webrtc/rtc_base/physicalsocketserver.cc

/*
 *  Copyright 2004 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 "webrtc/rtc_base/physicalsocketserver.h"

#if defined(_MSC_VER) && _MSC_VER < 1300
#pragma warning(disable:4786)
#endif

#ifdef MEMORY_SANITIZER
#include <sanitizer/msan_interface.h>
#endif

#if defined(WEBRTC_POSIX)
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#if defined(WEBRTC_USE_EPOLL)
// "poll" will be used to wait for the signal dispatcher.
#include <poll.h>
#endif
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/select.h>
#include <unistd.h>
#include <signal.h>
#endif

#if defined(WEBRTC_WIN)
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#undef SetPort
#endif

#include <algorithm>
#include <map>

#include "webrtc/rtc_base/arraysize.h"
#include "webrtc/rtc_base/basictypes.h"
#include "webrtc/rtc_base/byteorder.h"
#include "webrtc/rtc_base/checks.h"
#include "webrtc/rtc_base/logging.h"
#include "webrtc/rtc_base/networkmonitor.h"
#include "webrtc/rtc_base/nullsocketserver.h"
#include "webrtc/rtc_base/timeutils.h"
#include "webrtc/rtc_base/win32socketinit.h"

#if defined(WEBRTC_POSIX)
#include <netinet/tcp.h>  // for TCP_NODELAY
#define IP_MTU 14 // Until this is integrated from linux/in.h to netinet/in.h
typedef void* SockOptArg;

#endif  // WEBRTC_POSIX

#if defined(WEBRTC_POSIX) && !defined(WEBRTC_MAC) && !defined(__native_client__)

int64_t GetSocketRecvTimestamp(int socket) {
  struct timeval tv_ioctl;
  int ret = ioctl(socket, SIOCGSTAMP, &tv_ioctl);
  if (ret != 0)
    return -1;
  int64_t timestamp =
      rtc::kNumMicrosecsPerSec * static_cast<int64_t>(tv_ioctl.tv_sec) +
      static_cast<int64_t>(tv_ioctl.tv_usec);
  return timestamp;
}

#else

int64_t GetSocketRecvTimestamp(int socket) {
  return -1;
}
#endif

#if defined(WEBRTC_WIN)
typedef char* SockOptArg;
#endif

#if defined(WEBRTC_USE_EPOLL)
// POLLRDHUP / EPOLLRDHUP are only defined starting with Linux 2.6.17.
#if !defined(POLLRDHUP)
#define POLLRDHUP 0x2000
#endif
#if !defined(EPOLLRDHUP)
#define EPOLLRDHUP 0x2000
#endif
#endif

namespace rtc {

std::unique_ptr<SocketServer> SocketServer::CreateDefault() {
#if defined(__native_client__)
  return std::unique_ptr<SocketServer>(new rtc::NullSocketServer);
#else
  return std::unique_ptr<SocketServer>(new rtc::PhysicalSocketServer);
#endif
}

#if defined(WEBRTC_WIN)
// Standard MTUs, from RFC 1191
const uint16_t PACKET_MAXIMUMS[] = {
    65535,  // Theoretical maximum, Hyperchannel
    32000,  // Nothing
    17914,  // 16Mb IBM Token Ring
    8166,   // IEEE 802.4
    // 4464,   // IEEE 802.5 (4Mb max)
    4352,   // FDDI
    // 2048,   // Wideband Network
    2002,   // IEEE 802.5 (4Mb recommended)
    // 1536,   // Expermental Ethernet Networks
    // 1500,   // Ethernet, Point-to-Point (default)
    1492,   // IEEE 802.3
    1006,   // SLIP, ARPANET
    // 576,    // X.25 Networks
    // 544,    // DEC IP Portal
    // 512,    // NETBIOS
    508,    // IEEE 802/Source-Rt Bridge, ARCNET
    296,    // Point-to-Point (low delay)
    68,     // Official minimum
    0,      // End of list marker
};

static const int IP_HEADER_SIZE = 20u;
static const int IPV6_HEADER_SIZE = 40u;
static const int ICMP_HEADER_SIZE = 8u;
static const int ICMP_PING_TIMEOUT_MILLIS = 10000u;
#endif

PhysicalSocket::PhysicalSocket(PhysicalSocketServer* ss, SOCKET s)
  : ss_(ss), s_(s), error_(0),
    state_((s == INVALID_SOCKET) ? CS_CLOSED : CS_CONNECTED),
    resolver_(nullptr) {
#if defined(WEBRTC_WIN)
  // EnsureWinsockInit() ensures that winsock is initialized. The default
  // version of this function doesn't do anything because winsock is
  // initialized by constructor of a static object. If neccessary libjingle
  // users can link it with a different version of this function by replacing
  // win32socketinit.cc. See win32socketinit.cc for more details.
  EnsureWinsockInit();
#endif
  if (s_ != INVALID_SOCKET) {
    SetEnabledEvents(DE_READ | DE_WRITE);

    int type = SOCK_STREAM;
    socklen_t len = sizeof(type);
    const int res =
        getsockopt(s_, SOL_SOCKET, SO_TYPE, (SockOptArg)&type, &len);
    RTC_DCHECK_EQ(0, res);
    udp_ = (SOCK_DGRAM == type);
  }
}

PhysicalSocket::~PhysicalSocket() {
  Close();
}

bool PhysicalSocket::Create(int family, int type) {
  Close();
  s_ = ::socket(family, type, 0);
  udp_ = (SOCK_DGRAM == type);
  UpdateLastError();
  if (udp_) {
    SetEnabledEvents(DE_READ | DE_WRITE);
  }
  return s_ != INVALID_SOCKET;
}

SocketAddress PhysicalSocket::GetLocalAddress() const {
  sockaddr_storage addr_storage = {0};
  socklen_t addrlen = sizeof(addr_storage);
  sockaddr* addr = reinterpret_cast<sockaddr*>(&addr_storage);
  int result = ::getsockname(s_, addr, &addrlen);
  SocketAddress address;
  if (result >= 0) {
    SocketAddressFromSockAddrStorage(addr_storage, &address);
  } else {
    LOG(LS_WARNING) << "GetLocalAddress: unable to get local addr, socket="
                    << s_;
  }
  return address;
}

SocketAddress PhysicalSocket::GetRemoteAddress() const {
  sockaddr_storage addr_storage = {0};
  socklen_t addrlen = sizeof(addr_storage);
  sockaddr* addr = reinterpret_cast<sockaddr*>(&addr_storage);
  int result = ::getpeername(s_, addr, &addrlen);
  SocketAddress address;
  if (result >= 0) {
    SocketAddressFromSockAddrStorage(addr_storage, &address);
  } else {
    LOG(LS_WARNING) << "GetRemoteAddress: unable to get remote addr, socket="
                    << s_;
  }
  return address;
}

int PhysicalSocket::Bind(const SocketAddress& bind_addr) {
  SocketAddress copied_bind_addr = bind_addr;
  // If a network binder is available, use it to bind a socket to an interface
  // instead of bind(), since this is more reliable on an OS with a weak host
  // model.
  if (ss_->network_binder() && !bind_addr.IsAnyIP()) {
    NetworkBindingResult result =
        ss_->network_binder()->BindSocketToNetwork(s_, bind_addr.ipaddr());
    if (result == NetworkBindingResult::SUCCESS) {
      // Since the network binder handled binding the socket to the desired
      // network interface, we don't need to (and shouldn't) include an IP in
      // the bind() call; bind() just needs to assign a port.
      copied_bind_addr.SetIP(GetAnyIP(copied_bind_addr.ipaddr().family()));
    } else if (result == NetworkBindingResult::NOT_IMPLEMENTED) {
      LOG(LS_INFO) << "Can't bind socket to network because "
                      "network binding is not implemented for this OS.";
    } else {
      if (bind_addr.IsLoopbackIP()) {
        // If we couldn't bind to a loopback IP (which should only happen in
        // test scenarios), continue on. This may be expected behavior.
        LOG(LS_VERBOSE) << "Binding socket to loopback address "
                        << bind_addr.ipaddr().ToString()
                        << " failed; result: " << static_cast<int>(result);
      } else {
        LOG(LS_WARNING) << "Binding socket to network address "
                        << bind_addr.ipaddr().ToString()
                        << " failed; result: " << static_cast<int>(result);
        // If a network binding was attempted and failed, we should stop here
        // and not try to use the socket. Otherwise, we may end up sending
        // packets with an invalid source address.
        // See: https://bugs.chromium.org/p/webrtc/issues/detail?id=7026
        return -1;
      }
    }
  }
  sockaddr_storage addr_storage;
  size_t len = copied_bind_addr.ToSockAddrStorage(&addr_storage);
  sockaddr* addr = reinterpret_cast<sockaddr*>(&addr_storage);
  int err = ::bind(s_, addr, static_cast<int>(len));
  UpdateLastError();
#if !defined(NDEBUG)
  if (0 == err) {
    dbg_addr_ = "Bound @ ";
    dbg_addr_.append(GetLocalAddress().ToString());
  }
#endif
  return err;
}

int PhysicalSocket::Connect(const SocketAddress& addr) {
  // TODO(pthatcher): Implicit creation is required to reconnect...
  // ...but should we make it more explicit?
  if (state_ != CS_CLOSED) {
    SetError(EALREADY);
    return SOCKET_ERROR;
  }
  if (addr.IsUnresolvedIP()) {
    LOG(LS_VERBOSE) << "Resolving addr in PhysicalSocket::Connect";
    resolver_ = new AsyncResolver();
    resolver_->SignalDone.connect(this, &PhysicalSocket::OnResolveResult);
    resolver_->Start(addr);
    state_ = CS_CONNECTING;
    return 0;
  }

  return DoConnect(addr);
}

int PhysicalSocket::DoConnect(const SocketAddress& connect_addr) {
  if ((s_ == INVALID_SOCKET) &&
      !Create(connect_addr.family(), SOCK_STREAM)) {
    return SOCKET_ERROR;
  }
  sockaddr_storage addr_storage;
  size_t len = connect_addr.ToSockAddrStorage(&addr_storage);
  sockaddr* addr = reinterpret_cast<sockaddr*>(&addr_storage);
  int err = ::connect(s_, addr, static_cast<int>(len));
  UpdateLastError();
  uint8_t events = DE_READ | DE_WRITE;
  if (err == 0) {
    state_ = CS_CONNECTED;
  } else if (IsBlockingError(GetError())) {
    state_ = CS_CONNECTING;
    events |= DE_CONNECT;
  } else {
    return SOCKET_ERROR;
  }

  EnableEvents(events);
  return 0;
}

int PhysicalSocket::GetError() const {
  CritScope cs(&crit_);
  return error_;
}

void PhysicalSocket::SetError(int error) {
  CritScope cs(&crit_);
  error_ = error;
}

AsyncSocket::ConnState PhysicalSocket::GetState() const {
  return state_;
}

int PhysicalSocket::GetOption(Option opt, int* value) {
  int slevel;
  int sopt;
  if (TranslateOption(opt, &slevel, &sopt) == -1)
    return -1;
  socklen_t optlen = sizeof(*value);
  int ret = ::getsockopt(s_, slevel, sopt, (SockOptArg)value, &optlen);
  if (ret != -1 && opt == OPT_DONTFRAGMENT) {
#if defined(WEBRTC_LINUX) && !defined(WEBRTC_ANDROID)
    *value = (*value != IP_PMTUDISC_DONT) ? 1 : 0;
#endif
  }
  return ret;
}

int PhysicalSocket::SetOption(Option opt, int value) {
  int slevel;
  int sopt;
  if (TranslateOption(opt, &slevel, &sopt) == -1)
    return -1;
  if (opt == OPT_DONTFRAGMENT) {
#if defined(WEBRTC_LINUX) && !defined(WEBRTC_ANDROID)
    value = (value) ? IP_PMTUDISC_DO : IP_PMTUDISC_DONT;
#endif
  }
  return ::setsockopt(s_, slevel, sopt, (SockOptArg)&value, sizeof(value));
}

int PhysicalSocket::Send(const void* pv, size_t cb) {
  int sent = DoSend(s_, reinterpret_cast<const char *>(pv),
      static_cast<int>(cb),
#if defined(WEBRTC_LINUX) && !defined(WEBRTC_ANDROID)
      // Suppress SIGPIPE. Without this, attempting to send on a socket whose
      // other end is closed will result in a SIGPIPE signal being raised to
      // our process, which by default will terminate the process, which we
      // don't want. By specifying this flag, we'll just get the error EPIPE
      // instead and can handle the error gracefully.
      MSG_NOSIGNAL
#else
      0
#endif
      );
  UpdateLastError();
  MaybeRemapSendError();
  // We have seen minidumps where this may be false.
  RTC_DCHECK(sent <= static_cast<int>(cb));
  if ((sent > 0 && sent < static_cast<int>(cb)) ||
      (sent < 0 && IsBlockingError(GetError()))) {
    EnableEvents(DE_WRITE);
  }
  return sent;
}

int PhysicalSocket::SendTo(const void* buffer,
                           size_t length,
                           const SocketAddress& addr) {
  sockaddr_storage saddr;
  size_t len = addr.ToSockAddrStorage(&saddr);
  int sent = DoSendTo(
      s_, static_cast<const char *>(buffer), static_cast<int>(length),
#if defined(WEBRTC_LINUX) && !defined(WEBRTC_ANDROID)
      // Suppress SIGPIPE. See above for explanation.
      MSG_NOSIGNAL,
#else
      0,
#endif
      reinterpret_cast<sockaddr*>(&saddr), static_cast<int>(len));
  UpdateLastError();
  MaybeRemapSendError();
  // We have seen minidumps where this may be false.
  RTC_DCHECK(sent <= static_cast<int>(length));
  if ((sent > 0 && sent < static_cast<int>(length)) ||
      (sent < 0 && IsBlockingError(GetError()))) {
    EnableEvents(DE_WRITE);
  }
  return sent;
}

int PhysicalSocket::Recv(void* buffer, size_t length, int64_t* timestamp) {
  int received = ::recv(s_, static_cast<char*>(buffer),
                        static_cast<int>(length), 0);
  if ((received == 0) && (length != 0)) {
    // Note: on graceful shutdown, recv can return 0.  In this case, we
    // pretend it is blocking, and then signal close, so that simplifying
    // assumptions can be made about Recv.
    LOG(LS_WARNING) << "EOF from socket; deferring close event";
    // Must turn this back on so that the select() loop will notice the close
    // event.
    EnableEvents(DE_READ);
    SetError(EWOULDBLOCK);
    return SOCKET_ERROR;
  }
  if (timestamp) {
    *timestamp = GetSocketRecvTimestamp(s_);
  }
  UpdateLastError();
  int error = GetError();
  bool success = (received >= 0) || IsBlockingError(error);
  if (udp_ || success) {
    EnableEvents(DE_READ);
  }
  if (!success) {
    LOG_F(LS_VERBOSE) << "Error = " << error;
  }
  return received;
}

int PhysicalSocket::RecvFrom(void* buffer,
                             size_t length,
                             SocketAddress* out_addr,
                             int64_t* timestamp) {
  sockaddr_storage addr_storage;
  socklen_t addr_len = sizeof(addr_storage);
  sockaddr* addr = reinterpret_cast<sockaddr*>(&addr_storage);
  int received = ::recvfrom(s_, static_cast<char*>(buffer),
                            static_cast<int>(length), 0, addr, &addr_len);
  if (timestamp) {
    *timestamp = GetSocketRecvTimestamp(s_);
  }
  UpdateLastError();
  if ((received >= 0) && (out_addr != nullptr))
    SocketAddressFromSockAddrStorage(addr_storage, out_addr);
  int error = GetError();
  bool success = (received >= 0) || IsBlockingError(error);
  if (udp_ || success) {
    EnableEvents(DE_READ);
  }
  if (!success) {
    LOG_F(LS_VERBOSE) << "Error = " << error;
  }
  return received;
}

int PhysicalSocket::Listen(int backlog) {
  int err = ::listen(s_, backlog);
  UpdateLastError();
  if (err == 0) {
    state_ = CS_CONNECTING;
    EnableEvents(DE_ACCEPT);
#if !defined(NDEBUG)
    dbg_addr_ = "Listening @ ";
    dbg_addr_.append(GetLocalAddress().ToString());
#endif
  }
  return err;
}

AsyncSocket* PhysicalSocket::Accept(SocketAddress* out_addr) {
  // Always re-subscribe DE_ACCEPT to make sure new incoming connections will
  // trigger an event even if DoAccept returns an error here.
  EnableEvents(DE_ACCEPT);
  sockaddr_storage addr_storage;
  socklen_t addr_len = sizeof(addr_storage);
  sockaddr* addr = reinterpret_cast<sockaddr*>(&addr_storage);
  SOCKET s = DoAccept(s_, addr, &addr_len);
  UpdateLastError();
  if (s == INVALID_SOCKET)
    return nullptr;
  if (out_addr != nullptr)
    SocketAddressFromSockAddrStorage(addr_storage, out_addr);
  return ss_->WrapSocket(s);
}

int PhysicalSocket::Close() {
  if (s_ == INVALID_SOCKET)
    return 0;
  int err = ::closesocket(s_);
  UpdateLastError();
  s_ = INVALID_SOCKET;
  state_ = CS_CLOSED;
  SetEnabledEvents(0);
  if (resolver_) {
    resolver_->Destroy(false);
    resolver_ = nullptr;
  }
  return err;
}

SOCKET PhysicalSocket::DoAccept(SOCKET socket,
                                sockaddr* addr,
                                socklen_t* addrlen) {
  return ::accept(socket, addr, addrlen);
}

int PhysicalSocket::DoSend(SOCKET socket, const char* buf, int len, int flags) {
  return ::send(socket, buf, len, flags);
}

int PhysicalSocket::DoSendTo(SOCKET socket,
                             const char* buf,
                             int len,
                             int flags,
                             const struct sockaddr* dest_addr,
                             socklen_t addrlen) {
  return ::sendto(socket, buf, len, flags, dest_addr, addrlen);
}

void PhysicalSocket::OnResolveResult(AsyncResolverInterface* resolver) {
  if (resolver != resolver_) {
    return;
  }

  int error = resolver_->GetError();
  if (error == 0) {
    error = DoConnect(resolver_->address());
  } else {
    Close();
  }

  if (error) {
    SetError(error);
    SignalCloseEvent(this, error);
  }
}

void PhysicalSocket::UpdateLastError() {
  SetError(LAST_SYSTEM_ERROR);
}

void PhysicalSocket::MaybeRemapSendError() {
#if defined(WEBRTC_MAC)
  // https://developer.apple.com/library/mac/documentation/Darwin/
  // Reference/ManPages/man2/sendto.2.html
  // ENOBUFS - The output queue for a network interface is full.
  // This generally indicates that the interface has stopped sending,
  // but may be caused by transient congestion.
  if (GetError() == ENOBUFS) {
    SetError(EWOULDBLOCK);
  }
#endif
}

void PhysicalSocket::SetEnabledEvents(uint8_t events) {
  enabled_events_ = events;
}

void PhysicalSocket::EnableEvents(uint8_t events) {
  enabled_events_ |= events;
}

void PhysicalSocket::DisableEvents(uint8_t events) {
  enabled_events_ &= ~events;
}

int PhysicalSocket::TranslateOption(Option opt, int* slevel, int* sopt) {
  switch (opt) {
    case OPT_DONTFRAGMENT:
#if defined(WEBRTC_WIN)
      *slevel = IPPROTO_IP;
      *sopt = IP_DONTFRAGMENT;
      break;
#elif defined(WEBRTC_MAC) || defined(BSD) || defined(__native_client__)
      LOG(LS_WARNING) << "Socket::OPT_DONTFRAGMENT not supported.";
      return -1;
#elif defined(WEBRTC_POSIX)
      *slevel = IPPROTO_IP;
      *sopt = IP_MTU_DISCOVER;
      break;
#endif
    case OPT_RCVBUF:
      *slevel = SOL_SOCKET;
      *sopt = SO_RCVBUF;
      break;
    case OPT_SNDBUF:
      *slevel = SOL_SOCKET;
      *sopt = SO_SNDBUF;
      break;
    case OPT_NODELAY:
      *slevel = IPPROTO_TCP;
      *sopt = TCP_NODELAY;
      break;
    case OPT_DSCP:
      LOG(LS_WARNING) << "Socket::OPT_DSCP not supported.";
      return -1;
    case OPT_RTP_SENDTIME_EXTN_ID:
      return -1;  // No logging is necessary as this not a OS socket option.
    default:
      RTC_NOTREACHED();
      return -1;
  }
  return 0;
}

SocketDispatcher::SocketDispatcher(PhysicalSocketServer *ss)
#if defined(WEBRTC_WIN)
  : PhysicalSocket(ss), id_(0), signal_close_(false)
#else
  : PhysicalSocket(ss)
#endif
{
}

SocketDispatcher::SocketDispatcher(SOCKET s, PhysicalSocketServer *ss)
#if defined(WEBRTC_WIN)
  : PhysicalSocket(ss, s), id_(0), signal_close_(false)
#else
  : PhysicalSocket(ss, s)
#endif
{
}

SocketDispatcher::~SocketDispatcher() {
  Close();
}

bool SocketDispatcher::Initialize() {
  RTC_DCHECK(s_ != INVALID_SOCKET);
  // Must be a non-blocking
#if defined(WEBRTC_WIN)
  u_long argp = 1;
  ioctlsocket(s_, FIONBIO, &argp);
#elif defined(WEBRTC_POSIX)
  fcntl(s_, F_SETFL, fcntl(s_, F_GETFL, 0) | O_NONBLOCK);
#endif
#if defined(WEBRTC_IOS)
  // iOS may kill sockets when the app is moved to the background
  // (specifically, if the app doesn't use the "voip" UIBackgroundMode). When
  // we attempt to write to such a socket, SIGPIPE will be raised, which by
  // default will terminate the process, which we don't want. By specifying
  // this socket option, SIGPIPE will be disabled for the socket.
  int value = 1;
  ::setsockopt(s_, SOL_SOCKET, SO_NOSIGPIPE, &value, sizeof(value));
#endif
  ss_->Add(this);
  return true;
}

bool SocketDispatcher::Create(int type) {
  return Create(AF_INET, type);
}

bool SocketDispatcher::Create(int family, int type) {
  // Change the socket to be non-blocking.
  if (!PhysicalSocket::Create(family, type))
    return false;

  if (!Initialize())
    return false;

#if defined(WEBRTC_WIN)
  do { id_ = ++next_id_; } while (id_ == 0);
#endif
  return true;
}

#if defined(WEBRTC_WIN)

WSAEVENT SocketDispatcher::GetWSAEvent() {
  return WSA_INVALID_EVENT;
}

SOCKET SocketDispatcher::GetSocket() {
  return s_;
}

bool SocketDispatcher::CheckSignalClose() {
  if (!signal_close_)
    return false;

  char ch;
  if (recv(s_, &ch, 1, MSG_PEEK) > 0)
    return false;

  state_ = CS_CLOSED;
  signal_close_ = false;
  SignalCloseEvent(this, signal_err_);
  return true;
}

int SocketDispatcher::next_id_ = 0;

#elif defined(WEBRTC_POSIX)

int SocketDispatcher::GetDescriptor() {
  return s_;
}

bool SocketDispatcher::IsDescriptorClosed() {
  if (udp_) {
    // The MSG_PEEK trick doesn't work for UDP, since (at least in some
    // circumstances) it requires reading an entire UDP packet, which would be
    // bad for performance here. So, just check whether |s_| has been closed,
    // which should be sufficient.
    return s_ == INVALID_SOCKET;
  }
  // We don't have a reliable way of distinguishing end-of-stream
  // from readability.  So test on each readable call.  Is this
  // inefficient?  Probably.
  char ch;
  ssize_t res = ::recv(s_, &ch, 1, MSG_PEEK);
  if (res > 0) {
    // Data available, so not closed.
    return false;
  } else if (res == 0) {
    // EOF, so closed.
    return true;
  } else {  // error
    switch (errno) {
      // Returned if we've already closed s_.
      case EBADF:
      // Returned during ungraceful peer shutdown.
      case ECONNRESET:
        return true;
      // The normal blocking error; don't log anything.
      case EWOULDBLOCK:
      // Interrupted system call.
      case EINTR:
        return false;
      default:
        // Assume that all other errors are just blocking errors, meaning the
        // connection is still good but we just can't read from it right now.
        // This should only happen when connecting (and at most once), because
        // in all other cases this function is only called if the file
        // descriptor is already known to be in the readable state. However,
        // it's not necessary a problem if we spuriously interpret a
        // "connection lost"-type error as a blocking error, because typically
        // the next recv() will get EOF, so we'll still eventually notice that
        // the socket is closed.
        LOG_ERR(LS_WARNING) << "Assuming benign blocking error";
        return false;
    }
  }
}

#endif // WEBRTC_POSIX

uint32_t SocketDispatcher::GetRequestedEvents() {
  return enabled_events();
}

void SocketDispatcher::OnPreEvent(uint32_t ff) {
  if ((ff & DE_CONNECT) != 0)
    state_ = CS_CONNECTED;

#if defined(WEBRTC_WIN)
  // We set CS_CLOSED from CheckSignalClose.
#elif defined(WEBRTC_POSIX)
  if ((ff & DE_CLOSE) != 0)
    state_ = CS_CLOSED;
#endif
}

#if defined(WEBRTC_WIN)

void SocketDispatcher::OnEvent(uint32_t ff, int err) {
  int cache_id = id_;
  // Make sure we deliver connect/accept first. Otherwise, consumers may see
  // something like a READ followed by a CONNECT, which would be odd.
  if (((ff & DE_CONNECT) != 0) && (id_ == cache_id)) {
    if (ff != DE_CONNECT)
      LOG(LS_VERBOSE) << "Signalled with DE_CONNECT: " << ff;
    DisableEvents(DE_CONNECT);
#if !defined(NDEBUG)
    dbg_addr_ = "Connected @ ";
    dbg_addr_.append(GetRemoteAddress().ToString());
#endif
    SignalConnectEvent(this);
  }
  if (((ff & DE_ACCEPT) != 0) && (id_ == cache_id)) {
    DisableEvents(DE_ACCEPT);
    SignalReadEvent(this);
  }
  if ((ff & DE_READ) != 0) {
    DisableEvents(DE_READ);
    SignalReadEvent(this);
  }
  if (((ff & DE_WRITE) != 0) && (id_ == cache_id)) {
    DisableEvents(DE_WRITE);
    SignalWriteEvent(this);
  }
  if (((ff & DE_CLOSE) != 0) && (id_ == cache_id)) {
    signal_close_ = true;
    signal_err_ = err;
  }
}

#elif defined(WEBRTC_POSIX)

void SocketDispatcher::OnEvent(uint32_t ff, int err) {
#if defined(WEBRTC_USE_EPOLL)
  // Remember currently enabled events so we can combine multiple changes
  // into one update call later.
  // The signal handlers might re-enable events disabled here, so we can't
  // keep a list of events to disable at the end of the method. This list
  // would not be updated with the events enabled by the signal handlers.
  StartBatchedEventUpdates();
#endif
  // Make sure we deliver connect/accept first. Otherwise, consumers may see
  // something like a READ followed by a CONNECT, which would be odd.
  if ((ff & DE_CONNECT) != 0) {
    DisableEvents(DE_CONNECT);
    SignalConnectEvent(this);
  }
  if ((ff & DE_ACCEPT) != 0) {
    DisableEvents(DE_ACCEPT);
    SignalReadEvent(this);
  }
  if ((ff & DE_READ) != 0) {
    DisableEvents(DE_READ);
    SignalReadEvent(this);
  }
  if ((ff & DE_WRITE) != 0) {
    DisableEvents(DE_WRITE);
    SignalWriteEvent(this);
  }
  if ((ff & DE_CLOSE) != 0) {
    // The socket is now dead to us, so stop checking it.
    SetEnabledEvents(0);
    SignalCloseEvent(this, err);
  }
#if defined(WEBRTC_USE_EPOLL)
  FinishBatchedEventUpdates();
#endif
}

#endif // WEBRTC_POSIX

#if defined(WEBRTC_USE_EPOLL)

static int GetEpollEvents(uint32_t ff) {
  int events = 0;
  if (ff & (DE_READ | DE_ACCEPT)) {
    events |= EPOLLIN;
  }
  if (ff & (DE_WRITE | DE_CONNECT)) {
    events |= EPOLLOUT;
  }
  return events;
}

void SocketDispatcher::StartBatchedEventUpdates() {
  RTC_DCHECK_EQ(saved_enabled_events_, -1);
  saved_enabled_events_ = enabled_events();
}

void SocketDispatcher::FinishBatchedEventUpdates() {
  RTC_DCHECK_NE(saved_enabled_events_, -1);
  uint8_t old_events = static_cast<uint8_t>(saved_enabled_events_);
  saved_enabled_events_ = -1;
  MaybeUpdateDispatcher(old_events);
}

void SocketDispatcher::MaybeUpdateDispatcher(uint8_t old_events) {
  if (GetEpollEvents(enabled_events()) != GetEpollEvents(old_events) &&
      saved_enabled_events_ == -1) {
    ss_->Update(this);
  }
}

void SocketDispatcher::SetEnabledEvents(uint8_t events) {
  uint8_t old_events = enabled_events();
  PhysicalSocket::SetEnabledEvents(events);
  MaybeUpdateDispatcher(old_events);
}

void SocketDispatcher::EnableEvents(uint8_t events) {
  uint8_t old_events = enabled_events();
  PhysicalSocket::EnableEvents(events);
  MaybeUpdateDispatcher(old_events);
}

void SocketDispatcher::DisableEvents(uint8_t events) {
  uint8_t old_events = enabled_events();
  PhysicalSocket::DisableEvents(events);
  MaybeUpdateDispatcher(old_events);
}

#endif  // WEBRTC_USE_EPOLL

int SocketDispatcher::Close() {
  if (s_ == INVALID_SOCKET)
    return 0;

#if defined(WEBRTC_WIN)
  id_ = 0;
  signal_close_ = false;
#endif
  ss_->Remove(this);
  return PhysicalSocket::Close();
}

#if defined(WEBRTC_POSIX)
class EventDispatcher : public Dispatcher {
 public:
  EventDispatcher(PhysicalSocketServer* ss) : ss_(ss), fSignaled_(false) {
    if (pipe(afd_) < 0)
      LOG(LERROR) << "pipe failed";
    ss_->Add(this);
  }

  ~EventDispatcher() override {
    ss_->Remove(this);
    close(afd_[0]);
    close(afd_[1]);
  }

  virtual void Signal() {
    CritScope cs(&crit_);
    if (!fSignaled_) {
      const uint8_t b[1] = {0};
      const ssize_t res = write(afd_[1], b, sizeof(b));
      RTC_DCHECK_EQ(1, res);
      fSignaled_ = true;
    }
  }

  uint32_t GetRequestedEvents() override { return DE_READ; }

  void OnPreEvent(uint32_t ff) override {
    // It is not possible to perfectly emulate an auto-resetting event with
    // pipes.  This simulates it by resetting before the event is handled.

    CritScope cs(&crit_);
    if (fSignaled_) {
      uint8_t b[4];  // Allow for reading more than 1 byte, but expect 1.
      const ssize_t res = read(afd_[0], b, sizeof(b));
      RTC_DCHECK_EQ(1, res);
      fSignaled_ = false;
    }
  }

  void OnEvent(uint32_t ff, int err) override { RTC_NOTREACHED(); }

  int GetDescriptor() override { return afd_[0]; }

  bool IsDescriptorClosed() override { return false; }

 private:
  PhysicalSocketServer *ss_;
  int afd_[2];
  bool fSignaled_;
  CriticalSection crit_;
};

// These two classes use the self-pipe trick to deliver POSIX signals to our
// select loop. This is the only safe, reliable, cross-platform way to do
// non-trivial things with a POSIX signal in an event-driven program (until
// proper pselect() implementations become ubiquitous).

class PosixSignalHandler {
 public:
  // POSIX only specifies 32 signals, but in principle the system might have
  // more and the programmer might choose to use them, so we size our array
  // for 128.
  static const int kNumPosixSignals = 128;

  // There is just a single global instance. (Signal handlers do not get any
  // sort of user-defined void * parameter, so they can't access anything that
  // isn't global.)
  static PosixSignalHandler* Instance() {
    RTC_DEFINE_STATIC_LOCAL(PosixSignalHandler, instance, ());
    return &instance;
  }

  // Returns true if the given signal number is set.
  bool IsSignalSet(int signum) const {
    RTC_DCHECK(signum < static_cast<int>(arraysize(received_signal_)));
    if (signum < static_cast<int>(arraysize(received_signal_))) {
      return received_signal_[signum];
    } else {
      return false;
    }
  }

  // Clears the given signal number.
  void ClearSignal(int signum) {
    RTC_DCHECK(signum < static_cast<int>(arraysize(received_signal_)));
    if (signum < static_cast<int>(arraysize(received_signal_))) {
      received_signal_[signum] = false;
    }
  }

  // Returns the file descriptor to monitor for signal events.
  int GetDescriptor() const {
    return afd_[0];
  }

  // This is called directly from our real signal handler, so it must be
  // signal-handler-safe. That means it cannot assume anything about the
  // user-level state of the process, since the handler could be executed at any
  // time on any thread.
  void OnPosixSignalReceived(int signum) {
    if (signum >= static_cast<int>(arraysize(received_signal_))) {
      // We don't have space in our array for this.
      return;
    }
    // Set a flag saying we've seen this signal.
    received_signal_[signum] = true;
    // Notify application code that we got a signal.
    const uint8_t b[1] = {0};
    if (-1 == write(afd_[1], b, sizeof(b))) {
      // Nothing we can do here. If there's an error somehow then there's
      // nothing we can safely do from a signal handler.
      // No, we can't even safely log it.
      // But, we still have to check the return value here. Otherwise,
      // GCC 4.4.1 complains ignoring return value. Even (void) doesn't help.
      return;
    }
  }

 private:
  PosixSignalHandler() {
    if (pipe(afd_) < 0) {
      LOG_ERR(LS_ERROR) << "pipe failed";
      return;
    }
    if (fcntl(afd_[0], F_SETFL, O_NONBLOCK) < 0) {
      LOG_ERR(LS_WARNING) << "fcntl #1 failed";
    }
    if (fcntl(afd_[1], F_SETFL, O_NONBLOCK) < 0) {
      LOG_ERR(LS_WARNING) << "fcntl #2 failed";
    }
    memset(const_cast<void *>(static_cast<volatile void *>(received_signal_)),
           0,
           sizeof(received_signal_));
  }

  ~PosixSignalHandler() {
    int fd1 = afd_[0];
    int fd2 = afd_[1];
    // We clobber the stored file descriptor numbers here or else in principle
    // a signal that happens to be delivered during application termination
    // could erroneously write a zero byte to an unrelated file handle in
    // OnPosixSignalReceived() if some other file happens to be opened later
    // during shutdown and happens to be given the same file descriptor number
    // as our pipe had. Unfortunately even with this precaution there is still a
    // race where that could occur if said signal happens to be handled
    // concurrently with this code and happens to have already read the value of
    // afd_[1] from memory before we clobber it, but that's unlikely.
    afd_[0] = -1;
    afd_[1] = -1;
    close(fd1);
    close(fd2);
  }

  int afd_[2];
  // These are boolean flags that will be set in our signal handler and read
  // and cleared from Wait(). There is a race involved in this, but it is
  // benign. The signal handler sets the flag before signaling the pipe, so
  // we'll never end up blocking in select() while a flag is still true.
  // However, if two of the same signal arrive close to each other then it's
  // possible that the second time the handler may set the flag while it's still
  // true, meaning that signal will be missed. But the first occurrence of it
  // will still be handled, so this isn't a problem.
  // Volatile is not necessary here for correctness, but this data _is_ volatile
  // so I've marked it as such.
  volatile uint8_t received_signal_[kNumPosixSignals];
};

class PosixSignalDispatcher : public Dispatcher {
 public:
  PosixSignalDispatcher(PhysicalSocketServer *owner) : owner_(owner) {
    owner_->Add(this);
  }

  ~PosixSignalDispatcher() override {
    owner_->Remove(this);
  }

  uint32_t GetRequestedEvents() override { return DE_READ; }

  void OnPreEvent(uint32_t ff) override {
    // Events might get grouped if signals come very fast, so we read out up to
    // 16 bytes to make sure we keep the pipe empty.
    uint8_t b[16];
    ssize_t ret = read(GetDescriptor(), b, sizeof(b));
    if (ret < 0) {
      LOG_ERR(LS_WARNING) << "Error in read()";
    } else if (ret == 0) {
      LOG(LS_WARNING) << "Should have read at least one byte";
    }
  }

  void OnEvent(uint32_t ff, int err) override {
    for (int signum = 0; signum < PosixSignalHandler::kNumPosixSignals;
         ++signum) {
      if (PosixSignalHandler::Instance()->IsSignalSet(signum)) {
        PosixSignalHandler::Instance()->ClearSignal(signum);
        HandlerMap::iterator i = handlers_.find(signum);
        if (i == handlers_.end()) {
          // This can happen if a signal is delivered to our process at around
          // the same time as we unset our handler for it. It is not an error
          // condition, but it's unusual enough to be worth logging.
          LOG(LS_INFO) << "Received signal with no handler: " << signum;
        } else {
          // Otherwise, execute our handler.
          (*i->second)(signum);
        }
      }
    }
  }

  int GetDescriptor() override {
    return PosixSignalHandler::Instance()->GetDescriptor();
  }

  bool IsDescriptorClosed() override { return false; }

  void SetHandler(int signum, void (*handler)(int)) {
    handlers_[signum] = handler;
  }

  void ClearHandler(int signum) {
    handlers_.erase(signum);
  }

  bool HasHandlers() {
    return !handlers_.empty();
  }

 private:
  typedef std::map<int, void (*)(int)> HandlerMap;

  HandlerMap handlers_;
  // Our owner.
  PhysicalSocketServer *owner_;
};

#endif // WEBRTC_POSIX

#if defined(WEBRTC_WIN)
static uint32_t FlagsToEvents(uint32_t events) {
  uint32_t ffFD = FD_CLOSE;
  if (events & DE_READ)
    ffFD |= FD_READ;
  if (events & DE_WRITE)
    ffFD |= FD_WRITE;
  if (events & DE_CONNECT)
    ffFD |= FD_CONNECT;
  if (events & DE_ACCEPT)
    ffFD |= FD_ACCEPT;
  return ffFD;
}

class EventDispatcher : public Dispatcher {
 public:
  EventDispatcher(PhysicalSocketServer *ss) : ss_(ss) {
    hev_ = WSACreateEvent();
    if (hev_) {
      ss_->Add(this);
    }
  }

  ~EventDispatcher() {
    if (hev_ != nullptr) {
      ss_->Remove(this);
      WSACloseEvent(hev_);
      hev_ = nullptr;
    }
  }

  virtual void Signal() {
    if (hev_ != nullptr)
      WSASetEvent(hev_);
  }

  virtual uint32_t GetRequestedEvents() { return 0; }

  virtual void OnPreEvent(uint32_t ff) { WSAResetEvent(hev_); }

  virtual void OnEvent(uint32_t ff, int err) {}

  virtual WSAEVENT GetWSAEvent() {
    return hev_;
  }

  virtual SOCKET GetSocket() {
    return INVALID_SOCKET;
  }

  virtual bool CheckSignalClose() { return false; }

private:
  PhysicalSocketServer* ss_;
  WSAEVENT hev_;
};
#endif  // WEBRTC_WIN

// Sets the value of a boolean value to false when signaled.
class Signaler : public EventDispatcher {
 public:
  Signaler(PhysicalSocketServer* ss, bool* pf)
      : EventDispatcher(ss), pf_(pf) {
  }
  ~Signaler() override { }

  void OnEvent(uint32_t ff, int err) override {
    if (pf_)
      *pf_ = false;
  }

 private:
  bool *pf_;
};

PhysicalSocketServer::PhysicalSocketServer()
    : fWait_(false) {
#if defined(WEBRTC_USE_EPOLL)
  // Since Linux 2.6.8, the size argument is ignored, but must be greater than
  // zero. Before that the size served as hint to the kernel for the amount of
  // space to initially allocate in internal data structures.
  epoll_fd_ = epoll_create(FD_SETSIZE);
  if (epoll_fd_ == -1) {
    // Not an error, will fall back to "select" below.
    LOG_E(LS_WARNING, EN, errno) << "epoll_create";
    epoll_fd_ = INVALID_SOCKET;
  }
#endif
  signal_wakeup_ = new Signaler(this, &fWait_);
#if defined(WEBRTC_WIN)
  socket_ev_ = WSACreateEvent();
#endif
}

PhysicalSocketServer::~PhysicalSocketServer() {
#if defined(WEBRTC_WIN)
  WSACloseEvent(socket_ev_);
#endif
#if defined(WEBRTC_POSIX)
  signal_dispatcher_.reset();
#endif
  delete signal_wakeup_;
#if defined(WEBRTC_USE_EPOLL)
  if (epoll_fd_ != INVALID_SOCKET) {
    close(epoll_fd_);
  }
#endif
  RTC_DCHECK(dispatchers_.empty());
}

void PhysicalSocketServer::WakeUp() {
  signal_wakeup_->Signal();
}

Socket* PhysicalSocketServer::CreateSocket(int type) {
  return CreateSocket(AF_INET, type);
}

Socket* PhysicalSocketServer::CreateSocket(int family, int type) {
  PhysicalSocket* socket = new PhysicalSocket(this);
  if (socket->Create(family, type)) {
    return socket;
  } else {
    delete socket;
    return nullptr;
  }
}

AsyncSocket* PhysicalSocketServer::CreateAsyncSocket(int type) {
  return CreateAsyncSocket(AF_INET, type);
}

AsyncSocket* PhysicalSocketServer::CreateAsyncSocket(int family, int type) {
  SocketDispatcher* dispatcher = new SocketDispatcher(this);
  if (dispatcher->Create(family, type)) {
    return dispatcher;
  } else {
    delete dispatcher;
    return nullptr;
  }
}

AsyncSocket* PhysicalSocketServer::WrapSocket(SOCKET s) {
  SocketDispatcher* dispatcher = new SocketDispatcher(s, this);
  if (dispatcher->Initialize()) {
    return dispatcher;
  } else {
    delete dispatcher;
    return nullptr;
  }
}

void PhysicalSocketServer::Add(Dispatcher *pdispatcher) {
  CritScope cs(&crit_);
  if (processing_dispatchers_) {
    // A dispatcher is being added while a "Wait" call is processing the
    // list of socket events.
    // Defer adding to "dispatchers_" set until processing is done to avoid
    // invalidating the iterator in "Wait".
    pending_remove_dispatchers_.erase(pdispatcher);
    pending_add_dispatchers_.insert(pdispatcher);
  } else {
    dispatchers_.insert(pdispatcher);
  }
#if defined(WEBRTC_USE_EPOLL)
  if (epoll_fd_ != INVALID_SOCKET) {
    AddEpoll(pdispatcher);
  }
#endif  // WEBRTC_USE_EPOLL
}

void PhysicalSocketServer::Remove(Dispatcher *pdispatcher) {
  CritScope cs(&crit_);
  if (processing_dispatchers_) {
    // A dispatcher is being removed while a "Wait" call is processing the
    // list of socket events.
    // Defer removal from "dispatchers_" set until processing is done to avoid
    // invalidating the iterator in "Wait".
    if (!pending_add_dispatchers_.erase(pdispatcher) &&
        dispatchers_.find(pdispatcher) == dispatchers_.end()) {
      LOG(LS_WARNING) << "PhysicalSocketServer asked to remove a unknown "
                      << "dispatcher, potentially from a duplicate call to "
                      << "Add.";
      return;
    }

    pending_remove_dispatchers_.insert(pdispatcher);
  } else if (!dispatchers_.erase(pdispatcher)) {
    LOG(LS_WARNING) << "PhysicalSocketServer asked to remove a unknown "
                    << "dispatcher, potentially from a duplicate call to Add.";
    return;
  }
#if defined(WEBRTC_USE_EPOLL)
  if (epoll_fd_ != INVALID_SOCKET) {
    RemoveEpoll(pdispatcher);
  }
#endif  // WEBRTC_USE_EPOLL
}

void PhysicalSocketServer::Update(Dispatcher* pdispatcher) {
#if defined(WEBRTC_USE_EPOLL)
  if (epoll_fd_ == INVALID_SOCKET) {
    return;
  }

  CritScope cs(&crit_);
  if (dispatchers_.find(pdispatcher) == dispatchers_.end()) {
    return;
  }

  UpdateEpoll(pdispatcher);
#endif
}

void PhysicalSocketServer::AddRemovePendingDispatchers() {
  if (!pending_add_dispatchers_.empty()) {
    for (Dispatcher* pdispatcher : pending_add_dispatchers_) {
      dispatchers_.insert(pdispatcher);
    }
    pending_add_dispatchers_.clear();
  }

  if (!pending_remove_dispatchers_.empty()) {
    for (Dispatcher* pdispatcher : pending_remove_dispatchers_) {
      dispatchers_.erase(pdispatcher);
    }
    pending_remove_dispatchers_.clear();
  }
}

#if defined(WEBRTC_POSIX)

bool PhysicalSocketServer::Wait(int cmsWait, bool process_io) {
#if defined(WEBRTC_USE_EPOLL)
  // We don't keep a dedicated "epoll" descriptor containing only the non-IO
  // (i.e. signaling) dispatcher, so "poll" will be used instead of the default
  // "select" to support sockets larger than FD_SETSIZE.
  if (!process_io) {
    return WaitPoll(cmsWait, signal_wakeup_);
  } else if (epoll_fd_ != INVALID_SOCKET) {
    return WaitEpoll(cmsWait);
  }
#endif
  return WaitSelect(cmsWait, process_io);
}

static void ProcessEvents(Dispatcher* dispatcher,
                          bool readable,
                          bool writable,
                          bool check_error) {
  int errcode = 0;
  // TODO(pthatcher): Should we set errcode if getsockopt fails?
  if (check_error) {
    socklen_t len = sizeof(errcode);
    ::getsockopt(dispatcher->GetDescriptor(), SOL_SOCKET, SO_ERROR, &errcode,
                 &len);
  }

  uint32_t ff = 0;

  // Check readable descriptors. If we're waiting on an accept, signal
  // that. Otherwise we're waiting for data, check to see if we're
  // readable or really closed.
  // TODO(pthatcher): Only peek at TCP descriptors.
  if (readable) {
    if (dispatcher->GetRequestedEvents() & DE_ACCEPT) {
      ff |= DE_ACCEPT;
    } else if (errcode || dispatcher->IsDescriptorClosed()) {
      ff |= DE_CLOSE;
    } else {
      ff |= DE_READ;
    }
  }

  // Check writable descriptors. If we're waiting on a connect, detect
  // success versus failure by the reaped error code.
  if (writable) {
    if (dispatcher->GetRequestedEvents() & DE_CONNECT) {
      if (!errcode) {
        ff |= DE_CONNECT;
      } else {
        ff |= DE_CLOSE;
      }
    } else {
      ff |= DE_WRITE;
    }
  }

  // Tell the descriptor about the event.
  if (ff != 0) {
    dispatcher->OnPreEvent(ff);
    dispatcher->OnEvent(ff, errcode);
  }
}

bool PhysicalSocketServer::WaitSelect(int cmsWait, bool process_io) {
  // Calculate timing information

  struct timeval* ptvWait = nullptr;
  struct timeval tvWait;
  struct timeval tvStop;
  if (cmsWait != kForever) {
    // Calculate wait timeval
    tvWait.tv_sec = cmsWait / 1000;
    tvWait.tv_usec = (cmsWait % 1000) * 1000;
    ptvWait = &tvWait;

    // Calculate when to return in a timeval
    gettimeofday(&tvStop, nullptr);
    tvStop.tv_sec += tvWait.tv_sec;
    tvStop.tv_usec += tvWait.tv_usec;
    if (tvStop.tv_usec >= 1000000) {
      tvStop.tv_usec -= 1000000;
      tvStop.tv_sec += 1;
    }
  }

  // Zero all fd_sets. Don't need to do this inside the loop since
  // select() zeros the descriptors not signaled

  fd_set fdsRead;
  FD_ZERO(&fdsRead);
  fd_set fdsWrite;
  FD_ZERO(&fdsWrite);
  // Explicitly unpoison these FDs on MemorySanitizer which doesn't handle the
  // inline assembly in FD_ZERO.
  // http://crbug.com/344505
#ifdef MEMORY_SANITIZER
  __msan_unpoison(&fdsRead, sizeof(fdsRead));
  __msan_unpoison(&fdsWrite, sizeof(fdsWrite));
#endif

  fWait_ = true;

  while (fWait_) {
    int fdmax = -1;
    {
      CritScope cr(&crit_);
      // TODO(jbauch): Support re-entrant waiting.
      RTC_DCHECK(!processing_dispatchers_);
      for (Dispatcher* pdispatcher : dispatchers_) {
        // Query dispatchers for read and write wait state
        RTC_DCHECK(pdispatcher);
        if (!process_io && (pdispatcher != signal_wakeup_))
          continue;
        int fd = pdispatcher->GetDescriptor();
        // "select"ing a file descriptor that is equal to or larger than
        // FD_SETSIZE will result in undefined behavior.
        RTC_DCHECK_LT(fd, FD_SETSIZE);
        if (fd > fdmax)
          fdmax = fd;

        uint32_t ff = pdispatcher->GetRequestedEvents();
        if (ff & (DE_READ | DE_ACCEPT))
          FD_SET(fd, &fdsRead);
        if (ff & (DE_WRITE | DE_CONNECT))
          FD_SET(fd, &fdsWrite);
      }
    }

    // Wait then call handlers as appropriate
    // < 0 means error
    // 0 means timeout
    // > 0 means count of descriptors ready
    int n = select(fdmax + 1, &fdsRead, &fdsWrite, nullptr, ptvWait);

    // If error, return error.
    if (n < 0) {
      if (errno != EINTR) {
        LOG_E(LS_ERROR, EN, errno) << "select";
        return false;
      }
      // Else ignore the error and keep going. If this EINTR was for one of the
      // signals managed by this PhysicalSocketServer, the
      // PosixSignalDeliveryDispatcher will be in the signaled state in the next
      // iteration.
    } else if (n == 0) {
      // If timeout, return success
      return true;
    } else {
      // We have signaled descriptors
      CritScope cr(&crit_);
      processing_dispatchers_ = true;
      for (Dispatcher* pdispatcher : dispatchers_) {
        int fd = pdispatcher->GetDescriptor();

        bool readable = FD_ISSET(fd, &fdsRead);
        if (readable) {
          FD_CLR(fd, &fdsRead);
        }

        bool writable = FD_ISSET(fd, &fdsWrite);
        if (writable) {
          FD_CLR(fd, &fdsWrite);
        }

        // The error code can be signaled through reads or writes.
        ProcessEvents(pdispatcher, readable, writable, readable || writable);
      }

      processing_dispatchers_ = false;
      // Process deferred dispatchers that have been added/removed while the
      // events were handled above.
      AddRemovePendingDispatchers();
    }

    // Recalc the time remaining to wait. Doing it here means it doesn't get
    // calced twice the first time through the loop
    if (ptvWait) {
      ptvWait->tv_sec = 0;
      ptvWait->tv_usec = 0;
      struct timeval tvT;
      gettimeofday(&tvT, nullptr);
      if ((tvStop.tv_sec > tvT.tv_sec)
          || ((tvStop.tv_sec == tvT.tv_sec)
              && (tvStop.tv_usec > tvT.tv_usec))) {
        ptvWait->tv_sec = tvStop.tv_sec - tvT.tv_sec;
        ptvWait->tv_usec = tvStop.tv_usec - tvT.tv_usec;
        if (ptvWait->tv_usec < 0) {
          RTC_DCHECK(ptvWait->tv_sec > 0);
          ptvWait->tv_usec += 1000000;
          ptvWait->tv_sec -= 1;
        }
      }
    }
  }

  return true;
}

#if defined(WEBRTC_USE_EPOLL)

// Initial number of events to process with one call to "epoll_wait".
static const size_t kInitialEpollEvents = 128;

// Maximum number of events to process with one call to "epoll_wait".
static const size_t kMaxEpollEvents = 8192;

void PhysicalSocketServer::AddEpoll(Dispatcher* pdispatcher) {
  RTC_DCHECK(epoll_fd_ != INVALID_SOCKET);
  int fd = pdispatcher->GetDescriptor();
  RTC_DCHECK(fd != INVALID_SOCKET);
  if (fd == INVALID_SOCKET) {
    return;
  }

  struct epoll_event event = {0};
  event.events = GetEpollEvents(pdispatcher->GetRequestedEvents());
  event.data.ptr = pdispatcher;
  int err = epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, fd, &event);
  RTC_DCHECK_EQ(err, 0);
  if (err == -1) {
    LOG_E(LS_ERROR, EN, errno) << "epoll_ctl EPOLL_CTL_ADD";
  }
}

void PhysicalSocketServer::RemoveEpoll(Dispatcher* pdispatcher) {
  RTC_DCHECK(epoll_fd_ != INVALID_SOCKET);
  int fd = pdispatcher->GetDescriptor();
  RTC_DCHECK(fd != INVALID_SOCKET);
  if (fd == INVALID_SOCKET) {
    return;
  }

  struct epoll_event event = {0};
  int err = epoll_ctl(epoll_fd_, EPOLL_CTL_DEL, fd, &event);
  RTC_DCHECK(err == 0 || errno == ENOENT);
  if (err == -1) {
    if (errno == ENOENT) {
      // Socket has already been closed.
      LOG_E(LS_VERBOSE, EN, errno) << "epoll_ctl EPOLL_CTL_DEL";
    } else {
      LOG_E(LS_ERROR, EN, errno) << "epoll_ctl EPOLL_CTL_DEL";
    }
  }
}

void PhysicalSocketServer::UpdateEpoll(Dispatcher* pdispatcher) {
  RTC_DCHECK(epoll_fd_ != INVALID_SOCKET);
  int fd = pdispatcher->GetDescriptor();
  RTC_DCHECK(fd != INVALID_SOCKET);
  if (fd == INVALID_SOCKET) {
    return;
  }

  struct epoll_event event = {0};
  event.events = GetEpollEvents(pdispatcher->GetRequestedEvents());
  event.data.ptr = pdispatcher;
  int err = epoll_ctl(epoll_fd_, EPOLL_CTL_MOD, fd, &event);
  RTC_DCHECK_EQ(err, 0);
  if (err == -1) {
    LOG_E(LS_ERROR, EN, errno) << "epoll_ctl EPOLL_CTL_MOD";
  }
}

bool PhysicalSocketServer::WaitEpoll(int cmsWait) {
  RTC_DCHECK(epoll_fd_ != INVALID_SOCKET);
  int64_t tvWait = -1;
  int64_t tvStop = -1;
  if (cmsWait != kForever) {
    tvWait = cmsWait;
    tvStop = TimeAfter(cmsWait);
  }

  if (epoll_events_.empty()) {
    // The initial space to receive events is created only if epoll is used.
    epoll_events_.resize(kInitialEpollEvents);
  }

  fWait_ = true;

  while (fWait_) {
    // Wait then call handlers as appropriate
    // < 0 means error
    // 0 means timeout
    // > 0 means count of descriptors ready
    int n = epoll_wait(epoll_fd_, &epoll_events_[0],
                       static_cast<int>(epoll_events_.size()),
                       static_cast<int>(tvWait));
    if (n < 0) {
      if (errno != EINTR) {
        LOG_E(LS_ERROR, EN, errno) << "epoll";
        return false;
      }
      // Else ignore the error and keep going. If this EINTR was for one of the
      // signals managed by this PhysicalSocketServer, the
      // PosixSignalDeliveryDispatcher will be in the signaled state in the next
      // iteration.
    } else if (n == 0) {
      // If timeout, return success
      return true;
    } else {
      // We have signaled descriptors
      CritScope cr(&crit_);
      for (int i = 0; i < n; ++i) {
        const epoll_event& event = epoll_events_[i];
        Dispatcher* pdispatcher = static_cast<Dispatcher*>(event.data.ptr);
        if (dispatchers_.find(pdispatcher) == dispatchers_.end()) {
          // The dispatcher for this socket no longer exists.
          continue;
        }

        bool readable = (event.events & (EPOLLIN | EPOLLPRI));
        bool writable = (event.events & EPOLLOUT);
        bool check_error = (event.events & (EPOLLRDHUP | EPOLLERR | EPOLLHUP));

        ProcessEvents(pdispatcher, readable, writable, check_error);
      }
    }

    if (static_cast<size_t>(n) == epoll_events_.size() &&
        epoll_events_.size() < kMaxEpollEvents) {
      // We used the complete space to receive events, increase size for future
      // iterations.
      epoll_events_.resize(std::max(epoll_events_.size() * 2, kMaxEpollEvents));
    }

    if (cmsWait != kForever) {
      tvWait = TimeDiff(tvStop, TimeMillis());
      if (tvWait < 0) {
        // Return success on timeout.
        return true;
      }
    }
  }

  return true;
}

bool PhysicalSocketServer::WaitPoll(int cmsWait, Dispatcher* dispatcher) {
  RTC_DCHECK(dispatcher);
  int64_t tvWait = -1;
  int64_t tvStop = -1;
  if (cmsWait != kForever) {
    tvWait = cmsWait;
    tvStop = TimeAfter(cmsWait);
  }

  fWait_ = true;

  struct pollfd fds = {0};
  int fd = dispatcher->GetDescriptor();
  fds.fd = fd;

  while (fWait_) {
    uint32_t ff = dispatcher->GetRequestedEvents();
    fds.events = 0;
    if (ff & (DE_READ | DE_ACCEPT)) {
      fds.events |= POLLIN;
    }
    if (ff & (DE_WRITE | DE_CONNECT)) {
      fds.events |= POLLOUT;
    }
    fds.revents = 0;

    // Wait then call handlers as appropriate
    // < 0 means error
    // 0 means timeout
    // > 0 means count of descriptors ready
    int n = poll(&fds, 1, static_cast<int>(tvWait));
    if (n < 0) {
      if (errno != EINTR) {
        LOG_E(LS_ERROR, EN, errno) << "poll";
        return false;
      }
      // Else ignore the error and keep going. If this EINTR was for one of the
      // signals managed by this PhysicalSocketServer, the
      // PosixSignalDeliveryDispatcher will be in the signaled state in the next
      // iteration.
    } else if (n == 0) {
      // If timeout, return success
      return true;
    } else {
      // We have signaled descriptors (should only be the passed dispatcher).
      RTC_DCHECK_EQ(n, 1);
      RTC_DCHECK_EQ(fds.fd, fd);

      bool readable = (fds.revents & (POLLIN | POLLPRI));
      bool writable = (fds.revents & POLLOUT);
      bool check_error = (fds.revents & (POLLRDHUP | POLLERR | POLLHUP));

      ProcessEvents(dispatcher, readable, writable, check_error);
    }

    if (cmsWait != kForever) {
      tvWait = TimeDiff(tvStop, TimeMillis());
      if (tvWait < 0) {
        // Return success on timeout.
        return true;
      }
    }
  }

  return true;
}

#endif  // WEBRTC_USE_EPOLL

static void GlobalSignalHandler(int signum) {
  PosixSignalHandler::Instance()->OnPosixSignalReceived(signum);
}

bool PhysicalSocketServer::SetPosixSignalHandler(int signum,
                                                 void (*handler)(int)) {
  // If handler is SIG_IGN or SIG_DFL then clear our user-level handler,
  // otherwise set one.
  if (handler == SIG_IGN || handler == SIG_DFL) {
    if (!InstallSignal(signum, handler)) {
      return false;
    }
    if (signal_dispatcher_) {
      signal_dispatcher_->ClearHandler(signum);
      if (!signal_dispatcher_->HasHandlers()) {
        signal_dispatcher_.reset();
      }
    }
  } else {
    if (!signal_dispatcher_) {
      signal_dispatcher_.reset(new PosixSignalDispatcher(this));
    }
    signal_dispatcher_->SetHandler(signum, handler);
    if (!InstallSignal(signum, &GlobalSignalHandler)) {
      return false;
    }
  }
  return true;
}

Dispatcher* PhysicalSocketServer::signal_dispatcher() {
  return signal_dispatcher_.get();
}

bool PhysicalSocketServer::InstallSignal(int signum, void (*handler)(int)) {
  struct sigaction act;
  // It doesn't really matter what we set this mask to.
  if (sigemptyset(&act.sa_mask) != 0) {
    LOG_ERR(LS_ERROR) << "Couldn't set mask";
    return false;
  }
  act.sa_handler = handler;
#if !defined(__native_client__)
  // Use SA_RESTART so that our syscalls don't get EINTR, since we don't need it
  // and it's a nuisance. Though some syscalls still return EINTR and there's no
  // real standard for which ones. :(
  act.sa_flags = SA_RESTART;
#else
  act.sa_flags = 0;
#endif
  if (sigaction(signum, &act, nullptr) != 0) {
    LOG_ERR(LS_ERROR) << "Couldn't set sigaction";
    return false;
  }
  return true;
}
#endif  // WEBRTC_POSIX

#if defined(WEBRTC_WIN)
bool PhysicalSocketServer::Wait(int cmsWait, bool process_io) {
  int64_t cmsTotal = cmsWait;
  int64_t cmsElapsed = 0;
  int64_t msStart = Time();

  fWait_ = true;
  while (fWait_) {
    std::vector<WSAEVENT> events;
    std::vector<Dispatcher *> event_owners;

    events.push_back(socket_ev_);

    {
      CritScope cr(&crit_);
      // TODO(jbauch): Support re-entrant waiting.
      RTC_DCHECK(!processing_dispatchers_);

      // Calling "CheckSignalClose" might remove a closed dispatcher from the
      // set. This must be deferred to prevent invalidating the iterator.
      processing_dispatchers_ = true;
      for (Dispatcher* disp : dispatchers_) {
        if (!process_io && (disp != signal_wakeup_))
          continue;
        SOCKET s = disp->GetSocket();
        if (disp->CheckSignalClose()) {
          // We just signalled close, don't poll this socket
        } else if (s != INVALID_SOCKET) {
          WSAEventSelect(s,
                         events[0],
                         FlagsToEvents(disp->GetRequestedEvents()));
        } else {
          events.push_back(disp->GetWSAEvent());
          event_owners.push_back(disp);
        }
      }

      processing_dispatchers_ = false;
      // Process deferred dispatchers that have been added/removed while the
      // events were handled above.
      AddRemovePendingDispatchers();
    }

    // Which is shorter, the delay wait or the asked wait?

    int64_t cmsNext;
    if (cmsWait == kForever) {
      cmsNext = cmsWait;
    } else {
      cmsNext = std::max<int64_t>(0, cmsTotal - cmsElapsed);
    }

    // Wait for one of the events to signal
    DWORD dw = WSAWaitForMultipleEvents(static_cast<DWORD>(events.size()),
                                        &events[0],
                                        false,
                                        static_cast<DWORD>(cmsNext),
                                        false);

    if (dw == WSA_WAIT_FAILED) {
      // Failed?
      // TODO(pthatcher): need a better strategy than this!
      WSAGetLastError();
      RTC_NOTREACHED();
      return false;
    } else if (dw == WSA_WAIT_TIMEOUT) {
      // Timeout?
      return true;
    } else {
      // Figure out which one it is and call it
      CritScope cr(&crit_);
      int index = dw - WSA_WAIT_EVENT_0;
      if (index > 0) {
        --index; // The first event is the socket event
        Dispatcher* disp = event_owners[index];
        // The dispatcher could have been removed while waiting for events.
        if (dispatchers_.find(disp) != dispatchers_.end()) {
          disp->OnPreEvent(0);
          disp->OnEvent(0, 0);
        }
      } else if (process_io) {
        processing_dispatchers_ = true;
        for (Dispatcher* disp : dispatchers_) {
          SOCKET s = disp->GetSocket();
          if (s == INVALID_SOCKET)
            continue;

          WSANETWORKEVENTS wsaEvents;
          int err = WSAEnumNetworkEvents(s, events[0], &wsaEvents);
          if (err == 0) {
            {
              if ((wsaEvents.lNetworkEvents & FD_READ) &&
                  wsaEvents.iErrorCode[FD_READ_BIT] != 0) {
                LOG(WARNING) << "PhysicalSocketServer got FD_READ_BIT error "
                             << wsaEvents.iErrorCode[FD_READ_BIT];
              }
              if ((wsaEvents.lNetworkEvents & FD_WRITE) &&
                  wsaEvents.iErrorCode[FD_WRITE_BIT] != 0) {
                LOG(WARNING) << "PhysicalSocketServer got FD_WRITE_BIT error "
                             << wsaEvents.iErrorCode[FD_WRITE_BIT];
              }
              if ((wsaEvents.lNetworkEvents & FD_CONNECT) &&
                  wsaEvents.iErrorCode[FD_CONNECT_BIT] != 0) {
                LOG(WARNING) << "PhysicalSocketServer got FD_CONNECT_BIT error "
                             << wsaEvents.iErrorCode[FD_CONNECT_BIT];
              }
              if ((wsaEvents.lNetworkEvents & FD_ACCEPT) &&
                  wsaEvents.iErrorCode[FD_ACCEPT_BIT] != 0) {
                LOG(WARNING) << "PhysicalSocketServer got FD_ACCEPT_BIT error "
                             << wsaEvents.iErrorCode[FD_ACCEPT_BIT];
              }
              if ((wsaEvents.lNetworkEvents & FD_CLOSE) &&
                  wsaEvents.iErrorCode[FD_CLOSE_BIT] != 0) {
                LOG(WARNING) << "PhysicalSocketServer got FD_CLOSE_BIT error "
                             << wsaEvents.iErrorCode[FD_CLOSE_BIT];
              }
            }
            uint32_t ff = 0;
            int errcode = 0;
            if (wsaEvents.lNetworkEvents & FD_READ)
              ff |= DE_READ;
            if (wsaEvents.lNetworkEvents & FD_WRITE)
              ff |= DE_WRITE;
            if (wsaEvents.lNetworkEvents & FD_CONNECT) {
              if (wsaEvents.iErrorCode[FD_CONNECT_BIT] == 0) {
                ff |= DE_CONNECT;
              } else {
                ff |= DE_CLOSE;
                errcode = wsaEvents.iErrorCode[FD_CONNECT_BIT];
              }
            }
            if (wsaEvents.lNetworkEvents & FD_ACCEPT)
              ff |= DE_ACCEPT;
            if (wsaEvents.lNetworkEvents & FD_CLOSE) {
              ff |= DE_CLOSE;
              errcode = wsaEvents.iErrorCode[FD_CLOSE_BIT];
            }
            if (ff != 0) {
              disp->OnPreEvent(ff);
              disp->OnEvent(ff, errcode);
            }
          }
        }

        processing_dispatchers_ = false;
        // Process deferred dispatchers that have been added/removed while the
        // events were handled above.
        AddRemovePendingDispatchers();
      }

      // Reset the network event until new activity occurs
      WSAResetEvent(socket_ev_);
    }

    // Break?
    if (!fWait_)
      break;
    cmsElapsed = TimeSince(msStart);
    if ((cmsWait != kForever) && (cmsElapsed >= cmsWait)) {
       break;
    }
  }

  // Done
  return true;
}
#endif  // WEBRTC_WIN

}  // namespace rtc