Fix IPv6 support issue.

webrtc/base/nethelpers.cc

Index: webrtc/base/nethelpers.cc
diff --git a/webrtc/base/nethelpers.cc b/webrtc/base/nethelpers.cc
index fddfdaf58b5832318fe4f73d4f2ad7262f5b03bf..fa99523ec82d15371feea761eceb5cd0cea80c9f 100644
--- a/webrtc/base/nethelpers.cc
+++ b/webrtc/base/nethelpers.cc
@@ -44,8 +44,8 @@ int ResolveHostname(const std::string& hostname, int family,
   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;
+  // This should return both IPv4 and IPv6 addresses if available.
+  hints.ai_family = AF_UNSPEC;

[pthatcher1, 2016/06/21 05:26:54]

Can you make a separate CL for this in case we have to rollback either half of
this CL?

[andresp, 2016/06/21 11:36:10]

I am also not sure if this AF_UNSPEC is that correct. Documentation on behaviour
is scarce.

I guess since we trigger the resolve from the turnport itself, we do either
AF_INET or AF_INET6 depending on the turnport local address family.

[honghaiz3, 2016/06/21 18:36:06]

Will do it in a separate CL.

[pthatcher1, 2016/06/21 18:50:17]

Would it make sense to use the family already passed into this function?

hints.ai_family = family.

The the caller has control by setting the family of address passed into Start.


As for AF_UNSPEC, it supposedly works for Linux:

http://man7.org/linux/man-pages/man3/getaddrinfo.3.html

And for Android, the Bionic code makes two queries:

https://android.googlesource.com/platform/bionic/+/7e0bfb511e85834d7c6cb96312...

On Windows, it says INET+INET6:

https://msdn.microsoft.com/en-us/library/windows/desktop/ms738520(v=vs.85).aspx

On Mac, it's more complicated:

https://developer.apple.com/legacy/library/documentation/Darwin/Reference/Man...

But it says "    To best support NAT64 networks, it is recommended to resolve
all IP address literals with ai_family set to PF_UNSPEC and ai_flags set to
AI_DEFAULT."


So it seems to be roughly supported.  The only one I'm worried about is Mac/iOS.
 

[honghaiz3, 2016/06/21 20:06:49]

I think it is safer to pass in the family. But the one currently passed is the
address family of the named address. I do not think that will have a family
type.  

[pthatcher1, 2016/06/21 20:55:08]

Yeah, the caller would need to call address.SetFamily, which doesn't exist. 
Perhaps a better option is to require AsyncResolver::Start to pass in an extra
parameter that is the family that should be queried.  

Then the call could choose INET, INET6, or UNSPEC.  But then what do we do with
UNSPEC?  I think for Android, Linux, and Windows, it's safe to use it, according
to the docs.  And even Mac seems to be clear that they support it, even if in a
slightly different way. 

   hints.ai_flags = AI_ADDRCONFIG;
   int ret = getaddrinfo(hostname.c_str(), NULL, &hints, &result);
   if (ret != 0) {