1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
|
// Copyright 2013 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/quic/port_suggester.h"
#include "base/logging.h"
#include "net/base/host_port_pair.h"
namespace net {
PortSuggester::PortSuggester(const HostPortPair& server, uint64 seed)
: call_count_(0),
previous_suggestion_(-1) {
unsigned char hash_bytes[base::kSHA1Length];
base::SHA1HashBytes(
reinterpret_cast<const unsigned char*>(server.host().data()),
server.host().length(), hash_bytes);
COMPILE_ASSERT(sizeof(seed_) < sizeof(hash_bytes), seed_larger_than_hash);
memcpy(&seed_, hash_bytes, sizeof(seed_));
seed_ ^= seed ^ server.port();
}
int PortSuggester::SuggestPort(int min, int max) {
// Sometimes our suggestion can't be used, so we ensure that if additional
// calls are made, then each call (probably) provides a new suggestion.
if (++call_count_ > 1) {
// Evolve the seed.
unsigned char hash_bytes[base::kSHA1Length];
base::SHA1HashBytes(reinterpret_cast<const unsigned char *>(&seed_),
sizeof(seed_), hash_bytes);
memcpy(&seed_, hash_bytes, sizeof(seed_));
}
DCHECK_LE(min, max);
DCHECK_GT(min, 0);
int range = max - min + 1;
// Ports (and hence the extent of the |range|) are generally under 2^16, so
// the tiny non-uniformity in the pseudo-random distribution is not
// significant.
previous_suggestion_ = static_cast<int>(seed_ % range) + min;
return previous_suggestion_;
}
int PortSuggester::previous_suggestion() const {
DCHECK_LT(0u, call_count_);
return previous_suggestion_;
}
} // namespace net
|
