DnsTransaction::RecordLostPacketsIfAny shouldn't crash if some attempts failed to connect and thus …

net/dns/dns_transaction.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_transaction.h"
 
 #include <deque>
 #include <string>
 #include <vector>
 
@@ skipping 784 matching lines @@
     for (first_completed = 0; first_completed < attempts_.size();
         ++first_completed) {
       if (attempts_[first_completed]->is_completed())
         break;
     }
     // If there were no completed attempts, then we must be offline, so don't
     // record any attempts as lost packets.
     if (first_completed == attempts_.size())
       return;
 
-    std::vector<int> num_rounds(session_->config().nameservers.size());
+    size_t num_servers = session_->config().nameservers.size();
     for (size_t i = 0; i < first_completed; ++i) {
-      unsigned server_index = attempts_[i]->GetServerIndex();
-      int server_round = num_rounds[server_index]++;
       // Don't record lost packet unless attempt is in pending state.
       if (!attempts_[i]->is_pending())
         continue;
-      session_->RecordLostPacket(server_index, server_round);
+      unsigned server_index = attempts_[i]->GetServerIndex();
+      // Servers are rotated in round robin, so server round can be calculated
+      // from attempt index.
+      size_t server_round = i / num_servers;
+      session_->RecordLostPacket(server_index, static_cast<int>(server_round));
     }
   }
 
   void LogResponse(const DnsAttempt* attempt) {
     if (attempt && attempt->GetResponse()) {
       net_log_.AddEvent(
           NetLog::TYPE_DNS_TRANSACTION_RESPONSE,
           base::Bind(&DnsAttempt::NetLogResponseCallback,
                      base::Unretained(attempt)));
     }
@@ skipping 126 matching lines @@
 }  // namespace
 
 // static
 scoped_ptr<DnsTransactionFactory> DnsTransactionFactory::CreateFactory(
     DnsSession* session) {
   return scoped_ptr<DnsTransactionFactory>(
       new DnsTransactionFactoryImpl(session));
 }
 
 }  // namespace net