/******************************************************************************
 *                       ____    _    _____                                   *
 *                      / ___|  / \  |  ___|    C++                           *
 *                     | |     / _ \ | |_       Actor                         *
 *                     | |___ / ___ \|  _|      Framework                     *
 *                      \____/_/   \_|_|                                      *
 *                                                                            *
 * Copyright 2011-2018 Dominik Charousset                                     *
 *                                                                            *
 * Distributed under the terms and conditions of the BSD 3-Clause License or  *
 * (at your option) under the terms and conditions of the Boost Software      *
 * License 1.0. See accompanying files LICENSE and LICENSE_ALTERNATIVE.       *
 *                                                                            *
 * If you did not receive a copy of the license files, see                    *
 * http://opensource.org/licenses/BSD-3-Clause and                            *
 * http://www.boost.org/LICENSE_1_0.txt.                                      *
 ******************************************************************************/

#include "caf/io/network/default_multiplexer.hpp"

#include <utility>

#include "caf/actor_system_config.hpp"
#include "caf/config.hpp"
#include "caf/defaults.hpp"
#include "caf/make_counted.hpp"
#include "caf/optional.hpp"

#include "caf/io/broker.hpp"
#include "caf/io/middleman.hpp"
#include "caf/io/network/datagram_servant_impl.hpp"
#include "caf/io/network/doorman_impl.hpp"
#include "caf/io/network/interfaces.hpp"
#include "caf/io/network/protocol.hpp"
#include "caf/io/network/scribe_impl.hpp"

#include "caf/detail/call_cfun.hpp"
#include "caf/detail/socket_guard.hpp"

#include "caf/scheduler/abstract_coordinator.hpp"

#ifdef CAF_WINDOWS
#  ifndef WIN32_LEAN_AND_MEAN
#    define WIN32_LEAN_AND_MEAN
#  endif // WIN32_LEAN_AND_MEAN
#  ifndef NOMINMAX
#    define NOMINMAX
#  endif
#  ifdef CAF_MINGW
#    undef _WIN32_WINNT
#    undef WINVER
#    define _WIN32_WINNT WindowsVista
#    define WINVER WindowsVista
#    include <w32api.h>
#  endif
#  include <io.h>
#  include <windows.h>
#  include <winsock2.h>
#  include <ws2ipdef.h>
#  include <ws2tcpip.h>
#else
#  include <arpa/inet.h>
#  include <cerrno>
#  include <fcntl.h>
#  include <netdb.h>
#  include <netinet/in.h>
#  include <netinet/ip.h>
#  include <netinet/tcp.h>
#  include <sys/socket.h>
#  include <sys/types.h>
#  include <unistd.h>
#  ifdef CAF_POLL_MULTIPLEXER
#    include <poll.h>
#  elif defined(CAF_EPOLL_MULTIPLEXER)
#    include <sys/epoll.h>
#  else
#    error "neither CAF_POLL_MULTIPLEXER nor CAF_EPOLL_MULTIPLEXER defined"
#  endif

#endif

using std::string;

namespace {

// Save ourselves some typing.
constexpr auto ipv4 = caf::io::network::protocol::ipv4;
constexpr auto ipv6 = caf::io::network::protocol::ipv6;

auto addr_of(sockaddr_in& what) -> decltype(what.sin_addr)& {
  return what.sin_addr;
}

auto family_of(sockaddr_in& what) -> decltype(what.sin_family)& {
  return what.sin_family;
}

auto port_of(sockaddr_in& what) -> decltype(what.sin_port)& {
  return what.sin_port;
}

auto addr_of(sockaddr_in6& what) -> decltype(what.sin6_addr)& {
  return what.sin6_addr;
}

auto family_of(sockaddr_in6& what) -> decltype(what.sin6_family)& {
  return what.sin6_family;
}

auto port_of(sockaddr_in6& what) -> decltype(what.sin6_port)& {
  return what.sin6_port;
}

} // namespace

namespace caf {
namespace io {
namespace network {

// poll vs epoll backend
#ifdef CAF_POLL_MULTIPLEXER
#  ifndef POLLRDHUP
#    define POLLRDHUP POLLHUP
#  endif
#  ifndef POLLPRI
#    define POLLPRI POLLIN
#  endif
#  ifdef CAF_WINDOWS
// From the MSDN: If the POLLPRI flag is set on a socket for the Microsoft
//                Winsock provider, the WSAPoll function will fail.
const event_mask_type input_mask = POLLIN;
#  else
const event_mask_type input_mask = POLLIN | POLLPRI;
#  endif
const event_mask_type error_mask = POLLRDHUP | POLLERR | POLLHUP | POLLNVAL;
const event_mask_type output_mask = POLLOUT;
#else
const event_mask_type input_mask = EPOLLIN;
const event_mask_type error_mask = EPOLLRDHUP | EPOLLERR | EPOLLHUP;
const event_mask_type output_mask = EPOLLOUT;
#endif

// -- Platform-dependent abstraction over epoll() or poll() --------------------

#ifdef CAF_EPOLL_MULTIPLEXER

// In this implementation, shadow_ is the number of sockets we have
// registered to epoll.

default_multiplexer::default_multiplexer(actor_system* sys)
  : multiplexer(sys),
    epollfd_(invalid_native_socket),
    shadow_(1),
    pipe_reader_(*this),
    servant_ids_(0),
    max_throughput_(0) {
  init();
  epollfd_ = epoll_create1(EPOLL_CLOEXEC);
  if (epollfd_ == -1) {
    CAF_LOG_ERROR("epoll_create1: " << strerror(errno));
    exit(errno);
  }
  // handle at most 64 events at a time
  pollset_.resize(64);
  pipe_ = create_pipe();
  pipe_reader_.init(pipe_.first);
  epoll_event ee;
  ee.events = input_mask;
  ee.data.ptr = &pipe_reader_;
  if (epoll_ctl(epollfd_, EPOLL_CTL_ADD, pipe_reader_.fd(), &ee) < 0) {
    CAF_LOG_ERROR("epoll_ctl: " << strerror(errno));
    exit(errno);
  }
}

bool default_multiplexer::poll_once_impl(bool block) {
  CAF_LOG_TRACE("epoll()-based multiplexer");
  CAF_ASSERT(block == false || internally_posted_.empty());
  // Keep running in case of `EINTR`.
  for (;;) {
    int presult = epoll_wait(epollfd_, pollset_.data(),
                             static_cast<int>(pollset_.size()), block ? -1 : 0);
    CAF_LOG_DEBUG("epoll_wait() on" << shadow_ << "sockets reported" << presult
                                    << "event(s)");
    if (presult < 0) {
      switch (errno) {
        case EINTR: {
          // a signal was caught
          // just try again
          continue;
        }
        default: {
          perror("epoll_wait() failed");
          CAF_CRITICAL("epoll_wait() failed");
        }
      }
    }
    if (presult == 0)
      return false;
    auto iter = pollset_.begin();
    auto last = iter + presult;
    for (; iter != last; ++iter) {
      auto ptr = reinterpret_cast<event_handler*>(iter->data.ptr);
      auto fd = ptr ? ptr->fd() : pipe_.first;
      handle_socket_event(fd, static_cast<int>(iter->events), ptr);
    }
    handle_internal_events();
    return true;
  }
}

void default_multiplexer::run() {
  CAF_LOG_TRACE("epoll()-based multiplexer");
  while (shadow_ > 0)
    poll_once(true);
}

void default_multiplexer::handle(const default_multiplexer::event& e) {
  CAF_LOG_TRACE("e.fd = " << CAF_ARG(e.fd) << ", mask = " << CAF_ARG(e.mask));
  // ptr is only allowed to nullptr if fd is our pipe
  // read handle which is only registered for input
  CAF_ASSERT(e.ptr != nullptr || e.fd == pipe_.first);
  if (e.ptr && e.ptr->eventbf() == e.mask) {
    // nop
    return;
  }
  auto old = e.ptr ? e.ptr->eventbf() : input_mask;
  if (e.ptr) {
    e.ptr->eventbf(e.mask);
  }
  epoll_event ee;
  ee.events = static_cast<uint32_t>(e.mask);
  ee.data.ptr = e.ptr;
  int op;
  if (e.mask == 0) {
    CAF_LOG_DEBUG("attempt to remove socket " << CAF_ARG(e.fd)
                                              << " from epoll");
    op = EPOLL_CTL_DEL;
    --shadow_;
  } else if (old == 0) {
    CAF_LOG_DEBUG("attempt to add socket " << CAF_ARG(e.fd) << " to epoll");
    op = EPOLL_CTL_ADD;
    ++shadow_;
  } else {
    CAF_LOG_DEBUG("modify epoll event mask for socket "
                  << CAF_ARG(e.fd) << ": " << CAF_ARG(old) << " -> "
                  << CAF_ARG(e.mask));
    op = EPOLL_CTL_MOD;
  }
  if (epoll_ctl(epollfd_, op, e.fd, &ee) < 0) {
    switch (last_socket_error()) {
      // supplied file descriptor is already registered
      case EEXIST:
        CAF_LOG_ERROR("file descriptor registered twice");
        --shadow_;
        break;
      // op was EPOLL_CTL_MOD or EPOLL_CTL_DEL,
      // and fd is not registered with this epoll instance.
      case ENOENT:
        CAF_LOG_ERROR("cannot delete file descriptor "
                      "because it isn't registered");
        if (e.mask == 0) {
          ++shadow_;
        }
        break;
      default:
        CAF_LOG_ERROR(strerror(errno));
        perror("epoll_ctl() failed");
        CAF_CRITICAL("epoll_ctl() failed");
    }
  }
  if (e.ptr) {
    auto remove_from_loop_if_needed = [&](int flag, operation flag_op) {
      if ((old & flag) && !(e.mask & flag)) {
        e.ptr->removed_from_loop(flag_op);
      }
    };
    remove_from_loop_if_needed(input_mask, operation::read);
    remove_from_loop_if_needed(output_mask, operation::write);
  }
}

size_t default_multiplexer::num_socket_handlers() const noexcept {
  return shadow_;
}

#else // CAF_EPOLL_MULTIPLEXER

// Let's be honest: the API of poll() sucks. When dealing with 1000 sockets
// and the very last socket in your pollset triggers, you have to traverse
// all elements only to find a single event. Even worse, poll() does
// not give you a way of storing a user-defined pointer in the pollset.
// Hence, you need to find a pointer to the actual object managing the
// socket. When using a map, your already dreadful O(n) turns into
// a worst case of O(n * log n). To deal with this nonsense, we have two
// vectors in this implementation: pollset_ and shadow_. The former
// stores our pollset, the latter stores our pointers. Both vectors
// are sorted by the file descriptor. This allows us to quickly,
// i.e., O(1), access the actual object when handling socket events.

default_multiplexer::default_multiplexer(actor_system* sys)
  : multiplexer(sys), epollfd_(-1), pipe_reader_(*this), servant_ids_(0) {
  init();
  // initial setup
  pipe_ = create_pipe();
  pipe_reader_.init(pipe_.first);
  pollfd pipefd;
  pipefd.fd = pipe_reader_.fd();
  pipefd.events = input_mask;
  pipefd.revents = 0;
  pollset_.push_back(pipefd);
  shadow_.push_back(&pipe_reader_);
}

bool default_multiplexer::poll_once_impl(bool block) {
  CAF_LOG_TRACE("poll()-based multiplexer");
  CAF_ASSERT(block == false || internally_posted_.empty());
  // we store the results of poll() in a separate vector , because
  // altering the pollset while traversing it is not exactly a
  // bright idea ...
  struct fd_event {
    native_socket fd;   // our file descriptor
    short mask;         // the event mask returned by poll()
    event_handler* ptr; // nullptr in case of a pipe event
  };
  std::vector<fd_event> poll_res;
  for (;;) {
    int presult;
#  ifdef CAF_WINDOWS
    presult = ::WSAPoll(pollset_.data(), static_cast<ULONG>(pollset_.size()),
                        block ? -1 : 0);
#  else
    presult = ::poll(pollset_.data(), static_cast<nfds_t>(pollset_.size()),
                     block ? -1 : 0);
#  endif
    if (presult < 0) {
      switch (last_socket_error()) {
        case EINTR: {
          CAF_LOG_DEBUG("received EINTR, try again");
          // a signal was caught
          // just try again
          break;
        }
        case ENOMEM: {
          CAF_LOG_ERROR("poll() failed for reason ENOMEM");
          // there's not much we can do other than try again
          // in hope someone else releases memory
          break;
        }
        default: {
          perror("poll() failed");
          CAF_CRITICAL("poll() failed");
        }
      }
      continue; // rinse and repeat
    }
    CAF_LOG_DEBUG("poll() on" << pollset_.size() << "sockets reported"
                              << presult << "event(s)");
    if (presult == 0)
      return false;
    // scan pollset for events first, because we might alter pollset_
    // while running callbacks (not a good idea while traversing it)
    CAF_LOG_DEBUG("scan pollset for socket events");
    for (size_t i = 0; i < pollset_.size() && presult > 0; ++i) {
      auto& pfd = pollset_[i];
      if (pfd.revents != 0) {
        CAF_LOG_DEBUG("event on socket:" << CAF_ARG(pfd.fd)
                                         << CAF_ARG(pfd.revents));
        poll_res.push_back({pfd.fd, pfd.revents, shadow_[i]});
        pfd.revents = 0;
        --presult; // stop as early as possible
      }
    }
    CAF_LOG_DEBUG(CAF_ARG(poll_res.size()));
    for (auto& e : poll_res) {
      // we try to read/write as much as possible by ignoring
      // error states as long as there are still valid
      // operations possible on the socket
      handle_socket_event(e.fd, e.mask, e.ptr);
    }
    poll_res.clear();
    handle_internal_events();
    return true;
  }
}

void default_multiplexer::run() {
  CAF_LOG_TRACE("poll()-based multiplexer:" << CAF_ARG(input_mask)
                                            << CAF_ARG(output_mask)
                                            << CAF_ARG(error_mask));
  while (!pollset_.empty())
    poll_once(true);
}

void default_multiplexer::handle(const default_multiplexer::event& e) {
  CAF_ASSERT(e.fd != invalid_native_socket);
  CAF_ASSERT(pollset_.size() == shadow_.size());
  CAF_LOG_TRACE(CAF_ARG(e.fd) << CAF_ARG(e.mask));
  auto last = pollset_.end();
  auto i = std::lower_bound(pollset_.begin(), last, e.fd,
                            [](const pollfd& lhs, native_socket rhs) {
                              return lhs.fd < rhs;
                            });
  pollfd new_element;
  new_element.fd = e.fd;
  new_element.events = static_cast<short>(e.mask);
  new_element.revents = 0;
  int old_mask = 0;
  if (e.ptr != nullptr) {
    old_mask = e.ptr->eventbf();
    e.ptr->eventbf(e.mask);
  }
  // calculate shadow of i
  multiplexer_poll_shadow_data::iterator j;
  if (i == last) {
    j = shadow_.end();
  } else {
    j = shadow_.begin();
    std::advance(j, distance(pollset_.begin(), i));
  }
  // modify vectors
  if (i == last) { // append
    if (e.mask != 0) {
      pollset_.push_back(new_element);
      shadow_.push_back(e.ptr);
    }
  } else if (i->fd == e.fd) { // modify
    if (e.mask == 0) {
      // delete item
      pollset_.erase(i);
      shadow_.erase(j);
    } else {
      // update event mask of existing entry
      CAF_ASSERT(*j == e.ptr);
      i->events = static_cast<short>(e.mask);
    }
    if (e.ptr != nullptr) {
      auto remove_from_loop_if_needed = [&](int flag, operation flag_op) {
        if (((old_mask & flag) != 0) && ((e.mask & flag) == 0)) {
          e.ptr->removed_from_loop(flag_op);
        }
      };
      remove_from_loop_if_needed(input_mask, operation::read);
      remove_from_loop_if_needed(output_mask, operation::write);
    }
  } else { // insert at iterator pos
    pollset_.insert(i, new_element);
    shadow_.insert(j, e.ptr);
  }
}

size_t default_multiplexer::num_socket_handlers() const noexcept {
  return pollset_.size();
}

#endif // CAF_EPOLL_MULTIPLEXER

// -- Helper functions for defining bitmasks of event handlers -----------------

int add_flag(operation op, int bf) {
  switch (op) {
    case operation::read:
      return bf | input_mask;
    case operation::write:
      return bf | output_mask;
    case operation::propagate_error:
      CAF_LOG_ERROR("unexpected operation");
      break;
  }
  // weird stuff going on
  return 0;
}

int del_flag(operation op, int bf) {
  switch (op) {
    case operation::read:
      return bf & ~input_mask;
    case operation::write:
      return bf & ~output_mask;
    case operation::propagate_error:
      CAF_LOG_ERROR("unexpected operation");
      break;
  }
  // weird stuff going on
  return 0;
}

// -- Platform-independent parts of the default_multiplexer --------------------

bool default_multiplexer::try_run_once() {
  return poll_once(false);
}

void default_multiplexer::run_once() {
  poll_once(true);
}

void default_multiplexer::add(operation op, native_socket fd,
                              event_handler* ptr) {
  CAF_ASSERT(fd != invalid_native_socket);
  // ptr == nullptr is only allowed to store our pipe read handle
  // and the pipe read handle is added in the ctor (not allowed here)
  CAF_ASSERT(ptr != nullptr);
  CAF_LOG_TRACE(CAF_ARG(op) << CAF_ARG(fd));
  new_event(add_flag, op, fd, ptr);
}

void default_multiplexer::del(operation op, native_socket fd,
                              event_handler* ptr) {
  CAF_ASSERT(fd != invalid_native_socket);
  // ptr == nullptr is only allowed when removing our pipe read handle
  CAF_ASSERT(ptr != nullptr || fd == pipe_.first);
  CAF_LOG_TRACE(CAF_ARG(op) << CAF_ARG(fd));
  new_event(del_flag, op, fd, ptr);
}

void default_multiplexer::wr_dispatch_request(resumable* ptr) {
  intptr_t ptrval = reinterpret_cast<intptr_t>(ptr);
  // on windows, we actually have sockets, otherwise we have file handles
#ifdef CAF_WINDOWS
  auto res = ::send(pipe_.second, reinterpret_cast<socket_send_ptr>(&ptrval),
                    sizeof(ptrval), no_sigpipe_io_flag);
#else
  auto res = ::write(pipe_.second, &ptrval, sizeof(ptrval));
#endif
  if (res <= 0) {
    // pipe closed, discard resumable
    intrusive_ptr_release(ptr);
  } else if (static_cast<size_t>(res) < sizeof(ptrval)) {
    // must not happen: wrote invalid pointer to pipe
    std::cerr << "[CAF] Fatal error: wrote invalid data to pipe" << std::endl;
    abort();
  }
}

multiplexer::supervisor_ptr default_multiplexer::make_supervisor() {
  class impl : public multiplexer::supervisor {
  public:
    explicit impl(default_multiplexer* thisptr) : this_(thisptr) {
      // nop
    }
    ~impl() override {
      auto ptr = this_;
      ptr->dispatch([=] { ptr->close_pipe(); });
    }

  private:
    default_multiplexer* this_;
  };
  return supervisor_ptr{new impl(this)};
}

void default_multiplexer::close_pipe() {
  CAF_LOG_TRACE("");
  del(operation::read, pipe_.first, nullptr);
}

void default_multiplexer::handle_socket_event(native_socket fd, int mask,
                                              event_handler* ptr) {
  CAF_LOG_TRACE(CAF_ARG(fd) << CAF_ARG(mask));
  CAF_ASSERT(ptr != nullptr);
  bool checkerror = true;
  if ((mask & input_mask) != 0) {
    checkerror = false;
    // ignore read events if a previous event caused
    // this socket to be shut down for reading
    if (!ptr->read_channel_closed())
      ptr->handle_event(operation::read);
  }
  if ((mask & output_mask) != 0) {
    checkerror = false;
    ptr->handle_event(operation::write);
  }
  if (checkerror && ((mask & error_mask) != 0)) {
    CAF_LOG_DEBUG("error occured on socket:"
                  << CAF_ARG(fd) << CAF_ARG(last_socket_error())
                  << CAF_ARG(last_socket_error_as_string()));
    ptr->handle_event(operation::propagate_error);
    del(operation::read, fd, ptr);
    del(operation::write, fd, ptr);
  }
}

void default_multiplexer::init() {
#ifdef CAF_WINDOWS
  WSADATA WinsockData;
  if (WSAStartup(MAKEWORD(2, 2), &WinsockData) != 0) {
    CAF_CRITICAL("WSAStartup failed");
  }
#endif
  namespace sr = defaults::scheduler;
  max_throughput_ = get_or(system().config(), "scheduler.max-throughput",
                           sr::max_throughput);
}

bool default_multiplexer::poll_once(bool block) {
  CAF_LOG_TRACE(CAF_ARG(block));
  if (!internally_posted_.empty()) {
    // Don't iterate internally_posted_ directly, because resumables can
    // enqueue new elements into it.
    std::vector<intrusive_ptr<resumable>> xs;
    internally_posted_.swap(xs);
    for (auto& ptr : xs)
      resume(std::move(ptr));
    handle_internal_events();
    // Try to swap back to internall_posted_ to re-use allocated memory.
    if (internally_posted_.empty()) {
      xs.swap(internally_posted_);
      internally_posted_.clear();
    }
    poll_once_impl(false);
    return true;
  }
  return poll_once_impl(block);
}

void default_multiplexer::resume(intrusive_ptr<resumable> ptr) {
  CAF_LOG_TRACE("");
  switch (ptr->resume(this, max_throughput_)) {
    case resumable::resume_later:
      // Delay resumable until next cycle.
      internally_posted_.emplace_back(ptr.release(), false);
      break;
    case resumable::shutdown_execution_unit:
      // Don't touch reference count of shutdown helpers.
      ptr.release();
      break;
    default:; // Done. Release reference to resumable.
  }
}

default_multiplexer::~default_multiplexer() {
  if (epollfd_ != invalid_native_socket)
    close_socket(epollfd_);
  // close write handle first
  close_socket(pipe_.second);
  // flush pipe before closing it
  nonblocking(pipe_.first, true);
  auto ptr = pipe_reader_.try_read_next();
  while (ptr != nullptr) {
    scheduler::abstract_coordinator::cleanup_and_release(ptr);
    ptr = pipe_reader_.try_read_next();
  }
  // do cleanup for pipe reader manually, since WSACleanup needs to happen last
  close_socket(pipe_reader_.fd());
  pipe_reader_.init(invalid_native_socket);
#ifdef CAF_WINDOWS
  WSACleanup();
#endif
}

void default_multiplexer::exec_later(resumable* ptr) {
  CAF_LOG_TRACE(CAF_ARG(ptr));
  CAF_ASSERT(ptr != nullptr);
  switch (ptr->subtype()) {
    case resumable::io_actor:
    case resumable::function_object:
      if (std::this_thread::get_id() != thread_id())
        wr_dispatch_request(ptr);
      else
        internally_posted_.emplace_back(ptr, false);
      break;
    default:
      system().scheduler().enqueue(ptr);
  }
}

scribe_ptr default_multiplexer::new_scribe(native_socket fd) {
  CAF_LOG_TRACE("");
  keepalive(fd, true);
  return make_counted<scribe_impl>(*this, fd);
}

expected<scribe_ptr>
default_multiplexer::new_tcp_scribe(const std::string& host, uint16_t port) {
  auto fd = new_tcp_connection(host, port);
  if (!fd)
    return std::move(fd.error());
  return new_scribe(*fd);
}

doorman_ptr default_multiplexer::new_doorman(native_socket fd) {
  CAF_LOG_TRACE(CAF_ARG(fd));
  CAF_ASSERT(fd != network::invalid_native_socket);
  return make_counted<doorman_impl>(*this, fd);
}

expected<doorman_ptr> default_multiplexer::new_tcp_doorman(uint16_t port,
                                                           const char* in,
                                                           bool reuse_addr) {
  auto fd = new_tcp_acceptor_impl(port, in, reuse_addr);
  if (fd)
    return new_doorman(*fd);
  return std::move(fd.error());
}

datagram_servant_ptr
default_multiplexer::new_datagram_servant(native_socket fd) {
  CAF_LOG_TRACE(CAF_ARG(fd));
  CAF_ASSERT(fd != network::invalid_native_socket);
  return make_counted<datagram_servant_impl>(*this, fd, next_endpoint_id());
}

datagram_servant_ptr
default_multiplexer::new_datagram_servant_for_endpoint(native_socket fd,
                                                       const ip_endpoint& ep) {
  CAF_LOG_TRACE(CAF_ARG(ep));
  auto ds = new_datagram_servant(fd);
  ds->add_endpoint(ep, ds->hdl());
  return ds;
}

expected<datagram_servant_ptr>
default_multiplexer::new_remote_udp_endpoint(const std::string& host,
                                             uint16_t port) {
  auto res = new_remote_udp_endpoint_impl(host, port);
  if (!res)
    return std::move(res.error());
  return new_datagram_servant_for_endpoint(res->first, res->second);
}

expected<datagram_servant_ptr>
default_multiplexer::new_local_udp_endpoint(uint16_t port, const char* in,
                                            bool reuse_addr) {
  auto res = new_local_udp_endpoint_impl(port, in, reuse_addr);
  if (res)
    return new_datagram_servant((*res).first);
  return std::move(res.error());
}

int64_t default_multiplexer::next_endpoint_id() {
  return servant_ids_++;
}

void default_multiplexer::handle_internal_events() {
  CAF_LOG_TRACE(CAF_ARG2("num-events", events_.size()));
  for (auto& e : events_)
    handle(e);
  events_.clear();
}

// -- Related helper functions -------------------------------------------------

template <int Family>
bool ip_connect(native_socket fd, const std::string& host, uint16_t port) {
  CAF_LOG_TRACE("Family =" << (Family == AF_INET ? "AF_INET" : "AF_INET6")
                           << CAF_ARG(fd) << CAF_ARG(host));
  static_assert(Family == AF_INET || Family == AF_INET6, "invalid family");
  using sockaddr_type = typename std::conditional<
    Family == AF_INET, sockaddr_in, sockaddr_in6>::type;
  sockaddr_type sa;
  memset(&sa, 0, sizeof(sockaddr_type));
  inet_pton(Family, host.c_str(), &addr_of(sa));
  family_of(sa) = Family;
  port_of(sa) = htons(port);
  return connect(fd, reinterpret_cast<const sockaddr*>(&sa), sizeof(sa)) == 0;
}

expected<native_socket>
new_tcp_connection(const std::string& host, uint16_t port,
                   optional<protocol::network> preferred) {
  CAF_LOG_TRACE(CAF_ARG(host) << CAF_ARG(port) << CAF_ARG(preferred));
  CAF_LOG_DEBUG("try to connect to:" << CAF_ARG(host) << CAF_ARG(port));
  auto res = interfaces::native_address(host, std::move(preferred));
  if (!res) {
    CAF_LOG_DEBUG("no such host");
    return make_error(sec::cannot_connect_to_node, "no such host", host, port);
  }
  auto proto = res->second;
  CAF_ASSERT(proto == ipv4 || proto == ipv6);
  int socktype = SOCK_STREAM;
#ifdef SOCK_CLOEXEC
  socktype |= SOCK_CLOEXEC;
#endif
  CALL_CFUN(fd, detail::cc_valid_socket, "socket",
            socket(proto == ipv4 ? AF_INET : AF_INET6, socktype, 0));
  child_process_inherit(fd, false);
  detail::socket_guard sguard(fd);
  if (proto == ipv6) {
    if (ip_connect<AF_INET6>(fd, res->first, port)) {
      CAF_LOG_INFO("successfully connected to (IPv6):" << CAF_ARG(host)
                                                       << CAF_ARG(port));
      return sguard.release();
    }
    sguard.close();
    // IPv4 fallback
    return new_tcp_connection(host, port, ipv4);
  }
  if (!ip_connect<AF_INET>(fd, res->first, port)) {
    CAF_LOG_WARNING("could not connect to:" << CAF_ARG(host) << CAF_ARG(port));
    return make_error(sec::cannot_connect_to_node, "ip_connect failed", host,
                      port);
  }
  CAF_LOG_INFO("successfully connected to (IPv4):" << CAF_ARG(host)
                                                   << CAF_ARG(port));
  return sguard.release();
}

template <class SockAddrType>
expected<void> read_port(native_socket fd, SockAddrType& sa) {
  socket_size_type len = sizeof(SockAddrType);
  CALL_CFUN(res, detail::cc_zero, "getsockname",
            getsockname(fd, reinterpret_cast<sockaddr*>(&sa), &len));
  return unit;
}

expected<void> set_inaddr_any(native_socket, sockaddr_in& sa) {
  sa.sin_addr.s_addr = INADDR_ANY;
  return unit;
}

expected<void> set_inaddr_any(native_socket fd, sockaddr_in6& sa) {
  sa.sin6_addr = in6addr_any;
  // also accept ipv4 requests on this socket
  int off = 0;
  CALL_CFUN(res, detail::cc_zero, "setsockopt",
            setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY,
                       reinterpret_cast<setsockopt_ptr>(&off),
                       static_cast<socket_size_type>(sizeof(off))));
  return unit;
}

template <int Family, int SockType = SOCK_STREAM>
expected<native_socket> new_ip_acceptor_impl(uint16_t port, const char* addr,
                                             bool reuse_addr, bool any) {
  static_assert(Family == AF_INET || Family == AF_INET6, "invalid family");
  CAF_LOG_TRACE(CAF_ARG(port) << ", addr = " << (addr ? addr : "nullptr"));
  int socktype = SockType;
#ifdef SOCK_CLOEXEC
  socktype |= SOCK_CLOEXEC;
#endif
  CALL_CFUN(fd, detail::cc_valid_socket, "socket", socket(Family, socktype, 0));
  child_process_inherit(fd, false);
  // sguard closes the socket in case of exception
  detail::socket_guard sguard{fd};
  if (reuse_addr) {
    int on = 1;
    CALL_CFUN(tmp1, detail::cc_zero, "setsockopt",
              setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
                         reinterpret_cast<setsockopt_ptr>(&on),
                         static_cast<socket_size_type>(sizeof(on))));
  }
  using sockaddr_type = typename std::conditional<
    Family == AF_INET, sockaddr_in, sockaddr_in6>::type;
  sockaddr_type sa;
  memset(&sa, 0, sizeof(sockaddr_type));
  family_of(sa) = Family;
  if (any)
    set_inaddr_any(fd, sa);
  CALL_CFUN(tmp, detail::cc_one, "inet_pton",
            inet_pton(Family, addr, &addr_of(sa)));
  port_of(sa) = htons(port);
  CALL_CFUN(res, detail::cc_zero, "bind",
            bind(fd, reinterpret_cast<sockaddr*>(&sa),
                 static_cast<socket_size_type>(sizeof(sa))));
  return sguard.release();
}

expected<native_socket> new_tcp_acceptor_impl(uint16_t port, const char* addr,
                                              bool reuse_addr) {
  CAF_LOG_TRACE(CAF_ARG(port) << ", addr = " << (addr ? addr : "nullptr"));
  auto addrs = interfaces::server_address(port, addr);
  auto addr_str = std::string{addr == nullptr ? "" : addr};
  if (addrs.empty())
    return make_error(sec::cannot_open_port, "No local interface available",
                      addr_str);
  bool any = addr_str.empty() || addr_str == "::" || addr_str == "0.0.0.0";
  auto fd = invalid_native_socket;
  for (auto& elem : addrs) {
    auto hostname = elem.first.c_str();
    auto p = elem.second == ipv4
               ? new_ip_acceptor_impl<AF_INET>(port, hostname, reuse_addr, any)
               : new_ip_acceptor_impl<AF_INET6>(port, hostname, reuse_addr,
                                                any);
    if (!p) {
      CAF_LOG_DEBUG(p.error());
      continue;
    }
    fd = *p;
    break;
  }
  if (fd == invalid_native_socket) {
    CAF_LOG_WARNING("could not open tcp socket on:" << CAF_ARG(port)
                                                    << CAF_ARG(addr_str));
    return make_error(sec::cannot_open_port, "tcp socket creation failed", port,
                      addr_str);
  }
  detail::socket_guard sguard{fd};
  CALL_CFUN(tmp2, detail::cc_zero, "listen", listen(fd, SOMAXCONN));
  // ok, no errors so far
  CAF_LOG_DEBUG(CAF_ARG(fd));
  return sguard.release();
}

expected<std::pair<native_socket, ip_endpoint>>
new_remote_udp_endpoint_impl(const std::string& host, uint16_t port,
                             optional<protocol::network> preferred) {
  CAF_LOG_TRACE(CAF_ARG(host) << CAF_ARG(port) << CAF_ARG(preferred));
  auto lep = new_local_udp_endpoint_impl(0, nullptr, false, preferred);
  if (!lep)
    return std::move(lep.error());
  detail::socket_guard sguard{(*lep).first};
  std::pair<native_socket, ip_endpoint> info;
  memset(std::get<1>(info).address(), 0, sizeof(sockaddr_storage));
  if (!interfaces::get_endpoint(host, port, std::get<1>(info), (*lep).second))
    return make_error(sec::cannot_connect_to_node, "no such host", host, port);
  get<0>(info) = sguard.release();
  return info;
}

expected<std::pair<native_socket, protocol::network>>
new_local_udp_endpoint_impl(uint16_t port, const char* addr, bool reuse,
                            optional<protocol::network> preferred) {
  CAF_LOG_TRACE(CAF_ARG(port) << ", addr = " << (addr ? addr : "nullptr"));
  auto addrs = interfaces::server_address(port, addr, preferred);
  auto addr_str = std::string{addr == nullptr ? "" : addr};
  if (addrs.empty())
    return make_error(sec::cannot_open_port, "No local interface available",
                      addr_str);
  bool any = addr_str.empty() || addr_str == "::" || addr_str == "0.0.0.0";
  auto fd = invalid_native_socket;
  protocol::network proto;
  for (auto& elem : addrs) {
    auto host = elem.first.c_str();
    auto p = elem.second == ipv4
               ? new_ip_acceptor_impl<AF_INET, SOCK_DGRAM>(port, host, reuse,
                                                           any)
               : new_ip_acceptor_impl<AF_INET6, SOCK_DGRAM>(port, host, reuse,
                                                            any);
    if (!p) {
      CAF_LOG_DEBUG(p.error());
      continue;
    }
    fd = *p;
    proto = elem.second;
    break;
  }
  if (fd == invalid_native_socket) {
    CAF_LOG_WARNING("could not open udp socket on:" << CAF_ARG(port)
                                                    << CAF_ARG(addr_str));
    return make_error(sec::cannot_open_port, "udp socket creation failed", port,
                      addr_str);
  }
  CAF_LOG_DEBUG(CAF_ARG(fd));
  return std::make_pair(fd, proto);
}

} // namespace network
} // namespace io
} // namespace caf
