net/quic/port_suggester.cc

   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 #include "net/quic/port_suggester.h"
   6
   7 #include "base/logging.h"
   8 #include "net/base/host_port_pair.h"
   9
  10 namespace net {
  11
  12 PortSuggester::PortSuggester(const HostPortPair& server, uint64 seed)
  13     : call_count_(0),
  14       previous_suggestion_(-1) {
  15   unsigned char hash_bytes[base::kSHA1Length];
  16   base::SHA1HashBytes(
  17       reinterpret_cast<const unsigned char*>(server.host().data()),
  18       server.host().length(), hash_bytes);
  19   static_assert(sizeof(seed_) < sizeof(hash_bytes), "seed larger than hash");
  20   memcpy(&seed_, hash_bytes, sizeof(seed_));
  21   seed_ ^= seed ^ server.port();
  22 }
  23
  24 int PortSuggester::SuggestPort(int min, int max) {
  25   // Sometimes our suggestion can't be used, so we ensure that if additional
  26   // calls are made, then each call (probably) provides a new suggestion.
  27   if (++call_count_ > 1) {
  28     // Evolve the seed.
  29     unsigned char hash_bytes[base::kSHA1Length];
  30     base::SHA1HashBytes(reinterpret_cast<const unsigned char *>(&seed_),
  31                         sizeof(seed_), hash_bytes);
  32     memcpy(&seed_, hash_bytes, sizeof(seed_));
  33   }
  34   DCHECK_LE(min, max);
  35   DCHECK_GT(min, 0);
  36   int range = max - min + 1;
  37   // Ports (and hence the extent of the |range|) are generally under 2^16, so
  38   // the tiny non-uniformity in the pseudo-random distribution is not
  39   // significant.
  40   previous_suggestion_ = static_cast<int>(seed_ % range) + min;
  41   return previous_suggestion_;
  42 }
  43
  44 int PortSuggester::previous_suggestion() const {
  45   DCHECK_LT(0u, call_count_);
  46   return previous_suggestion_;
  47 }
  48
  49 }  // namespace net