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

net/dns/address_sorter.h

+// 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/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+class AddressList;
+
+// Sorts AddressList according to RFC3484, by likelihood of successful
+// connection. Depending on the platform, the sort could be performed
+// asynchronously by the OS, or synchronously by local implementation.
+// AddressSorter does not necessarily preserve port numbers on the sorted list.
+class NET_EXPORT AddressSorter {
+ public:
+  typedef base::Callback<void(bool success,
+                              const AddressList& list)> CallbackType;
+
+  virtual ~AddressSorter() {}
+
+  // Sorts |list|, which must include at least one IPv6 address.
+  // Calls |callback| upon completion. Could complete synchronously. Could
+  // complete after this AddressSorter is destroyed.
+  virtual void Sort(const AddressList& list,
+                    const CallbackType& callback) const = 0;
+
+  // Creates platform-dependent AddressSorter.
+  static scoped_ptr<AddressSorter> CreateAddressSorter();
+
+ protected:
+  AddressSorter() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(AddressSorter);
+};
+
+}  // namespace net
+
+#endif  // NET_DNS_ADDRESS_SORTER_H_