Isolates generic DnsClient from AsyncHostResolver.

net/dns/dns_session.h

+// Copyright (c) 2011 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_DNS_SESSION_H_
+#define NET_DNS_DNS_SESSION_H_
+#pragma once
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/time.h"
+#include "net/base/net_export.h"
+#include "net/base/rand_callback.h"
+#include "net/dns/dns_config_service.h"
+
+namespace net {
+
+class ClientSocketFactory;
+class NetLog;
+
+// Session parameters and state shared between DNS transactions.
+// Ref-counted so that DnsClient::Request can keep working in absence of
+// DnsClient. A DnsSession must be recreated when DnsConfig changes.
+class NET_EXPORT_PRIVATE DnsSession
+    : NON_EXPORTED_BASE(public base::RefCounted<DnsSession>) {
+ public:
+  typedef base::Callback<int()> RandCallback;
+
+  DnsSession(const DnsConfig& config,
+             ClientSocketFactory* factory,
+             const RandIntCallback& rand_int_callback,
+             NetLog* net_log);
+
+  ClientSocketFactory* socket_factory() const { return socket_factory_.get(); }
+  const DnsConfig& config() const { return config_; }
+  NetLog* net_log() const { return net_log_; }
+
+  // Return the next random query ID.
+  int NextId() const;
+
+  // Return the next server address.
+  const IPEndPoint& NextServer();
+
+  // Return the timeout for the next transaction.
+  base::TimeDelta NextTimeout(int attempt);
+
+ private:
+  friend class base::RefCounted<DnsSession>;
+  ~DnsSession();
+
+  const DnsConfig config_;
+  scoped_ptr<ClientSocketFactory> socket_factory_;
+  RandCallback rand_callback_;
+  NetLog* net_log_;
+
+  // Current index into |config_.nameservers|.
+  int server_index_;
+
+  // TODO(szym): add current RTT estimate
+  // TODO(szym): add flag to indicate DNSSEC is supported
+  // TODO(szym): add TCP connection pool to support DNS over TCP
+  // TODO(szym): add UDP socket pool ?
+
+  DISALLOW_COPY_AND_ASSIGN(DnsSession);
+};
+
+}  // namespace net
+
+#endif  // NET_DNS_DNS_SESSION_H_
+