[net/dns] Add test DualFamilyLocalhost and fix it when DnsClient enabled.

net/dns/host_resolver_impl.cc

Index: net/dns/host_resolver_impl.cc
diff --git a/net/dns/host_resolver_impl.cc b/net/dns/host_resolver_impl.cc
index 74a76755ce4ebe5c1eaae88a8ac1b21ff9a555a2..d96ec2667502879ae5cfee6a784497de22724ba4 100644
--- a/net/dns/host_resolver_impl.cc
+++ b/net/dns/host_resolver_impl.cc
@@ -250,6 +250,26 @@ AddressList EnsurePortOnAddressList(const AddressList& list, uint16 port) {
   return AddressList::CopyWithPort(list, port);
 }
 
+bool IsAllLocalhostOfOneFamily(const AddressList& list) {

[mmenke, 2013/04/17 15:42:32]

Think this function is worth a short description.

[mmenke, 2013/04/17 15:42:32]

This function name seems to be inaccurate.  We check if they're localhost of any
family, rather than all of the same family.  The other function with this name
makes sure they were all in the same family.

[mmenke, 2013/04/17 15:42:32]

optional nit:  Suggest using "addresses" rather than "list" to match the calling
function.

[szym, 2013/04/17 17:09:16]

Done.

[szym, 2013/04/17 17:09:16]

Done. Also changed "localhost" to "loopback" which is more accurate.

[szym, 2013/04/17 17:09:16]

Done.

+  const uint8 kIPv6Loopback[] = { 0, 0, 0, 0, 0, 0, 0, 0,
+                                  0, 0, 0, 0, 0, 0, 0, 1 };
+  for (unsigned i = 0; i < list.size(); ++i) {
+    const IPAddressNumber& address = list[i].address();
+    switch (list[i].GetFamily()) {

[mmenke, 2013/04/17 15:42:32]

nit:  address.GetFamily()

[szym, 2013/04/17 17:09:16]

GetFamily is a function of IPEndPoint. IPAddressNumber is just a std::vector.

+      case ADDRESS_FAMILY_IPV4:
+        if (address[0] != 127) return false;

[mmenke, 2013/04/17 15:42:32]

nit:  Line break before "return".

[szym, 2013/04/17 17:09:16]

Done.

+        break;
+      case ADDRESS_FAMILY_IPV6:

[mmenke, 2013/04/17 15:42:32]

Do we even need to check for IPv6?  I'm not particularly opposed to it, but
since we don't currently detect the IPv6-only support...

[szym, 2013/04/17 17:09:16]

We don't, and this code path will not be exercised (only called if
DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6).

Could change it to IsAllIPv4Loopback.

[mmenke, 2013/04/17 17:35:00]

I think we should go ahead and do that.  If we need more functionality in the
future, can add it.

+        if (!std::equal(address.begin(), address.end(), kIPv6Loopback))
+          return false;
+        break;
+      default:
+        NOTREACHED();
+    }
+  }
+  return true;
+}
+
 // Creates NetLog parameters when the resolve failed.
 base::Value* NetLogProcTaskFailedCallback(uint32 attempt_number,
                                           int net_error,
@@ -1950,7 +1970,6 @@ bool HostResolverImpl::ServeFromHosts(const Key& key,
   DCHECK(addresses);
   if (!HaveDnsConfig())
     return false;
-
   addresses->clear();
 
   // HOSTS lookups are case-insensitive.
@@ -1979,6 +1998,17 @@ bool HostResolverImpl::ServeFromHosts(const Key& key,
       addresses->push_back(IPEndPoint(it->second, info.port()));
   }
 
+  // If got only loopback addresses and the family was restricted, resolve
+  // again, without restrictions. See SystemHostResolverCall for rationale.
+  if ((key.host_resolver_flags &
+          HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6) &&
+      IsAllLocalhostOfOneFamily(*addresses)) {
+    Key new_key(key);
+    new_key.address_family = ADDRESS_FAMILY_UNSPECIFIED;
+    new_key.host_resolver_flags &=
+        ~HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6;
+    return ServeFromHosts(new_key, info, addresses);
+  }
   return !addresses->empty();
 }
 
@@ -2118,6 +2148,7 @@ void HostResolverImpl::OnIPAddressChanged() {
 void HostResolverImpl::OnDNSChanged() {
   DnsConfig dns_config;
   NetworkChangeNotifier::GetDnsConfig(&dns_config);
+
   if (net_log_) {
     net_log_->AddGlobalEntry(
         NetLog::TYPE_DNS_CONFIG_CHANGED,