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Merge with 3.2: Issue #13158: Fix decoding and encoding of base-256 number fields in tarfile.

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The nti() function that converts a number field from a tar header to a number
failed to decode GNU tar specific base-256 fields. I also added support for
decoding and encoding negative base-256 number fields.
This commit is contained in:
Lars Gustäbel 2011-10-14 12:53:10 +02:00
commit 01277d166a
3 changed files with 49 additions and 21 deletions
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43
Lib/tarfile.py
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@ -194,16 +194,18 @@ def nti(s):
"""
# There are two possible encodings for a number field, see
# itn() below.
if s[0] != chr(0o200):
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:
n = int(nts(s, "ascii", "strict") or "0", 8)
except ValueError:
raise InvalidHeaderError("invalid header")
else:
n = 0
for i in range(len(s) - 1):
n <<= 8
n += ord(s[i + 1])
return n
def itn(n, digits=8, format=DEFAULT_FORMAT):
@ -212,25 +214,26 @@ def itn(n, digits=8, format=DEFAULT_FORMAT):
# 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 byte indicates this particular
# encoding, the following digits-1 bytes are a big-endian
# representation. This allows values up to (256**(digits-1))-1.
# 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.
if 0 <= n < 8 ** (digits - 1):
s = bytes("%0*o" % (digits - 1, n), "ascii") + NUL
else:
if format != GNU_FORMAT or n >= 256 ** (digits - 1):
raise ValueError("overflow in number field")
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
if n < 0:
# XXX We mimic GNU tar's behaviour with negative numbers,
# this could raise OverflowError.
n = struct.unpack("L", struct.pack("l", n))[0]
s = bytearray()
for i in range(digits - 1):
s.insert(0, n & 0o377)
s.insert(1, n & 0o377)
n >>= 8
s.insert(0, 0o200)
else:
raise ValueError("overflow in number field")
return s
def calc_chksums(buf):