From 8a6a2f9c9c214b94bd945acd97ac8b28c25e194e Mon Sep 17 00:00:00 2001
From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Tue, 6 Mar 2012 16:27:48 +0100
Subject: [PATCH] update seamless uncompression code

This change makes "tar tf hello_world.txz" work without
adding special-casing for ".txz" extension. It also removes
ever-growing magic checking code in rpm2cpio and get_header_tar -
we reuse one which lives in setup_unzip_on_fd.

function                                             old     new   delta
unpack_gz_stream                                       7     566    +559
check_signature16                                      -      70     +70
setup_unzip_on_fd                                     99     142     +43
handle_SIGCHLD                                         -      41     +41
unpack_bz2_stream                                    342     376     +34
unzip_main                                          2352    2385     +33
bbunpack                                             503     533     +30
open_transformer                                      74     102     +28
unpack_Z_stream                                     1278    1304     +26
unpack_gunzip                                        101     123     +22
init_transformer_aux_data                              -      18     +18
unpack_xz_stream                                    2388    2402     +14
open_zipped                                          131     141     +10
rpm_main                                            1358    1363      +5
get_header_tar_lzma                                   52      57      +5
get_header_tar_bz2                                    52      57      +5
unpack_lzma_stream                                  2698    2702      +4
hash_find                                            234     233      -1
get_header_tar                                      1759    1733     -26
get_header_tar_gz                                     92      57     -35
unpack_uncompress                                     51      12     -39
rpm2cpio_main                                        201     147     -54
unpack_unxz                                           67      12     -55
unpack_bz2_stream_prime                               55       -     -55
get_header_tar_Z                                      86       -     -86
unpack_gz_stream_with_info                           539       -    -539
------------------------------------------------------------------------------
(add/remove: 3/3 grow/shrink: 14/6 up/down: 947/-890)          Total: 57 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
---
 archival/bbunzip.c                          |  76 ++++++-------
 archival/bzip2.c                            |   2 +-
 archival/gzip.c                             |   2 +-
 archival/libarchive/decompress_bunzip2.c    |  18 +---
 archival/libarchive/decompress_gunzip.c     |  27 +++--
 archival/libarchive/decompress_uncompress.c |   5 +-
 archival/libarchive/decompress_unlzma.c     |   2 +-
 archival/libarchive/decompress_unxz.c       |  12 ++-
 archival/libarchive/get_header_tar.c        |  35 +-----
 archival/libarchive/get_header_tar_bz2.c    |   2 +-
 archival/libarchive/get_header_tar_gz.c     |  17 +--
 archival/libarchive/get_header_tar_lzma.c   |   2 +-
 archival/libarchive/open_transformer.c      | 113 ++++++++++----------
 archival/lzop.c                             |   2 +-
 archival/rpm.c                              |   2 +-
 archival/rpm2cpio.c                         |  73 ++++++-------
 archival/tar.c                              |  71 ++++++------
 archival/unzip.c                            |  10 +-
 docs/keep_data_small.txt                    |   2 +-
 include/bb_archive.h                        |  54 +++++-----
 include/libbb.h                             |  14 ++-
 21 files changed, 231 insertions(+), 310 deletions(-)

diff --git a/archival/bbunzip.c b/archival/bbunzip.c
index 853c653c0..1bc04ed33 100644
--- a/archival/bbunzip.c
+++ b/archival/bbunzip.c
@@ -33,7 +33,7 @@ char* FAST_FUNC append_ext(char *filename, const char *expected_ext)
 }
 
 int FAST_FUNC bbunpack(char **argv,
-	IF_DESKTOP(long long) int FAST_FUNC (*unpacker)(unpack_info_t *info),
+	IF_DESKTOP(long long) int FAST_FUNC (*unpacker)(transformer_aux_data_t *aux),
 	char* FAST_FUNC (*make_new_name)(char *filename, const char *expected_ext),
 	const char *expected_ext
 )
@@ -42,7 +42,7 @@ int FAST_FUNC bbunpack(char **argv,
 	IF_DESKTOP(long long) int status;
 	char *filename, *new_name;
 	smallint exitcode = 0;
-	unpack_info_t info;
+	transformer_aux_data_t aux;
 
 	do {
 		/* NB: new_name is *maybe* malloc'ed! */
@@ -98,9 +98,9 @@ int FAST_FUNC bbunpack(char **argv,
 					"use -f to force it");
 		}
 
-		/* memset(&info, 0, sizeof(info)); */
-		info.mtime = 0; /* so far it has one member only */
-		status = unpacker(&info);
+		init_transformer_aux_data(&aux);
+		aux.check_signature = 1;
+		status = unpacker(&aux);
 		if (status < 0)
 			exitcode = 1;
 
@@ -111,10 +111,10 @@ int FAST_FUNC bbunpack(char **argv,
 			char *del = new_name;
 			if (status >= 0) {
 				/* TODO: restore other things? */
-				if (info.mtime) {
+				if (aux.mtime != 0) {
 					struct timeval times[2];
 
-					times[1].tv_sec = times[0].tv_sec = info.mtime;
+					times[1].tv_sec = times[0].tv_sec = aux.mtime;
 					times[1].tv_usec = times[0].tv_usec = 0;
 					/* Note: we closed it first.
 					 * On some systems calling utimes
@@ -182,16 +182,9 @@ char* FAST_FUNC make_new_name_generic(char *filename, const char *expected_ext)
 
 #if ENABLE_UNCOMPRESS
 static
-IF_DESKTOP(long long) int FAST_FUNC unpack_uncompress(unpack_info_t *info UNUSED_PARAM)
+IF_DESKTOP(long long) int FAST_FUNC unpack_uncompress(transformer_aux_data_t *aux)
 {
-	IF_DESKTOP(long long) int status = -1;
-
-	if ((xread_char(STDIN_FILENO) != 0x1f) || (xread_char(STDIN_FILENO) != 0x9d)) {
-		bb_error_msg("invalid magic");
-	} else {
-		status = unpack_Z_stream(STDIN_FILENO, STDOUT_FILENO);
-	}
-	return status;
+	return unpack_Z_stream(aux, STDIN_FILENO, STDOUT_FILENO);
 }
 int uncompress_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int uncompress_main(int argc UNUSED_PARAM, char **argv)
@@ -279,30 +272,30 @@ char* FAST_FUNC make_new_name_gunzip(char *filename, const char *expected_ext UN
 	return filename;
 }
 static
-IF_DESKTOP(long long) int FAST_FUNC unpack_gunzip(unpack_info_t *info)
+IF_DESKTOP(long long) int FAST_FUNC unpack_gunzip(transformer_aux_data_t *aux)
 {
 	IF_DESKTOP(long long) int status = -1;
+	uint16_t magic2;
 
-	/* do the decompression, and cleanup */
-	if (xread_char(STDIN_FILENO) == 0x1f) {
-		unsigned char magic2;
+//TODO: fold below into unpack_gz_stream? Then the whole level of indirection
+// unpack_FOO() -> unpack_FOO_stream can be collapsed in this module!
 
-		magic2 = xread_char(STDIN_FILENO);
-		if (ENABLE_FEATURE_SEAMLESS_Z && magic2 == 0x9d) {
-			status = unpack_Z_stream(STDIN_FILENO, STDOUT_FILENO);
-		} else if (magic2 == 0x8b) {
-			status = unpack_gz_stream_with_info(STDIN_FILENO, STDOUT_FILENO, info);
-		} else {
-			goto bad_magic;
-		}
-		if (status < 0) {
-			bb_error_msg("error inflating");
-		}
+	aux->check_signature = 0; /* we will check it here, not in unpack_*_stream */
+
+	if (full_read(STDIN_FILENO, &magic2, 2) != 2)
+		goto bad_magic;
+	if (ENABLE_FEATURE_SEAMLESS_Z && magic2 == COMPRESS_MAGIC) {
+		status = unpack_Z_stream(aux, STDIN_FILENO, STDOUT_FILENO);
+	} else if (magic2 == GZIP_MAGIC) {
+		status = unpack_gz_stream(aux, STDIN_FILENO, STDOUT_FILENO);
 	} else {
  bad_magic:
 		bb_error_msg("invalid magic");
 		/* status is still == -1 */
 	}
+	if (status < 0) {
+		bb_error_msg("error inflating");
+	}
 	return status;
 }
 /*
@@ -352,9 +345,9 @@ int gunzip_main(int argc UNUSED_PARAM, char **argv)
 //applet:IF_BUNZIP2(APPLET_ODDNAME(bzcat, bunzip2, BB_DIR_USR_BIN, BB_SUID_DROP, bzcat))
 #if ENABLE_BUNZIP2
 static
-IF_DESKTOP(long long) int FAST_FUNC unpack_bunzip2(unpack_info_t *info UNUSED_PARAM)
+IF_DESKTOP(long long) int FAST_FUNC unpack_bunzip2(transformer_aux_data_t *aux)
 {
-	return unpack_bz2_stream_prime(STDIN_FILENO, STDOUT_FILENO);
+	return unpack_bz2_stream(aux, STDIN_FILENO, STDOUT_FILENO);
 }
 int bunzip2_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int bunzip2_main(int argc UNUSED_PARAM, char **argv)
@@ -420,9 +413,9 @@ int bunzip2_main(int argc UNUSED_PARAM, char **argv)
 
 #if ENABLE_UNLZMA
 static
-IF_DESKTOP(long long) int FAST_FUNC unpack_unlzma(unpack_info_t *info UNUSED_PARAM)
+IF_DESKTOP(long long) int FAST_FUNC unpack_unlzma(transformer_aux_data_t *aux)
 {
-	return unpack_lzma_stream(STDIN_FILENO, STDOUT_FILENO);
+	return unpack_lzma_stream(aux, STDIN_FILENO, STDOUT_FILENO);
 }
 int unlzma_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int unlzma_main(int argc UNUSED_PARAM, char **argv)
@@ -445,18 +438,9 @@ int unlzma_main(int argc UNUSED_PARAM, char **argv)
 
 #if ENABLE_UNXZ
 static
-IF_DESKTOP(long long) int FAST_FUNC unpack_unxz(unpack_info_t *info UNUSED_PARAM)
+IF_DESKTOP(long long) int FAST_FUNC unpack_unxz(transformer_aux_data_t *aux)
 {
-	struct {
-		uint32_t v1;
-		uint16_t v2;
-	} magic;
-	xread(STDIN_FILENO, &magic, 6);
-	if (magic.v1 != XZ_MAGIC1a || magic.v2 != XZ_MAGIC2a) {
-		bb_error_msg("invalid magic");
-		return -1;
-	}
-	return unpack_xz_stream(STDIN_FILENO, STDOUT_FILENO);
+	return unpack_xz_stream(aux, STDIN_FILENO, STDOUT_FILENO);
 }
 int unxz_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int unxz_main(int argc UNUSED_PARAM, char **argv)
diff --git a/archival/bzip2.c b/archival/bzip2.c
index 0716fa89b..dd77c8efc 100644
--- a/archival/bzip2.c
+++ b/archival/bzip2.c
@@ -111,7 +111,7 @@ IF_DESKTOP(long long) int bz_write(bz_stream *strm, void* rbuf, ssize_t rlen, vo
 }
 
 static
-IF_DESKTOP(long long) int FAST_FUNC compressStream(unpack_info_t *info UNUSED_PARAM)
+IF_DESKTOP(long long) int FAST_FUNC compressStream(transformer_aux_data_t *aux UNUSED_PARAM)
 {
 	IF_DESKTOP(long long) int total;
 	ssize_t count;
diff --git a/archival/gzip.c b/archival/gzip.c
index 929107389..80db4f969 100644
--- a/archival/gzip.c
+++ b/archival/gzip.c
@@ -2015,7 +2015,7 @@ static void zip(ulg time_stamp)
 
 /* ======================================================================== */
 static
-IF_DESKTOP(long long) int FAST_FUNC pack_gzip(unpack_info_t *info UNUSED_PARAM)
+IF_DESKTOP(long long) int FAST_FUNC pack_gzip(transformer_aux_data_t *aux UNUSED_PARAM)
 {
 	struct stat s;
 
diff --git a/archival/libarchive/decompress_bunzip2.c b/archival/libarchive/decompress_bunzip2.c
index c4640d489..dc252bb82 100644
--- a/archival/libarchive/decompress_bunzip2.c
+++ b/archival/libarchive/decompress_bunzip2.c
@@ -721,7 +721,7 @@ void FAST_FUNC dealloc_bunzip(bunzip_data *bd)
 
 /* Decompress src_fd to dst_fd.  Stops at end of bzip data, not end of file. */
 IF_DESKTOP(long long) int FAST_FUNC
-unpack_bz2_stream(int src_fd, int dst_fd)
+unpack_bz2_stream(transformer_aux_data_t *aux, int src_fd, int dst_fd)
 {
 	IF_DESKTOP(long long total_written = 0;)
 	bunzip_data *bd;
@@ -729,6 +729,9 @@ unpack_bz2_stream(int src_fd, int dst_fd)
 	int i;
 	unsigned len;
 
+	if (check_signature16(aux, src_fd, BZIP2_MAGIC))
+		return -1;
+
 	outbuf = xmalloc(IOBUF_SIZE);
 	len = 0;
 	while (1) { /* "Process one BZ... stream" loop */
@@ -794,17 +797,6 @@ unpack_bz2_stream(int src_fd, int dst_fd)
 	return i ? i : IF_DESKTOP(total_written) + 0;
 }
 
-IF_DESKTOP(long long) int FAST_FUNC
-unpack_bz2_stream_prime(int src_fd, int dst_fd)
-{
-	uint16_t magic2;
-	xread(src_fd, &magic2, 2);
-	if (magic2 != BZIP2_MAGIC) {
-		bb_error_msg_and_die("invalid magic");
-	}
-	return unpack_bz2_stream(src_fd, dst_fd);
-}
-
 #ifdef TESTING
 
 static char *const bunzip_errors[] = {
@@ -819,7 +811,7 @@ int main(int argc, char **argv)
 	int i;
 	char c;
 
-	int i = unpack_bz2_stream_prime(0, 1);
+	int i = unpack_bz2_stream(0, 1);
 	if (i < 0)
 		fprintf(stderr, "%s\n", bunzip_errors[-i]);
 	else if (read(STDIN_FILENO, &c, 1))
diff --git a/archival/libarchive/decompress_gunzip.c b/archival/libarchive/decompress_gunzip.c
index 50873e3f6..f1c9a79e5 100644
--- a/archival/libarchive/decompress_gunzip.c
+++ b/archival/libarchive/decompress_gunzip.c
@@ -1034,22 +1034,22 @@ inflate_unzip_internal(STATE_PARAM int in, int out)
 /* For unzip */
 
 IF_DESKTOP(long long) int FAST_FUNC
-inflate_unzip(inflate_unzip_result *res, off_t compr_size, int in, int out)
+inflate_unzip(transformer_aux_data_t *aux, int in, int out)
 {
 	IF_DESKTOP(long long) int n;
 	DECLARE_STATE;
 
 	ALLOC_STATE;
 
-	to_read = compr_size;
+	to_read = aux->bytes_in;
 //	bytebuffer_max = 0x8000;
 	bytebuffer_offset = 4;
 	bytebuffer = xmalloc(bytebuffer_max);
 	n = inflate_unzip_internal(PASS_STATE in, out);
 	free(bytebuffer);
 
-	res->crc = gunzip_crc;
-	res->bytes_out = gunzip_bytes_out;
+	aux->crc32 = gunzip_crc;
+	aux->bytes_out = gunzip_bytes_out;
 	DEALLOC_STATE;
 	return n;
 }
@@ -1107,7 +1107,7 @@ static uint32_t buffer_read_le_u32(STATE_PARAM_ONLY)
 	return res;
 }
 
-static int check_header_gzip(STATE_PARAM unpack_info_t *info)
+static int check_header_gzip(STATE_PARAM transformer_aux_data_t *aux)
 {
 	union {
 		unsigned char raw[8];
@@ -1169,8 +1169,8 @@ static int check_header_gzip(STATE_PARAM unpack_info_t *info)
 		}
 	}
 
-	if (info)
-		info->mtime = SWAP_LE32(header.formatted.mtime);
+	if (aux)
+		aux->mtime = SWAP_LE32(header.formatted.mtime);
 
 	/* Read the header checksum */
 	if (header.formatted.flags & 0x02) {
@@ -1182,12 +1182,15 @@ static int check_header_gzip(STATE_PARAM unpack_info_t *info)
 }
 
 IF_DESKTOP(long long) int FAST_FUNC
-unpack_gz_stream_with_info(int src_fd, int dst_fd, unpack_info_t *info)
+unpack_gz_stream(transformer_aux_data_t *aux, int src_fd, int dst_fd)
 {
 	uint32_t v32;
 	IF_DESKTOP(long long) int total, n;
 	DECLARE_STATE;
 
+	if (check_signature16(aux, src_fd, GZIP_MAGIC))
+		return -1;
+
 	total = 0;
 
 	ALLOC_STATE;
@@ -1197,7 +1200,7 @@ unpack_gz_stream_with_info(int src_fd, int dst_fd, unpack_info_t *info)
 	gunzip_src_fd = src_fd;
 
  again:
-	if (!check_header_gzip(PASS_STATE info)) {
+	if (!check_header_gzip(PASS_STATE aux)) {
 		bb_error_msg("corrupted data");
 		total = -1;
 		goto ret;
@@ -1248,9 +1251,3 @@ unpack_gz_stream_with_info(int src_fd, int dst_fd, unpack_info_t *info)
 	DEALLOC_STATE;
 	return total;
 }
-
-IF_DESKTOP(long long) int FAST_FUNC
-unpack_gz_stream(int in, int out)
-{
-	return unpack_gz_stream_with_info(in, out, NULL);
-}
diff --git a/archival/libarchive/decompress_uncompress.c b/archival/libarchive/decompress_uncompress.c
index 289f9e233..e9bbfb9bd 100644
--- a/archival/libarchive/decompress_uncompress.c
+++ b/archival/libarchive/decompress_uncompress.c
@@ -73,7 +73,7 @@
  */
 
 IF_DESKTOP(long long) int FAST_FUNC
-unpack_Z_stream(int src_fd, int dst_fd)
+unpack_Z_stream(transformer_aux_data_t *aux, int src_fd, int dst_fd)
 {
 	IF_DESKTOP(long long total_written = 0;)
 	IF_DESKTOP(long long) int retval = -1;
@@ -103,6 +103,9 @@ unpack_Z_stream(int src_fd, int dst_fd)
 	/* block compress mode -C compatible with 2.0 */
 	int block_mode; /* = BLOCK_MODE; */
 
+	if (check_signature16(aux, src_fd, COMPRESS_MAGIC))
+		return -1;
+
 	inbuf = xzalloc(IBUFSIZ + 64);
 	outbuf = xzalloc(OBUFSIZ + 2048);
 	htab = xzalloc(HSIZE);  /* wasn't zeroed out before, maybe can xmalloc? */
diff --git a/archival/libarchive/decompress_unlzma.c b/archival/libarchive/decompress_unlzma.c
index 3631b50cc..cfde8ea56 100644
--- a/archival/libarchive/decompress_unlzma.c
+++ b/archival/libarchive/decompress_unlzma.c
@@ -213,7 +213,7 @@ enum {
 
 
 IF_DESKTOP(long long) int FAST_FUNC
-unpack_lzma_stream(int src_fd, int dst_fd)
+unpack_lzma_stream(transformer_aux_data_t *aux UNUSED_PARAM, int src_fd, int dst_fd)
 {
 	IF_DESKTOP(long long total_written = 0;)
 	lzma_header_t header;
diff --git a/archival/libarchive/decompress_unxz.c b/archival/libarchive/decompress_unxz.c
index 3e5d4edca..79b48a152 100644
--- a/archival/libarchive/decompress_unxz.c
+++ b/archival/libarchive/decompress_unxz.c
@@ -38,7 +38,7 @@ static uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc)
 #include "unxz/xz_dec_stream.c"
 
 IF_DESKTOP(long long) int FAST_FUNC
-unpack_xz_stream(int src_fd, int dst_fd)
+unpack_xz_stream(transformer_aux_data_t *aux, int src_fd, int dst_fd)
 {
 	struct xz_buf iobuf;
 	struct xz_dec *state;
@@ -49,13 +49,17 @@ unpack_xz_stream(int src_fd, int dst_fd)
 		global_crc32_table = crc32_filltable(NULL, /*endian:*/ 0);
 
 	memset(&iobuf, 0, sizeof(iobuf));
-	/* Preload XZ file signature */
-	membuf = (void*) strcpy(xmalloc(2 * BUFSIZ), HEADER_MAGIC);
+	membuf = xmalloc(2 * BUFSIZ);
 	iobuf.in = membuf;
-	iobuf.in_size = HEADER_MAGIC_SIZE;
 	iobuf.out = membuf + BUFSIZ;
 	iobuf.out_size = BUFSIZ;
 
+	if (!aux || aux->check_signature == 0) {
+		/* Preload XZ file signature */
+		strcpy((char*)membuf, HEADER_MAGIC);
+		iobuf.in_size = HEADER_MAGIC_SIZE;
+	} /* else: let xz code read & check it */
+
 	/* Limit memory usage to about 64 MiB. */
 	state = xz_dec_init(XZ_DYNALLOC, 64*1024*1024);
 
diff --git a/archival/libarchive/get_header_tar.c b/archival/libarchive/get_header_tar.c
index 8c699754b..80a709144 100644
--- a/archival/libarchive/get_header_tar.c
+++ b/archival/libarchive/get_header_tar.c
@@ -235,43 +235,18 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
 	     || memcmp(tar.magic, "\0\0\0\0", 5) != 0)
 	) {
 #if ENABLE_FEATURE_TAR_AUTODETECT
-		char FAST_FUNC (*get_header_ptr)(archive_handle_t *);
-		uint16_t magic2;
-
  autodetect:
-		magic2 = *(bb__aliased_uint16_t*)tar.name;
-		/* 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().
-		 * Needs seekable fd. I wish recv(MSG_PEEK) works
-		 * on any fd... */
-# if ENABLE_FEATURE_SEAMLESS_GZ
-		if (magic2 == GZIP_MAGIC) {
-			get_header_ptr = get_header_tar_gz;
-		} else
-# endif
-# if ENABLE_FEATURE_SEAMLESS_BZ2
-		if (magic2 == BZIP2_MAGIC
-		 && tar.name[2] == 'h' && isdigit(tar.name[3])
-		) { /* bzip2 */
-			get_header_ptr = get_header_tar_bz2;
-		} else
-# endif
-# if ENABLE_FEATURE_SEAMLESS_XZ
-		//TODO: if (magic2 == XZ_MAGIC1)...
-		//else
-# endif
-			goto err;
 		/* 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, -i, SEEK_CUR) != 0)
 			goto err;
-		while (get_header_ptr(archive_handle) == EXIT_SUCCESS)
-			continue;
-		return EXIT_FAILURE;
+		if (setup_unzip_on_fd(archive_handle->src_fd, /*fail_if_not_detected:*/ 0) != 0)
  err:
-#endif /* FEATURE_TAR_AUTODETECT */
+			bb_error_msg_and_die("invalid tar magic");
+		archive_handle->offset = 0;
+		goto again_after_align;
+#endif
 		bb_error_msg_and_die("invalid tar magic");
 	}
 
diff --git a/archival/libarchive/get_header_tar_bz2.c b/archival/libarchive/get_header_tar_bz2.c
index e012dec3b..0ee00df53 100644
--- a/archival/libarchive/get_header_tar_bz2.c
+++ b/archival/libarchive/get_header_tar_bz2.c
@@ -11,7 +11,7 @@ char FAST_FUNC get_header_tar_bz2(archive_handle_t *archive_handle)
 	/* Can't lseek over pipes */
 	archive_handle->seek = seek_by_read;
 
-	open_transformer(archive_handle->src_fd, unpack_bz2_stream_prime, "bunzip2");
+	open_transformer_with_sig(archive_handle->src_fd, unpack_bz2_stream, "bunzip2");
 	archive_handle->offset = 0;
 	while (get_header_tar(archive_handle) == EXIT_SUCCESS)
 		continue;
diff --git a/archival/libarchive/get_header_tar_gz.c b/archival/libarchive/get_header_tar_gz.c
index b9679b0bd..03284342b 100644
--- a/archival/libarchive/get_header_tar_gz.c
+++ b/archival/libarchive/get_header_tar_gz.c
@@ -8,25 +8,10 @@
 
 char FAST_FUNC get_header_tar_gz(archive_handle_t *archive_handle)
 {
-#if BB_MMU
-	uint16_t magic;
-#endif
-
 	/* Can't lseek over pipes */
 	archive_handle->seek = seek_by_read;
 
-	/* Check gzip magic only if open_transformer will invoke unpack_gz_stream (MMU case).
-	 * Otherwise, it will invoke an external helper "gunzip -cf" (NOMMU case) which will
-	 * 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 != GZIP_MAGIC) {
-		bb_error_msg_and_die("invalid gzip magic");
-	}
-#endif
-
-	open_transformer(archive_handle->src_fd, unpack_gz_stream, "gunzip");
+	open_transformer_with_sig(archive_handle->src_fd, unpack_gz_stream, "gunzip");
 	archive_handle->offset = 0;
 	while (get_header_tar(archive_handle) == EXIT_SUCCESS)
 		continue;
diff --git a/archival/libarchive/get_header_tar_lzma.c b/archival/libarchive/get_header_tar_lzma.c
index 666700729..d565a217d 100644
--- a/archival/libarchive/get_header_tar_lzma.c
+++ b/archival/libarchive/get_header_tar_lzma.c
@@ -14,7 +14,7 @@ char FAST_FUNC get_header_tar_lzma(archive_handle_t *archive_handle)
 	/* Can't lseek over pipes */
 	archive_handle->seek = seek_by_read;
 
-	open_transformer(archive_handle->src_fd, unpack_lzma_stream, "unlzma");
+	open_transformer_with_sig(archive_handle->src_fd, unpack_lzma_stream, "unlzma");
 	archive_handle->offset = 0;
 	while (get_header_tar(archive_handle) == EXIT_SUCCESS)
 		continue;
diff --git a/archival/libarchive/open_transformer.c b/archival/libarchive/open_transformer.c
index 743ffee02..693ae9995 100644
--- a/archival/libarchive/open_transformer.c
+++ b/archival/libarchive/open_transformer.c
@@ -6,24 +6,36 @@
 #include "libbb.h"
 #include "bb_archive.h"
 
-#define ZIPPED (ENABLE_FEATURE_SEAMLESS_LZMA \
-	|| ENABLE_FEATURE_SEAMLESS_BZ2 \
-	|| ENABLE_FEATURE_SEAMLESS_GZ \
-	/* || ENABLE_FEATURE_SEAMLESS_Z */ \
-)
+void FAST_FUNC init_transformer_aux_data(transformer_aux_data_t *aux)
+{
+	memset(aux, 0, sizeof(*aux));
+}
 
-#if ZIPPED
-# include "bb_archive.h"
+int FAST_FUNC check_signature16(transformer_aux_data_t *aux, int src_fd, unsigned magic16)
+{
+	if (aux && aux->check_signature) {
+		uint16_t magic2;
+		if (full_read(src_fd, &magic2, 2) != 2 || magic2 != magic16) {
+			bb_error_msg("invalid magic");
+#if 0 /* possible future extension */
+			if (aux->check_signature > 1)
+				xfunc_die();
 #endif
+			return -1;
+		}
+	}
+	return 0;
+}
 
 /* transformer(), more than meets the eye */
-/*
- * On MMU machine, the transform_prog is removed by macro magic
- * in include/archive.h. On NOMMU, transformer is removed.
- */
+#if BB_MMU
 void FAST_FUNC open_transformer(int fd,
-	IF_DESKTOP(long long) int FAST_FUNC (*transformer)(int src_fd, int dst_fd),
-	const char *transform_prog)
+	int check_signature,
+	IF_DESKTOP(long long) int FAST_FUNC (*transformer)(transformer_aux_data_t *aux, int src_fd, int dst_fd)
+)
+#else
+void FAST_FUNC open_transformer(int fd, const char *transform_prog)
+#endif
 {
 	struct fd_pair fd_pipe;
 	int pid;
@@ -35,13 +47,18 @@ void FAST_FUNC open_transformer(int fd,
 		close(fd_pipe.rd); /* we don't want to read from the parent */
 		// FIXME: error check?
 #if BB_MMU
-		transformer(fd, fd_pipe.wr);
-		if (ENABLE_FEATURE_CLEAN_UP) {
-			close(fd_pipe.wr); /* send EOF */
-			close(fd);
+		{
+			transformer_aux_data_t aux;
+			init_transformer_aux_data(&aux);
+			aux.check_signature = check_signature;
+			transformer(&aux, fd, fd_pipe.wr);
+			if (ENABLE_FEATURE_CLEAN_UP) {
+				close(fd_pipe.wr); /* send EOF */
+				close(fd);
+			}
+			/* must be _exit! bug was actually seen here */
+			_exit(EXIT_SUCCESS);
 		}
-		/* must be _exit! bug was actually seen here */
-		_exit(EXIT_SUCCESS);
 #else
 		{
 			char *argv[4];
@@ -64,26 +81,21 @@ void FAST_FUNC open_transformer(int fd,
 }
 
 
+#if SEAMLESS_COMPRESSION
+
 /* Used by e.g. rpm which gives us a fd without filename,
  * thus we can't guess the format from filename's extension.
  */
-#if ZIPPED
-void FAST_FUNC setup_unzip_on_fd(int fd /*, int fail_if_not_detected*/)
+int FAST_FUNC setup_unzip_on_fd(int fd, int fail_if_not_detected)
 {
-	const int fail_if_not_detected = 1;
 	union {
 		uint8_t b[4];
 		uint16_t b16[2];
 		uint32_t b32[1];
 	} magic;
 	int offset = -2;
-# if BB_MMU
-	IF_DESKTOP(long long) int FAST_FUNC (*xformer)(int src_fd, int dst_fd);
-	enum { xformer_prog = 0 };
-# else
-	enum { xformer = 0 };
-	const char *xformer_prog;
-# endif
+	USE_FOR_MMU(IF_DESKTOP(long long) int FAST_FUNC (*xformer)(transformer_aux_data_t *aux, int src_fd, int dst_fd);)
+	USE_FOR_NOMMU(const char *xformer_prog;)
 
 	/* .gz and .bz2 both have 2-byte signature, and their
 	 * unpack_XXX_stream wants this header skipped. */
@@ -91,21 +103,15 @@ void FAST_FUNC setup_unzip_on_fd(int fd /*, int fail_if_not_detected*/)
 	if (ENABLE_FEATURE_SEAMLESS_GZ
 	 && magic.b16[0] == GZIP_MAGIC
 	) {
-# if BB_MMU
-		xformer = unpack_gz_stream;
-# else
-		xformer_prog = "gunzip";
-# endif
+		USE_FOR_MMU(xformer = unpack_gz_stream;)
+		USE_FOR_NOMMU(xformer_prog = "gunzip";)
 		goto found_magic;
 	}
 	if (ENABLE_FEATURE_SEAMLESS_BZ2
 	 && magic.b16[0] == BZIP2_MAGIC
 	) {
-# if BB_MMU
-		xformer = unpack_bz2_stream;
-# else
-		xformer_prog = "bunzip2";
-# endif
+		USE_FOR_MMU(xformer = unpack_bz2_stream;)
+		USE_FOR_NOMMU(xformer_prog = "bunzip2";)
 		goto found_magic;
 	}
 	if (ENABLE_FEATURE_SEAMLESS_XZ
@@ -114,13 +120,8 @@ void FAST_FUNC setup_unzip_on_fd(int fd /*, int fail_if_not_detected*/)
 		offset = -6;
 		xread(fd, magic.b32, sizeof(magic.b32[0]));
 		if (magic.b32[0] == XZ_MAGIC2) {
-# if BB_MMU
-			xformer = unpack_xz_stream;
-			/* unpack_xz_stream wants fd at position 6, no need to seek */
-			//xlseek(fd, offset, SEEK_CUR);
-# else
-			xformer_prog = "unxz";
-# endif
+			USE_FOR_MMU(xformer = unpack_xz_stream;)
+			USE_FOR_NOMMU(xformer_prog = "unxz";)
 			goto found_magic;
 		}
 	}
@@ -132,24 +133,23 @@ void FAST_FUNC setup_unzip_on_fd(int fd /*, int fail_if_not_detected*/)
 			IF_FEATURE_SEAMLESS_XZ("/xz")
 			" magic");
 	xlseek(fd, offset, SEEK_CUR);
-	return;
+	return 1;
 
  found_magic:
-# if !BB_MMU
+# if BB_MMU
+	open_transformer_with_no_sig(fd, xformer);
+# else
 	/* NOMMU version of open_transformer execs
 	 * an external unzipper that wants
 	 * file position at the start of the file */
 	xlseek(fd, offset, SEEK_CUR);
+	open_transformer_with_sig(fd, xformer, xformer_prog);
 # endif
-	open_transformer(fd, xformer, xformer_prog);
+	return 0;
 }
-#endif /* ZIPPED */
 
 int FAST_FUNC open_zipped(const char *fname)
 {
-#if !ZIPPED
-	return open(fname, O_RDONLY);
-#else
 	char *sfx;
 	int fd;
 
@@ -162,20 +162,21 @@ int FAST_FUNC open_zipped(const char *fname)
 		sfx++;
 		if (ENABLE_FEATURE_SEAMLESS_LZMA && strcmp(sfx, "lzma") == 0)
 			/* .lzma has no header/signature, just trust it */
-			open_transformer(fd, unpack_lzma_stream, "unlzma");
+			open_transformer_with_sig(fd, unpack_lzma_stream, "unlzma");
 		else
 		if ((ENABLE_FEATURE_SEAMLESS_GZ && strcmp(sfx, "gz") == 0)
 		 || (ENABLE_FEATURE_SEAMLESS_BZ2 && strcmp(sfx, "bz2") == 0)
 		 || (ENABLE_FEATURE_SEAMLESS_XZ && strcmp(sfx, "xz") == 0)
 		) {
-			setup_unzip_on_fd(fd /*, fail_if_not_detected: 1*/);
+			setup_unzip_on_fd(fd, /*fail_if_not_detected:*/ 1);
 		}
 	}
 
 	return fd;
-#endif
 }
 
+#endif /* SEAMLESS_COMPRESSION */
+
 void* FAST_FUNC xmalloc_open_zipped_read_close(const char *fname, size_t *maxsz_p)
 {
 	int fd;
diff --git a/archival/lzop.c b/archival/lzop.c
index 67baeff7e..fbe08417d 100644
--- a/archival/lzop.c
+++ b/archival/lzop.c
@@ -1077,7 +1077,7 @@ static char* FAST_FUNC make_new_name_lzop(char *filename, const char *expected_e
 	return xasprintf("%s.lzo", filename);
 }
 
-static IF_DESKTOP(long long) int FAST_FUNC pack_lzop(unpack_info_t *info UNUSED_PARAM)
+static IF_DESKTOP(long long) int FAST_FUNC pack_lzop(transformer_aux_data_t *aux UNUSED_PARAM)
 {
 	if (option_mask32 & OPT_DECOMPRESS)
 		return do_lzo_decompress();
diff --git a/archival/rpm.c b/archival/rpm.c
index 089b68983..6757a6ceb 100644
--- a/archival/rpm.c
+++ b/archival/rpm.c
@@ -236,7 +236,7 @@ static void extract_cpio(int fd, const char *source_rpm)
 	archive_handle->src_fd = fd;
 	/*archive_handle->offset = 0; - init_handle() did it */
 
-	setup_unzip_on_fd(archive_handle->src_fd /*, fail_if_not_detected: 1*/);
+	setup_unzip_on_fd(archive_handle->src_fd, /*fail_if_not_detected:*/ 1);
 	while (get_header_cpio(archive_handle) == EXIT_SUCCESS)
 		continue;
 }
diff --git a/archival/rpm2cpio.c b/archival/rpm2cpio.c
index 28b43a181..7256aae6b 100644
--- a/archival/rpm2cpio.c
+++ b/archival/rpm2cpio.c
@@ -42,6 +42,26 @@ static unsigned skip_header(void)
 	return sizeof(header) + len;
 }
 
+#if SEAMLESS_COMPRESSION
+static void handle_SIGCHLD(int signo UNUSED_PARAM)
+{
+	int status;
+
+	/* Wait for any child without blocking */
+	for (;;) {
+		if (wait_any_nohang(&status) < 0)
+			/* wait failed?! I'm confused... */
+			return;
+		if (WIFEXITED(status) && WEXITSTATUS(status) == 0)
+			/* this child exited with 0 */
+			continue;
+		/* Cannot happen?
+		if (!WIFSIGNALED(status) && !WIFEXITED(status)) ???; */
+		bb_got_signal = 1;
+	}
+}
+#endif
+
 /* No getopt required */
 int rpm2cpio_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int rpm2cpio_main(int argc UNUSED_PARAM, char **argv)
@@ -66,54 +86,23 @@ int rpm2cpio_main(int argc UNUSED_PARAM, char **argv)
 	/* Skip the main header */
 	skip_header();
 
-#if 0
+#if SEAMLESS_COMPRESSION
+	/* We need to know whether child (gzip/bzip/etc) exits abnormally */
+	signal(SIGCHLD, handle_SIGCHLD);
+#endif
+
 	/* This works, but doesn't report uncompress errors (they happen in child) */
-	setup_unzip_on_fd(rpm_fd /*fail_if_not_detected: 1*/);
+	setup_unzip_on_fd(rpm_fd, /*fail_if_not_detected:*/ 1);
 	if (bb_copyfd_eof(rpm_fd, STDOUT_FILENO) < 0)
 		bb_error_msg_and_die("error unpacking");
-#else
-	/* BLOAT */
-	{
-		union {
-			uint8_t b[4];
-			uint16_t b16[2];
-			uint32_t b32[1];
-		} magic;
-		IF_DESKTOP(long long) int FAST_FUNC (*unpack)(int src_fd, int dst_fd);
-
-		xread(rpm_fd, magic.b16, sizeof(magic.b16[0]));
-		if (magic.b16[0] == GZIP_MAGIC) {
-			unpack = unpack_gz_stream;
-		} else
-		if (ENABLE_FEATURE_SEAMLESS_BZ2
-		 && magic.b16[0] == BZIP2_MAGIC
-		) {
-			unpack = unpack_bz2_stream;
-		} else
-		if (ENABLE_FEATURE_SEAMLESS_XZ
-		 && magic.b16[0] == XZ_MAGIC1
-		) {
-			xread(rpm_fd, magic.b32, sizeof(magic.b32[0]));
-			if (magic.b32[0] != XZ_MAGIC2)
-				goto no_magic;
-			/* unpack_xz_stream wants fd at position 6, no need to seek */
-			//xlseek(rpm_fd, -6, SEEK_CUR);
-			unpack = unpack_xz_stream;
-		} else {
- no_magic:
-			bb_error_msg_and_die("no gzip"
-					IF_FEATURE_SEAMLESS_BZ2("/bzip2")
-					IF_FEATURE_SEAMLESS_XZ("/xz")
-					" magic");
-		}
-		if (unpack(rpm_fd, STDOUT_FILENO) < 0)
-			bb_error_msg_and_die("error unpacking");
-	}
-#endif
 
 	if (ENABLE_FEATURE_CLEAN_UP) {
 		close(rpm_fd);
 	}
 
-	return 0;
+#if SEAMLESS_COMPRESSION
+	return bb_got_signal;
+#else
+	return EXIT_SUCCESS;
+#endif
 }
diff --git a/archival/tar.c b/archival/tar.c
index 766b79b2b..af38ac59f 100644
--- a/archival/tar.c
+++ b/archival/tar.c
@@ -690,31 +690,6 @@ static llist_t *append_file_list_to_list(llist_t *list)
 # define append_file_list_to_list(x) 0
 #endif
 
-#if ENABLE_FEATURE_SEAMLESS_Z
-static char FAST_FUNC get_header_tar_Z(archive_handle_t *archive_handle)
-{
-	/* Can't lseek over pipes */
-	archive_handle->seek = seek_by_read;
-
-	/* do the decompression, and cleanup */
-	if (xread_char(archive_handle->src_fd) != 0x1f
-	 || xread_char(archive_handle->src_fd) != 0x9d
-	) {
-		bb_error_msg_and_die("invalid magic");
-	}
-
-	open_transformer(archive_handle->src_fd, unpack_Z_stream, "uncompress");
-	archive_handle->offset = 0;
-	while (get_header_tar(archive_handle) == EXIT_SUCCESS)
-		continue;
-
-	/* Can only do one file at a time */
-	return EXIT_FAILURE;
-}
-#else
-# define get_header_tar_Z NULL
-#endif
-
 #ifdef CHECK_FOR_CHILD_EXITCODE
 /* Looks like it isn't needed - tar detects malformed (truncated)
  * archive if e.g. bunzip2 fails */
@@ -843,6 +818,8 @@ enum {
 	OPT_NUMERIC_OWNER   = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_NUMERIC_OWNER  )) + 0, // numeric-owner
 	OPT_NOPRESERVE_PERM = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_NOPRESERVE_PERM)) + 0, // no-same-permissions
 	OPT_OVERWRITE       = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_OVERWRITE      )) + 0, // overwrite
+
+	OPT_ANY_COMPRESS = (OPT_BZIP2 | OPT_LZMA | OPT_GZIP | OPT_COMPRESS),
 };
 #if ENABLE_FEATURE_TAR_LONG_OPTIONS
 static const char tar_longopts[] ALIGN1 =
@@ -901,7 +878,6 @@ static const char tar_longopts[] ALIGN1 =
 int tar_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int tar_main(int argc UNUSED_PARAM, char **argv)
 {
-	char FAST_FUNC (*get_header_ptr)(archive_handle_t *) = get_header_tar;
 	archive_handle_t *tar_handle;
 	char *base_dir = NULL;
 	const char *tar_filename = "-";
@@ -1017,18 +993,6 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
 		tar_handle->ah_flags |= ARCHIVE_O_TRUNC;
 	}
 
-	if (opt & OPT_GZIP)
-		get_header_ptr = get_header_tar_gz;
-
-	if (opt & OPT_BZIP2)
-		get_header_ptr = get_header_tar_bz2;
-
-	if (opt & OPT_LZMA)
-		get_header_ptr = get_header_tar_lzma;
-
-	if (opt & OPT_COMPRESS)
-		get_header_ptr = get_header_tar_Z;
-
 	if (opt & OPT_NOPRESERVE_TIME)
 		tar_handle->ah_flags &= ~ARCHIVE_RESTORE_DATE;
 
@@ -1081,7 +1045,7 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
 		} else {
 			if (ENABLE_FEATURE_TAR_AUTODETECT
 			 && flags == O_RDONLY
-			 && get_header_ptr == get_header_tar
+			 && !(opt & OPT_ANY_COMPRESS)
 			) {
 				tar_handle->src_fd = open_zipped(tar_filename);
 				if (tar_handle->src_fd < 0)
@@ -1115,7 +1079,30 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
 				tar_handle->reject, zipMode);
 	}
 
-	while (get_header_ptr(tar_handle) == EXIT_SUCCESS)
+	if (opt & OPT_ANY_COMPRESS) {
+		USE_FOR_MMU(IF_DESKTOP(long long) int FAST_FUNC (*xformer)(transformer_aux_data_t *aux, int src_fd, int dst_fd);)
+		USE_FOR_NOMMU(const char *xformer_prog;)
+
+		if (opt & OPT_COMPRESS)
+			USE_FOR_MMU(xformer = unpack_Z_stream;)
+			USE_FOR_NOMMU(xformer_prog = "uncompress";)
+		if (opt & OPT_GZIP)
+			USE_FOR_MMU(xformer = unpack_gz_stream;)
+			USE_FOR_NOMMU(xformer_prog = "gunzip";)
+		if (opt & OPT_BZIP2)
+			USE_FOR_MMU(xformer = unpack_bz2_stream;)
+			USE_FOR_NOMMU(xformer_prog = "bunzip2";)
+		if (opt & OPT_LZMA)
+			USE_FOR_MMU(xformer = unpack_lzma_stream;)
+			USE_FOR_NOMMU(xformer_prog = "unlzma";)
+
+		open_transformer_with_sig(tar_handle->src_fd, xformer, xformer_prog);
+		/* Can't lseek over pipes */
+		tar_handle->seek = seek_by_read;
+		/*tar_handle->offset = 0; - already is */
+	}
+
+	while (get_header_tar(tar_handle) == EXIT_SUCCESS)
 		continue;
 
 	/* Check that every file that should have been extracted was */
@@ -1131,5 +1118,9 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
 	if (ENABLE_FEATURE_CLEAN_UP /* && tar_handle->src_fd != STDIN_FILENO */)
 		close(tar_handle->src_fd);
 
+#ifdef CHECK_FOR_CHILD_EXITCODE
+	return bb_got_signal;
+#else
 	return EXIT_SUCCESS;
+#endif
 }
diff --git a/archival/unzip.c b/archival/unzip.c
index 3a11f78a5..3c76cdafc 100644
--- a/archival/unzip.c
+++ b/archival/unzip.c
@@ -249,15 +249,17 @@ static void unzip_extract(zip_header_t *zip_header, int dst_fd)
 			bb_copyfd_exact_size(zip_fd, dst_fd, size);
 	} else {
 		/* Method 8 - inflate */
-		inflate_unzip_result res;
-		if (inflate_unzip(&res, zip_header->formatted.cmpsize, zip_fd, dst_fd) < 0)
+		transformer_aux_data_t aux;
+		init_transformer_aux_data(&aux);
+		aux.bytes_in = zip_header->formatted.cmpsize;
+		if (inflate_unzip(&aux, zip_fd, dst_fd) < 0)
 			bb_error_msg_and_die("inflate error");
 		/* Validate decompression - crc */
-		if (zip_header->formatted.crc32 != (res.crc ^ 0xffffffffL)) {
+		if (zip_header->formatted.crc32 != (aux.crc32 ^ 0xffffffffL)) {
 			bb_error_msg_and_die("crc error");
 		}
 		/* Validate decompression - size */
-		if (zip_header->formatted.ucmpsize != res.bytes_out) {
+		if (zip_header->formatted.ucmpsize != aux.bytes_out) {
 			/* Don't die. Who knows, maybe len calculation
 			 * was botched somewhere. After all, crc matched! */
 			bb_error_msg("bad length");
diff --git a/docs/keep_data_small.txt b/docs/keep_data_small.txt
index 9e77a9097..21d732674 100644
--- a/docs/keep_data_small.txt
+++ b/docs/keep_data_small.txt
@@ -59,7 +59,7 @@ wait
 		Example 1
 
 One example how to reduce global data usage is in
-archival/libarchive/decompress_gunzip.c:
+archival/libarchive/decompress_unzip.c:
 
 /* This is somewhat complex-looking arrangement, but it allows
  * to place decompressor state either in bss or in
diff --git a/include/bb_archive.h b/include/bb_archive.h
index 4987de6cf..bd08115da 100644
--- a/include/bb_archive.h
+++ b/include/bb_archive.h
@@ -156,12 +156,6 @@ struct BUG_tar_header {
 
 
 
-/* Info struct unpackers can fill out to inform users of thing like
- * timestamps of unpacked files */
-typedef struct unpack_info_t {
-	time_t mtime;
-} unpack_info_t;
-
 archive_handle_t *init_handle(void) FAST_FUNC;
 
 char filter_accept_all(archive_handle_t *archive_handle) FAST_FUNC;
@@ -204,40 +198,46 @@ int start_bunzip(bunzip_data **bdp, int in_fd, const void *inbuf, int len) FAST_
 int read_bunzip(bunzip_data *bd, char *outbuf, int len) FAST_FUNC;
 void dealloc_bunzip(bunzip_data *bd) FAST_FUNC;
 
-typedef struct inflate_unzip_result {
-	off_t bytes_out;
-	uint32_t crc;
-} inflate_unzip_result;
+/* Meaning and direction (input/output) of the fields are transformer-specific */
+typedef struct transformer_aux_data_t {
+	smallint check_signature; /* most often referenced member */
+	off_t    bytes_out;
+	off_t    bytes_in;  /* used in unzip code only: needs to know packed size */
+	uint32_t crc32;
+	time_t   mtime;     /* gunzip code may set this on exit */
+} transformer_aux_data_t;
 
-IF_DESKTOP(long long) int inflate_unzip(inflate_unzip_result *res, off_t compr_size, int src_fd, int dst_fd) FAST_FUNC;
-/* xz unpacker takes .xz stream from offset 6 */
-IF_DESKTOP(long long) int unpack_xz_stream(int src_fd, int dst_fd) FAST_FUNC;
-/* lzma unpacker takes .lzma stream from offset 0 */
-IF_DESKTOP(long long) int unpack_lzma_stream(int src_fd, int dst_fd) FAST_FUNC;
-/* the rest wants 2 first bytes already skipped by the caller */
-IF_DESKTOP(long long) int unpack_bz2_stream(int src_fd, int dst_fd) FAST_FUNC;
-IF_DESKTOP(long long) int unpack_gz_stream(int src_fd, int dst_fd) FAST_FUNC;
-IF_DESKTOP(long long) int unpack_gz_stream_with_info(int src_fd, int dst_fd, unpack_info_t *info) FAST_FUNC;
-IF_DESKTOP(long long) int unpack_Z_stream(int src_fd, int dst_fd) FAST_FUNC;
-/* wrapper which checks first two bytes to be "BZ" */
-IF_DESKTOP(long long) int unpack_bz2_stream_prime(int src_fd, int dst_fd) FAST_FUNC;
+void init_transformer_aux_data(transformer_aux_data_t *aux) FAST_FUNC;
+int FAST_FUNC check_signature16(transformer_aux_data_t *aux, int src_fd, unsigned magic16) FAST_FUNC;
+
+IF_DESKTOP(long long) int inflate_unzip(transformer_aux_data_t *aux, int src_fd, int dst_fd) FAST_FUNC;
+IF_DESKTOP(long long) int unpack_Z_stream(transformer_aux_data_t *aux, int src_fd, int dst_fd) FAST_FUNC;
+IF_DESKTOP(long long) int unpack_gz_stream(transformer_aux_data_t *aux, int src_fd, int dst_fd) FAST_FUNC;
+IF_DESKTOP(long long) int unpack_bz2_stream(transformer_aux_data_t *aux, int src_fd, int dst_fd) FAST_FUNC;
+IF_DESKTOP(long long) int unpack_lzma_stream(transformer_aux_data_t *aux, int src_fd, int dst_fd) FAST_FUNC;
+IF_DESKTOP(long long) int unpack_xz_stream(transformer_aux_data_t *aux, int src_fd, int dst_fd) FAST_FUNC;
 
 char* append_ext(char *filename, const char *expected_ext) FAST_FUNC;
 int bbunpack(char **argv,
-	    IF_DESKTOP(long long) int FAST_FUNC (*unpacker)(unpack_info_t *info),
+	    IF_DESKTOP(long long) int FAST_FUNC (*unpacker)(transformer_aux_data_t *aux),
 	    char* FAST_FUNC (*make_new_name)(char *filename, const char *expected_ext),
 	    const char *expected_ext
 ) FAST_FUNC;
 
 #if BB_MMU
 void open_transformer(int fd,
-	IF_DESKTOP(long long) int FAST_FUNC (*transformer)(int src_fd, int dst_fd)) FAST_FUNC;
-#define open_transformer(fd, transformer, transform_prog) open_transformer(fd, transformer)
+	int check_signature,
+	IF_DESKTOP(long long) int FAST_FUNC (*transformer)(transformer_aux_data_t *aux, int src_fd, int dst_fd)
+) FAST_FUNC;
+#define open_transformer_with_sig(fd, transformer, transform_prog) open_transformer((fd), 1, (transformer))
+#define open_transformer_with_no_sig(fd, transformer)              open_transformer((fd), 0, (transformer))
 #else
-void open_transformer(int src_fd, const char *transform_prog) FAST_FUNC;
-#define open_transformer(fd, transformer, transform_prog) open_transformer(fd, transform_prog)
+void open_transformer(int fd, const char *transform_prog) FAST_FUNC;
+#define open_transformer_with_sig(fd, transformer, transform_prog) open_transformer((fd), (transform_prog))
+/* open_transformer_with_no_sig() does not exist on NOMMU */
 #endif
 
+
 POP_SAVED_FUNCTION_VISIBILITY
 
 #endif
diff --git a/include/libbb.h b/include/libbb.h
index c896e5484..2cc146631 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -721,17 +721,15 @@ extern void *xmalloc_xopen_read_close(const char *filename, size_t *maxsz_p) FAS
  || ENABLE_FEATURE_SEAMLESS_GZ \
  || ENABLE_FEATURE_SEAMLESS_Z)
 
+#if SEAMLESS_COMPRESSION
 /* Autodetects gzip/bzip2 formats. fd may be in the middle of the file! */
-#if ENABLE_FEATURE_SEAMLESS_LZMA \
- || ENABLE_FEATURE_SEAMLESS_BZ2 \
- || ENABLE_FEATURE_SEAMLESS_GZ \
- /* || ENABLE_FEATURE_SEAMLESS_Z */
-extern void setup_unzip_on_fd(int fd /*, int fail_if_not_detected*/) FAST_FUNC;
-#else
-# define setup_unzip_on_fd(...) ((void)0)
-#endif
+extern int setup_unzip_on_fd(int fd, int fail_if_not_detected) FAST_FUNC;
 /* Autodetects .gz etc */
 extern int open_zipped(const char *fname) FAST_FUNC;
+#else
+# define setup_unzip_on_fd(...) (0)
+# define open_zipped(fname)     open((fname), O_RDONLY);
+#endif
 extern void *xmalloc_open_zipped_read_close(const char *fname, size_t *maxsz_p) FAST_FUNC RETURNS_MALLOC;
 
 extern ssize_t safe_write(int fd, const void *buf, size_t count) FAST_FUNC;