SocketCommunication.cpp

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#include <algorithm>
#include <boost/asio.hpp>
#include <boost/asio/deadline_timer.hpp>
 
#include <filesystem>
#include <sstream>
#include <stdexcept>
#include <utility>
 
#include "ConnectionInfoPublisher.hpp"
#include "SocketCommunication.hpp"
#include "SocketRequest.hpp"
#include "logging/LogMacros.hpp"
#include "precice/impl/Types.hpp"
#include "utils/assertion.hpp"
#include "utils/networking.hpp"
#include "utils/span_tools.hpp"
 
namespace precice::com {
 
namespace asio = boost::asio;
 
SocketCommunication::SocketCommunication(unsigned short portNumber,
                                         bool           reuseAddress,
                                         std::string    networkName,
                                         std::string    addressDirectory)
    : _portNumber(portNumber),
      _reuseAddress(reuseAddress),
      _networkName(std::move(networkName)),
      _addressDirectory(std::move(addressDirectory)),
      _ioContext(new IOContext)
{
  if (_addressDirectory.empty()) {
    _addressDirectory = ".";
  }
}
 
SocketCommunication::SocketCommunication(std::string const &addressDirectory)
    : SocketCommunication(0, false, utils::networking::loopbackInterfaceName(), addressDirectory)
{
}
 
SocketCommunication::~SocketCommunication()
{
  PRECICE_TRACE(_isConnected);
  closeConnection();
}
 
size_t SocketCommunication::getRemoteCommunicatorSize()
{
  PRECICE_TRACE();
  PRECICE_ASSERT(isConnected());
  return _sockets.size();
}
 
void SocketCommunication::acceptConnection(std::string const &acceptorName,
                                           std::string const &requesterName,
                                           std::string const &tag,
                                           int                acceptorRank,
                                           int                rankOffset)
{
  PRECICE_TRACE(acceptorName, requesterName);
 
  PRECICE_ASSERT(not isConnected());
 
  setRankOffset(rankOffset);
 
  std::string address;
 
  try {
    std::string ipAddress = getIpAddress();
    PRECICE_CHECK(not ipAddress.empty(), "Network \"{}\" not found for socket connection!", _networkName);
 
    using asio::ip::tcp;
 
    tcp::acceptor acceptor(*_ioContext);
    tcp::endpoint endpoint(tcp::v4(), _portNumber);
 
    acceptor.open(endpoint.protocol());
    acceptor.set_option(tcp::acceptor::reuse_address(_reuseAddress));
    acceptor.bind(endpoint);
    acceptor.listen();
 
    _portNumber = acceptor.local_endpoint().port();
    address     = ipAddress + ":" + std::to_string(_portNumber);
    ConnectionInfoWriter conInfo(acceptorName, requesterName, tag, _addressDirectory);
    conInfo.write(address);
    PRECICE_DEBUG("Accept connection at {}", address);
 
    int peerCurrent               = 0;  // Current peer to connect to
    int peerCount                 = -1; // The total count of peers (initialized in the first iteration)
    int requesterCommunicatorSize = -1;
 
    do {
      auto socket = std::make_shared<Socket>(*_ioContext);
 
      acceptor.accept(*socket);
      boost::asio::ip::tcp::no_delay option(true);
      socket->set_option(option);
 
      PRECICE_DEBUG("Accepted connection at {}", address);
      _isConnected = true;
 
      int requesterRank = -1;
 
      asio::read(*socket, asio::buffer(&requesterRank, sizeof(int)));
 
      PRECICE_ASSERT(_sockets.count(requesterRank) == 0,
                     "Rank {} has already been connected. Duplicate requests are not allowed.", requesterRank);
 
      _sockets[requesterRank] = std::move(socket);
      // send and receive expect a rank from the acceptor perspective.
      // Thus we need to apply given rankOffset before passing it to send/receive.
      // This is essentially the inverse of adjustRank().
      auto adjustedRequesterRank = requesterRank + rankOffset;
      send(acceptorRank, adjustedRequesterRank);
      receive(requesterCommunicatorSize, adjustedRequesterRank);
 
      // Initialize the count of peers to connect to
      if (peerCurrent == 0) {
        peerCount = requesterCommunicatorSize;
      }
 
      PRECICE_ASSERT(requesterCommunicatorSize > 0,
                     "Requester communicator size is {} which is invalid.", requesterCommunicatorSize);
      PRECICE_ASSERT(requesterCommunicatorSize == peerCount,
                     "Current requester size from rank {} is {} but should be {}", requesterRank, requesterCommunicatorSize, peerCount);
    } while (++peerCurrent < requesterCommunicatorSize);
 
    acceptor.close();
  } catch (std::exception &e) {
    PRECICE_ERROR("Accepting a socket connection at {} failed with the system error: {}", address, e.what());
  }
 
  // NOTE: Keep IO context running so that it fires asynchronous handlers from another thread.
  _workGuard = std::make_unique<WorkGuard>(boost::asio::make_work_guard(_ioContext->get_executor()));
  _thread    = std::thread([this] { _ioContext->run(); });
}
 
void SocketCommunication::acceptConnectionAsServer(std::string const &acceptorName,
                                                   std::string const &requesterName,
                                                   std::string const &tag,
                                                   int                acceptorRank,
                                                   int                requesterCommunicatorSize)
{
  PRECICE_TRACE(acceptorName, requesterName, acceptorRank, requesterCommunicatorSize);
  PRECICE_ASSERT(requesterCommunicatorSize >= 0, "Requester communicator size has to be positive.");
  PRECICE_ASSERT(not isConnected());
 
  if (requesterCommunicatorSize == 0) {
    PRECICE_DEBUG("Accepting no connections.");
    _isConnected = true;
    return;
  }
 
  std::string address;
 
  try {
    std::string ipAddress = getIpAddress();
    PRECICE_ASSERT(not ipAddress.empty(), "Network \"{}\" not found for socket connection!", _networkName);
 
    using asio::ip::tcp;
 
    tcp::acceptor acceptor(*_ioContext);
    {
      tcp::endpoint endpoint(tcp::v4(), _portNumber);
 
      acceptor.open(endpoint.protocol());
      acceptor.set_option(tcp::acceptor::reuse_address(_reuseAddress));
      acceptor.bind(endpoint);
      acceptor.listen();
 
      _portNumber = acceptor.local_endpoint().port();
    }
 
    address = ipAddress + ":" + std::to_string(_portNumber);
    ConnectionInfoWriter conInfo(acceptorName, requesterName, tag, acceptorRank, _addressDirectory);
    conInfo.write(address);
 
    PRECICE_DEBUG("Accepting connection at {}", address);
 
    for (int connection = 0; connection < requesterCommunicatorSize; ++connection) {
      auto socket = std::make_shared<Socket>(*_ioContext);
      acceptor.accept(*socket);
      boost::asio::ip::tcp::no_delay option(true);
      socket->set_option(option);
      PRECICE_DEBUG("Accepted connection at {}", address);
      _isConnected = true;
 
      int requesterRank;
      asio::read(*socket, asio::buffer(&requesterRank, sizeof(int)));
      _sockets[requesterRank] = std::move(socket);
    }
 
    acceptor.close();
  } catch (std::exception &e) {
    PRECICE_ERROR("Accepting a socket connection at {} failed with the system error: {}", address, e.what());
  }
 
  // NOTE: Keep IO context running so that it fires asynchronous handlers from another thread.
  _workGuard = std::make_unique<WorkGuard>(boost::asio::make_work_guard(_ioContext->get_executor()));
  _thread    = std::thread([this] { _ioContext->run(); });
}
 
void SocketCommunication::requestConnection(std::string const &acceptorName,
                                            std::string const &requesterName,
                                            std::string const &tag,
                                            int                requesterRank,
                                            int                requesterCommunicatorSize)
{
  PRECICE_TRACE(acceptorName, requesterName);
  PRECICE_ASSERT(not isConnected());
 
  ConnectionInfoReader conInfo(acceptorName, requesterName, tag, _addressDirectory);
  std::string const    address = conInfo.read();
  PRECICE_DEBUG("Request connection to {}", address);
  auto const        sepidx     = address.find(':');
  std::string const ipAddress  = address.substr(0, sepidx);
  std::string const portNumber = address.substr(sepidx + 1);
  _portNumber                  = static_cast<unsigned short>(std::stoul(portNumber));
 
  try {
    auto socket = std::make_shared<Socket>(*_ioContext);
 
    using asio::ip::tcp;
 
    while (not isConnected()) {
      tcp::resolver resolver(*_ioContext);
      auto          results = resolver.resolve(ipAddress, portNumber, boost::asio::ip::resolver_base::numeric_host);
 
      auto                      endpoint = results.begin()->endpoint();
      boost::system::error_code error    = asio::error::host_not_found;
      socket->connect(endpoint, error);
 
      _isConnected = not error;
 
      if (not isConnected()) {
        // Wait a little, since after a couple of ten-thousand trials the system
        // seems to get confused and the requester connects wrongly to itself.
        boost::asio::deadline_timer timer(*_ioContext, boost::posix_time::milliseconds(1));
        timer.wait();
      }
    }
    boost::asio::ip::tcp::no_delay option(true);
    socket->set_option(option);
 
    PRECICE_DEBUG("Requested connection to {}", address);
 
    asio::write(*socket, asio::buffer(&requesterRank, sizeof(int)));
 
    int acceptorRank = -1;
    asio::read(*socket, asio::buffer(&acceptorRank, sizeof(int)));
    _sockets[0] = std::move(socket); // should be acceptorRank instead of 0, likewise all communication below
 
    send(requesterCommunicatorSize, 0);
 
  } catch (std::exception &e) {
    PRECICE_ERROR("Requesting a socket connection at {} failed with the system error: {}", address, e.what());
  }
 
  // NOTE: Keep IO context running so that it fires asynchronous handlers from another thread.
  _workGuard = std::make_unique<WorkGuard>(boost::asio::make_work_guard(_ioContext->get_executor()));
  _thread    = std::thread([this] { _ioContext->run(); });
}
 
void SocketCommunication::requestConnectionAsClient(std::string const   &acceptorName,
                                                    std::string const   &requesterName,
                                                    std::string const   &tag,
                                                    std::set<int> const &acceptorRanks,
                                                    int                  requesterRank)
 
{
  PRECICE_TRACE(acceptorName, requesterName, acceptorRanks, requesterRank);
  PRECICE_ASSERT(not isConnected());
 
  for (auto const &acceptorRank : acceptorRanks) {
    _isConnected = false;
    ConnectionInfoReader conInfo(acceptorName, requesterName, tag, acceptorRank, _addressDirectory);
    std::string const    address    = conInfo.read();
    auto const           sepidx     = address.find(':');
    std::string const    ipAddress  = address.substr(0, sepidx);
    std::string const    portNumber = address.substr(sepidx + 1);
    _portNumber                     = static_cast<unsigned short>(std::stoul(portNumber));
 
    try {
      auto socket = std::make_shared<Socket>(*_ioContext);
 
      using asio::ip::tcp;
 
      PRECICE_DEBUG("Requesting connection to {}, port {}", ipAddress, portNumber);
 
      while (not isConnected()) {
        tcp::resolver resolver(*_ioContext);
        auto          endpoints = resolver.resolve(ipAddress, portNumber, boost::asio::ip::resolver_base::numeric_host);
 
        boost::system::error_code error = asio::error::host_not_found;
        boost::asio::connect(*socket, endpoints, error);
 
        _isConnected = not error;
 
        if (not isConnected()) {
          // Wait a little, since after a couple of ten-thousand trials the system
          // seems to get confused and the requester connects wrongly to itself.
          boost::asio::deadline_timer timer(*_ioContext, boost::posix_time::milliseconds(1));
          timer.wait();
        }
      }
      boost::asio::ip::tcp::no_delay option(true);
      socket->set_option(option);
 
      PRECICE_DEBUG("Requested connection to {}, rank = {}", address, acceptorRank);
      _sockets[acceptorRank] = std::move(socket);
      send(requesterRank, acceptorRank); // send my rank
 
    } catch (std::exception &e) {
      PRECICE_ERROR("Requesting a socket connection at {} failed with the system error: {}", address, e.what());
    }
  }
  // NOTE: Keep IO context running so that it fires asynchronous handlers from another thread.
  _workGuard = std::make_unique<WorkGuard>(boost::asio::make_work_guard(_ioContext->get_executor()));
  _thread    = std::thread([this] { _ioContext->run(); });
}
 
void SocketCommunication::closeConnection()
{
  PRECICE_TRACE();
 
  if (not isConnected())
    return;
 
  if (_thread.joinable()) {
    _workGuard.reset();
    _ioContext->stop();
    _thread.join();
  }
 
  for (auto &socket : _sockets) {
    PRECICE_ASSERT(socket.second->is_open());
 
    try {
      socket.second->shutdown(Socket::shutdown_send);
      socket.second->close();
    } catch (std::exception &e) {
      PRECICE_WARN("Socket shutdown failed with system error: {}", e.what());
    }
  }
 
  _isConnected = false;
}
 
void SocketCommunication::send(std::string const &itemToSend, Rank rankReceiver)
{
  PRECICE_TRACE(itemToSend, rankReceiver);
 
  rankReceiver = adjustRank(rankReceiver);
 
  PRECICE_ASSERT(rankReceiver >= 0, rankReceiver);
  PRECICE_ASSERT(isConnected());
 
  size_t size = itemToSend.size() + 1;
  try {
    asio::write(*_sockets[rankReceiver], asio::buffer(&size, sizeof(size_t)));
    asio::write(*_sockets[rankReceiver], asio::buffer(itemToSend.c_str(), size));
  } catch (std::exception &e) {
    PRECICE_ERROR("Sending data to another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
void SocketCommunication::send(precice::span<const int> itemsToSend, Rank rankReceiver)
{
  PRECICE_TRACE(itemsToSend.size(), rankReceiver);
 
  rankReceiver = adjustRank(rankReceiver);
 
  PRECICE_ASSERT(rankReceiver >= 0, rankReceiver);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::write(*_sockets[rankReceiver], asio::buffer(itemsToSend.data(), itemsToSend.size() * sizeof(int)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Sending data to another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
void SocketCommunication::prepareEstablishment(std::string const &acceptorName,
                                               std::string const &requesterName)
{
  using namespace std::filesystem;
  path dir = com::impl::localDirectory(acceptorName, requesterName, _addressDirectory);
  PRECICE_DEBUG("Creating connection exchange directory {}", dir.generic_string());
  try {
    create_directories(dir);
  } catch (const std::filesystem::filesystem_error &e) {
    PRECICE_WARN("Creating directory for connection info failed with filesystem error: {}", e.what());
  }
}
 
void SocketCommunication::cleanupEstablishment(std::string const &acceptorName,
                                               std::string const &requesterName)
{
  using namespace std::filesystem;
  path dir = com::impl::localDirectory(acceptorName, requesterName, _addressDirectory);
  PRECICE_DEBUG("Removing connection exchange directory {}", dir.generic_string());
  try {
    remove_all(dir);
  } catch (const std::filesystem::filesystem_error &e) {
    PRECICE_WARN("Cleaning up connection info failed with filesystem error {}", e.what());
  }
}
 
PtrRequest SocketCommunication::aSend(precice::span<const int> itemsToSend, Rank rankReceiver)
{
  PRECICE_TRACE(itemsToSend.size(), rankReceiver);
 
  rankReceiver = adjustRank(rankReceiver);
 
  PRECICE_ASSERT(rankReceiver >= 0, rankReceiver);
  PRECICE_ASSERT(isConnected());
 
  PtrRequest request(new SocketRequest);
 
  _queue.dispatch(_sockets[rankReceiver],
                  asio::buffer(itemsToSend.data(), itemsToSend.size() * sizeof(int)),
                  [request] {
                    std::static_pointer_cast<SocketRequest>(request)->complete();
                  });
  return request;
}
 
void SocketCommunication::send(precice::span<const double> itemsToSend, Rank rankReceiver)
{
  PRECICE_TRACE(itemsToSend.size(), rankReceiver);
 
  rankReceiver = adjustRank(rankReceiver);
 
  PRECICE_ASSERT(rankReceiver >= 0, rankReceiver);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::write(*_sockets[rankReceiver], asio::buffer(itemsToSend.data(), itemsToSend.size() * sizeof(double)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Sending data to another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
PtrRequest SocketCommunication::aSend(precice::span<const double> itemsToSend, Rank rankReceiver)
{
  PRECICE_TRACE(itemsToSend.size(), rankReceiver);
 
  rankReceiver = adjustRank(rankReceiver);
 
  PRECICE_ASSERT(rankReceiver >= 0, rankReceiver);
  PRECICE_ASSERT(isConnected());
 
  PtrRequest request(new SocketRequest);
 
  _queue.dispatch(_sockets[rankReceiver],
                  asio::buffer(itemsToSend.data(), itemsToSend.size() * sizeof(double)),
                  [request] {
                    std::static_pointer_cast<SocketRequest>(request)->complete();
                  });
  return request;
}
 
void SocketCommunication::send(double itemToSend, Rank rankReceiver)
{
  PRECICE_TRACE(itemToSend, rankReceiver);
 
  rankReceiver = adjustRank(rankReceiver);
 
  PRECICE_ASSERT(rankReceiver >= 0, rankReceiver);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::write(*_sockets[rankReceiver], asio::buffer(&itemToSend, sizeof(double)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Sending data to another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
PtrRequest SocketCommunication::aSend(const double &itemToSend, Rank rankReceiver)
{
  return aSend(precice::refToSpan<const double>(itemToSend), rankReceiver);
}
 
void SocketCommunication::send(int itemToSend, Rank rankReceiver)
{
  PRECICE_TRACE(itemToSend, rankReceiver);
 
  rankReceiver = adjustRank(rankReceiver);
 
  PRECICE_ASSERT(rankReceiver >= 0, rankReceiver);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::write(*_sockets[rankReceiver], asio::buffer(&itemToSend, sizeof(int)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Sending data to another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
PtrRequest SocketCommunication::aSend(const int &itemToSend, Rank rankReceiver)
{
  return aSend(precice::refToSpan<const int>(itemToSend), rankReceiver);
}
 
void SocketCommunication::send(bool itemToSend, Rank rankReceiver)
{
  PRECICE_TRACE(itemToSend, rankReceiver);
 
  rankReceiver = adjustRank(rankReceiver);
 
  PRECICE_ASSERT(rankReceiver >= 0, rankReceiver);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::write(*_sockets[rankReceiver], asio::buffer(&itemToSend, sizeof(bool)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Sending data to another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
PtrRequest SocketCommunication::aSend(const bool &itemToSend, Rank rankReceiver)
{
  PRECICE_TRACE(rankReceiver);
 
  rankReceiver = adjustRank(rankReceiver);
 
  PRECICE_ASSERT(rankReceiver >= 0, rankReceiver);
  PRECICE_ASSERT(isConnected());
 
  PtrRequest request(new SocketRequest);
 
  _queue.dispatch(_sockets[rankReceiver],
                  asio::buffer(&itemToSend, sizeof(bool)),
                  [request] {
                    std::static_pointer_cast<SocketRequest>(request)->complete();
                  });
  return request;
}
 
void SocketCommunication::receive(std::string &itemToReceive, Rank rankSender)
{
  PRECICE_TRACE(rankSender);
 
  rankSender = adjustRank(rankSender);
 
  PRECICE_ASSERT(rankSender >= 0, rankSender);
  PRECICE_ASSERT(isConnected());
 
  size_t size = 0;
 
  try {
    asio::read(*_sockets[rankSender], asio::buffer(&size, sizeof(size_t)));
    std::vector<char> msg(size);
    asio::read(*_sockets[rankSender], asio::buffer(msg.data(), size));
    itemToReceive = msg.data();
  } catch (std::exception &e) {
    PRECICE_ERROR("Receiving data from another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
void SocketCommunication::receive(precice::span<int> itemsToReceive, Rank rankSender)
{
  PRECICE_TRACE(itemsToReceive.size(), rankSender);
 
  rankSender = adjustRank(rankSender);
 
  PRECICE_ASSERT(rankSender >= 0, rankSender);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::read(*_sockets[rankSender], asio::buffer(itemsToReceive.data(), itemsToReceive.size() * sizeof(int)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Receiving data from another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
void SocketCommunication::receive(precice::span<double> itemsToReceive, Rank rankSender)
{
  PRECICE_TRACE(itemsToReceive.size(), rankSender);
 
  rankSender = adjustRank(rankSender);
 
  PRECICE_ASSERT(rankSender >= 0, rankSender);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::read(*_sockets[rankSender], asio::buffer(itemsToReceive.data(), itemsToReceive.size() * sizeof(double)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Receiving data from another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
PtrRequest SocketCommunication::aReceive(precice::span<double> itemsToReceive,
                                         int                   rankSender)
{
  PRECICE_TRACE(itemsToReceive.size(), rankSender);
 
  rankSender = adjustRank(rankSender);
 
  PRECICE_ASSERT(rankSender >= 0, rankSender);
  PRECICE_ASSERT(isConnected());
 
  PtrRequest request(new SocketRequest);
 
  try {
    asio::async_read(*_sockets[rankSender],
                     asio::buffer(itemsToReceive.data(), itemsToReceive.size() * sizeof(double)),
                     [request](boost::system::error_code const &, std::size_t) {
                       std::static_pointer_cast<SocketRequest>(request)->complete();
                     });
  } catch (std::exception &e) {
    PRECICE_ERROR("Receiving data from another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
 
  return request;
}
 
void SocketCommunication::receive(double &itemToReceive, Rank rankSender)
{
  PRECICE_TRACE(rankSender);
 
  rankSender = adjustRank(rankSender);
 
  PRECICE_ASSERT(rankSender >= 0, rankSender);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::read(*_sockets[rankSender], asio::buffer(&itemToReceive, sizeof(double)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Receiving data from another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
PtrRequest SocketCommunication::aReceive(double &itemToReceive, Rank rankSender)
{
  return aReceive(precice::refToSpan<double>(itemToReceive), rankSender);
}
 
void SocketCommunication::receive(int &itemToReceive, Rank rankSender)
{
  PRECICE_TRACE(rankSender);
 
  rankSender = adjustRank(rankSender);
 
  PRECICE_ASSERT(rankSender >= 0, rankSender);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::read(*_sockets[rankSender], asio::buffer(&itemToReceive, sizeof(int)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Receiving data from another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
PtrRequest SocketCommunication::aReceive(int &itemToReceive, Rank rankSender)
{
  PRECICE_TRACE(rankSender);
 
  rankSender = adjustRank(rankSender);
 
  PRECICE_ASSERT((rankSender >= 0) && (rankSender < (int) _sockets.size()),
                 rankSender, _sockets.size());
  PRECICE_ASSERT(isConnected());
 
  PtrRequest request(new SocketRequest);
 
  try {
    asio::async_read(*_sockets[rankSender],
                     asio::buffer(&itemToReceive, sizeof(int)),
                     [request](boost::system::error_code const &, std::size_t) {
                       std::static_pointer_cast<SocketRequest>(request)->complete();
                     });
  } catch (std::exception &e) {
    PRECICE_ERROR("Receiving data from another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
 
  return request;
}
 
void SocketCommunication::receive(bool &itemToReceive, Rank rankSender)
{
  PRECICE_TRACE(rankSender);
 
  rankSender = adjustRank(rankSender);
 
  PRECICE_ASSERT(rankSender >= 0, rankSender);
  PRECICE_ASSERT(isConnected());
 
  try {
    asio::read(*_sockets[rankSender], asio::buffer(&itemToReceive, sizeof(bool)));
  } catch (std::exception &e) {
    PRECICE_ERROR("Receiving data from another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
}
 
PtrRequest SocketCommunication::aReceive(bool &itemToReceive, Rank rankSender)
{
  PRECICE_TRACE(rankSender);
 
  rankSender = adjustRank(rankSender);
 
  PRECICE_ASSERT(rankSender >= 0, rankSender);
  PRECICE_ASSERT(isConnected());
 
  PtrRequest request(new SocketRequest);
 
  try {
    asio::async_read(*_sockets[rankSender],
                     asio::buffer(&itemToReceive, sizeof(bool)),
                     [request](boost::system::error_code const &, std::size_t) {
                       std::static_pointer_cast<SocketRequest>(request)->complete();
                     });
  } catch (std::exception &e) {
    PRECICE_ERROR("Receiving data from another participant (using sockets) failed with a system error: {}. This often means that the other participant exited with an error (look there).", e.what());
  }
 
  return request;
}
 
#ifndef _WIN32
namespace {
struct Interface {
  unsigned int index;
  std::string  name;
  std::string  address;
};
 
std::vector<Interface> detectInterfaces()
{
  std::vector<Interface> interfaces;
 
  // Collect interface indices and names
  struct if_nameindex *nameInterface = if_nameindex();
  for (struct if_nameindex *itNameInterface = nameInterface; itNameInterface->if_index != 0; ++itNameInterface) {
    Interface interface;
    interface.index = itNameInterface->if_index;
    interface.name  = itNameInterface->if_name;
    interfaces.emplace_back(std::move(interface));
  }
  if_freenameindex(nameInterface);
 
  // Resolve addresses for interfaces
  for (auto &interface : interfaces) {
    struct ifreq request;
    strncpy(request.ifr_name,
            interface.name.c_str(),
            IFNAMSIZ - 1); // Copy interface name
 
    auto socketfd = socket(AF_INET, SOCK_STREAM, 0);
    if (socketfd == -1) {
      continue;
    }
    auto err = ioctl(socketfd, SIOCGIFADDR, &request);
    close(socketfd);
    if (err) {
      continue;
    }
 
    const char *addr = inet_ntoa((reinterpret_cast<struct sockaddr_in *>(&request.ifr_addr))->sin_addr);
    if (!addr) {
      continue;
    }
    interface.address = addr;
  }
 
  return interfaces;
}
} // namespace
#endif
 
std::string SocketCommunication::getIpAddress()
{
  PRECICE_TRACE();
 
#ifdef _WIN32
  return "127.0.0.1";
#else
 
  PRECICE_DEBUG("Looking for IP address of network \"{}\"", _networkName);
 
  auto interfaces = detectInterfaces();
 
  auto pos = std::find_if(interfaces.begin(), interfaces.end(),
                          [&](Interface const &interface) { return interface.name == _networkName; });
  if (pos == interfaces.end()) {
    PRECICE_DEBUG("There's NOTHING");
    std::ostringstream err;
    err << "Cannot find network interface \"" << _networkName << "\". Available interfaces are: ";
    for (const auto &interface : interfaces) {
      err << interface.name << ' ';
    }
    err << " Please check \"network\" attributes in your configuration file.";
    PRECICE_ERROR(err.str());
  }
 
  // Unconnected interfaces don't have an IP address.
  PRECICE_CHECK(not pos->address.empty(), "The interface \"{}\" does not have an IP address. Please select another interface.", _networkName);
 
  PRECICE_DEBUG("Detected network IP address of interface \"{}\": {}.", _networkName, pos->address);
  return pos->address;
#endif
}
 
} // namespace precice::com