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>

10 files changed, 95 insertions, 138 deletions

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;