[net/dns] Reuse pre-connected sockets in DnsTransaction to add entropy to source ports.

net/dns/dns_session.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_DNS_SESSION_H_
 #define NET_DNS_DNS_SESSION_H_
 
+#include <map>
+#include <vector>
+
 #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"
+#include "net/udp/datagram_client_socket.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;
 
+  class SocketLease {
+   public:
+    SocketLease(scoped_refptr<DnsSession> session,
+                int server_index,
+                scoped_ptr<DatagramClientSocket> socket);
+    ~SocketLease();
+
+    DatagramClientSocket* socket() { return socket_.get(); }
+
+   private:
+    scoped_refptr<DnsSession> session_;
+    int server_index_;
+    scoped_ptr<DatagramClientSocket> socket_;
+  };
+
   DnsSession(const DnsConfig& config,
              ClientSocketFactory* factory,
              const RandIntCallback& rand_int_callback,
              NetLog* net_log);
 
   const DnsConfig& config() const { return config_; }
   NetLog* net_log() const { return net_log_; }
 
-  ClientSocketFactory* socket_factory() { return socket_factory_; }
-
   // Return the next random query ID.
   int NextQueryId() const;
 
   // Return the index of the first configured server to use on first attempt.
   int NextFirstServerIndex();
 
   // Return the timeout for the next query.
   base::TimeDelta NextTimeout(int attempt);
 
+  // Allocate a socket, already connected to the server address.
+  // TODO(szym): add NetLog param?
+  scoped_ptr<SocketLease> AllocateSocket(int server_index);
+
  private:
   friend class base::RefCounted<DnsSession>;
+  typedef std::vector<DatagramClientSocket*> SocketVector;
+  typedef std::vector<SocketVector> SocketPool;
+
   ~DnsSession();
 
+  // Release a socket.
+  void FreeSocket(int server_index, scoped_ptr<DatagramClientSocket> socket);
+
   const DnsConfig config_;
   ClientSocketFactory* socket_factory_;
   RandCallback rand_callback_;
   NetLog* net_log_;
 
+  SocketPool sockets_;
+
   // Current index into |config_.nameservers| to begin resolution with.
   int server_index_;
 
   // TODO(szym): Add current RTT estimate.
   // TODO(szym): Add TCP connection pool to support DNS over TCP.
-  // TODO(szym): Add UDP port pool to avoid NAT table overload.
 
   DISALLOW_COPY_AND_ASSIGN(DnsSession);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_SESSION_H_