/*
 *  Copyright 2019 The WebRTC Project Authors. All rights reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "p2p/base/connection.h"

#include <math.h>

#include <algorithm>
#include <memory>
#include <utility>
#include <vector>

#include "absl/algorithm/container.h"
#include "absl/strings/match.h"
#include "p2p/base/port_allocator.h"
#include "rtc_base/checks.h"
#include "rtc_base/crc32.h"
#include "rtc_base/helpers.h"
#include "rtc_base/logging.h"
#include "rtc_base/mdns_responder_interface.h"
#include "rtc_base/message_digest.h"
#include "rtc_base/network.h"
#include "rtc_base/numerics/safe_minmax.h"
#include "rtc_base/string_encode.h"
#include "rtc_base/string_utils.h"
#include "rtc_base/third_party/base64/base64.h"
#include "system_wrappers/include/field_trial.h"

namespace {

// Determines whether we have seen at least the given maximum number of
// pings fail to have a response.
inline bool TooManyFailures(
    const std::vector<cricket::Connection::SentPing>& pings_since_last_response,
    uint32_t maximum_failures,
    int rtt_estimate,
    int64_t now) {
  // If we haven't sent that many pings, then we can't have failed that many.
  if (pings_since_last_response.size() < maximum_failures)
    return false;

  // Check if the window in which we would expect a response to the ping has
  // already elapsed.
  int64_t expected_response_time =
      pings_since_last_response[maximum_failures - 1].sent_time + rtt_estimate;
  return now > expected_response_time;
}

// Determines whether we have gone too long without seeing any response.
inline bool TooLongWithoutResponse(
    const std::vector<cricket::Connection::SentPing>& pings_since_last_response,
    int64_t maximum_time,
    int64_t now) {
  if (pings_since_last_response.size() == 0)
    return false;

  auto first = pings_since_last_response[0];
  return now > (first.sent_time + maximum_time);
}

// Helper methods for converting string values of log description fields to
// enum.
webrtc::IceCandidateType GetCandidateTypeByString(const std::string& type) {
  if (type == cricket::LOCAL_PORT_TYPE) {
    return webrtc::IceCandidateType::kLocal;
  } else if (type == cricket::STUN_PORT_TYPE) {
    return webrtc::IceCandidateType::kStun;
  } else if (type == cricket::PRFLX_PORT_TYPE) {
    return webrtc::IceCandidateType::kPrflx;
  } else if (type == cricket::RELAY_PORT_TYPE) {
    return webrtc::IceCandidateType::kRelay;
  }
  return webrtc::IceCandidateType::kUnknown;
}

webrtc::IceCandidatePairProtocol GetProtocolByString(
    const std::string& protocol) {
  if (protocol == cricket::UDP_PROTOCOL_NAME) {
    return webrtc::IceCandidatePairProtocol::kUdp;
  } else if (protocol == cricket::TCP_PROTOCOL_NAME) {
    return webrtc::IceCandidatePairProtocol::kTcp;
  } else if (protocol == cricket::SSLTCP_PROTOCOL_NAME) {
    return webrtc::IceCandidatePairProtocol::kSsltcp;
  } else if (protocol == cricket::TLS_PROTOCOL_NAME) {
    return webrtc::IceCandidatePairProtocol::kTls;
  }
  return webrtc::IceCandidatePairProtocol::kUnknown;
}

webrtc::IceCandidatePairAddressFamily GetAddressFamilyByInt(
    int address_family) {
  if (address_family == AF_INET) {
    return webrtc::IceCandidatePairAddressFamily::kIpv4;
  } else if (address_family == AF_INET6) {
    return webrtc::IceCandidatePairAddressFamily::kIpv6;
  }
  return webrtc::IceCandidatePairAddressFamily::kUnknown;
}

webrtc::IceCandidateNetworkType ConvertNetworkType(rtc::AdapterType type) {
  if (type == rtc::ADAPTER_TYPE_ETHERNET) {
    return webrtc::IceCandidateNetworkType::kEthernet;
  } else if (type == rtc::ADAPTER_TYPE_LOOPBACK) {
    return webrtc::IceCandidateNetworkType::kLoopback;
  } else if (type == rtc::ADAPTER_TYPE_WIFI) {
    return webrtc::IceCandidateNetworkType::kWifi;
  } else if (type == rtc::ADAPTER_TYPE_VPN) {
    return webrtc::IceCandidateNetworkType::kVpn;
  } else if (type == rtc::ADAPTER_TYPE_CELLULAR) {
    return webrtc::IceCandidateNetworkType::kCellular;
  }
  return webrtc::IceCandidateNetworkType::kUnknown;
}

// When we don't have any RTT data, we have to pick something reasonable.  We
// use a large value just in case the connection is really slow.
const int DEFAULT_RTT = 3000;  // 3 seconds

// We will restrict RTT estimates (when used for determining state) to be
// within a reasonable range.
const int MINIMUM_RTT = 100;    // 0.1 seconds
const int MAXIMUM_RTT = 60000;  // 60 seconds

const int DEFAULT_RTT_ESTIMATE_HALF_TIME_MS = 500;

// Computes our estimate of the RTT given the current estimate.
inline int ConservativeRTTEstimate(int rtt) {
  return rtc::SafeClamp(2 * rtt, MINIMUM_RTT, MAXIMUM_RTT);
}

// Weighting of the old rtt value to new data.
const int RTT_RATIO = 3;  // 3 : 1

constexpr int64_t kMinExtraPingDelayMs = 100;

// Default field trials.
const cricket::IceFieldTrials kDefaultFieldTrials;

}  // namespace

namespace cricket {

// A ConnectionRequest is a simple STUN ping used to determine writability.
ConnectionRequest::ConnectionRequest(Connection* connection)
    : StunRequest(new IceMessage()), connection_(connection) {}

void ConnectionRequest::Prepare(StunMessage* request) {
  request->SetType(STUN_BINDING_REQUEST);
  std::string username;
  connection_->port()->CreateStunUsername(
      connection_->remote_candidate().username(), &username);
  // Note that the order of attributes does not impact the parsing on the
  // receiver side. The attribute is retrieved then by iterating and matching
  // over all parsed attributes. See StunMessage::GetAttribute.
  request->AddAttribute(
      std::make_unique<StunByteStringAttribute>(STUN_ATTR_USERNAME, username));

  // connection_ already holds this ping, so subtract one from count.
  if (connection_->port()->send_retransmit_count_attribute()) {
    request->AddAttribute(std::make_unique<StunUInt32Attribute>(
        STUN_ATTR_RETRANSMIT_COUNT,
        static_cast<uint32_t>(connection_->pings_since_last_response_.size() -
                              1)));
  }
  uint32_t network_info = connection_->port()->Network()->id();
  network_info = (network_info << 16) | connection_->port()->network_cost();
  request->AddAttribute(std::make_unique<StunUInt32Attribute>(
      STUN_ATTR_NETWORK_INFO, network_info));

  if (webrtc::field_trial::IsEnabled(
          "WebRTC-PiggybackIceCheckAcknowledgement") &&
      connection_->last_ping_id_received()) {
    request->AddAttribute(std::make_unique<StunByteStringAttribute>(
        STUN_ATTR_LAST_ICE_CHECK_RECEIVED,
        connection_->last_ping_id_received().value()));
  }

  // Adding ICE_CONTROLLED or ICE_CONTROLLING attribute based on the role.
  if (connection_->port()->GetIceRole() == ICEROLE_CONTROLLING) {
    request->AddAttribute(std::make_unique<StunUInt64Attribute>(
        STUN_ATTR_ICE_CONTROLLING, connection_->port()->IceTiebreaker()));
    // We should have either USE_CANDIDATE attribute or ICE_NOMINATION
    // attribute but not both. That was enforced in p2ptransportchannel.
    if (connection_->use_candidate_attr()) {
      request->AddAttribute(
          std::make_unique<StunByteStringAttribute>(STUN_ATTR_USE_CANDIDATE));
    }
    if (connection_->nomination() &&
        connection_->nomination() != connection_->acked_nomination()) {
      request->AddAttribute(std::make_unique<StunUInt32Attribute>(
          STUN_ATTR_NOMINATION, connection_->nomination()));
    }
  } else if (connection_->port()->GetIceRole() == ICEROLE_CONTROLLED) {
    request->AddAttribute(std::make_unique<StunUInt64Attribute>(
        STUN_ATTR_ICE_CONTROLLED, connection_->port()->IceTiebreaker()));
  } else {
    RTC_NOTREACHED();
  }

  // Adding PRIORITY Attribute.
  // Changing the type preference to Peer Reflexive and local preference
  // and component id information is unchanged from the original priority.
  // priority = (2^24)*(type preference) +
  //           (2^8)*(local preference) +
  //           (2^0)*(256 - component ID)
  uint32_t type_preference =
      (connection_->local_candidate().protocol() == TCP_PROTOCOL_NAME)
          ? ICE_TYPE_PREFERENCE_PRFLX_TCP
          : ICE_TYPE_PREFERENCE_PRFLX;
  uint32_t prflx_priority =
      type_preference << 24 |
      (connection_->local_candidate().priority() & 0x00FFFFFF);
  request->AddAttribute(std::make_unique<StunUInt32Attribute>(
      STUN_ATTR_PRIORITY, prflx_priority));

  // Adding Message Integrity attribute.
  request->AddMessageIntegrity(connection_->remote_candidate().password());
  // Adding Fingerprint.
  request->AddFingerprint();
}

void ConnectionRequest::OnResponse(StunMessage* response) {
  connection_->OnConnectionRequestResponse(this, response);
}

void ConnectionRequest::OnErrorResponse(StunMessage* response) {
  connection_->OnConnectionRequestErrorResponse(this, response);
}

void ConnectionRequest::OnTimeout() {
  connection_->OnConnectionRequestTimeout(this);
}

void ConnectionRequest::OnSent() {
  connection_->OnConnectionRequestSent(this);
  // Each request is sent only once.  After a single delay , the request will
  // time out.
  timeout_ = true;
}

int ConnectionRequest::resend_delay() {
  return CONNECTION_RESPONSE_TIMEOUT;
}

Connection::Connection(Port* port,
                       size_t index,
                       const Candidate& remote_candidate)
    : id_(rtc::CreateRandomId()),
      port_(port),
      local_candidate_index_(index),
      remote_candidate_(remote_candidate),
      recv_rate_tracker_(100, 10u),
      send_rate_tracker_(100, 10u),
      write_state_(STATE_WRITE_INIT),
      receiving_(false),
      connected_(true),
      pruned_(false),
      use_candidate_attr_(false),
      remote_ice_mode_(ICEMODE_FULL),
      requests_(port->thread()),
      rtt_(DEFAULT_RTT),
      last_ping_sent_(0),
      last_ping_received_(0),
      last_data_received_(0),
      last_ping_response_received_(0),
      reported_(false),
      state_(IceCandidatePairState::WAITING),
      time_created_ms_(rtc::TimeMillis()),
      field_trials_(&kDefaultFieldTrials),
      rtt_estimate_(DEFAULT_RTT_ESTIMATE_HALF_TIME_MS) {
  // All of our connections start in WAITING state.
  // TODO(mallinath) - Start connections from STATE_FROZEN.
  // Wire up to send stun packets
  requests_.SignalSendPacket.connect(this, &Connection::OnSendStunPacket);
  RTC_LOG(LS_INFO) << ToString() << ": Connection created";
}

Connection::~Connection() {}

const Candidate& Connection::local_candidate() const {
  RTC_DCHECK(local_candidate_index_ < port_->Candidates().size());
  return port_->Candidates()[local_candidate_index_];
}

const Candidate& Connection::remote_candidate() const {
  return remote_candidate_;
}

const rtc::Network* Connection::network() const {
  return port()->Network();
}

int Connection::generation() const {
  return port()->generation();
}

uint64_t Connection::priority() const {
  uint64_t priority = 0;
  // RFC 5245 - 5.7.2.  Computing Pair Priority and Ordering Pairs
  // Let G be the priority for the candidate provided by the controlling
  // agent.  Let D be the priority for the candidate provided by the
  // controlled agent.
  // pair priority = 2^32*MIN(G,D) + 2*MAX(G,D) + (G>D?1:0)
  IceRole role = port_->GetIceRole();
  if (role != ICEROLE_UNKNOWN) {
    uint32_t g = 0;
    uint32_t d = 0;
    if (role == ICEROLE_CONTROLLING) {
      g = local_candidate().priority();
      d = remote_candidate_.priority();
    } else {
      g = remote_candidate_.priority();
      d = local_candidate().priority();
    }
    priority = std::min(g, d);
    priority = priority << 32;
    priority += 2 * std::max(g, d) + (g > d ? 1 : 0);
  }
  return priority;
}

void Connection::set_write_state(WriteState value) {
  WriteState old_value = write_state_;
  write_state_ = value;
  if (value != old_value) {
    RTC_LOG(LS_VERBOSE) << ToString() << ": set_write_state from: " << old_value
                        << " to " << value;
    SignalStateChange(this);
  }
}

void Connection::UpdateReceiving(int64_t now) {
  bool receiving;
  if (last_ping_sent() < last_ping_response_received()) {
    // We consider any candidate pair that has its last connectivity check
    // acknowledged by a response as receiving, particularly for backup
    // candidate pairs that send checks at a much slower pace than the selected
    // one. Otherwise, a backup candidate pair constantly becomes not receiving
    // as a side effect of a long ping interval, since we do not have a separate
    // receiving timeout for backup candidate pairs. See
    // IceConfig.ice_backup_candidate_pair_ping_interval,
    // IceConfig.ice_connection_receiving_timeout and their default value.
    receiving = true;
  } else {
    receiving =
        last_received() > 0 && now <= last_received() + receiving_timeout();
  }
  if (receiving_ == receiving) {
    return;
  }
  RTC_LOG(LS_VERBOSE) << ToString() << ": set_receiving to " << receiving;
  receiving_ = receiving;
  receiving_unchanged_since_ = now;
  SignalStateChange(this);
}

void Connection::set_state(IceCandidatePairState state) {
  IceCandidatePairState old_state = state_;
  state_ = state;
  if (state != old_state) {
    RTC_LOG(LS_VERBOSE) << ToString() << ": set_state";
  }
}

void Connection::set_connected(bool value) {
  bool old_value = connected_;
  connected_ = value;
  if (value != old_value) {
    RTC_LOG(LS_VERBOSE) << ToString() << ": Change connected_ to " << value;
    SignalStateChange(this);
  }
}

void Connection::set_use_candidate_attr(bool enable) {
  use_candidate_attr_ = enable;
}

int Connection::unwritable_timeout() const {
  return unwritable_timeout_.value_or(CONNECTION_WRITE_CONNECT_TIMEOUT);
}

int Connection::unwritable_min_checks() const {
  return unwritable_min_checks_.value_or(CONNECTION_WRITE_CONNECT_FAILURES);
}

int Connection::inactive_timeout() const {
  return inactive_timeout_.value_or(CONNECTION_WRITE_TIMEOUT);
}

int Connection::receiving_timeout() const {
  return receiving_timeout_.value_or(WEAK_CONNECTION_RECEIVE_TIMEOUT);
}

void Connection::SetIceFieldTrials(const IceFieldTrials* field_trials) {
  field_trials_ = field_trials;
  rtt_estimate_.SetHalfTime(field_trials->rtt_estimate_halftime_ms);
}

void Connection::OnSendStunPacket(const void* data,
                                  size_t size,
                                  StunRequest* req) {
  rtc::PacketOptions options(port_->StunDscpValue());
  options.info_signaled_after_sent.packet_type =
      rtc::PacketType::kIceConnectivityCheck;
  auto err =
      port_->SendTo(data, size, remote_candidate_.address(), options, false);
  if (err < 0) {
    RTC_LOG(LS_WARNING) << ToString()
                        << ": Failed to send STUN ping "
                           " err="
                        << err << " id=" << rtc::hex_encode(req->id());
  }
}

void Connection::OnReadPacket(const char* data,
                              size_t size,
                              int64_t packet_time_us) {
  std::unique_ptr<IceMessage> msg;
  std::string remote_ufrag;
  const rtc::SocketAddress& addr(remote_candidate_.address());
  if (!port_->GetStunMessage(data, size, addr, &msg, &remote_ufrag)) {
    // The packet did not parse as a valid STUN message
    // This is a data packet, pass it along.
    last_data_received_ = rtc::TimeMillis();
    UpdateReceiving(last_data_received_);
    recv_rate_tracker_.AddSamples(size);
    SignalReadPacket(this, data, size, packet_time_us);

    // If timed out sending writability checks, start up again
    if (!pruned_ && (write_state_ == STATE_WRITE_TIMEOUT)) {
      RTC_LOG(LS_WARNING)
          << "Received a data packet on a timed-out Connection. "
             "Resetting state to STATE_WRITE_INIT.";
      set_write_state(STATE_WRITE_INIT);
    }
  } else if (!msg) {
    // The packet was STUN, but failed a check and was handled internally.
  } else {
    // The packet is STUN and passed the Port checks.
    // Perform our own checks to ensure this packet is valid.
    // If this is a STUN request, then update the receiving bit and respond.
    // If this is a STUN response, then update the writable bit.
    // Log at LS_INFO if we receive a ping on an unwritable connection.
    rtc::LoggingSeverity sev = (!writable() ? rtc::LS_INFO : rtc::LS_VERBOSE);
    switch (msg->type()) {
      case STUN_BINDING_REQUEST:
        RTC_LOG_V(sev) << ToString() << ": Received STUN ping, id="
                       << rtc::hex_encode(msg->transaction_id());

        if (remote_ufrag == remote_candidate_.username()) {
          HandleBindingRequest(msg.get());
        } else {
          // The packet had the right local username, but the remote username
          // was not the right one for the remote address.
          RTC_LOG(LS_ERROR)
              << ToString()
              << ": Received STUN request with bad remote username "
              << remote_ufrag;
          port_->SendBindingErrorResponse(msg.get(), addr,
                                          STUN_ERROR_UNAUTHORIZED,
                                          STUN_ERROR_REASON_UNAUTHORIZED);
        }
        break;

      // Response from remote peer. Does it match request sent?
      // This doesn't just check, it makes callbacks if transaction
      // id's match.
      case STUN_BINDING_RESPONSE:
      case STUN_BINDING_ERROR_RESPONSE:
        if (msg->ValidateMessageIntegrity(data, size,
                                          remote_candidate().password())) {
          requests_.CheckResponse(msg.get());
        }
        // Otherwise silently discard the response message.
        break;

      // Remote end point sent an STUN indication instead of regular binding
      // request. In this case |last_ping_received_| will be updated but no
      // response will be sent.
      case STUN_BINDING_INDICATION:
        ReceivedPing(msg->transaction_id());
        break;

      default:
        RTC_NOTREACHED();
        break;
    }
  }
}

void Connection::HandleBindingRequest(IceMessage* msg) {
  // This connection should now be receiving.
  ReceivedPing(msg->transaction_id());
  if (webrtc::field_trial::IsEnabled("WebRTC-ExtraICEPing") &&
      last_ping_response_received_ == 0) {
    if (local_candidate().type() == RELAY_PORT_TYPE ||
        local_candidate().type() == PRFLX_PORT_TYPE ||
        remote_candidate().type() == RELAY_PORT_TYPE ||
        remote_candidate().type() == PRFLX_PORT_TYPE) {
      const int64_t now = rtc::TimeMillis();
      if (last_ping_sent_ + kMinExtraPingDelayMs <= now) {
        RTC_LOG(LS_INFO) << ToString()
                         << "WebRTC-ExtraICEPing/Sending extra ping"
                         << " last_ping_sent_: " << last_ping_sent_
                         << " now: " << now
                         << " (diff: " << (now - last_ping_sent_) << ")";
        Ping(now);
      } else {
        RTC_LOG(LS_INFO) << ToString()
                         << "WebRTC-ExtraICEPing/Not sending extra ping"
                         << " last_ping_sent_: " << last_ping_sent_
                         << " now: " << now
                         << " (diff: " << (now - last_ping_sent_) << ")";
      }
    }
  }

  const rtc::SocketAddress& remote_addr = remote_candidate_.address();
  const std::string& remote_ufrag = remote_candidate_.username();
  // Check for role conflicts.
  if (!port_->MaybeIceRoleConflict(remote_addr, msg, remote_ufrag)) {
    // Received conflicting role from the peer.
    RTC_LOG(LS_INFO) << "Received conflicting role from the peer.";
    return;
  }

  stats_.recv_ping_requests++;
  LogCandidatePairEvent(webrtc::IceCandidatePairEventType::kCheckReceived,
                        msg->reduced_transaction_id());

  // This is a validated stun request from remote peer.
  port_->SendBindingResponse(msg, remote_addr);

  // If it timed out on writing check, start up again
  if (!pruned_ && write_state_ == STATE_WRITE_TIMEOUT) {
    set_write_state(STATE_WRITE_INIT);
  }

  if (port_->GetIceRole() == ICEROLE_CONTROLLED) {
    const StunUInt32Attribute* nomination_attr =
        msg->GetUInt32(STUN_ATTR_NOMINATION);
    uint32_t nomination = 0;
    if (nomination_attr) {
      nomination = nomination_attr->value();
      if (nomination == 0) {
        RTC_LOG(LS_ERROR) << "Invalid nomination: " << nomination;
      }
    } else {
      const StunByteStringAttribute* use_candidate_attr =
          msg->GetByteString(STUN_ATTR_USE_CANDIDATE);
      if (use_candidate_attr) {
        nomination = 1;
      }
    }
    // We don't un-nominate a connection, so we only keep a larger nomination.
    if (nomination > remote_nomination_) {
      set_remote_nomination(nomination);
      SignalNominated(this);
    }
  }
  // Set the remote cost if the network_info attribute is available.
  // Note: If packets are re-ordered, we may get incorrect network cost
  // temporarily, but it should get the correct value shortly after that.
  const StunUInt32Attribute* network_attr =
      msg->GetUInt32(STUN_ATTR_NETWORK_INFO);
  if (network_attr) {
    uint32_t network_info = network_attr->value();
    uint16_t network_cost = static_cast<uint16_t>(network_info);
    if (network_cost != remote_candidate_.network_cost()) {
      remote_candidate_.set_network_cost(network_cost);
      // Network cost change will affect the connection ranking, so signal
      // state change to force a re-sort in P2PTransportChannel.
      SignalStateChange(this);
    }
  }

  if (webrtc::field_trial::IsEnabled(
          "WebRTC-PiggybackIceCheckAcknowledgement")) {
    HandlePiggybackCheckAcknowledgementIfAny(msg);
  }
}

void Connection::OnReadyToSend() {
  SignalReadyToSend(this);
}

void Connection::Prune() {
  if (!pruned_ || active()) {
    RTC_LOG(LS_INFO) << ToString() << ": Connection pruned";
    pruned_ = true;
    requests_.Clear();
    set_write_state(STATE_WRITE_TIMEOUT);
  }
}

void Connection::Destroy() {
  // TODO(deadbeef, nisse): This may leak if an application closes a
  // PeerConnection and then quickly destroys the PeerConnectionFactory (along
  // with the networking thread on which this message is posted). Also affects
  // tests, with a workaround in
  // AutoSocketServerThread::~AutoSocketServerThread.
  RTC_LOG(LS_VERBOSE) << ToString() << ": Connection destroyed";
  port_->thread()->Post(RTC_FROM_HERE, this, MSG_DELETE);
  LogCandidatePairConfig(webrtc::IceCandidatePairConfigType::kDestroyed);
}

void Connection::FailAndDestroy() {
  set_state(IceCandidatePairState::FAILED);
  Destroy();
}

void Connection::FailAndPrune() {
  set_state(IceCandidatePairState::FAILED);
  Prune();
}

void Connection::PrintPingsSinceLastResponse(std::string* s, size_t max) {
  rtc::StringBuilder oss;
  if (pings_since_last_response_.size() > max) {
    for (size_t i = 0; i < max; i++) {
      const SentPing& ping = pings_since_last_response_[i];
      oss << rtc::hex_encode(ping.id) << " ";
    }
    oss << "... " << (pings_since_last_response_.size() - max) << " more";
  } else {
    for (const SentPing& ping : pings_since_last_response_) {
      oss << rtc::hex_encode(ping.id) << " ";
    }
  }
  *s = oss.str();
}

void Connection::UpdateState(int64_t now) {
  int rtt = ConservativeRTTEstimate(rtt_);

  if (RTC_LOG_CHECK_LEVEL(LS_VERBOSE)) {
    std::string pings;
    PrintPingsSinceLastResponse(&pings, 5);
    RTC_LOG(LS_VERBOSE) << ToString()
                        << ": UpdateState()"
                           ", ms since last received response="
                        << now - last_ping_response_received_
                        << ", ms since last received data="
                        << now - last_data_received_ << ", rtt=" << rtt
                        << ", pings_since_last_response=" << pings;
  }

  // Check the writable state.  (The order of these checks is important.)
  //
  // Before becoming unwritable, we allow for a fixed number of pings to fail
  // (i.e., receive no response).  We also have to give the response time to
  // get back, so we include a conservative estimate of this.
  //
  // Before timing out writability, we give a fixed amount of time.  This is to
  // allow for changes in network conditions.

  if ((write_state_ == STATE_WRITABLE) &&
      TooManyFailures(pings_since_last_response_, unwritable_min_checks(), rtt,
                      now) &&
      TooLongWithoutResponse(pings_since_last_response_, unwritable_timeout(),
                             now)) {
    uint32_t max_pings = unwritable_min_checks();
    RTC_LOG(LS_INFO) << ToString() << ": Unwritable after " << max_pings
                     << " ping failures and "
                     << now - pings_since_last_response_[0].sent_time
                     << " ms without a response,"
                        " ms since last received ping="
                     << now - last_ping_received_
                     << " ms since last received data="
                     << now - last_data_received_ << " rtt=" << rtt;
    set_write_state(STATE_WRITE_UNRELIABLE);
  }
  if ((write_state_ == STATE_WRITE_UNRELIABLE ||
       write_state_ == STATE_WRITE_INIT) &&
      TooLongWithoutResponse(pings_since_last_response_, inactive_timeout(),
                             now)) {
    RTC_LOG(LS_INFO) << ToString() << ": Timed out after "
                     << now - pings_since_last_response_[0].sent_time
                     << " ms without a response, rtt=" << rtt;
    set_write_state(STATE_WRITE_TIMEOUT);
  }

  // Update the receiving state.
  UpdateReceiving(now);
  if (dead(now)) {
    Destroy();
  }
}

void Connection::Ping(int64_t now) {
  last_ping_sent_ = now;
  ConnectionRequest* req = new ConnectionRequest(this);
  // If not using renomination, we use "1" to mean "nominated" and "0" to mean
  // "not nominated". If using renomination, values greater than 1 are used for
  // re-nominated pairs.
  int nomination = use_candidate_attr_ ? 1 : 0;
  if (nomination_ > 0) {
    nomination = nomination_;
  }
  pings_since_last_response_.push_back(SentPing(req->id(), now, nomination));
  RTC_LOG(LS_VERBOSE) << ToString() << ": Sending STUN ping, id="
                      << rtc::hex_encode(req->id())
                      << ", nomination=" << nomination_;
  requests_.Send(req);
  state_ = IceCandidatePairState::IN_PROGRESS;
  num_pings_sent_++;
}

void Connection::ReceivedPing(const absl::optional<std::string>& request_id) {
  last_ping_received_ = rtc::TimeMillis();
  last_ping_id_received_ = request_id;
  UpdateReceiving(last_ping_received_);
}

void Connection::HandlePiggybackCheckAcknowledgementIfAny(StunMessage* msg) {
  RTC_DCHECK(msg->type() == STUN_BINDING_REQUEST);
  const StunByteStringAttribute* last_ice_check_received_attr =
      msg->GetByteString(STUN_ATTR_LAST_ICE_CHECK_RECEIVED);
  if (last_ice_check_received_attr) {
    const std::string request_id = last_ice_check_received_attr->GetString();
    auto iter = absl::c_find_if(
        pings_since_last_response_,
        [&request_id](const SentPing& ping) { return ping.id == request_id; });
    if (iter != pings_since_last_response_.end()) {
      rtc::LoggingSeverity sev = !writable() ? rtc::LS_INFO : rtc::LS_VERBOSE;
      RTC_LOG_V(sev) << ToString()
                     << ": Received piggyback STUN ping response, id="
                     << rtc::hex_encode(request_id);
      const int64_t rtt = rtc::TimeMillis() - iter->sent_time;
      ReceivedPingResponse(rtt, request_id, iter->nomination);
    }
  }
}

void Connection::ReceivedPingResponse(
    int rtt,
    const std::string& request_id,
    const absl::optional<uint32_t>& nomination) {
  RTC_DCHECK_GE(rtt, 0);
  // We've already validated that this is a STUN binding response with
  // the correct local and remote username for this connection.
  // So if we're not already, become writable. We may be bringing a pruned
  // connection back to life, but if we don't really want it, we can always
  // prune it again.
  if (nomination && nomination.value() > acked_nomination_) {
    acked_nomination_ = nomination.value();
  }

  int64_t now = rtc::TimeMillis();
  total_round_trip_time_ms_ += rtt;
  current_round_trip_time_ms_ = static_cast<uint32_t>(rtt);
  rtt_estimate_.AddSample(now, rtt);

  pings_since_last_response_.clear();
  last_ping_response_received_ = now;
  UpdateReceiving(last_ping_response_received_);
  set_write_state(STATE_WRITABLE);
  set_state(IceCandidatePairState::SUCCEEDED);
  if (rtt_samples_ > 0) {
    rtt_ = rtc::GetNextMovingAverage(rtt_, rtt, RTT_RATIO);
  } else {
    rtt_ = rtt;
  }
  rtt_samples_++;
}

bool Connection::dead(int64_t now) const {
  if (last_received() > 0) {
    // If it has ever received anything, we keep it alive until it hasn't
    // received anything for DEAD_CONNECTION_RECEIVE_TIMEOUT. This covers the
    // normal case of a successfully used connection that stops working. This
    // also allows a remote peer to continue pinging over a locally inactive
    // (pruned) connection.
    return (now > (last_received() + DEAD_CONNECTION_RECEIVE_TIMEOUT));
  }

  if (active()) {
    // If it has never received anything, keep it alive as long as it is
    // actively pinging and not pruned. Otherwise, the connection might be
    // deleted before it has a chance to ping. This is the normal case for a
    // new connection that is pinging but hasn't received anything yet.
    return false;
  }

  // If it has never received anything and is not actively pinging (pruned), we
  // keep it around for at least MIN_CONNECTION_LIFETIME to prevent connections
  // from being pruned too quickly during a network change event when two
  // networks would be up simultaneously but only for a brief period.
  return now > (time_created_ms_ + MIN_CONNECTION_LIFETIME);
}

bool Connection::stable(int64_t now) const {
  // A connection is stable if it's RTT has converged and it isn't missing any
  // responses.  We should send pings at a higher rate until the RTT converges
  // and whenever a ping response is missing (so that we can detect
  // unwritability faster)
  return rtt_converged() && !missing_responses(now);
}

std::string Connection::ToDebugId() const {
  return rtc::ToHex(reinterpret_cast<uintptr_t>(this));
}

uint32_t Connection::ComputeNetworkCost() const {
  // TODO(honghaiz): Will add rtt as part of the network cost.
  return port()->network_cost() + remote_candidate_.network_cost();
}

std::string Connection::ToString() const {
  const absl::string_view CONNECT_STATE_ABBREV[2] = {
      "-",  // not connected (false)
      "C",  // connected (true)
  };
  const absl::string_view RECEIVE_STATE_ABBREV[2] = {
      "-",  // not receiving (false)
      "R",  // receiving (true)
  };
  const absl::string_view WRITE_STATE_ABBREV[4] = {
      "W",  // STATE_WRITABLE
      "w",  // STATE_WRITE_UNRELIABLE
      "-",  // STATE_WRITE_INIT
      "x",  // STATE_WRITE_TIMEOUT
  };
  const absl::string_view ICESTATE[4] = {
      "W",  // STATE_WAITING
      "I",  // STATE_INPROGRESS
      "S",  // STATE_SUCCEEDED
      "F"   // STATE_FAILED
  };
  const absl::string_view SELECTED_STATE_ABBREV[2] = {
      "-",  // candidate pair not selected (false)
      "S",  // selected (true)
  };
  const Candidate& local = local_candidate();
  const Candidate& remote = remote_candidate();
  rtc::StringBuilder ss;
  ss << "Conn[" << ToDebugId() << ":" << port_->content_name() << ":"
     << port_->Network()->ToString() << ":" << local.id() << ":"
     << local.component() << ":" << local.generation() << ":" << local.type()
     << ":" << local.protocol() << ":" << local.address().ToSensitiveString()
     << "->" << remote.id() << ":" << remote.component() << ":"
     << remote.priority() << ":" << remote.type() << ":" << remote.protocol()
     << ":" << remote.address().ToSensitiveString() << "|"
     << CONNECT_STATE_ABBREV[connected()] << RECEIVE_STATE_ABBREV[receiving()]
     << WRITE_STATE_ABBREV[write_state()] << ICESTATE[static_cast<int>(state())]
     << "|" << SELECTED_STATE_ABBREV[selected()] << "|" << remote_nomination()
     << "|" << nomination() << "|" << priority() << "|";
  if (rtt_ < DEFAULT_RTT) {
    ss << rtt_ << "]";
  } else {
    ss << "-]";
  }
  return ss.Release();
}

std::string Connection::ToSensitiveString() const {
  return ToString();
}

const webrtc::IceCandidatePairDescription& Connection::ToLogDescription() {
  if (log_description_.has_value()) {
    return log_description_.value();
  }
  const Candidate& local = local_candidate();
  const Candidate& remote = remote_candidate();
  const rtc::Network* network = port()->Network();
  log_description_ = webrtc::IceCandidatePairDescription();
  log_description_->local_candidate_type =
      GetCandidateTypeByString(local.type());
  log_description_->local_relay_protocol =
      GetProtocolByString(local.relay_protocol());
  log_description_->local_network_type = ConvertNetworkType(network->type());
  log_description_->local_address_family =
      GetAddressFamilyByInt(local.address().family());
  log_description_->remote_candidate_type =
      GetCandidateTypeByString(remote.type());
  log_description_->remote_address_family =
      GetAddressFamilyByInt(remote.address().family());
  log_description_->candidate_pair_protocol =
      GetProtocolByString(local.protocol());
  return log_description_.value();
}

void Connection::LogCandidatePairConfig(
    webrtc::IceCandidatePairConfigType type) {
  if (ice_event_log_ == nullptr) {
    return;
  }
  ice_event_log_->LogCandidatePairConfig(type, id(), ToLogDescription());
}

void Connection::LogCandidatePairEvent(webrtc::IceCandidatePairEventType type,
                                       uint32_t transaction_id) {
  if (ice_event_log_ == nullptr) {
    return;
  }
  ice_event_log_->LogCandidatePairEvent(type, id(), transaction_id);
}

void Connection::OnConnectionRequestResponse(ConnectionRequest* request,
                                             StunMessage* response) {
  // Log at LS_INFO if we receive a ping response on an unwritable
  // connection.
  rtc::LoggingSeverity sev = !writable() ? rtc::LS_INFO : rtc::LS_VERBOSE;

  int rtt = request->Elapsed();

  if (RTC_LOG_CHECK_LEVEL_V(sev)) {
    std::string pings;
    PrintPingsSinceLastResponse(&pings, 5);
    RTC_LOG_V(sev) << ToString() << ": Received STUN ping response, id="
                   << rtc::hex_encode(request->id())
                   << ", code=0"  // Makes logging easier to parse.
                      ", rtt="
                   << rtt << ", pings_since_last_response=" << pings;
  }
  absl::optional<uint32_t> nomination;
  const std::string request_id = request->id();
  auto iter = absl::c_find_if(
      pings_since_last_response_,
      [&request_id](const SentPing& ping) { return ping.id == request_id; });
  if (iter != pings_since_last_response_.end()) {
    nomination.emplace(iter->nomination);
  }
  ReceivedPingResponse(rtt, request_id, nomination);

  stats_.recv_ping_responses++;
  LogCandidatePairEvent(
      webrtc::IceCandidatePairEventType::kCheckResponseReceived,
      response->reduced_transaction_id());

  MaybeUpdateLocalCandidate(request, response);
}

void Connection::OnConnectionRequestErrorResponse(ConnectionRequest* request,
                                                  StunMessage* response) {
  int error_code = response->GetErrorCodeValue();
  RTC_LOG(LS_WARNING) << ToString() << ": Received STUN error response id="
                      << rtc::hex_encode(request->id())
                      << " code=" << error_code
                      << " rtt=" << request->Elapsed();

  if (error_code == STUN_ERROR_UNKNOWN_ATTRIBUTE ||
      error_code == STUN_ERROR_SERVER_ERROR ||
      error_code == STUN_ERROR_UNAUTHORIZED) {
    // Recoverable error, retry
  } else if (error_code == STUN_ERROR_STALE_CREDENTIALS) {
    // Race failure, retry
  } else if (error_code == STUN_ERROR_ROLE_CONFLICT) {
    HandleRoleConflictFromPeer();
  } else {
    // This is not a valid connection.
    RTC_LOG(LS_ERROR) << ToString()
                      << ": Received STUN error response, code=" << error_code
                      << "; killing connection";
    FailAndDestroy();
  }
}

void Connection::OnConnectionRequestTimeout(ConnectionRequest* request) {
  // Log at LS_INFO if we miss a ping on a writable connection.
  rtc::LoggingSeverity sev = writable() ? rtc::LS_INFO : rtc::LS_VERBOSE;
  RTC_LOG_V(sev) << ToString() << ": Timing-out STUN ping "
                 << rtc::hex_encode(request->id()) << " after "
                 << request->Elapsed() << " ms";
}

void Connection::OnConnectionRequestSent(ConnectionRequest* request) {
  // Log at LS_INFO if we send a ping on an unwritable connection.
  rtc::LoggingSeverity sev = !writable() ? rtc::LS_INFO : rtc::LS_VERBOSE;
  RTC_LOG_V(sev) << ToString()
                 << ": Sent STUN ping, id=" << rtc::hex_encode(request->id())
                 << ", use_candidate=" << use_candidate_attr()
                 << ", nomination=" << nomination();
  stats_.sent_ping_requests_total++;
  LogCandidatePairEvent(webrtc::IceCandidatePairEventType::kCheckSent,
                        request->reduced_transaction_id());
  if (stats_.recv_ping_responses == 0) {
    stats_.sent_ping_requests_before_first_response++;
  }
}

void Connection::HandleRoleConflictFromPeer() {
  port_->SignalRoleConflict(port_);
}

void Connection::MaybeSetRemoteIceParametersAndGeneration(
    const IceParameters& ice_params,
    int generation) {
  if (remote_candidate_.username() == ice_params.ufrag &&
      remote_candidate_.password().empty()) {
    remote_candidate_.set_password(ice_params.pwd);
  }
  // TODO(deadbeef): A value of '0' for the generation is used for both
  // generation 0 and "generation unknown". It should be changed to an
  // absl::optional to fix this.
  if (remote_candidate_.username() == ice_params.ufrag &&
      remote_candidate_.password() == ice_params.pwd &&
      remote_candidate_.generation() == 0) {
    remote_candidate_.set_generation(generation);
  }
}

void Connection::MaybeUpdatePeerReflexiveCandidate(
    const Candidate& new_candidate) {
  if (remote_candidate_.type() == PRFLX_PORT_TYPE &&
      new_candidate.type() != PRFLX_PORT_TYPE &&
      remote_candidate_.protocol() == new_candidate.protocol() &&
      remote_candidate_.address() == new_candidate.address() &&
      remote_candidate_.username() == new_candidate.username() &&
      remote_candidate_.password() == new_candidate.password() &&
      remote_candidate_.generation() == new_candidate.generation()) {
    remote_candidate_ = new_candidate;
  }
}

void Connection::OnMessage(rtc::Message* pmsg) {
  RTC_DCHECK(pmsg->message_id == MSG_DELETE);
  RTC_LOG(LS_INFO) << "Connection deleted with number of pings sent: "
                   << num_pings_sent_;
  SignalDestroyed(this);
  delete this;
}

int64_t Connection::last_received() const {
  return std::max(last_data_received_,
                  std::max(last_ping_received_, last_ping_response_received_));
}

ConnectionInfo Connection::stats() {
  stats_.recv_bytes_second = round(recv_rate_tracker_.ComputeRate());
  stats_.recv_total_bytes = recv_rate_tracker_.TotalSampleCount();
  stats_.sent_bytes_second = round(send_rate_tracker_.ComputeRate());
  stats_.sent_total_bytes = send_rate_tracker_.TotalSampleCount();
  stats_.receiving = receiving_;
  stats_.writable = write_state_ == STATE_WRITABLE;
  stats_.timeout = write_state_ == STATE_WRITE_TIMEOUT;
  stats_.new_connection = !reported_;
  stats_.rtt = rtt_;
  stats_.key = this;
  stats_.state = state_;
  stats_.priority = priority();
  stats_.nominated = nominated();
  stats_.total_round_trip_time_ms = total_round_trip_time_ms_;
  stats_.current_round_trip_time_ms = current_round_trip_time_ms_;
  stats_.local_candidate = local_candidate();
  stats_.remote_candidate = remote_candidate();
  return stats_;
}

void Connection::MaybeUpdateLocalCandidate(ConnectionRequest* request,
                                           StunMessage* response) {
  // RFC 5245
  // The agent checks the mapped address from the STUN response.  If the
  // transport address does not match any of the local candidates that the
  // agent knows about, the mapped address represents a new candidate -- a
  // peer reflexive candidate.
  const StunAddressAttribute* addr =
      response->GetAddress(STUN_ATTR_XOR_MAPPED_ADDRESS);
  if (!addr) {
    RTC_LOG(LS_WARNING)
        << "Connection::OnConnectionRequestResponse - "
           "No MAPPED-ADDRESS or XOR-MAPPED-ADDRESS found in the "
           "stun response message";
    return;
  }

  for (size_t i = 0; i < port_->Candidates().size(); ++i) {
    if (port_->Candidates()[i].address() == addr->GetAddress()) {
      if (local_candidate_index_ != i) {
        RTC_LOG(LS_INFO) << ToString()
                         << ": Updating local candidate type to srflx.";
        local_candidate_index_ = i;
        // SignalStateChange to force a re-sort in P2PTransportChannel as this
        // Connection's local candidate has changed.
        SignalStateChange(this);
      }
      return;
    }
  }

  // RFC 5245
  // Its priority is set equal to the value of the PRIORITY attribute
  // in the Binding request.
  const StunUInt32Attribute* priority_attr =
      request->msg()->GetUInt32(STUN_ATTR_PRIORITY);
  if (!priority_attr) {
    RTC_LOG(LS_WARNING) << "Connection::OnConnectionRequestResponse - "
                           "No STUN_ATTR_PRIORITY found in the "
                           "stun response message";
    return;
  }
  const uint32_t priority = priority_attr->value();
  std::string id = rtc::CreateRandomString(8);

  Candidate new_local_candidate;
  new_local_candidate.set_id(id);
  new_local_candidate.set_component(local_candidate().component());
  new_local_candidate.set_type(PRFLX_PORT_TYPE);
  new_local_candidate.set_protocol(local_candidate().protocol());
  new_local_candidate.set_address(addr->GetAddress());
  new_local_candidate.set_priority(priority);
  new_local_candidate.set_username(local_candidate().username());
  new_local_candidate.set_password(local_candidate().password());
  new_local_candidate.set_network_name(local_candidate().network_name());
  new_local_candidate.set_network_type(local_candidate().network_type());
  new_local_candidate.set_related_address(local_candidate().address());
  new_local_candidate.set_generation(local_candidate().generation());
  new_local_candidate.set_foundation(Port::ComputeFoundation(
      PRFLX_PORT_TYPE, local_candidate().protocol(),
      local_candidate().relay_protocol(), local_candidate().address()));
  new_local_candidate.set_network_id(local_candidate().network_id());
  new_local_candidate.set_network_cost(local_candidate().network_cost());

  // Change the local candidate of this Connection to the new prflx candidate.
  RTC_LOG(LS_INFO) << ToString() << ": Updating local candidate type to prflx.";
  local_candidate_index_ = port_->AddPrflxCandidate(new_local_candidate);

  // SignalStateChange to force a re-sort in P2PTransportChannel as this
  // Connection's local candidate has changed.
  SignalStateChange(this);
}

bool Connection::rtt_converged() const {
  return rtt_samples_ > (RTT_RATIO + 1);
}

bool Connection::missing_responses(int64_t now) const {
  if (pings_since_last_response_.empty()) {
    return false;
  }

  int64_t waiting = now - pings_since_last_response_[0].sent_time;
  return waiting > 2 * rtt();
}

bool Connection::TooManyOutstandingPings(
    const absl::optional<int>& max_outstanding_pings) const {
  if (!max_outstanding_pings.has_value()) {
    return false;
  }
  if (static_cast<int>(pings_since_last_response_.size()) <
      *max_outstanding_pings) {
    return false;
  }
  return true;
}

ProxyConnection::ProxyConnection(Port* port,
                                 size_t index,
                                 const Candidate& remote_candidate)
    : Connection(port, index, remote_candidate) {}

int ProxyConnection::Send(const void* data,
                          size_t size,
                          const rtc::PacketOptions& options) {
  stats_.sent_total_packets++;
  int sent =
      port_->SendTo(data, size, remote_candidate_.address(), options, true);
  if (sent <= 0) {
    RTC_DCHECK(sent < 0);
    error_ = port_->GetError();
    stats_.sent_discarded_packets++;
  } else {
    send_rate_tracker_.AddSamples(sent);
  }
  return sent;
}

int ProxyConnection::GetError() {
  return error_;
}

}  // namespace cricket