22.00

CPP/7zip/Archive/Tar/TarHeader.cpp

@@ -18,9 +18,82 @@ namespace NFileHeader {
     // const char * const kGNUTar = "GNUtar "; // 7 chars and a null
     // const char * const kEmpty = "\0\0\0\0\0\0\0\0";
     // 7-Zip used kUsTar_00 before 21.07:
-    // const char kUsTar_00[8] = { 'u', 's', 't', 'a', 'r', 0, '0', '0' } ;
+    const char k_Posix_ustar_00[8]  = { 'u', 's', 't', 'a', 'r', 0, '0', '0' } ;
     // GNU TAR uses such header:
-    const char kUsTar_GNU[8] = { 'u', 's', 't', 'a', 'r', ' ', ' ', 0 } ;
+    const char k_GNU_ustar__[8] = { 'u', 's', 't', 'a', 'r', ' ', ' ', 0 } ;
   }
 
+/*
+pre-POSIX.1-1988 (i.e. v7) tar header:
+-----
+Link indicator:
+'0' or 0 : Normal file
+'1' : Hard link
+'2' : Symbolic link
+Some pre-POSIX.1-1988 tar implementations indicated a directory by having
+a trailing slash (/) in the name.
+
+Numeric values : octal with leading zeroes.
+For historical reasons, a final NUL or space character should also be used.
+Thus only 11 octal digits can be stored from 12 bytes field.
+
+2001 star : introduced a base-256 coding that is indicated by
+setting the high-order bit of the leftmost byte of a numeric field.
+GNU-tar and BSD-tar followed this idea.
+ 
+versions of tar from before the first POSIX standard from 1988
+pad the values with spaces instead of zeroes.
+
+UStar
+-----
+UStar (Unix Standard TAR) : POSIX IEEE P1003.1 : 1988.
+    257 signature: "ustar", 0, "00"
+    265 32  Owner user name
+    297 32  Owner group name
+    329 8 Device major number
+    337 8 Device minor number
+    345 155 Filename prefix
+
+POSIX.1-2001/pax
+----
+format is known as extended tar format or pax format
+vendor-tagged vendor-specific enhancements.
+tags Defined by the POSIX standard:
+  atime, mtime, path, linkpath, uname, gname, size, uid, gid, ...
+
+
+PAX EXTENSION
+-----------
+Hard links
+A further difference from the ustar header block is that data blocks
+for files of typeflag 1 (hard link) may be included,
+which means that the size field may be greater than zero.
+Archives created by pax -o linkdata shall include these data
+blocks with the hard links.
+*
+
+compatiblity
+------------
+  7-Zip 16.03 supports "PaxHeader/"
+  7-Zip 20.01 supports "PaxHeaders.X/" with optional "./"
+  7-Zip 21.02 supports "@PaxHeader" with optional "./" "./"
+
+  GNU tar --format=posix uses "PaxHeaders/" in folder of file
+  
+
+GNU TAR format
+==============
+v7      - Unix V7
+oldgnu  - GNU tar <=1.12  : writes zero in last character in name
+gnu     - GNU tar 1.13    : doesn't write  zero in last character in name
+                            as 7-zip 21.07
+ustar       - POSIX.1-1988
+posix (pax) - POSIX.1-2001
+
+  gnu tar:
+  if (S_ISCHR (st->stat.st_mode) || S_ISBLK (st->stat.st_mode)) {
+      major_t devmajor = major (st->stat.st_rdev);
+      minor_t devminor = minor (st->stat.st_rdev); }
+*/
+
 }}}