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Replace symlink heuristic with a well-defined test.

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As per the PKWARE ZIP File Format Specification (6.3.2), this
patch tests the file 'version made by' field for the UNIX (3)
constant, and then interprets the external file attributes accordingly,
assuming an st_mode field in the high 16 bits.
This commit is contained in:
Landon Fuller
2014-01-16 11:53:45 -05:00
parent d3c40f0e95
commit 653caaa9b2
1 changed files with 12 additions and 18 deletions
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SSZipArchive/SSZipArchive.m
+12 -18
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@@ -114,28 +114,22 @@
filename[fileInfo.size_filename] = '\0';
//
// NOTE
// I used the ZIP spec from here:
// http://www.pkware.com/documents/casestudies/APPNOTE.TXT
// Determine whether this is a symbolic link:
// - File is stored with 'version made by' value of UNIX (3),
// as per http://www.pkware.com/documents/casestudies/APPNOTE.TXT
// in the upper byte of the version field.
// - BSD4.4 st_mode constants are stored in the high 16 bits of the
// external file attributes (defacto standard, verified against libarchive)
//
// ...to deduce this method of detecting whether the file in the ZIP is a symbolic link.
// If it is, it is listed as a directory but has a data size greater than zero (real
// directories have it equal to 0) and the included, uncompressed data is the symbolic link path.
// The original constants can be found here:
// http://minnie.tuhs.org/cgi-bin/utree.pl?file=4.4BSD/usr/include/sys/stat.h
//
// ZIP files did not originally include support for symbolic links so the specification
// doesn't include anything in them that isn't part of a unix extension that isn't being used
// by the archivers we're testing. Most of this is figured out through trial and error and
// reading ZIP headers in hex editors. This seems to do the trick though.
//
const uLong ZipCompressionMethodStore = 0;
const uLong ZipUNIXVersion = 3;
const uLong BSD_SFMT = 0170000;
const uLong BSD_IFLNK = 0120000;
BOOL fileIsSymbolicLink = NO;
if((fileInfo.compression_method == ZipCompressionMethodStore) && // Is it compressed?
(S_ISDIR(fileInfo.external_fa)) && // Is it marked as a directory
(fileInfo.compressed_size > 0)) // Is there any data?
{
if (((fileInfo.version >> 8) == ZipUNIXVersion) && BSD_IFLNK == (BSD_SFMT & (fileInfo.external_fa >> 16))) {
fileIsSymbolicLink = YES;
}