[PATCH] Add RES_OPTIONS support for resolv.conf options overriding

[Stefan Sedich <stefan.sedich@gmail.com>]

Currently glibc supports using the RES_OPTIONS environment variable
to customize the resolv.conf options on a per-process basis, this
adds the same support to musl
---
 src/network/resolvconf.c | 48 ++++++++++++++++++++++++++++++------------------
 1 file changed, 30 insertions(+), 18 deletions(-)

diff --git a/src/network/resolvconf.c b/src/network/resolvconf.c
index 4c3e4c4b..c759ff61 100644
--- a/src/network/resolvconf.c
+++ b/src/network/resolvconf.c
@@ -5,6 +5,30 @@
 #include <string.h>
 #include <netinet/in.h>
 
+void __parse_resolv_opts(struct resolvconf *conf, char *opts)
+{
+	char *p, *z;
+
+	p = strstr(opts, "ndots:");
+	if (p && isdigit(p[6])) {
+		p += 6;
+		unsigned long x = strtoul(p, &z, 10);
+		if (z != p) conf->ndots = x > 15 ? 15 : x;
+	}
+	p = strstr(opts, "attempts:");
+	if (p && isdigit(p[9])) {
+		p += 9;
+		unsigned long x = strtoul(p, &z, 10);
+		if (z != p) conf->attempts = x > 10 ? 10 : x;
+	}
+	p = strstr(opts, "timeout:");
+	if (p && (isdigit(p[8]) || p[8]=='.')) {
+		p += 8;
+		unsigned long x = strtoul(p, &z, 10);
+		if (z != p) conf->timeout = x > 60 ? 60 : x;
+	}
+}
+
 int __get_resolv_conf(struct resolvconf *conf, char *search, size_t search_sz)
 {
 	char line[256];
@@ -38,24 +62,7 @@ int __get_resolv_conf(struct resolvconf *conf, char *search, size_t search_sz)
 			continue;
 		}
 		if (!strncmp(line, "options", 7) && isspace(line[7])) {
-			p = strstr(line, "ndots:");
-			if (p && isdigit(p[6])) {
-				p += 6;
-				unsigned long x = strtoul(p, &z, 10);
-				if (z != p) conf->ndots = x > 15 ? 15 : x;
-			}
-			p = strstr(line, "attempts:");
-			if (p && isdigit(p[9])) {
-				p += 9;
-				unsigned long x = strtoul(p, &z, 10);
-				if (z != p) conf->attempts = x > 10 ? 10 : x;
-			}
-			p = strstr(line, "timeout:");
-			if (p && (isdigit(p[8]) || p[8]=='.')) {
-				p += 8;
-				unsigned long x = strtoul(p, &z, 10);
-				if (z != p) conf->timeout = x > 60 ? 60 : x;
-			}
+			__parse_resolv_opts(conf, line);
 			continue;
 		}
 		if (!strncmp(line, "nameserver", 10) && isspace(line[10])) {
@@ -79,6 +86,11 @@ int __get_resolv_conf(struct resolvconf *conf, char *search, size_t search_sz)
 		memcpy(search, p, l+1);
 	}
 
+	char *res_opts_env;
+	if ((res_opts_env = getenv("RES_OPTIONS")) != NULL) {
+		__parse_resolv_opts(conf, res_opts_env);
+	}
+
 	__fclose_ca(f);
 
 no_resolv_conf:
-- 
2.11.0