Add realhostname() - a function to correctly lookup

a name by address and ensure that the name resolves
back to the original address.

1 files changed, 73 insertions, 0 deletions

diff --git a/lib/libutil/realhostname.c b/lib/libutil/realhostname.c
new file mode 100644
index 0000000..ff57011
--- /dev/null
+++ b/lib/libutil/realhostname.c
@@ -0,0 +1,73 @@
+/*-
+ * Copyright (c) 1999 Brian Somers <brian@Awfulhak.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *	$Id:$
+ */
+
+#include <sys/param.h>
+
+#include <sys/socket.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <stdio.h>
+#include <string.h>
+
+#include "libutil.h"
+
+int
+realhostname(char *host, size_t hsize, const struct in_addr *ip)
+{
+	int result;
+	struct hostent *hp;
+
+	result = HOSTNAME_INVALIDADDR;
+	hp = gethostbyaddr((char *)ip, sizeof *ip, AF_INET);
+
+	if (hp != NULL && strlen(hp->h_name) <= hsize) {
+		char lookup[MAXHOSTNAMELEN + 1];
+
+		strncpy(lookup, hp->h_name, sizeof lookup - 1);
+		lookup[sizeof lookup - 1] = '\0';
+		hp = gethostbyname(lookup);
+		if (hp == NULL)
+			result = HOSTNAME_INVALIDNAME;
+		else for (; ; hp->h_addr_list++) {
+			if (hp->h_addr_list[0] == NULL) {
+				result = HOSTNAME_INCORRECTNAME;
+				break;
+			}
+			if (!memcmp(*hp->h_addr_list, ip, sizeof *ip)) {
+				strncpy(host, lookup, hsize);
+				return HOSTNAME_FOUND;
+			}
+		}
+	}
+
+	strncpy(host, inet_ntoa(*ip), hsize);
+
+	return result;
+}