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.
+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();
+
+  DnsConfig config_;

[mmenke, 2011/12/02 00:53:55]

It looks to me like your intention is to create a new DnsClient/DnsSession when
the DnsConfig changes.  If this is the case, I'd go ahead and make this const,
and update the DnsSession class description to mention that it must be recreated
when the config changes.

[szym, 2011/12/05 23:06:28]

Done.

+  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_
+