dns: Support Musl

src/net/dns/dns_config_service_posix.cc

@@ -93,7 +93,7 @@ absl::optional<DnsConfig> ReadDnsConfig() {
 
   absl::optional<DnsConfig> dns_config;
 // TODO(fuchsia): Use res_ninit() when it's implemented on Fuchsia.
-#if defined(OS_OPENBSD) || defined(OS_FUCHSIA)
+#if defined(OS_OPENBSD) || defined(OS_FUCHSIA) || defined(__MUSL__)
   // Note: res_ninit in glibc always returns 0 and sets RES_INIT.
   // res_init behaves the same way.
   memset(&_res, 0, sizeof(_res));

src/net/dns/dns_reloader.cc

@@ -63,20 +63,32 @@ class DnsReloader : public NetworkChangeNotifier::DNSObserver {
     if (!reload_state) {
       auto new_reload_state = std::make_unique<ReloadState>();
       new_reload_state->resolver_generation = resolver_generation_;
+#ifdef __MUSL__
+      res_init();
+#else
       res_ninit(&_res);
+#endif
       tls_reload_state_.Set(std::move(new_reload_state));
     } else if (reload_state->resolver_generation != resolver_generation_) {
       reload_state->resolver_generation = resolver_generation_;
       // It is safe to call res_nclose here since we know res_ninit will have
       // been called above.
+#ifdef __MUSL__
+      res_init();
+#else
       res_nclose(&_res);
       res_ninit(&_res);
+#endif
     }
   }
 
  private:
   struct ReloadState {
-    ~ReloadState() { res_nclose(&_res); }
+    ~ReloadState() {
+#ifndef __MUSL__
+      res_nclose(&_res);
+#endif
+    }
 
     int resolver_generation;
   };

src/net/dns/public/resolv_reader.cc

@@ -23,16 +23,23 @@ std::unique_ptr<struct __res_state> ResolvReader::GetResState() {
   auto res = std::make_unique<struct __res_state>();
   memset(res.get(), 0, sizeof(struct __res_state));
 
+#if defined(__MUSL__)
+  if (res_init() != 0)
+    return nullptr;
+#else
   if (res_ninit(res.get()) != 0) {
     CloseResState(res.get());
     return nullptr;
   }
+#endif
 
   return res;
 }
 
 void ResolvReader::CloseResState(struct __res_state* res) {
+#if !defined(__MUSL__)
   res_nclose(res);
+#endif
 }
 
 absl::optional<std::vector<IPEndPoint>> GetNameservers(