resolv: Move ns_makecanon into its own file, and into libc

But only as an internal symbol, __libc_ns_makecanon.  The libresolv
ABI is preserved.  This is because the function is deprecated, and
it does not make sense to add new symbol versions for deprecated
functions.

Also reformat the implementation to GNU style.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>

include/arpa/nameser.h

@@ -69,9 +69,10 @@ libresolv_hidden_proto (ns_sprintrr)
 libresolv_hidden_proto (ns_sprintrrf)
 libresolv_hidden_proto (ns_samedomain)
 libresolv_hidden_proto (ns_samename)
-libresolv_hidden_proto (ns_makecanon)
 libresolv_hidden_proto (ns_format_ttl)
 
+extern __typeof (ns_makecanon) __libc_ns_makecanon;
+libc_hidden_proto (__libc_ns_makecanon)
 extern __typeof (ns_name_compress) __ns_name_compress;
 libc_hidden_proto (__ns_name_compress)
 extern __typeof (ns_name_ntop) __ns_name_ntop;

resolv/Makefile

@@ -35,6 +35,7 @@ routines := \
   inet_addr \
   inet_ntop \
   inet_pton \
+  ns_makecanon \
   ns_name_compress \
   ns_name_ntop \
   ns_name_pack \
@@ -151,6 +152,7 @@ libresolv-routines := \
   res_mkquery \
   res_query \
   res_send \
+  resolv-deprecated \
   # libresolv-routines
 
 $(libanl-routines-var) += \

resolv/Versions

@@ -72,6 +72,7 @@ libc {
     __inet_pton_length;
     __libc_dn_expand;
     __libc_dn_skipname;
+    __libc_ns_makecanon;
     __libc_res_dnok;
     __libc_res_hnok;
     __ns_name_compress;

resolv/ns_makecanon.c

@@ -0,0 +1,50 @@
+/* Add missing "." to domain names.
+ * Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
+ * Copyright (c) 1995,1999 by Internet Software Consortium.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
+ * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
+ * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+ * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+ * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
+ * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+ * SOFTWARE.
+ */
+
+#include <arpa/nameser.h>
+#include <errno.h>
+#include <string.h>
+
+/* Make a canonical copy of domain name SRC in DST.  Behavior:
+      foo -> foo.
+      foo. -> foo.
+      foo.. -> foo.
+      foo\. -> foo\..
+      foo\\. -> foo\\.  */
+int
+__libc_ns_makecanon (const char *src, char *dst, size_t dstsize)
+{
+  size_t n = strlen (src);
+
+  if (n + sizeof "." > dstsize) /* sizeof == 2.  */
+    {
+      __set_errno (EMSGSIZE);
+      return -1;
+    }
+  strcpy (dst, src);
+  while (n >= 1U && dst[n - 1] == '.')   /* Ends in ".".  */
+    if (n >= 2U && dst[n - 2] == '\\' && /* Ends in "\.".  */
+        (n < 3U || dst[n - 3] != '\\'))  /* But not "\\.".  */
+      break;
+    else
+      dst[--n] = '\0';
+  dst[n++] = '.';
+  dst[n] = '\0';
+  return 0;
+}
+libc_hidden_def (__libc_ns_makecanon)

resolv/ns_samedomain.c

@@ -143,40 +143,6 @@ ns_subdomain(const char *a, const char *b) {
 	return (ns_samename(a, b) != 1 && ns_samedomain(a, b));
 }
 
-/*%
- *	make a canonical copy of domain name "src"
- *
- * notes:
- * \code
- *	foo -> foo.
- *	foo. -> foo.
- *	foo.. -> foo.
- *	foo\. -> foo\..
- *	foo\\. -> foo\\.
- * \endcode
- */
-
-int
-ns_makecanon(const char *src, char *dst, size_t dstsize) {
-	size_t n = strlen(src);
-
-	if (n + sizeof "." > dstsize) {			/*%< Note: sizeof == 2 */
-		__set_errno (EMSGSIZE);
-		return (-1);
-	}
-	strcpy(dst, src);
-	while (n >= 1U && dst[n - 1] == '.')		/*%< Ends in "." */
-		if (n >= 2U && dst[n - 2] == '\\' &&	/*%< Ends in "\." */
-		    (n < 3U || dst[n - 3] != '\\'))	/*%< But not "\\." */
-			break;
-		else
-			dst[--n] = '\0';
-	dst[n++] = '.';
-	dst[n] = '\0';
-	return (0);
-}
-libresolv_hidden_def (ns_makecanon)
-
 /*%
  *	determine whether domain name "a" is the same as domain name "b"
  *
@@ -190,8 +156,8 @@ int
 ns_samename(const char *a, const char *b) {
 	char ta[NS_MAXDNAME], tb[NS_MAXDNAME];
 
-	if (ns_makecanon(a, ta, sizeof ta) < 0 ||
-	    ns_makecanon(b, tb, sizeof tb) < 0)
+	if (__libc_ns_makecanon(a, ta, sizeof ta) < 0 ||
+	    __libc_ns_makecanon(b, tb, sizeof tb) < 0)
 		return (-1);
 	if (strcasecmp(ta, tb) == 0)
 		return (1);

resolv/resolv-deprecated.c

@@ -0,0 +1,35 @@
+/* Forwarders for deprecated libresolv functions which are implemented in libc.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* Some functions are used by the stub resolver implementation
+   internally and thus have to be located in libc.  They have been
+   historially exported for application use as well.  However, the
+   stub resolver dependency on those functions is not intrinsic to
+   what the stub resolver does, and it is possible that a future
+   version of the stub resolver will not need them anymore.  The
+   public symbols for these functions remain in libresolv, and are not
+   moved to libc, to avoid adding new symbol versions for legacy
+   functions.  */
+
+#include <arpa/nameser.h>
+
+int
+ns_makecanon (const char *src, char *dst, size_t dstsize)
+{
+  return __libc_ns_makecanon (src, dst, dstsize);
+}