[net/dns] Resolve AF_UNSPEC on dual-stacked systems. Sort addresses according to RFC3484.

net/dns/address_sorter.h

Index: net/dns/address_sorter.h
diff --git a/net/dns/address_sorter.h b/net/dns/address_sorter.h
new file mode 100644
index 0000000000000000000000000000000000000000..9ddaca6a598c700c1d3782caae6c3212a9e386e0
--- /dev/null
+++ b/net/dns/address_sorter.h
@@ -0,0 +1,28 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_DNS_ADDRESS_SORTER_H_
+#define NET_DNS_ADDRESS_SORTER_H_
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace net {

[cbentzel, 2012/07/30 15:30:14]

Would help to have file/class specific comment here.

+
+class AddressList;
+
+class AddressSorter {

[cbentzel, 2012/07/30 15:30:14]

Are there any thread restrictions?

[szym, 2012/07/30 16:28:45]

This is implementation-dependent, but also not expected to be used from more
than one thread. Current implementations are NonThreadSafe, like most other
classes in net/. Should I make it explicit in the ABC or in the implementation?

[cbentzel, 2012/07/30 18:18:47]

I think thread-safety is actually part of the interface, not the implementation
(assuming it impacts which threads it can be created and destroyed on, as well
as where Sort can be called).

[szym, 2012/07/30 18:24:16]

AddressSorterWin* has no essential state so it could be entirely thread-safe. It
currently caches the socket for ioctl, but once I move it to a WorkerPool, I'll
have to open a new socket every time. Consequently, AddressSorterWin* will be
entirely thread-safe.

In contrast, AddressSorterPosix maintains a SourceAddressMap which makes it
NonThreadSafe. It also uses a ClientSocketFactory (which is NonThreadSafe).
Therefore, Sort and dtor must be called on the same thread as ctor.

+ public:
+  virtual ~AddressSorter() {}
+
+  // Sorts |list| according to revised RFC3484.
+  virtual bool Sort(AddressList* list) const = 0;
+
+  // Creates platform-dependent AddressSorter.

[cbentzel, 2012/07/30 15:30:14]

Can it be created multiple times?

[szym, 2012/07/30 16:28:45]

I was hoping that scoped_ptr<> indicated that the caller owned it, so there's no
reason to suspect that it couldn't be created multiple times.

[cbentzel, 2012/07/30 18:18:47]

Yeah, I think this is reasonable.

+  static scoped_ptr<AddressSorter> CreateAddressSorter();
+};
+
+}  // namespace net
+
+#endif  // NET_DNS_ADDRESS_SORTER_H_