Move compression file name utilities to lib/

This makes more sense as a home for plain file name manipulation
utilities.  I also merged `include/comp_src.h.in` into
`lib/compression.c`, because structure definitions (as opposed to
declarations) don't belong in header files.

* src/compression.c: Move to ...
* lib/compression.c: ... here.  Remove unnecessary `pipeline.h` include.
* src/compression.h: Move to ...
* lib/compression.h: ... here.  Update positioning of all includes.
* lib/Makefile.am (libman_la_SOURCES): Add `compression.c` and
`compression.h`.
* lib/README: Add `compression.*`.
* src/Makefile.am (lexgrog_SOURCES, man_SOURCES, man_recode_SOURCES,
mandb_SOURCES): Remove `compression.c` and `compression.h`.

* include/comp_src.h (comp_list): Move to ...
* lib/compression.c (comp_list): ... here.  Update all references.
* include/manconfig.h (struct compression, comp_list): Move to ...
* lib/compression.h (struct compression, comp_list): ... here.  Add
includes where necessary.
* Makefile.am (noinst_HEADERS): Remove `include/comp_src.h`.

4 files changed, 237 insertions, 0 deletions

diff --git a/lib/Makefile.am b/lib/Makefile.am
index 49f7809f..449f3356 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -36,6 +36,8 @@ libman_la_SOURCES = \
 	appendstr.h \
 	cleanup.c \
 	cleanup.h \
+	compression.c \
+	compression.h \
 	debug.c \
 	debug.h \
 	encodings.c \
diff --git a/lib/README b/lib/README
index 4f2a0705..6a991200 100644
--- a/lib/README
+++ b/lib/README
@@ -7,6 +7,7 @@ information.
 
 appendstr.*			author - Markus Armbruster
 cleanup.*			author - Markus Armbruster, Colin Watson
+compression.*			author - Wilf., Colin Watson
 debug.*				author - Colin Watson
 encodings.*			author - Colin Watson
 glcontainers.*			author - Colin Watson
diff --git a/lib/compression.c b/lib/compression.c
new file mode 100644
index 00000000..3f3205ab
--- /dev/null
+++ b/lib/compression.c
@@ -0,0 +1,194 @@
+/*
+ * compression.c: code to find decompressor / compression extension
+ *
+ * Copyright (C) 1994, 1995 Graeme W. Wilford. (Wilf.)
+ * Copyright (C) 2001-2022 Colin Watson.
+ *
+ * This file is part of man-db.
+ *
+ * man-db is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * man-db is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with man-db; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Sat Aug 20 15:01:02 BST 1994  Wilf. (G.Wilford@ee.surrey.ac.uk)
+ */
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif /* HAVE_CONFIG_H */
+
+#include <assert.h>
+#include <stdio.h>
+#include <errno.h>
+#include <signal.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "error.h"
+#include "xstrndup.h"
+#include "xvasprintf.h"
+
+#include "manconfig.h"
+
+#include "appendstr.h"
+#include "compression.h"
+
+/*--------------------------------------------------------------------------*/
+/* This is where we define the decompressors used to decompress any nroff   */
+/* source that we find. All cat pages are compressed with either gzip (if   */
+/* available) or compress. This is not the place to define _the_ cat page   */
+/* decompressor - see ./manconfig.h for that.                               */
+/*                                                                          */
+/* To add a decompressor all you need to know is its name (preferrably its  */
+/* location), and the unique extension that it gives to files compressed    */
+/* with it. Here is an example. You have a compressor named foobar and      */
+/* compressed files have an extension of .fb . It is located in /usr/bin    */
+/* and requires a -d option to be used as a decompressor. Add the following */
+/* line to the structure below.                                             */
+/*                                                                          */
+/* {"/usr/bin/foobar -d", "fb", NULL},                                      */
+/*--------------------------------------------------------------------------*/
+
+struct compression comp_list[] = {
+
+/* If we have gzip, incorporate the following */
+#ifdef HAVE_GZIP
+	{PROG_GUNZIP, "gz", NULL},
+	{PROG_GUNZIP, "z", NULL},
+#endif /* HAVE_GZIP */
+
+/* If we have compress, incorporate the following */
+#ifdef HAVE_COMPRESS
+	{PROG_UNCOMPRESS, "Z", NULL},
+/* Else if we have gzip, incorporate the following */
+#elif defined (HAVE_GZIP)
+	{PROG_GUNZIP, "Z", NULL},
+#endif /* HAVE_COMPRESS || HAVE_GZIP */
+
+/* If we have bzip2, incorporate the following */
+#ifdef HAVE_BZIP2
+	{PROG_BUNZIP2, "bz2", NULL},
+#endif /* HAVE_BZIP2 */
+
+/* If we have xz, incorporate the following */
+#ifdef HAVE_XZ
+	{PROG_UNXZ, "xz", NULL},
+	{PROG_UNXZ, "lzma", NULL},
+/* Else if we have lzma, incorporate the following */
+#elif defined (HAVE_LZMA)
+	{PROG_UNLZMA, "lzma", NULL},
+#endif /* HAVE_XZ || HAVE_LZMA */
+
+/* If we have lzip, incorporate the following */
+#ifdef HAVE_LZIP
+	{PROG_UNLZIP, "lz", NULL},
+#endif /* HAVE_LZIP */
+
+/* If we have zstd, incorporate the following */
+#ifdef HAVE_ZSTD
+	{PROG_UNZSTD, "zst", NULL},
+	{PROG_UNZSTD, "zstd", NULL},
+#endif /* HAVE_ZSTD */
+
+/*------------------------------------------------------*/
+/* Add your decompressor(s) and extension(s) below here */
+/*------------------------------------------------------*/
+
+/*----------------*/
+/* and above here */
+/*----------------*/
+
+/* ... and the last structure is */
+	{NULL, NULL, NULL}
+};
+
+/* Take filename as arg, return structure containing decompressor
+   and extension, or NULL if no comp extension found.
+   If want_stem, set comp->stem to the filename without extension, which
+   the caller should free.
+
+   eg.
+   	filename = /usr/man/man1/foo.1.gz
+
+	comp->prog = "/usr/bin/gzip -dc";
+   	comp->ext = "gz";
+   	comp->stem = "/usr/man/man1/foo.1";
+ */
+struct compression *comp_info (const char *filename, int want_stem)
+{
+	const char *ext;
+	static struct compression hpux_comp =
+		{PROG_GUNZIP " -S \"\"", "", NULL};
+
+	ext = strrchr (filename, '.');
+
+	if (ext) {
+		struct compression *comp;
+		for (comp = comp_list; comp->ext; comp++) {
+			if (strcmp (comp->ext, ext + 1) == 0) {
+				if (want_stem)
+					comp->stem = xstrndup (filename,
+							       ext - filename);
+				else
+					comp->stem = NULL;
+				return comp;
+			}
+		}
+	}
+
+	if (*PROG_GUNZIP) {
+		ext = strstr (filename, ".Z/");
+		if (ext) {
+			if (want_stem)
+				hpux_comp.stem = xstrndup (filename,
+							   ext - filename);
+			else
+				hpux_comp.stem = NULL;
+			return &hpux_comp;
+		}
+	}
+
+	return NULL;
+}
+
+/* take filename w/o comp ext. as arg, return comp->stem as a relative
+   compressed file or NULL if none found */
+struct compression *comp_file (const char *filename)
+{
+	size_t len;
+	char *compfile;
+	struct compression *comp;
+
+	compfile = xasprintf ("%s.", filename);
+	assert (compfile);
+	len = strlen (compfile);
+
+	for (comp = comp_list; comp->ext; comp++) {
+		struct stat buf;
+
+		compfile = appendstr (compfile, comp->ext, (void *) 0);
+
+		if (stat (compfile, &buf) == 0) {
+			comp->stem = compfile;
+			return comp;
+		}
+
+		*(compfile + len) = '\0';
+	}
+	free (compfile);
+	return NULL;
+}
diff --git a/lib/compression.h b/lib/compression.h
new file mode 100644
index 00000000..15df2dc2
--- /dev/null
+++ b/lib/compression.h
@@ -0,0 +1,40 @@
+/*
+ * compression.h: interface to finding decompressor / compression extension
+ *
+ * Copyright (C) 1994, 1995 Graeme W. Wilford. (Wilf.)
+ * Copyright (C) 2001-2022 Colin Watson.
+ *
+ * This file is part of man-db.
+ *
+ * man-db is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * man-db is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with man-db; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+struct compression {
+	/* The following are const because they should be pointers to parts
+	 * of strings allocated elsewhere and should not be written through
+	 * or freed themselves.
+	 */
+	const char *prog;
+	const char *ext;
+	/* The following should be freed when discarding an instance of this
+	 * structure.
+	 */
+	char *stem;
+};
+
+extern struct compression comp_list[];
+
+extern struct compression *comp_info (const char *filename, int want_stem);
+extern struct compression *comp_file (const char *filename);