New file. Determine compression algorithm by archive file name suffix. Suggested by Jean-Pierre Demailly.

src/suffix.c

@@ -0,0 +1,78 @@
+/* This file is part of GNU tar.
+   Copyright (C) 2007 Free Software Foundation, Inc.
+
+   Written by Sergey Poznyakoff.
+
+   GNU tar 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 3, or (at your option) any later
+   version.
+
+   GNU tar 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 GNU tar.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <system.h>
+#include "common.h"
+
+struct compression_suffix
+{
+  const char *suffix;
+  size_t length;
+  const char *program;
+};
+
+struct compression_suffix compression_suffixes[] = {
+#define S(s,p) #s, sizeof (#s) - 1, #p
+  { S(gz, gzip) },
+  { S(tgz, gzip) },
+  { S(taz, gzip) },
+  { S(Z, compress) },
+  { S(taZ, compress) },
+  { S(bz2, bzip2) },
+  { S(tbz, bzip2) },
+  { S(tbz2, bzip2) },
+  { S(tz2, bzip2) },
+  { S(lzma, lzma) },
+  { S(tlz, lzma) },
+#undef S
+};
+
+int nsuffixes = sizeof (compression_suffixes) /
+                  sizeof (compression_suffixes[0]);
+
+static const char *
+find_compression_program (const char *name, const char *defprog)
+{
+  char *suf = strrchr (name, '.');
+    
+  if (suf)
+    {
+      int i;
+      size_t len;
+
+      suf++;
+      len = strlen (suf);
+
+      for (i = 0; i < nsuffixes; i++)
+	{
+	  if (compression_suffixes[i].length == len
+	      && memcmp (compression_suffixes[i].suffix, suf, len) == 0)
+	    return compression_suffixes[i].program;
+	}
+    }
+  return defprog;
+}
+
+void
+set_comression_program_by_suffix (const char *name, const char *defprog)
+{
+  const char *program = find_compression_program (name, defprog);
+  if (program)
+    use_compress_program_option = program;
+}
+