tar: optional autodetection of gz/bz2 compressed tarballs.

+130 bytes. Closes bug 992.

3 files changed, 92 insertions, 31 deletions

diff --git a/archival/Config.in b/archival/Config.in
index 160c54d64..6f803f4fe 100644
--- a/archival/Config.in
+++ b/archival/Config.in
@@ -166,6 +166,14 @@ config FEATURE_TAR_CREATE
           If you enable this option you'll be able to create
           tar archives using the `-c' option.
 
+config FEATURE_TAR_GZIP
+        bool "Enable -z option"
+        default y
+        depends on TAR
+        help
+          If you enable this option tar will be able to call gzip,
+          when creating or extracting tar gziped archives.
+
 config FEATURE_TAR_BZIP2
         bool "Enable -j option to handle .tar.bz2 files"
         default n
@@ -182,29 +190,29 @@ config FEATURE_TAR_LZMA
           If you enable this option you'll be able to extract
           archives compressed with lzma.
 
-config FEATURE_TAR_FROM
-        bool "Enable -X (exclude from) and -T (include from) options)"
+config FEATURE_TAR_COMPRESS
+        bool "Enable -Z option"
         default n
         depends on TAR
         help
-          If you enable this option you'll be able to specify
-          a list of files to include or exclude from an archive.
+          If you enable this option tar will be able to call uncompress,
+          when extracting .tar.Z archives.
 
-config FEATURE_TAR_GZIP
-        bool "Enable -z option"
-        default y
-        depends on TAR
+config FEATURE_TAR_AUTODETECT
+        bool "Let tar autodetect gz/bz2 compresses tarballs"
+        default n
+        depends on FEATURE_TAR_GZIP || FEATURE_TAR_BZIP2
         help
-          If you enable this option tar will be able to call gzip,
-          when creating or extracting tar gziped archives.
+          With this option tar can automatically detect gzip/bzip2 compressed
+          tarballs. Currently it works only on seekable streams.
 
-config FEATURE_TAR_COMPRESS
-        bool "Enable -Z option"
+config FEATURE_TAR_FROM
+        bool "Enable -X (exclude from) and -T (include from) options)"
         default n
         depends on TAR
         help
-          If you enable this option tar will be able to call uncompress,
-          when extracting .tar.Z archives.
+          If you enable this option you'll be able to specify
+          a list of files to include or exclude from an archive.
 
 config FEATURE_TAR_OLDGNU_COMPATIBILITY
         bool "Enable support for old tar header format"
diff --git a/archival/libunarchive/get_header_tar.c b/archival/libunarchive/get_header_tar.c
index 893cd5b79..54c8f7665 100644
--- a/archival/libunarchive/get_header_tar.c
+++ b/archival/libunarchive/get_header_tar.c
@@ -46,6 +46,9 @@ void BUG_tar_header_size(void);
 char get_header_tar(archive_handle_t *archive_handle)
 {
         static smallint end;
+#if ENABLE_FEATURE_TAR_AUTODETECT
+        static smallint not_first;
+#endif
 
         file_header_t *file_header = archive_handle->file_header;
         struct {
@@ -115,7 +118,7 @@ char get_header_tar(archive_handle_t *archive_handle)
                          * Read until the end to empty the pipe from gz or bz2
                          */
                         while (full_read(archive_handle->src_fd, &tar, 512) == 512)
-                                /* repeat */;
+                                continue;
                         return EXIT_FAILURE;
                 }
                 end = 1;
@@ -123,16 +126,49 @@ char get_header_tar(archive_handle_t *archive_handle)
         }
         end = 0;
 
-        /* Check header has valid magic, "ustar" is for the proper tar
-         * 0's are for the old tar format
-         */
-        if (strncmp(tar.magic, "ustar", 5) != 0) {
-#if ENABLE_FEATURE_TAR_OLDGNU_COMPATIBILITY
-                if (memcmp(tar.magic, "\0\0\0\0", 5) != 0)
+        /* Check header has valid magic, "ustar" is for the proper tar,
+         * five NULs are for the old tar format  */
+        if (strncmp(tar.magic, "ustar", 5) != 0
+         && (!ENABLE_FEATURE_TAR_OLDGNU_COMPATIBILITY
+             || memcmp(tar.magic, "\0\0\0\0", 5) != 0)
+        ) {
+#if ENABLE_FEATURE_TAR_AUTODETECT
+                char (*get_header_ptr)(archive_handle_t *);
+
+                /* tar gz/bz autodetect: check for gz/bz2 magic.
+                 * If it is the very first block, and we see the magic,
+                 * we can switch to get_header_tar_gz/bz2/lzma().
+                 * Needs seekable fd. I wish recv(MSG_PEEK) would work
+                 * on any fd... */
+                if (not_first)
+                        goto err;
+#if ENABLE_FEATURE_TAR_GZIP
+                if (tar.name[0] == 0x1f && tar.name[1] == 0x8b) { /* gzip */
+                        get_header_ptr = get_header_tar_gz;
+                } else
 #endif
-                        bb_error_msg_and_die("invalid tar magic");
+#if ENABLE_FEATURE_TAR_BZIP2
+                if (tar.name[0] == 'B' && tar.name[1] == 'Z'
+                 && tar.name[2] == 'h' && isdigit(tar.name[3])
+                ) { /* bzip2 */
+                        get_header_ptr = get_header_tar_bz2;
+                } else
+#endif
+                        goto err;
+                if (lseek(archive_handle->src_fd, -512, SEEK_CUR) != 0)
+                        goto err;
+                while (get_header_ptr(archive_handle) == EXIT_SUCCESS)
+                        continue;
+                return EXIT_FAILURE;
+ err:
+#endif /* FEATURE_TAR_AUTODETECT */
+                bb_error_msg_and_die("invalid tar magic");
         }
 
+#if ENABLE_FEATURE_TAR_AUTODETECT
+        not_first = 1;
+#endif
+
         /* Do checksum on headers.
          * POSIX says that checksum is done on unsigned bytes, but
          * Sun and HP-UX gets it wrong... more details in
diff --git a/archival/tar.c b/archival/tar.c
index 4ec454b88..e790f28ea 100644
--- a/archival/tar.c
+++ b/archival/tar.c
@@ -33,8 +33,17 @@
 #define FNM_LEADING_DIR 0
 #endif
 
+
 #define block_buf bb_common_bufsiz1
 
+
+#if !ENABLE_FEATURE_TAR_GZIP && !ENABLE_FEATURE_TAR_BZIP2
+/* Do not pass gzip flag to writeTarFile() */
+#define writeTarFile(tar_fd, verboseFlag, dereferenceFlag, include, exclude, gzip) \
+        writeTarFile(tar_fd, verboseFlag, dereferenceFlag, include, exclude)
+#endif
+
+
 #if ENABLE_FEATURE_TAR_CREATE
 
 /* Tar file constants  */
@@ -514,18 +523,23 @@ static int writeTarFile(const int tar_fd, const int verboseFlag,
         if (fstat(tbInfo.tarFd, &tbInfo.statBuf) < 0)
                 bb_perror_msg_and_die("cannot stat tar file");
 
-        if ((ENABLE_FEATURE_TAR_GZIP || ENABLE_FEATURE_TAR_BZIP2) && gzip) {
-// On Linux, vfork never unpauses parent early, although standard
-// allows for that. Do we want to waste bytes checking for it?
+#if ENABLE_FEATURE_TAR_GZIP || ENABLE_FEATURE_TAR_BZIP2
+        if (gzip) {
+#if ENABLE_FEATURE_TAR_GZIP && ENABLE_FEATURE_TAR_BZIP2
+                const char *zip_exec = (gzip == 1) ? "gzip" : "bzip2";
+#elif ENABLE_FEATURE_TAR_GZIP
+                const char *zip_exec = "gzip";
+#else /* only ENABLE_FEATURE_TAR_BZIP2 */
+                const char *zip_exec = "bzip2";
+#endif
+        // On Linux, vfork never unpauses parent early, although standard
+        // allows for that. Do we want to waste bytes checking for it?
 #define WAIT_FOR_CHILD 0
-
                 volatile int vfork_exec_errno = 0;
 #if WAIT_FOR_CHILD
                 struct fd_pair gzipStatusPipe;
 #endif
                 struct fd_pair gzipDataPipe;
-                const char *zip_exec = (gzip == 1) ? "gzip" : "bzip2";
-
                 xpiped_pair(gzipDataPipe);
 #if WAIT_FOR_CHILD
                 xpiped_pair(gzipStatusPipe);
@@ -584,6 +598,7 @@ static int writeTarFile(const int tar_fd, const int verboseFlag,
                         bb_perror_msg_and_die("cannot exec %s", zip_exec);
                 }
         }
+#endif
 
         tbInfo.excludeList = exclude;
 
@@ -934,11 +949,13 @@ int tar_main(int argc, char **argv)
 
         /* create an archive */
         if (opt & OPT_CREATE) {
+#if ENABLE_FEATURE_TAR_GZIP || ENABLE_FEATURE_TAR_BZIP2
                 int zipMode = 0;
-                if (ENABLE_FEATURE_TAR_GZIP && get_header_ptr == get_header_tar_gz)
+                if (ENABLE_FEATURE_TAR_GZIP && (opt & OPT_GZIP))
                         zipMode = 1;
-                if (ENABLE_FEATURE_TAR_BZIP2 && get_header_ptr == get_header_tar_bz2)
+                if (ENABLE_FEATURE_TAR_BZIP2 && (opt & OPT_BZIP2))
                         zipMode = 2;
+#endif
                 /* NB: writeTarFile() closes tar_handle->src_fd */
                 return writeTarFile(tar_handle->src_fd, verboseFlag, opt & OPT_DEREFERENCE,
                                 tar_handle->accept,
@@ -946,7 +963,7 @@ int tar_main(int argc, char **argv)
         }
 
         while (get_header_ptr(tar_handle) == EXIT_SUCCESS)
-                /* nothing */;
+                continue;
 
         /* Check that every file that should have been extracted was */
         while (tar_handle->accept) {