Allow evdns_base_new to succeed with no nameservers configured (#1389)

* evdns-no-ns:
  Allow evdns_base_new to succeed with no nameservers configured
  Replace magic numbers with consts for evdns_base_resolv_conf_parse() errors

evdns.c

@@ -4471,12 +4471,13 @@ resolv_conf_parse_line(struct evdns_base *base, char *const start, int flags) {
 
 /* exported function */
 /* returns: */
-/*   0 no errors */
-/*   1 failed to open file */
-/*   2 failed to stat file */
-/*   3 file too large */
-/*   4 out of memory */
-/*   5 short read from file */
+/*   EVDNS_ERROR_NONE (0) no errors */
+/*   EVDNS_ERROR_FAILED_TO_OPEN_FILE (1) failed to open file */
+/*   EVDNS_ERROR_FAILED_TO_STAT_FILE (2) failed to stat file */
+/*   EVDNS_ERROR_FILE_TOO_LARGE (3) file too large */
+/*   EVDNS_ERROR_OUT_OF_MEMORY (4) out of memory */
+/*   EVDNS_ERROR_SHORT_READ_FROM_FILE (5) short read from file */
+/*   EVDNS_ERROR_NO_NAMESERVERS_CONFIGURED (6) no nameservers configured */
 int
 evdns_base_resolv_conf_parse(struct evdns_base *base, int flags, const char *const filename) {
 	int res;
@@ -4516,7 +4517,7 @@ evdns_base_resolv_conf_parse_impl(struct evdns_base *base, int flags, const char
 	size_t n;
 	char *resolv;
 	char *start;
-	int err = 0;
+	int err = EVDNS_ERROR_NONE;
 	int add_default;
 
 	log(EVDNS_LOG_DEBUG, "Parsing resolv.conf file %s", filename);
@@ -4534,16 +4535,16 @@ evdns_base_resolv_conf_parse_impl(struct evdns_base *base, int flags, const char
 
 	if (!filename) {
 		evdns_resolv_set_defaults(base, flags);
-		return 1;
+		return EVDNS_ERROR_FAILED_TO_OPEN_FILE;
 	}
 
 	if ((err = evutil_read_file_(filename, &resolv, &n, 0)) < 0) {
 		if (err == -1) {
 			/* No file. */
 			evdns_resolv_set_defaults(base, flags);
-			return 1;
+			return EVDNS_ERROR_FAILED_TO_OPEN_FILE;
 		} else {
-			return 2;
+			return EVDNS_ERROR_FAILED_TO_STAT_FILE;
 		}
 	}
 
@@ -4563,7 +4564,7 @@ evdns_base_resolv_conf_parse_impl(struct evdns_base *base, int flags, const char
 	if (!base->server_head && add_default) {
 		/* no nameservers were configured. */
 		evdns_base_nameserver_ip_add(base, "127.0.0.1");
-		err = 6;
+		err = EVDNS_ERROR_NO_NAMESERVERS_CONFIGURED;
 	}
 	if (flags & DNS_OPTION_SEARCH && (!base->global_search_state || base->global_search_state->num_domains == 0)) {
 		search_set_from_hostname(base);
@@ -4891,7 +4892,7 @@ evdns_base_new(struct event_base *event_base, int flags)
 #else
 		r = evdns_base_resolv_conf_parse(base, opts, "/etc/resolv.conf");
 #endif
-		if (r) {
+		if (r && (EVDNS_ERROR_NO_NAMESERVERS_CONFIGURED != r)) {
 			evdns_base_free_and_unlock(base, 0);
 			return NULL;
 		}

include/event2/dns.h

@@ -261,6 +261,21 @@ struct event_base;
  * @see DNS_OPTION_NAMESERVERS_NO_DEFAULT */
 #define EVDNS_BASE_NAMESERVERS_NO_DEFAULT 0x10000
 
+/* No errors */
+#define EVDNS_ERROR_NONE 0
+/* Failed to open file */
+#define EVDNS_ERROR_FAILED_TO_OPEN_FILE 1
+/* Failed to stat file */
+#define EVDNS_ERROR_FAILED_TO_STAT_FILE 2
+/* File too large */
+#define EVDNS_ERROR_FILE_TOO_LARGE 3
+/* Out of memory */
+#define EVDNS_ERROR_OUT_OF_MEMORY 4
+/* Short read from file */
+#define EVDNS_ERROR_SHORT_READ_FROM_FILE 5
+/* No nameservers configured */
+#define EVDNS_ERROR_NO_NAMESERVERS_CONFIGURED 6
+
 /**
   Initialize the asynchronous DNS library.
 
@@ -511,9 +526,13 @@ int evdns_base_set_option(struct evdns_base *base, const char *option, const cha
   The following directives are not parsed from the file: sortlist, rotate,
   no-check-names, inet6, debug.
 
-  If this function encounters an error, the possible return values are: 1 =
-  failed to open file, 2 = failed to stat file, 3 = file too large, 4 = out of
-  memory, 5 = short read from file, 6 = no nameservers listed in the file
+  If this function encounters an error, the possible return values are:
+   EVDNS_ERROR_FAILED_TO_OPEN_FILE (1) - failed to open file
+   EVDNS_ERROR_FAILED_TO_STAT_FILE (2) - failed to stat file
+   EVDNS_ERROR_FILE_TOO_LARGE (3) - file too large
+   EVDNS_ERROR_OUT_OF_MEMORY (4) - out of memory
+   EVDNS_ERROR_SHORT_READ_FROM_FILE (5) - short read from file
+   EVDNS_ERROR_NO_NAMESERVERS_CONFIGURED (6) - no nameservers configured.
 
   @param base the evdns_base to which to apply this operation
   @param flags any of DNS_OPTION_NAMESERVERS|DNS_OPTION_SEARCH|DNS_OPTION_MISC|

test/regress_dns.c

@@ -42,6 +42,9 @@
 #include <sys/queue.h>
 #ifndef _WIN32
 #include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include <signal.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
@@ -1203,12 +1206,14 @@ dns_nameservers_no_default_test(void *arg)
 	 * EVDNS_BASE_INITIALIZE_NAMESERVERS|EVDNS_BASE_NAMESERVERS_NO_DEFAULT
 	 * because we cannot mock "/etc/resolv.conf" (yet). */
 
-	evdns_base_resolv_conf_parse(dns,
+	ok = evdns_base_resolv_conf_parse(dns,
 		DNS_OPTIONS_ALL|DNS_OPTION_NAMESERVERS_NO_DEFAULT, RESOLV_FILE);
+	tt_int_op(ok, ==, EVDNS_ERROR_FAILED_TO_OPEN_FILE);
 	tt_int_op(evdns_base_get_nameserver_addr(dns, 0, NULL, 0), ==, -1);
 	tt_int_op(evdns_base_get_nameserver_fd(dns, 0), ==, -1);
 
-	evdns_base_resolv_conf_parse(dns, DNS_OPTIONS_ALL, RESOLV_FILE);
+	ok = evdns_base_resolv_conf_parse(dns, DNS_OPTIONS_ALL, RESOLV_FILE);
+	tt_int_op(ok, ==, EVDNS_ERROR_FAILED_TO_OPEN_FILE);
 	tt_int_op(evdns_base_get_nameserver_addr(dns, 0, NULL, 0), ==, sizeof(struct sockaddr));
 	tt_int_op(evdns_base_get_nameserver_fd(dns, 0), !=, -1);
 
@@ -1216,6 +1221,39 @@ end:
 	if (dns)
 		evdns_base_free(dns, 0);
 }
+
+static void
+dns_nameservers_no_nameservers_configured_test(void *arg)
+{
+	struct basic_test_data *data = arg;
+	struct event_base *base = data->base;
+	struct evdns_base *dns = NULL;
+	int fd = -1;
+	char *tmpfilename = NULL;
+	const char filecontents[] = "# tmp empty resolv.conf\n";
+	const size_t filecontentssize = sizeof(filecontents);
+	int ok;
+	
+	fd = regress_make_tmpfile(filecontents, filecontentssize, &tmpfilename);
+	if (fd < 0)
+		tt_skip();
+
+	dns = evdns_base_new(base, 0);
+	tt_assert(dns);
+
+	ok = evdns_base_resolv_conf_parse(dns, DNS_OPTIONS_ALL, tmpfilename);
+	tt_int_op(ok, ==, EVDNS_ERROR_NO_NAMESERVERS_CONFIGURED);
+
+end:
+	if (fd != -1)
+		close(fd);
+	if (dns)
+		evdns_base_free(dns, 0);
+	if (tmpfilename) {
+		unlink(tmpfilename);
+		free(tmpfilename);
+	}
+}
 #endif
 
 /* === Test for bufferevent_socket_connect_hostname */
@@ -3005,6 +3043,8 @@ struct testcase_t dns_testcases[] = {
 #ifndef _WIN32
 	{ "nameservers_no_default", dns_nameservers_no_default_test,
 	  TT_FORK|TT_NEED_BASE, &basic_setup, NULL },
+	{ "no_nameservers_configured", dns_nameservers_no_nameservers_configured_test,
+	  TT_FORK|TT_NEED_BASE, &basic_setup, NULL },
 #endif
 
 	{ "getaddrinfo_async", test_getaddrinfo_async,

test/regress_main.c

@@ -144,11 +144,11 @@ regress_make_tmpfile(const void *data, size_t datalen, char **filename_out)
 		return (-1);
 	if (write(fd, data, datalen) != (int)datalen) {
 		close(fd);
+		unlink(tmpfilename);
 		return (-1);
 	}
 	lseek(fd, 0, SEEK_SET);
-	/* remove it from the file system */
-	unlink(tmpfilename);
+	*filename_out = strdup(tmpfilename);
 	return (fd);
 #else
 	/* XXXX actually delete the file later */