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

net/dns/dns_session.cc

 // 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.
 
 #include "net/dns/dns_session.h"
 
 #include "base/basictypes.h"
 #include "base/bind.h"
+#include "base/rand_util.h"
+#include "base/stl_util.h"
 #include "base/time.h"
 #include "net/base/ip_endpoint.h"
+#include "net/base/net_errors.h"
 #include "net/dns/dns_config_service.h"
 #include "net/socket/client_socket_factory.h"
 
 namespace net {
 
+DnsSession::SocketLease::SocketLease(scoped_refptr<DnsSession> session,
+                                     int server_index,
+                                     scoped_ptr<DatagramClientSocket> socket)
+    : session_(session), server_index_(server_index), socket_(socket.Pass()) {}
+
+DnsSession::SocketLease::~SocketLease() {
+  session_->FreeSocket(server_index_, socket_.Pass());
+}
+
 DnsSession::DnsSession(const DnsConfig& config,
                        ClientSocketFactory* factory,
                        const RandIntCallback& rand_int_callback,
                        NetLog* net_log)
     : config_(config),
       socket_factory_(factory),
       rand_callback_(base::Bind(rand_int_callback, 0, kuint16max)),
       net_log_(net_log),
+      sockets_(config.nameservers.size()),
       server_index_(0) {
 }
 
 int DnsSession::NextQueryId() const {
   return rand_callback_.Run();
 }
 
 int DnsSession::NextFirstServerIndex() {
   int index = server_index_;
   if (config_.rotate)
     server_index_ = (server_index_ + 1) % config_.nameservers.size();
   return index;
 }
 
 base::TimeDelta DnsSession::NextTimeout(int attempt) {
   // The timeout doubles every full round (each nameserver once).
   // TODO(szym): Adapt timeout to observed RTT. http://crbug.com/110197
   return config_.timeout * (1 << (attempt / config_.nameservers.size()));
 }
 
-DnsSession::~DnsSession() {}
+// Allocate a socket, already connected to the server address.
+scoped_ptr<DnsSession::SocketLease> DnsSession::AllocateSocket(int index) {
+#if defined(OS_WIN)
+  // TODO(szym): Require N sockets for entropy. (N = 1000?)
+  if (!sockets_[index].empty()) {
+    // TODO(szym): Pick a random socket.
+    return scoped_ptr<SocketLease>(new SocketLease(this, index,
+                                                   sockets_[index].pop_back()));
+  }
+  // Allocate a socket.
+  scoped_ptr<DatagramClientSocket> socket(
+        socket_factory_->CreateDatagramClientSocket(
+            DatagramSocket::DEFAULT_BIND,
+            base::Bind(&base::RandInt),
+            net_log_,
+            NetLog::Source()));
+
+#else
+  scoped_ptr<DatagramClientSocket> socket(
+      socket_factory_->CreateDatagramClientSocket(
+          DatagramSocket::RANDOM_BIND,
+          base::Bind(&base::RandInt),
+          net_log_,
+          NetLog::Source()));
+#endif
+
+  if (!socket.get())
+    return scoped_ptr<SocketLease>(NULL);
+
+  int rv = socket->Connect(config_.nameservers[index]);
+  if (rv != OK)
+    return scoped_ptr<SocketLease>(NULL);
+
+  return scoped_ptr<SocketLease>(new SocketLease(this, index, socket.Pass()));
+}
+
+// Release a socket.
+void DnsSession::FreeSocket(int index,
+                            scoped_ptr<DatagramClientSocket> socket) {
+#if defined(OS_WIN)
+  // TODO(szym): DCHECK(config.nameservers[index] == socket.GetPeerAddress())
+  sockets_[index].push_back(socket.release());
+#endif
+  // else: Do nothing. This destroys the socket.
+}
+
+DnsSession::~DnsSession() {
+  for (size_t i = 0; i < sockets_.size(); ++i) {
+    STLDeleteElements(&sockets_[i]);
+  }
+}
+
 
 }  // namespace net