// 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/quic/quic_utils.h"

#include <ctype.h>
#include <stdint.h>

#include <algorithm>
#include <vector>

#include "base/containers/adapters.h"
#include "base/logging.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_split.h"
#include "base/strings/stringprintf.h"
#include "net/base/ip_address.h"
#include "net/quic/quic_flags.h"
#include "net/quic/quic_write_blocked_list.h"

using base::StringPiece;
using std::string;

namespace net {
namespace {

// We know that >= GCC 4.8 and Clang have a __uint128_t intrinsic. Other
// compilers don't necessarily, notably MSVC.
#if defined(__x86_64__) &&                                         \
    ((defined(__GNUC__) &&                                         \
      (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 8))) || \
     defined(__clang__))
#define QUIC_UTIL_HAS_UINT128 1
#endif

#ifdef QUIC_UTIL_HAS_UINT128
uint128 IncrementalHashFast(uint128 uhash, const char* data, size_t len) {
  // This code ends up faster than the naive implementation for 2 reasons:
  // 1. uint128 from base/int128.h is sufficiently complicated that the compiler
  //    cannot transform the multiplication by kPrime into a shift-multiply-add;
  //    it has go through all of the instructions for a 128-bit multiply.
  // 2. Because there are so fewer instructions (around 13), the hot loop fits
  //    nicely in the instruction queue of many Intel CPUs.
  // kPrime = 309485009821345068724781371
  static const __uint128_t kPrime =
      (static_cast<__uint128_t>(16777216) << 64) + 315;
  __uint128_t xhash = (static_cast<__uint128_t>(Uint128High64(uhash)) << 64) +
                      Uint128Low64(uhash);
  const uint8_t* octets = reinterpret_cast<const uint8_t*>(data);
  for (size_t i = 0; i < len; ++i) {
    xhash = (xhash ^ octets[i]) * kPrime;
  }
  return uint128(static_cast<uint64_t>(xhash >> 64),
                 static_cast<uint64_t>(xhash & UINT64_C(0xFFFFFFFFFFFFFFFF)));
}
#endif

#ifndef QUIC_UTIL_HAS_UINT128
// Slow implementation of IncrementalHash. In practice, only used by Chromium.
uint128 IncrementalHashSlow(uint128 hash, const char* data, size_t len) {
  // kPrime = 309485009821345068724781371
  static const uint128 kPrime(16777216, 315);
  const uint8_t* octets = reinterpret_cast<const uint8_t*>(data);
  for (size_t i = 0; i < len; ++i) {
    hash = hash ^ uint128(0, octets[i]);
    hash = hash * kPrime;
  }
  return hash;
}
#endif

uint128 IncrementalHash(uint128 hash, const char* data, size_t len) {
#ifdef QUIC_UTIL_HAS_UINT128
  return IncrementalHashFast(hash, data, len);
#else
  return IncrementalHashSlow(hash, data, len);
#endif
}

bool IsInitializedIPEndPoint(const IPEndPoint& address) {
  return address.address().IsValid();
}

}  // namespace

// static
uint64_t QuicUtils::FNV1a_64_Hash(const char* data, int len) {
  static const uint64_t kOffset = UINT64_C(14695981039346656037);
  static const uint64_t kPrime = UINT64_C(1099511628211);

  const uint8_t* octets = reinterpret_cast<const uint8_t*>(data);

  uint64_t hash = kOffset;

  for (int i = 0; i < len; ++i) {
    hash = hash ^ octets[i];
    hash = hash * kPrime;
  }

  return hash;
}

// static
uint128 QuicUtils::FNV1a_128_Hash(const char* data, int len) {
  return FNV1a_128_Hash_Two(data, len, nullptr, 0);
}

// static
uint128 QuicUtils::FNV1a_128_Hash_Two(const char* data1,
                                      int len1,
                                      const char* data2,
                                      int len2) {
  // The two constants are defined as part of the hash algorithm.
  // see http://www.isthe.com/chongo/tech/comp/fnv/
  // kOffset = 144066263297769815596495629667062367629
  const uint128 kOffset(UINT64_C(7809847782465536322),
                        UINT64_C(7113472399480571277));

  uint128 hash = IncrementalHash(kOffset, data1, len1);
  if (data2 == nullptr) {
    return hash;
  }
  return IncrementalHash(hash, data2, len2);
}

// static
bool QuicUtils::FindMutualTag(const QuicTagVector& our_tags_vector,
                              const QuicTag* their_tags,
                              size_t num_their_tags,
                              Priority priority,
                              QuicTag* out_result,
                              size_t* out_index) {
  if (our_tags_vector.empty()) {
    return false;
  }
  const size_t num_our_tags = our_tags_vector.size();
  const QuicTag* our_tags = &our_tags_vector[0];

  size_t num_priority_tags, num_inferior_tags;
  const QuicTag* priority_tags;
  const QuicTag* inferior_tags;
  if (priority == LOCAL_PRIORITY) {
    num_priority_tags = num_our_tags;
    priority_tags = our_tags;
    num_inferior_tags = num_their_tags;
    inferior_tags = their_tags;
  } else {
    num_priority_tags = num_their_tags;
    priority_tags = their_tags;
    num_inferior_tags = num_our_tags;
    inferior_tags = our_tags;
  }

  for (size_t i = 0; i < num_priority_tags; i++) {
    for (size_t j = 0; j < num_inferior_tags; j++) {
      if (priority_tags[i] == inferior_tags[j]) {
        *out_result = priority_tags[i];
        if (out_index) {
          if (priority == LOCAL_PRIORITY) {
            *out_index = j;
          } else {
            *out_index = i;
          }
        }
        return true;
      }
    }
  }

  return false;
}

// static
void QuicUtils::SerializeUint128Short(uint128 v, uint8_t* out) {
  const uint64_t lo = Uint128Low64(v);
  const uint64_t hi = Uint128High64(v);
  // This assumes that the system is little-endian.
  memcpy(out, &lo, sizeof(lo));
  memcpy(out + sizeof(lo), &hi, sizeof(hi) / 2);
}

#define RETURN_STRING_LITERAL(x) \
  case x:                        \
    return #x;

// static
const char* QuicUtils::StreamErrorToString(QuicRstStreamErrorCode error) {
  switch (error) {
    RETURN_STRING_LITERAL(QUIC_STREAM_NO_ERROR);
    RETURN_STRING_LITERAL(QUIC_STREAM_CONNECTION_ERROR);
    RETURN_STRING_LITERAL(QUIC_ERROR_PROCESSING_STREAM);
    RETURN_STRING_LITERAL(QUIC_MULTIPLE_TERMINATION_OFFSETS);
    RETURN_STRING_LITERAL(QUIC_BAD_APPLICATION_PAYLOAD);
    RETURN_STRING_LITERAL(QUIC_STREAM_PEER_GOING_AWAY);
    RETURN_STRING_LITERAL(QUIC_STREAM_CANCELLED);
    RETURN_STRING_LITERAL(QUIC_RST_ACKNOWLEDGEMENT);
    RETURN_STRING_LITERAL(QUIC_REFUSED_STREAM);
    RETURN_STRING_LITERAL(QUIC_STREAM_LAST_ERROR);
    RETURN_STRING_LITERAL(QUIC_INVALID_PROMISE_URL);
    RETURN_STRING_LITERAL(QUIC_UNAUTHORIZED_PROMISE_URL);
    RETURN_STRING_LITERAL(QUIC_DUPLICATE_PROMISE_URL);
    RETURN_STRING_LITERAL(QUIC_PROMISE_VARY_MISMATCH);
    RETURN_STRING_LITERAL(QUIC_INVALID_PROMISE_METHOD);
  }
  // Return a default value so that we return this when |error| doesn't match
  // any of the QuicRstStreamErrorCodes. This can happen when the RstStream
  // frame sent by the peer (attacker) has invalid error code.
  return "INVALID_RST_STREAM_ERROR_CODE";
}

// static
const char* QuicUtils::ErrorToString(QuicErrorCode error) {
  switch (error) {
    RETURN_STRING_LITERAL(QUIC_NO_ERROR);
    RETURN_STRING_LITERAL(QUIC_INTERNAL_ERROR);
    RETURN_STRING_LITERAL(QUIC_STREAM_DATA_AFTER_TERMINATION);
    RETURN_STRING_LITERAL(QUIC_INVALID_PACKET_HEADER);
    RETURN_STRING_LITERAL(QUIC_INVALID_FRAME_DATA);
    RETURN_STRING_LITERAL(QUIC_MISSING_PAYLOAD);
    RETURN_STRING_LITERAL(QUIC_INVALID_FEC_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_STREAM_DATA);
    RETURN_STRING_LITERAL(QUIC_OVERLAPPING_STREAM_DATA);
    RETURN_STRING_LITERAL(QUIC_UNENCRYPTED_STREAM_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_RST_STREAM_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_CONNECTION_CLOSE_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_GOAWAY_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_WINDOW_UPDATE_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_BLOCKED_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_STOP_WAITING_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_PATH_CLOSE_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_ACK_DATA);
    RETURN_STRING_LITERAL(QUIC_INVALID_VERSION_NEGOTIATION_PACKET);
    RETURN_STRING_LITERAL(QUIC_INVALID_PUBLIC_RST_PACKET);
    RETURN_STRING_LITERAL(QUIC_DECRYPTION_FAILURE);
    RETURN_STRING_LITERAL(QUIC_ENCRYPTION_FAILURE);
    RETURN_STRING_LITERAL(QUIC_PACKET_TOO_LARGE);
    RETURN_STRING_LITERAL(QUIC_PEER_GOING_AWAY);
    RETURN_STRING_LITERAL(QUIC_HANDSHAKE_FAILED);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_TAGS_OUT_OF_ORDER);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_TOO_MANY_ENTRIES);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_TOO_MANY_REJECTS);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_INVALID_VALUE_LENGTH)
    RETURN_STRING_LITERAL(QUIC_CRYPTO_MESSAGE_AFTER_HANDSHAKE_COMPLETE);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_INTERNAL_ERROR);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_VERSION_NOT_SUPPORTED);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_HANDSHAKE_STATELESS_REJECT);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_NO_SUPPORT);
    RETURN_STRING_LITERAL(QUIC_INVALID_CRYPTO_MESSAGE_TYPE);
    RETURN_STRING_LITERAL(QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_MESSAGE_PARAMETER_NOT_FOUND);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_MESSAGE_PARAMETER_NO_OVERLAP);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_MESSAGE_INDEX_NOT_FOUND);
    RETURN_STRING_LITERAL(QUIC_INVALID_STREAM_ID);
    RETURN_STRING_LITERAL(QUIC_INVALID_PRIORITY);
    RETURN_STRING_LITERAL(QUIC_TOO_MANY_OPEN_STREAMS);
    RETURN_STRING_LITERAL(QUIC_PUBLIC_RESET);
    RETURN_STRING_LITERAL(QUIC_INVALID_VERSION);
    RETURN_STRING_LITERAL(QUIC_INVALID_HEADER_ID);
    RETURN_STRING_LITERAL(QUIC_INVALID_NEGOTIATED_VALUE);
    RETURN_STRING_LITERAL(QUIC_DECOMPRESSION_FAILURE);
    RETURN_STRING_LITERAL(QUIC_NETWORK_IDLE_TIMEOUT);
    RETURN_STRING_LITERAL(QUIC_HANDSHAKE_TIMEOUT);
    RETURN_STRING_LITERAL(QUIC_ERROR_MIGRATING_ADDRESS);
    RETURN_STRING_LITERAL(QUIC_ERROR_MIGRATING_PORT);
    RETURN_STRING_LITERAL(QUIC_PACKET_WRITE_ERROR);
    RETURN_STRING_LITERAL(QUIC_PACKET_READ_ERROR);
    RETURN_STRING_LITERAL(QUIC_EMPTY_STREAM_FRAME_NO_FIN);
    RETURN_STRING_LITERAL(QUIC_INVALID_HEADERS_STREAM_DATA);
    RETURN_STRING_LITERAL(QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA);
    RETURN_STRING_LITERAL(QUIC_FLOW_CONTROL_SENT_TOO_MUCH_DATA);
    RETURN_STRING_LITERAL(QUIC_FLOW_CONTROL_INVALID_WINDOW);
    RETURN_STRING_LITERAL(QUIC_CONNECTION_IP_POOLED);
    RETURN_STRING_LITERAL(QUIC_PROOF_INVALID);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_DUPLICATE_TAG);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_ENCRYPTION_LEVEL_INCORRECT);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_SERVER_CONFIG_EXPIRED);
    RETURN_STRING_LITERAL(QUIC_INVALID_CHANNEL_ID_SIGNATURE);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_SYMMETRIC_KEY_SETUP_FAILED);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_MESSAGE_WHILE_VALIDATING_CLIENT_HELLO);
    RETURN_STRING_LITERAL(QUIC_CRYPTO_UPDATE_BEFORE_HANDSHAKE_COMPLETE);
    RETURN_STRING_LITERAL(QUIC_VERSION_NEGOTIATION_MISMATCH);
    RETURN_STRING_LITERAL(QUIC_TOO_MANY_OUTSTANDING_SENT_PACKETS);
    RETURN_STRING_LITERAL(QUIC_TOO_MANY_OUTSTANDING_RECEIVED_PACKETS);
    RETURN_STRING_LITERAL(QUIC_CONNECTION_CANCELLED);
    RETURN_STRING_LITERAL(QUIC_BAD_PACKET_LOSS_RATE);
    RETURN_STRING_LITERAL(QUIC_PUBLIC_RESETS_POST_HANDSHAKE);
    RETURN_STRING_LITERAL(QUIC_TIMEOUTS_WITH_OPEN_STREAMS);
    RETURN_STRING_LITERAL(QUIC_FAILED_TO_SERIALIZE_PACKET);
    RETURN_STRING_LITERAL(QUIC_TOO_MANY_AVAILABLE_STREAMS);
    RETURN_STRING_LITERAL(QUIC_UNENCRYPTED_FEC_DATA);
    RETURN_STRING_LITERAL(QUIC_BAD_MULTIPATH_FLAG);
    RETURN_STRING_LITERAL(QUIC_IP_ADDRESS_CHANGED);
    RETURN_STRING_LITERAL(QUIC_CONNECTION_MIGRATION_NO_MIGRATABLE_STREAMS);
    RETURN_STRING_LITERAL(QUIC_CONNECTION_MIGRATION_TOO_MANY_CHANGES);
    RETURN_STRING_LITERAL(QUIC_CONNECTION_MIGRATION_NO_NEW_NETWORK);
    RETURN_STRING_LITERAL(QUIC_CONNECTION_MIGRATION_NON_MIGRATABLE_STREAM);
    RETURN_STRING_LITERAL(QUIC_TOO_MANY_RTOS);
    RETURN_STRING_LITERAL(QUIC_ATTEMPT_TO_SEND_UNENCRYPTED_STREAM_DATA);
    RETURN_STRING_LITERAL(QUIC_LAST_ERROR);
    // Intentionally have no default case, so we'll break the build
    // if we add errors and don't put them here.
  }
  // Return a default value so that we return this when |error| doesn't match
  // any of the QuicErrorCodes. This can happen when the ConnectionClose
  // frame sent by the peer (attacker) has invalid error code.
  return "INVALID_ERROR_CODE";
}

// static
const char* QuicUtils::EncryptionLevelToString(EncryptionLevel level) {
  switch (level) {
    RETURN_STRING_LITERAL(ENCRYPTION_NONE);
    RETURN_STRING_LITERAL(ENCRYPTION_INITIAL);
    RETURN_STRING_LITERAL(ENCRYPTION_FORWARD_SECURE);
    RETURN_STRING_LITERAL(NUM_ENCRYPTION_LEVELS);
  }
  return "INVALID_ENCRYPTION_LEVEL";
}

// static
const char* QuicUtils::TransmissionTypeToString(TransmissionType type) {
  switch (type) {
    RETURN_STRING_LITERAL(NOT_RETRANSMISSION);
    RETURN_STRING_LITERAL(HANDSHAKE_RETRANSMISSION);
    RETURN_STRING_LITERAL(LOSS_RETRANSMISSION);
    RETURN_STRING_LITERAL(ALL_UNACKED_RETRANSMISSION);
    RETURN_STRING_LITERAL(ALL_INITIAL_RETRANSMISSION);
    RETURN_STRING_LITERAL(RTO_RETRANSMISSION);
    RETURN_STRING_LITERAL(TLP_RETRANSMISSION);
  }
  return "INVALID_TRANSMISSION_TYPE";
}

// static
string QuicUtils::TagToString(QuicTag tag) {
  char chars[sizeof tag];
  bool ascii = true;
  const QuicTag orig_tag = tag;

  for (size_t i = 0; i < arraysize(chars); i++) {
    chars[i] = static_cast<char>(tag);
    if ((chars[i] == 0 || chars[i] == '\xff') && i == arraysize(chars) - 1) {
      chars[i] = ' ';
    }
    if (!isprint(static_cast<unsigned char>(chars[i]))) {
      ascii = false;
      break;
    }
    tag >>= 8;
  }

  if (ascii) {
    return string(chars, sizeof(chars));
  }

  return base::UintToString(orig_tag);
}

// static
QuicTagVector QuicUtils::ParseQuicConnectionOptions(
    const std::string& connection_options) {
  QuicTagVector options;
  // Tokens are expected to be no more than 4 characters long, but we
  // handle overflow gracefully.
  for (const base::StringPiece& token :
       base::SplitStringPiece(connection_options, ",", base::TRIM_WHITESPACE,
                              base::SPLIT_WANT_ALL)) {
    uint32_t option = 0;
    for (char token_char : base::Reversed(token)) {
      option <<= 8;
      option |= static_cast<unsigned char>(token_char);
    }
    options.push_back(option);
  }
  return options;
}

// static
string QuicUtils::StringToHexASCIIDump(StringPiece in_buffer) {
  int offset = 0;
  const int kBytesPerLine = 16;  // Max bytes dumped per line
  const char* buf = in_buffer.data();
  int bytes_remaining = in_buffer.size();
  string s;  // our output
  const char* p = buf;
  while (bytes_remaining > 0) {
    const int line_bytes = std::min(bytes_remaining, kBytesPerLine);
    base::StringAppendF(&s, "0x%04x:  ", offset);  // Do the line header
    for (int i = 0; i < kBytesPerLine; ++i) {
      if (i < line_bytes) {
        base::StringAppendF(&s, "%02x", static_cast<unsigned char>(p[i]));
      } else {
        s += "  ";  // two-space filler instead of two-space hex digits
      }
      if (i % 2)
        s += ' ';
    }
    s += ' ';
    for (int i = 0; i < line_bytes; ++i) {  // Do the ASCII dump
      s += (p[i] > 32 && p[i] < 127) ? p[i] : '.';
    }

    bytes_remaining -= line_bytes;
    offset += line_bytes;
    p += line_bytes;
    s += '\n';
  }
  return s;
}

// static
void QuicUtils::DeleteFrames(QuicFrames* frames) {
  for (QuicFrame& frame : *frames) {
    switch (frame.type) {
      // Frames smaller than a pointer are inlined, so don't need to be deleted.
      case PADDING_FRAME:
      case MTU_DISCOVERY_FRAME:
      case PING_FRAME:
        break;
      case STREAM_FRAME:
        delete frame.stream_frame;
        break;
      case ACK_FRAME:
        delete frame.ack_frame;
        break;
      case STOP_WAITING_FRAME:
        delete frame.stop_waiting_frame;
        break;
      case RST_STREAM_FRAME:
        delete frame.rst_stream_frame;
        break;
      case CONNECTION_CLOSE_FRAME:
        delete frame.connection_close_frame;
        break;
      case GOAWAY_FRAME:
        delete frame.goaway_frame;
        break;
      case BLOCKED_FRAME:
        delete frame.blocked_frame;
        break;
      case WINDOW_UPDATE_FRAME:
        delete frame.window_update_frame;
        break;
      case PATH_CLOSE_FRAME:
        delete frame.path_close_frame;
        break;
      case NUM_FRAME_TYPES:
        DCHECK(false) << "Cannot delete type: " << frame.type;
    }
  }
  frames->clear();
}

// static
void QuicUtils::RemoveFramesForStream(QuicFrames* frames,
                                      QuicStreamId stream_id) {
  QuicFrames::iterator it = frames->begin();
  while (it != frames->end()) {
    if (it->type != STREAM_FRAME || it->stream_frame->stream_id != stream_id) {
      ++it;
      continue;
    }
    delete it->stream_frame;
    it = frames->erase(it);
  }
}

// static
void QuicUtils::ClearSerializedPacket(SerializedPacket* serialized_packet) {
  if (!serialized_packet->retransmittable_frames.empty()) {
    DeleteFrames(&serialized_packet->retransmittable_frames);
  }
  serialized_packet->encrypted_buffer = nullptr;
  serialized_packet->encrypted_length = 0;
}

// static
uint64_t QuicUtils::PackPathIdAndPacketNumber(QuicPathId path_id,
                                              QuicPacketNumber packet_number) {
  // Setting the nonce below relies on QuicPathId and QuicPacketNumber being
  // specific sizes.
  static_assert(sizeof(path_id) == 1, "Size of QuicPathId changed.");
  static_assert(sizeof(packet_number) == 8,
                "Size of QuicPacketNumber changed.");
  // Use path_id and lower 7 bytes of packet_number as lower 8 bytes of nonce.
  uint64_t path_id_packet_number =
      (static_cast<uint64_t>(path_id) << 56) | packet_number;
  DCHECK(path_id != kDefaultPathId || path_id_packet_number == packet_number);
  return path_id_packet_number;
}

// static
char* QuicUtils::CopyBuffer(const SerializedPacket& packet) {
  char* dst_buffer = new char[packet.encrypted_length];
  memcpy(dst_buffer, packet.encrypted_buffer, packet.encrypted_length);
  return dst_buffer;
}

// static
PeerAddressChangeType QuicUtils::DetermineAddressChangeType(
    const IPEndPoint& old_address,
    const IPEndPoint& new_address) {
  if (!IsInitializedIPEndPoint(old_address) ||
      !IsInitializedIPEndPoint(new_address) || old_address == new_address) {
    return NO_CHANGE;
  }

  if (old_address.address() == new_address.address()) {
    return PORT_CHANGE;
  }

  bool old_ip_is_ipv4 = old_address.address().IsIPv4();
  bool migrating_ip_is_ipv4 = new_address.address().IsIPv4();
  if (old_ip_is_ipv4 && !migrating_ip_is_ipv4) {
    return IPV4_TO_IPV6_CHANGE;
  }

  if (!old_ip_is_ipv4) {
    return migrating_ip_is_ipv4 ? IPV6_TO_IPV4_CHANGE : IPV6_TO_IPV6_CHANGE;
  }

  if (IPAddressMatchesPrefix(old_address.address(), new_address.address(),
                             24)) {
    // Subnet part does not change (here, we use /24), which is considered to be
    // caused by NATs.
    return IPV4_SUBNET_CHANGE;
  }

  return UNSPECIFIED_CHANGE;
}

}  // namespace net