libcli/dns: Add resolv.conf parsing

Right now this only looks at the nameserver setting. It is initally made for
asynchronous AD DC lookup routines, where we don't need the "search", "domain"
and other settings. When we convert general "net", "smbclient" and others to
use this, we might either add "domain" handling to this code or look at
something like c-ares which already does it.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

1 files changed, 123 insertions, 0 deletions

diff --git a/libcli/dns/resolvconf.c b/libcli/dns/resolvconf.c
new file mode 100644
index 00000000000..90d4e6a74b6
--- /dev/null
+++ b/libcli/dns/resolvconf.c
@@ -0,0 +1,123 @@
+/*
+ *  Unix SMB/CIFS implementation.
+ *  Internal DNS query structures
+ *  Copyright (C) Volker Lendecke 2018
+ *
+ *  This program 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 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program 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 this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "replace.h"
+#include <stdio.h>
+#include <errno.h>
+#include "libcli/dns/resolvconf.h"
+#include "lib/util/memory.h"
+
+int parse_resolvconf_fp(
+	FILE *fp,
+	TALLOC_CTX *mem_ctx,
+	char ***pnameservers,
+	size_t *pnum_nameservers)
+{
+	char *line = NULL;
+	char **nameservers = NULL;
+	size_t num_nameservers = 0;
+	int ret = 0;
+
+	while (true) {
+		char *saveptr, *option, *ns;
+		char **tmp;
+		ssize_t n;
+		size_t len;
+
+		n = getline(&line, &len, fp);
+		if (n < 0) {
+			if (!feof(fp)) {
+				/* real error */
+				ret = errno;
+			}
+			break;
+		}
+		if ((n > 0) && (line[n-1] == '\n')) {
+			line[n-1] = '\0';
+		}
+
+		if ((line[0] == '#') || (line[0] == ';')) {
+			continue;
+		}
+
+		option = strtok_r(line, " \t", &saveptr);
+		if (option == NULL) {
+			continue;
+		}
+
+		if (strcmp(option, "nameserver") != 0) {
+			continue;
+		}
+
+		ns = strtok_r(NULL, " \t", &saveptr);
+		if (ns == NULL) {
+			continue;
+		}
+
+		tmp = talloc_realloc(
+			mem_ctx,
+			nameservers,
+			char *,
+			num_nameservers+1);
+		if (tmp == NULL) {
+			ret = ENOMEM;
+			break;
+		}
+		nameservers = tmp;
+
+		nameservers[num_nameservers] = talloc_strdup(nameservers, ns);
+		if (nameservers[num_nameservers] == NULL) {
+			ret = ENOMEM;
+			break;
+		}
+		num_nameservers += 1;
+	}
+
+	SAFE_FREE(line);
+
+	if (ret == 0) {
+		*pnameservers = nameservers;
+		*pnum_nameservers = num_nameservers;
+	} else {
+		TALLOC_FREE(nameservers);
+	}
+
+	return ret;
+}
+
+int parse_resolvconf(
+	const char *resolvconf,
+	TALLOC_CTX *mem_ctx,
+	char ***pnameservers,
+	size_t *pnum_nameservers)
+{
+	FILE *fp;
+	int ret;
+
+	fp = fopen(resolvconf ? resolvconf : "/etc/resolv.conf", "r");
+	if (fp == NULL) {
+		return errno;
+	}
+
+	ret = parse_resolvconf_fp(fp, mem_ctx, pnameservers, pnum_nameservers);
+
+	fclose(fp);
+
+	return ret;
+}