[PATCH v2] gweb/gresolv.c: make use of res_ninit optional and subject to __RES

From: Khem Raj <[email protected]>

Not all libc implementation have those functions, and the way to determine
if they do is to check __RES which is explained in resolv.h thusly:

/*
 * Revision information.  This is the release date in YYYYMMDD format.
 * It can change every day so the right thing to do with it is use it
 * in preprocessor commands such as "#if (__RES > 19931104)".  Do not
 * compare for equality; rather, use it to determine whether your resolver
 * is new enough to contain a certain feature.
 */

Indeed, it needs to be at least 19991006.

The portion of the patch that implements a fallback is ported from
Alpine Linux:
http://git.alpinelinux.org/cgit/aports/plain/testing/connman/libresolv.patch
---
 gweb/gresolv.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/gweb/gresolv.c b/gweb/gresolv.c
index 8101d718..136b31f6 100644
--- a/gweb/gresolv.c
+++ b/gweb/gresolv.c
@@ -879,7 +879,9 @@ GResolv *g_resolv_new(int index)
 	resolv->index = index;
 	resolv->nameserver_list = NULL;
 
+#if (__RES >= 19991006)
 	res_ninit(&resolv->res);
+#endif
 
 	return resolv;
 }
@@ -920,7 +922,9 @@ void g_resolv_unref(GResolv *resolv)
 
 	flush_nameservers(resolv);
 
+#if (__RES >= 19991006)
 	res_nclose(&resolv->res);
+#endif
 
 	g_free(resolv);
 }
@@ -1013,6 +1017,26 @@ static gint add_query(struct resolv_lookup *lookup, const char *hostname, int ty
 	return 0;
 }
 
+#if (__RES < 19991006)
+static void read_nameservers_directly(GResolv *resolv)
+{
+	FILE *f = fopen("/etc/resolv.conf", "r");
+	if (f) {
+		char line[256], *s;
+		int i;
+		while (fgets(line, sizeof(line), f)) {
+			if (strncmp(line, "nameserver", 10) || !isspace(line[10]))
+				continue;
+			for (s = &line[11]; isspace(s[0]); s++);
+			for (i = 0; s[i] && !isspace(s[i]); i++);
+			s[i] = 0;
+			g_resolv_add_nameserver(resolv, s, 53, 0);
+		}
+		fclose(f);
+	}
+}
+#endif
+
 guint g_resolv_lookup_hostname(GResolv *resolv, const char *hostname,
 				GResolvResultFunc func, gpointer user_data)
 {
@@ -1024,6 +1048,7 @@ guint g_resolv_lookup_hostname(GResolv *resolv, const char *hostname,
 	debug(resolv, "hostname %s", hostname);
 
 	if (!resolv->nameserver_list) {
+#if (__RES >= 19991006)
 		int i;
 
 		for (i = 0; i < resolv->res.nscount; i++) {
@@ -1043,6 +1068,9 @@ guint g_resolv_lookup_hostname(GResolv *resolv, const char *hostname,
 			if (inet_ntop(family, sa_addr, buf, sizeof(buf)))
 				g_resolv_add_nameserver(resolv, buf, 53, 0);
 		}
+#else
+		read_nameservers_directly(resolv);
+#endif
 
 		if (!resolv->nameserver_list)
 			g_resolv_add_nameserver(resolv, "127.0.0.1", 53, 0);
-- 
2.43.0