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Define lots of constants for indexes into the structures for the file

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header and central directory structures, and use them as appropriate.
The point being to make it easier to tell what is getting pulled out
where; magic numbers are evil!

Change the computation of the ZipInfo.file_offset field to use the
length of the relevant "extra" field -- there are two different ones,
and the wrong one had been used.  ;-(

This closes SF tracker patch #403276, but more verbosely than the
proposed patch.
This commit is contained in:
Fred Drake 2001-02-28 17:56:26 +00:00
parent 62e2c7e3df
commit 3e038e5e25
1 changed files with 51 additions and 7 deletions
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58
Lib/zipfile.py
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@ -27,6 +27,41 @@ class BadZipfile(Exception):
structFileHeader = "<4s2B4H3l2H" # 12 items, file header record, 30 bytes
stringFileHeader = "PK\003\004" # magic number for file header
# indexes of entries in the central directory structure
_CD_SIGNATURE = 0
_CD_CREATE_VERSION = 1
_CD_CREATE_SYSTEM = 2
_CD_EXTRACT_VERSION = 3
_CD_EXTRACT_SYSTEM = 4 # is this meaningful?
_CD_FLAG_BITS = 5
_CD_COMPRESS_TYPE = 6
_CD_TIME = 7
_CD_DATE = 8
_CD_CRC = 9
_CD_COMPRESSED_SIZE = 10
_CD_UNCOMPRESSED_SIZE = 11
_CD_FILENAME_LENGTH = 12
_CD_EXTRA_FIELD_LENGTH = 13
_CD_COMMENT_LENGTH = 14
_CD_DISK_NUMBER_START = 15
_CD_INTERNAL_FILE_ATTRIBUTES = 16
_CD_EXTERNAL_FILE_ATTRIBUTES = 17
_CD_LOCAL_HEADER_OFFSET = 18
# indexes of entries in the local file header structure
_FH_SIGNATURE = 0
_FH_EXTRACT_VERSION = 1
_FH_EXTRACT_SYSTEM = 2 # is this meaningful?
_FH_GENERAL_PURPOSE_FLAG_BITS = 3
_FH_COMPRESSION_METHOD = 4
_FH_LAST_MOD_TIME = 5
_FH_LAST_MOD_DATE = 6
_FH_CRC = 7
_FH_COMPRESSED_SIZE = 8
_FH_UNCOMPRESSED_SIZE = 9
_FH_FILENAME_LENGTH = 10
_FH_EXTRA_FIELD_LENGTH = 11
def is_zipfile(filename):
"""Quickly see if file is a ZIP file by checking the magic number.
@ -159,14 +194,16 @@ def _GetContents(self):
centdir = struct.unpack(structCentralDir, centdir)
if self.debug > 2:
print centdir
filename = fp.read(centdir[12])
filename = fp.read(centdir[_CD_FILENAME_LENGTH])
# Create ZipInfo instance to store file information
x = ZipInfo(filename)
x.extra = fp.read(centdir[13])
x.comment = fp.read(centdir[14])
total = total + centdir[12] + centdir[13] + centdir[14]
x.header_offset = centdir[18] + concat
x.file_offset = x.header_offset + 30 + centdir[12] + centdir[13]
x.extra = fp.read(centdir[_CD_EXTRA_FIELD_LENGTH])
x.comment = fp.read(centdir[_CD_COMMENT_LENGTH])
total = (total + centdir[_CD_FILENAME_LENGTH]
+ centdir[_CD_EXTRA_FIELD_LENGTH]
+ centdir[_CD_COMMENT_LENGTH])
x.header_offset = centdir[_CD_LOCAL_HEADER_OFFSET] + concat
# file_offset must be computed below...
(x.create_version, x.create_system, x.extract_version, x.reserved,
x.flag_bits, x.compress_type, t, d,
x.CRC, x.compress_size, x.file_size) = centdir[1:12]
@ -184,7 +221,14 @@ def _GetContents(self):
if fheader[0:4] != stringFileHeader:
raise BadZipfile, "Bad magic number for file header"
fheader = struct.unpack(structFileHeader, fheader)
fname = fp.read(fheader[10])
# file_offset is computed here, since the extra field for
# the central directory and for the local file header
# refer to different fields, and they can have different
# lengths
data.file_offset = (data.header_offset + 30
+ fheader[_FH_FILENAME_LENGTH]
+ fheader[_FH_EXTRA_FIELD_LENGTH])
fname = fp.read(fheader[_FH_FILENAME_LENGTH])
if fname != data.filename:
raise RuntimeError, \
'File name in directory "%s" and header "%s" differ.' % (