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      1 // Copyright 2013 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 //
      5 // Manages the packet entropy calculation for both sent and received packets
      6 // for a connection.
      7 
      8 #ifndef NET_QUIC_QUIC_SENT_ENTROPY_MANAGER_H_
      9 #define NET_QUIC_QUIC_SENT_ENTROPY_MANAGER_H_
     10 
     11 #include <deque>
     12 
     13 #include "net/base/linked_hash_map.h"
     14 #include "net/quic/quic_framer.h"
     15 #include "net/quic/quic_protocol.h"
     16 
     17 namespace net {
     18 
     19 namespace test {
     20 class QuicConnectionPeer;
     21 }  // namespace test
     22 
     23 // Records all sent packets by a connection to track the cumulative entropy of
     24 // sent packets.  It is used by the connection to validate an ack
     25 // frame sent by the peer as a preventive measure against the optimistic ack
     26 // attack.
     27 class NET_EXPORT_PRIVATE QuicSentEntropyManager {
     28  public:
     29   QuicSentEntropyManager();
     30   virtual ~QuicSentEntropyManager();
     31 
     32   // Record |entropy_hash| for sent packet corresponding to |sequence_number|.
     33   void RecordPacketEntropyHash(QuicPacketSequenceNumber sequence_number,
     34                                QuicPacketEntropyHash entropy_hash);
     35 
     36   // Retrieves the cumulative entropy up to |sequence_number|.
     37   // Must always be called with a monotonically increasing |sequence_number|.
     38   QuicPacketEntropyHash GetCumulativeEntropy(
     39       QuicPacketSequenceNumber sequence_number);
     40 
     41   // Returns true if |entropy_hash| matches the expected sent entropy hash
     42   // up to |largest_observed| removing sequence numbers from |missing_packets|.
     43   // Must always be called with a monotonically increasing |largest_observed|.
     44   bool IsValidEntropy(QuicPacketSequenceNumber largest_observed,
     45                       const SequenceNumberSet& missing_packets,
     46                       QuicPacketEntropyHash entropy_hash);
     47 
     48   // Removes unnecessary entries before |sequence_number|.
     49   void ClearEntropyBefore(QuicPacketSequenceNumber sequence_number);
     50 
     51  private:
     52   friend class test::QuicConnectionPeer;
     53 
     54   typedef std::deque<QuicPacketEntropyHash> SentEntropyMap;
     55 
     56   struct CumulativeEntropy {
     57     CumulativeEntropy() : sequence_number(0), entropy(0) {}
     58 
     59     QuicPacketSequenceNumber sequence_number;
     60     QuicPacketEntropyHash entropy;
     61   };
     62 
     63   // Convenience methods to get the largest and smallest packets with entropies.
     64   QuicPacketSequenceNumber GetLargestPacketWithEntropy() const;
     65   QuicPacketSequenceNumber GetSmallestPacketWithEntropy() const;
     66   // Convenience method to get the entropy hash for |sequence_number|.
     67   QuicPacketEntropyHash GetPacketEntropy(
     68       QuicPacketSequenceNumber sequence_number) const;
     69 
     70   // Update the cumulative entropy to |sequence_number|.
     71   void UpdateCumulativeEntropy(QuicPacketSequenceNumber sequence_number,
     72                                CumulativeEntropy* cumulative) const;
     73 
     74   // Maps sequence numbers to the sent entropy hash for the sequence number.
     75   SentEntropyMap packets_entropy_;
     76   QuicPacketSequenceNumber map_offset_;
     77 
     78   // Cache the cumulative entropy for IsValidEntropy.
     79   CumulativeEntropy last_valid_entropy_;
     80 
     81   // Cache the cumulative entropy for the sequence number used by EntropyHash.
     82   CumulativeEntropy last_cumulative_entropy_;
     83 
     84   DISALLOW_COPY_AND_ASSIGN(QuicSentEntropyManager);
     85 };
     86 
     87 }  // namespace net
     88 
     89 #endif  // NET_QUIC_QUIC_SENT_ENTROPY_MANAGER_H_
     90