dpkg_deb: slight code shrink

ar: reuse existing ar unpacking code
get_header_tar: handle autodetection for tiny .tar.gz files too
unarchive.h: do not include CONFIGed out things

function                                             old     new   delta
get_header_tar                                      1521    1534     +13
dpkg_deb_main                                        400     380     -20
ar_main                                              260     196     -64
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/2 up/down: 13/-84)            Total: -71 bytes

9 files changed, 65 insertions, 45 deletions

diff --git a/archival/Config.in b/archival/Config.in
index 4599b68d4..02daae1a0 100644
--- a/archival/Config.in
+++ b/archival/Config.in
@@ -90,10 +90,11 @@ config DPKG
         bool "dpkg"
         default n
         help
-          dpkg is a medium-level tool to install, build, remove and manage Debian packages.
+          dpkg is a medium-level tool to install, build, remove and manage
+          Debian packages.
 
-          This implementation of dpkg has a number of limitations, you should use the
-          official dpkg if possible.
+          This implementation of dpkg has a number of limitations,
+          you should use the official dpkg if possible.
 
 config DPKG_DEB
         bool "dpkg_deb"
@@ -103,8 +104,8 @@ config DPKG_DEB
 
           This implementation of dpkg-deb cannot pack archives.
 
-          Unless you have a specific application which requires dpkg-deb, you should
-          probably say N here.
+          Unless you have a specific application which requires dpkg-deb,
+          say N here.
 
 config FEATURE_DPKG_DEB_EXTRACT_ONLY
         bool "Extract only (-x)"
diff --git a/archival/ar.c b/archival/ar.c
index d49329ce9..dbff6775e 100644
--- a/archival/ar.c
+++ b/archival/ar.c
@@ -45,7 +45,6 @@ int ar_main(int argc, char **argv)
 
         archive_handle_t *archive_handle;
         unsigned opt;
-        char magic[8];
 
         archive_handle = init_handle();
 
@@ -82,14 +81,7 @@ int ar_main(int argc, char **argv)
                 llist_add_to(&(archive_handle->accept), argv[optind++]);
         }
 
-        xread(archive_handle->src_fd, magic, 7);
-        if (strncmp(magic, "!<arch>", 7) != 0) {
-                bb_error_msg_and_die("invalid ar magic");
-        }
-        archive_handle->offset += 7;
-
-        while (get_header_ar(archive_handle) == EXIT_SUCCESS)
-                continue;
+        unpack_ar_archive(archive_handle);
 
         return EXIT_SUCCESS;
 }
diff --git a/archival/dpkg_deb.c b/archival/dpkg_deb.c
index cbacc91f8..9e6340fd3 100644
--- a/archival/dpkg_deb.c
+++ b/archival/dpkg_deb.c
@@ -20,8 +20,8 @@ int dpkg_deb_main(int argc, char **argv)
         archive_handle_t *tar_archive;
         llist_t *control_tar_llist = NULL;
         unsigned opt;
-        const char *extract_dir = NULL;
-        short argcount = 1;
+        const char *extract_dir;
+        int need_args;
 
         /* Setup the tar archive handle */
         tar_archive = init_handle();
@@ -43,17 +43,21 @@ int dpkg_deb_main(int argc, char **argv)
 
         opt_complementary = "c--efXx:e--cfXx:f--ceXx:X--cefx:x--cefX";
         opt = getopt32(argv, "cefXx");
+        argv += optind;
+        argc -= optind;
 
         if (opt & DPKG_DEB_OPT_CONTENTS) {
                 tar_archive->action_header = header_verbose_list;
         }
+        extract_dir = NULL;
+        need_args = 1;
         if (opt & DPKG_DEB_OPT_CONTROL) {
                 ar_archive->accept = control_tar_llist;
                 tar_archive->action_data = data_extract_all;
-                if (optind + 1 == argc) {
+                if (1 == argc) {
                         extract_dir = "./DEBIAN";
                 } else {
-                        argcount++;
+                        need_args++;
                 }
         }
         if (opt & DPKG_DEB_OPT_FIELD) {
@@ -70,28 +74,31 @@ int dpkg_deb_main(int argc, char **argv)
         }
         if (opt & (DPKG_DEB_OPT_EXTRACT_VERBOSE | DPKG_DEB_OPT_EXTRACT)) {
                 tar_archive->action_data = data_extract_all;
-                argcount = 2;
+                need_args = 2;
         }
 
-        if ((optind + argcount) != argc) {
+        if (need_args != argc) {
                 bb_show_usage();
         }
 
-        tar_archive->src_fd = ar_archive->src_fd = xopen(argv[optind++], O_RDONLY);
+        tar_archive->src_fd = ar_archive->src_fd = xopen(argv[0], O_RDONLY);
 
-        /* Workout where to extract the files */
+        /* Work out where to extract the files */
         /* 2nd argument is a dir name */
-        if (argv[optind]) {
-                extract_dir = argv[optind];
+        if (argv[1]) {
+                extract_dir = argv[1];
         }
         if (extract_dir) {
                 mkdir(extract_dir, 0777); /* bb_make_directory(extract_dir, 0777, 0) */
                 xchdir(extract_dir);
         }
+
+        /* Do it */
         unpack_ar_archive(ar_archive);
 
         /* Cleanup */
-        close(ar_archive->src_fd);
+        if (ENABLE_FEATURE_CLEAN_UP)
+                close(ar_archive->src_fd);
 
         return EXIT_SUCCESS;
 }
diff --git a/archival/libunarchive/filter_accept_list_reassign.c b/archival/libunarchive/filter_accept_list_reassign.c
index 4f2d4cde5..4dbc2d13e 100644
--- a/archival/libunarchive/filter_accept_list_reassign.c
+++ b/archival/libunarchive/filter_accept_list_reassign.c
@@ -8,6 +8,8 @@
 #include "libbb.h"
 #include "unarchive.h"
 
+/* Built and used only if ENABLE_DPKG || ENABLE_DPKG_DEB */
+
 /*
  * Reassign the subarchive metadata parser based on the filename extension
  * e.g. if its a .tar.gz modify archive_handle->sub_archive to process a .tar.gz
@@ -19,23 +21,25 @@ char FAST_FUNC filter_accept_list_reassign(archive_handle_t *archive_handle)
         if (find_list_entry(archive_handle->accept, archive_handle->file_header->name)) {
                 const char *name_ptr;
 
-                /* Extract the last 2 extensions */
+                /* Find extension */
                 name_ptr = strrchr(archive_handle->file_header->name, '.');
 
                 /* Modify the subarchive handler based on the extension */
-#if ENABLE_FEATURE_DEB_TAR_GZ
-                if (strcmp(name_ptr, ".gz") == 0) {
+                if (ENABLE_FEATURE_DEB_TAR_GZ
+                 && strcmp(name_ptr, ".gz") == 0
+                ) {
                         archive_handle->action_data_subarchive = get_header_tar_gz;
                         return EXIT_SUCCESS;
                 }
-#endif
-#if ENABLE_FEATURE_DEB_TAR_BZ2
-                if (strcmp(name_ptr, ".bz2") == 0) {
+                if (ENABLE_FEATURE_DEB_TAR_BZ2
+                 && strcmp(name_ptr, ".bz2") == 0
+                ) {
                         archive_handle->action_data_subarchive = get_header_tar_bz2;
                         return EXIT_SUCCESS;
                 }
-#endif
-                if (ENABLE_FEATURE_DEB_TAR_LZMA && !strcmp(name_ptr, ".lzma")) {
+                if (ENABLE_FEATURE_DEB_TAR_LZMA
+                 && strcmp(name_ptr, ".lzma") == 0
+                ) {
                         archive_handle->action_data_subarchive = get_header_tar_lzma;
                         return EXIT_SUCCESS;
                 }
diff --git a/archival/libunarchive/get_header_ar.c b/archival/libunarchive/get_header_ar.c
index 59fd34c73..d476a9d24 100644
--- a/archival/libunarchive/get_header_ar.c
+++ b/archival/libunarchive/get_header_ar.c
@@ -108,12 +108,13 @@ char FAST_FUNC get_header_ar(archive_handle_t *archive_handle)
 
         if (archive_handle->filter(archive_handle) == EXIT_SUCCESS) {
                 archive_handle->action_header(typed);
+#if ENABLE_DPKG || ENABLE_DPKG_DEB
                 if (archive_handle->sub_archive) {
                         while (archive_handle->action_data_subarchive(archive_handle->sub_archive) == EXIT_SUCCESS)
                                 continue;
-                } else {
+                } else
+#endif
                         archive_handle->action_data(archive_handle);
-                }
         } else {
                 data_skip(archive_handle);
         }
diff --git a/archival/libunarchive/get_header_tar.c b/archival/libunarchive/get_header_tar.c
index 69362f1cc..cf35d41a0 100644
--- a/archival/libunarchive/get_header_tar.c
+++ b/archival/libunarchive/get_header_tar.c
@@ -92,22 +92,32 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
  again_after_align:
 
 #if ENABLE_DESKTOP
+        /* to prevent misdetection of bz2 sig */
+        *(uint32_t*)(&tar) = 0;
         i = full_read(archive_handle->src_fd, &tar, 512);
         /* If GNU tar sees EOF in above read, it says:
          * "tar: A lone zero block at N", where N = kilobyte
          * where EOF was met (not EOF block, actual EOF!),
-         * and tar will exit with error code 0.
+         * and exits with EXIT_SUCCESS.
          * We will mimic exit(EXIT_SUCCESS), although we will not mimic
          * the message and we don't check whether we indeed
          * saw zero block directly before this. */
-        if (i == 0)
+        if (i == 0) {
                 xfunc_error_retval = 0;
-        if (i != 512)
+ short_read:
                 bb_error_msg_and_die("short read");
+        }
+        if (i != 512) {
+                if (ENABLE_FEATURE_TAR_AUTODETECT)
+                        goto autodetect;
+                goto short_read;
+        }
+
 #else
-        xread(archive_handle->src_fd, &tar, 512);
+        i = 512;
+        xread(archive_handle->src_fd, &tar, i);
 #endif
-        archive_handle->offset += 512;
+        archive_handle->offset += i;
 
         /* If there is no filename its an empty header */
         if (tar.name[0] == 0 && tar.prefix[0] == 0) {
@@ -133,6 +143,7 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
 #if ENABLE_FEATURE_TAR_AUTODETECT
                 char FAST_FUNC (*get_header_ptr)(archive_handle_t *);
 
+ USE_DESKTOP(autodetect:)
                 /* tar gz/bz autodetect: check for gz/bz2 magic.
                  * If we see the magic, and it is the very first block,
                  * we can switch to get_header_tar_gz/bz2/lzma().
@@ -154,7 +165,7 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
                 /* Two different causes for lseek() != 0:
                  * unseekable fd (would like to support that too, but...),
                  * or not first block (false positive, it's not .gz/.bz2!) */
-                if (lseek(archive_handle->src_fd, -512, SEEK_CUR) != 0)
+                if (lseek(archive_handle->src_fd, -i, SEEK_CUR) != 0)
                         goto err;
                 while (get_header_ptr(archive_handle) == EXIT_SUCCESS)
                         continue;
@@ -328,7 +339,7 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
                 p_linkname = NULL;
         }
 #endif
-        if (!strncmp(file_header->name, "/../"+1, 3)
+        if (strncmp(file_header->name, "/../"+1, 3) == 0
          || strstr(file_header->name, "/../")
         ) {
                 bb_error_msg_and_die("name with '..' encountered: '%s'",
@@ -340,7 +351,7 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
         cp = last_char_is(file_header->name, '/');
 
         if (archive_handle->filter(archive_handle) == EXIT_SUCCESS) {
-                archive_handle->action_header(archive_handle->file_header);
+                archive_handle->action_header(/*archive_handle->*/ file_header);
                 /* Note that we kill the '/' only after action_header() */
                 /* (like GNU tar 1.15.1: verbose mode outputs "dir/dir/") */
                 if (cp) *cp = '\0';
diff --git a/archival/libunarchive/get_header_tar_gz.c b/archival/libunarchive/get_header_tar_gz.c
index 086c6df42..e88b720a8 100644
--- a/archival/libunarchive/get_header_tar_gz.c
+++ b/archival/libunarchive/get_header_tar_gz.c
@@ -20,6 +20,7 @@ char FAST_FUNC get_header_tar_gz(archive_handle_t *archive_handle)
          * need the header. */
 #if BB_MMU
         xread(archive_handle->src_fd, &magic, 2);
+        /* Can skip this check, but error message will be less clear */
         if ((magic[0] != 0x1f) || (magic[1] != 0x8b)) {
                 bb_error_msg_and_die("invalid gzip magic");
         }
diff --git a/archival/libunarchive/unpack_ar_archive.c b/archival/libunarchive/unpack_ar_archive.c
index 9c2f68b14..dc2eec223 100644
--- a/archival/libunarchive/unpack_ar_archive.c
+++ b/archival/libunarchive/unpack_ar_archive.c
@@ -16,5 +16,6 @@ void FAST_FUNC unpack_ar_archive(archive_handle_t *ar_archive)
         }
         ar_archive->offset += 7;
 
-        while (get_header_ar(ar_archive) == EXIT_SUCCESS);
+        while (get_header_ar(ar_archive) == EXIT_SUCCESS)
+                continue;
 }
diff --git a/include/unarchive.h b/include/unarchive.h
index 0e380db08..5b71d3e62 100644
--- a/include/unarchive.h
+++ b/include/unarchive.h
@@ -47,11 +47,13 @@ typedef struct archive_handle_t {
         /* Process the data component, e.g. extract to filesystem */
         void FAST_FUNC (*action_data)(struct archive_handle_t *);
 
+#if ENABLE_DPKG || ENABLE_DPKG_DEB
+        /* "subarchive" is used only by dpkg[-deb] applets */
         /* How to process any sub archive, e.g. get_header_tar_gz */
         char FAST_FUNC (*action_data_subarchive)(struct archive_handle_t *);
-
         /* Contains the handle to a sub archive */
         struct archive_handle_t *sub_archive;
+#endif
 
         /* The raw stream as read from disk or stdin */
         int src_fd;