_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(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:
        shutil.copyfileobj(src, dst, 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")
        dst.write(buf)

    if remainder != 0:
        buf = src.read(remainder)
        if len(buf) < remainder:
            raise exception("unexpected end of data")
        dst.write(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]
        if hasattr(os, "O_BINARY"):
            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 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      = 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()))
        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.
        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)
        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

        self.closed = True
        try:
            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 = b""
                if self.comptype == "gz":
                    self.fileobj.write(struct.pack("<L", self.crc))
                    self.fileobj.write(struct.pack("<L", self.pos & 0xffffFFFF))
        finally:
            if not self._extfileobj:
                self.fileobj.close()

    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".
    def _getpath(self):
        return self.name
    def _setpath(self, name):
        self.name = name
    path = property(_getpath, _setpath)

    def _getlinkpath(self):
        return self.linkname
    def _setlinkpath(self, linkname):
        self.linkname = linkname
    linkpath = property(_getlinkpath, _setlinkpath)

    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: