Return both IPv6 and IPv4 address from the lookup.

webrtc/base/nethelpers.cc

 /*
  *  Copyright 2008 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 26 matching lines @@
   ASSERT(false);
   LOG(LS_WARNING) << "ResolveHostname() is not implemented for NaCl";
   return -1;
 #else  // __native_client__
   if (!addresses) {
     return -1;
   }
   addresses->clear();
   struct addrinfo* result = NULL;
   struct addrinfo hints = {0};
-  // TODO(djw): For now this is IPv4 only so existing users remain unaffected.
-  hints.ai_family = AF_INET;
+  hints.ai_family = family;
+  // |family| here will almost always be AF_UNSPEC, because |family| comes from
+  // AsyncResolver::addr_.family(), which comes from a SocketAddress constructed
+  // with a hostname. When a SocketAddress is constructed with a hostname, its
+  // family is AF_UNSPEC. However, if someday in the future we construct
+  // a SocketAddress with both a hostname and a family other than AF_UNSPEC,
+  // then it would be possible to get a specific family value here.
+
+  // The behavior of AF_UNSPEC is roughly "get both ipv4 and ipv6", as
+  // documented by the various operating systems:
+  // Linux: http://man7.org/linux/man-pages/man3/getaddrinfo.3.html
+  // Windows: https://msdn.microsoft.com/en-us/library/windows/desktop/
+  // ms738520(v=vs.85).aspx
+  // Mac: https://developer.apple.com/legacy/library/documentation/Darwin/
+  // Reference/ManPages/man3/getaddrinfo.3.html
+  // Android (source code, not documentation):
+  // https://android.googlesource.com/platform/bionic/+/
+  // 7e0bfb511e85834d7c6cb9631206b62f82701d60/libc/netbsd/net/getaddrinfo.c#1657
   hints.ai_flags = AI_ADDRCONFIG;
   int ret = getaddrinfo(hostname.c_str(), NULL, &hints, &result);
   if (ret != 0) {
     return ret;
   }
   struct addrinfo* cursor = result;
   for (; cursor; cursor = cursor->ai_next) {
     if (family == AF_UNSPEC || cursor->ai_family == family) {
       IPAddress ip;
       if (IPFromAddrInfo(cursor, &ip)) {
@@ skipping 114 matching lines @@
       break;
     }
   }
   freeifaddrs(ifa);
   return has_ipv6;
 #else
   return true;
 #endif
 }
 }  // namespace rtc