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 "chrome/browser/net/probe_message.h"
6
7#include <string>
8
9#include "base/logging.h"
10
11namespace chrome_browser_net {
12
13const uint32 ProbeMessage::kVersion = 2;
14const uint32 ProbeMessage::kMaxNumberProbePackets = 21;
15const uint32 ProbeMessage::kMaxProbePacketBytes = 1500;
16// Maximum pacing interval is 300 seconds (for testing NAT binding).
17const uint32 ProbeMessage::kMaxPacingIntervalMicros = 300000000;
18const char ProbeMessage::kEncodingString[] =
19    "T\xd3?\xa5h2\x9c\x8en\xf1Q6\xbc{\xc6-4\xfa$f\xb9[\xa6\xcd@6,\xdf\xb3i-\xe6"
20    "v\x9eV\x8dXd\xd9kE\xf6=\xbeO";
21
22ProbeMessage::ProbeMessage() {}
23
24bool ProbeMessage::ParseInput(const std::string& input,
25                              ProbePacket* probe_packet) const {
26  // Encode is used for decoding here.
27  std::string input_decoded = Encode(input);
28
29  bool parse_result = probe_packet->ParseFromString(input_decoded);
30  if (!parse_result) {
31    DVLOG(1) << "ProtoBuffer string parsing error. Input size:" << input.size();
32    return false;
33  }
34  const ProbePacket_Header& header = probe_packet->header();
35  DVLOG(2) << "version " << header.version() << " checksum "
36           << header.checksum() << " type " << header.type();
37  if (header.version() != kVersion) {
38    DVLOG(1) << "Bad version number: " << header.version()
39             << " expected: " << kVersion;
40    return false;
41  }
42
43  // Checksum is computed on padding only.
44  if (probe_packet->has_padding()) {
45    DVLOG(3) << "received padding: " << probe_packet->padding();
46    uint32 computed_checksum = Checksum(probe_packet->padding());
47    if (computed_checksum != header.checksum()) {
48      DVLOG(1) << "Checksum mismatch.  Got: " << header.checksum()
49               << " expected: " << computed_checksum;
50      return false;
51    }
52  }
53
54  if (header.type() != ProbePacket_Type_HELLO_REPLY &&
55      header.type() != ProbePacket_Type_PROBE_REPLY) {
56    DVLOG(1) << "Received unknown packet type:" << header.type();
57    return false;
58  }
59  return true;
60}
61
62uint32 ProbeMessage::Checksum(const std::string& str) const {
63  uint32 ret = 0;
64  for (std::string::const_iterator i = str.begin(); i != str.end(); ++i) {
65    ret += static_cast<uint8>(*i);
66  }
67  return ret;
68}
69
70void ProbeMessage::GenerateProbeRequest(const ProbePacket_Token& token,
71                                        uint32 group_id,
72                                        uint32 probe_size,
73                                        uint32 pacing_interval_micros,
74                                        uint32 number_probe_packets,
75                                        ProbePacket* probe_packet) {
76  DCHECK_LE(number_probe_packets, kMaxNumberProbePackets);
77  DCHECK_LE(probe_size, kMaxProbePacketBytes);
78  DCHECK_LE(pacing_interval_micros, kMaxPacingIntervalMicros);
79
80  SetPacketHeader(ProbePacket_Type_PROBE_REQUEST, probe_packet);
81  *(probe_packet->mutable_token()) = token;
82  probe_packet->set_group_id(group_id);
83  probe_packet->set_probe_size_bytes(probe_size);
84  probe_packet->set_pacing_interval_micros(pacing_interval_micros);
85  probe_packet->set_number_probe_packets(number_probe_packets);
86
87  // Add padding to mitigate amplification attack.
88  std::string* padding = probe_packet->mutable_padding();
89  int padding_size = probe_size - probe_packet->ByteSize();
90  padding->append(std::string(std::max(0, padding_size), 0));
91  probe_packet->mutable_header()->set_checksum(Checksum(*padding));
92  DVLOG(3) << "Request size " << probe_packet->ByteSize() << " probe size "
93           << probe_size;
94  DCHECK_LE(probe_size, static_cast<uint32>(probe_packet->ByteSize()));
95}
96
97void ProbeMessage::SetPacketHeader(ProbePacket_Type packet_type,
98                                   ProbePacket* probe_packet) const {
99  ProbePacket_Header* header = probe_packet->mutable_header();
100  header->set_version(kVersion);
101  header->set_type(packet_type);
102}
103
104std::string ProbeMessage::Encode(const std::string& input) const {
105
106  std::string output(input.size(), 0);
107  int key_pos = 0;
108  // kEncodingString contains a ending '\0' character, excluded for encoding.
109  int key_size = sizeof(kEncodingString) - 1;
110  for (size_t i = 0; i < input.size(); ++i) {
111    output[i] = input[i] ^ kEncodingString[key_pos];
112    ++key_pos;
113    if (key_pos >= key_size)
114      key_pos = 0;
115  }
116  return output;
117}
118
119std::string ProbeMessage::MakeEncodedPacket(
120    const ProbePacket& probe_packet) const {
121  std::string output;
122  probe_packet.SerializeToString(&output);
123  return Encode(output);
124}
125
126}  // namespace chrome_browser_net
127