tar: try harder to detect old tar files

The code to autodetect compressed tar files failed to detect a
bunzip2-compressed archive.  When tar was invoked with the 'j'
option it worked fine.

The autodetection code looks for the magic string 'ustar' or a
series of five NULs to determine that an archive is uncompressed.
The failing archives had more than five NULs in the header and
were taken to be uncompressed.

Look for a longer run of NULs: 16 is certainly sufficient for the
archives in question.

Adds 8-16 bytes.

(GitHub issue #475)

1 files changed, 5 insertions, 0 deletions

diff --git a/archival/libarchive/get_header_tar.c b/archival/libarchive/get_header_tar.c
index cc6f3f0ad..5fd5a7980 100644
--- a/archival/libarchive/get_header_tar.c
+++ b/archival/libarchive/get_header_tar.c
@@ -239,8 +239,13 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
         /* Check header has valid magic, "ustar" is for the proper tar,
          * five NULs are for the old tar format  */
         if (!is_prefixed_with(tar.magic, "ustar")
+#if !ENABLE_PLATFORM_MINGW32
          && (!ENABLE_FEATURE_TAR_OLDGNU_COMPATIBILITY
              || memcmp(tar.magic, "\0\0\0\0", 5) != 0)
+#else
+         && (!ENABLE_FEATURE_TAR_OLDGNU_COMPATIBILITY
+             || memcmp(tar.magic, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16) != 0)
+#endif
         ) {
 #if ENABLE_FEATURE_TAR_AUTODETECT
  autodetect: