複数インターフェイス環境でのマルチキャスト通信テスト

client.cc

#include <iostream>
#include <map>
#include <memory>
#include <string_view>

#include <boost/asio.hpp>
#include <boost/asio/spawn.hpp>
#include <boost/lexical_cast.hpp>

using namespace std::chrono_literals;
using namespace std::string_literals;

auto main(int argc, char** argv) -> int {
  if (argc != 4) return -1;

  const auto addr = boost::asio::ip::make_address_v4(argv[1]);
  const auto port = boost::lexical_cast<unsigned short>(argv[2]);
  const auto name = std::string{argv[3]};

  boost::asio::io_context ctx{1};

  boost::asio::ip::udp::endpoint listen_ep{boost::asio::ip::udp::v4(), port};
  boost::asio::ip::udp::endpoint mcast_ep{addr, port};

  boost::asio::ip::udp::socket sock{ctx, listen_ep.protocol()};
  sock.set_option(boost::asio::ip::udp::socket::reuse_address(true));
  sock.bind(listen_ep);
  sock.set_option(boost::asio::ip::multicast::enable_loopback(false));
  sock.set_option(boost::asio::ip::multicast::join_group(addr));

  boost::asio::steady_timer timer{ctx};

  boost::asio::spawn(ctx, [&sock, &mcast_ep, &timer, &name](auto&& yield) {
    for (;;) {
      sock.async_send_to(boost::asio::buffer("I'm "s + name + '!'), mcast_ep, yield);

      timer.expires_after(1s);
      timer.async_wait(yield);
    }
  });

  boost::asio::spawn(ctx, [&sock](auto&& yield) {
    char buf[1024];
    boost::asio::ip::udp::endpoint sender_ep{};
    for (;;) {
      const auto len = sock.async_receive_from(boost::asio::buffer(buf), sender_ep, yield);
      std::cout << sender_ep.address() << "> " << std::string_view{buf, len} << std::endl;
    }
  });

  ctx.run();
}

docker-compose.yaml

version: "3"
services:

  # Gist に置けるようにするため build context を全て同じディレクトリにしている
  # build context を不必要に広く取るのはよろしくないので普段はやめるべき

  server:
    build:
      context: .
      args:
        src: server.cc
        bin: &server-bin /server
    command: [*server-bin, &mcast-addr "224.5.0.1", &mcast-port "20001"]
    networks:
      net1:
      net2:
      net3:

  client-1:
    build: &build-client
      context: .
      args:
        src: client.cc
        bin: &client-bin /client
    command: [*client-bin, *mcast-addr, *mcast-port, "client-1"]
    networks:
      net1:

  client-2:
    build: *build-client
    command: [*client-bin, *mcast-addr, *mcast-port, "client-2"]
    networks:
      net2:

  client-3:
    build: *build-client
    command: [*client-bin, *mcast-addr, *mcast-port, "client-3"]
    networks:
      net3:

networks:
  net1:
  net2:
  net3:

Dockerfile

FROM alpine as builder
RUN apk add boost-dev g++
ARG src
ARG bin
COPY "${src}" /
RUN g++ -Wall -Wextra -Werror -pedantic-errors -std=c++17 -O3 /${src} -o /${bin} -lboost_coroutine

FROM alpine
RUN apk add --no-cache libstdc++ boost-coroutine
ARG bin
COPY --from=builder /${bin} /${bin}

server.cc

#include <iostream>
#include <map>
#include <memory>
#include <string_view>

#include <boost/asio.hpp>
#include <boost/asio/spawn.hpp>
#include <boost/lexical_cast.hpp>

extern "C" {
#include <arpa/inet.h>
#include <ifaddrs.h>
#include <sys/types.h>
}

using namespace std::chrono_literals;
using namespace std::string_literals;

auto main(int argc, char** argv) -> int {
  if (argc != 3) return -1;

  const auto port = boost::lexical_cast<unsigned short>(argv[2]);

  // join_group, outbound_interface に設定してみる IP アドレスのリスト
  std::map<std::string, boost::asio::ip::address_v4> ifaddrs{};
  ifaddrs.emplace("address_v4::any", boost::asio::ip::address_v4::any());

  // ネットワークインターフェイスと設定された IPv4 アドレスの列挙
  {
    ::ifaddrs* ifa_head;
    if (::getifaddrs(&ifa_head) != 0) return -1;

    for (auto ifa = ifa_head; ifa; ifa = ifa->ifa_next) {
      if (ifa->ifa_addr->sa_family != AF_INET) continue;
      if (std::string_view{ifa->ifa_name} == "lo") continue;

      const auto addr_native = reinterpret_cast<::sockaddr_in*>(ifa->ifa_addr);
      const auto addr = ::ntohl(addr_native->sin_addr.s_addr);
      ifaddrs.emplace(ifa->ifa_name, addr);
    }

    ::freeifaddrs(ifa_head);
  }

  boost::asio::io_context ctx{1};

  boost::asio::ip::udp::endpoint listen_ep{boost::asio::ip::udp::v4(), port};
  boost::asio::ip::udp::endpoint mcast_ep{boost::asio::ip::make_address_v4(argv[1]), port};

  boost::asio::ip::udp::socket sock{ctx, listen_ep.protocol()};
  sock.set_option(boost::asio::ip::udp::socket::reuse_address(true));
  sock.bind(listen_ep);
  sock.set_option(boost::asio::ip::multicast::enable_loopback(false));

  boost::asio::steady_timer timer{ctx};

  boost::asio::spawn(ctx, [&sock, mcast_ep, &ifaddrs, &timer](auto&& yield) {
    for (;;) {
      for (const auto& [name, ifaddr] : ifaddrs) {
        std::cout << "changing comm i/f: " << name << " (" << ifaddr << ')' << std::endl;

        sock.set_option(boost::asio::ip::multicast::join_group(mcast_ep.address().to_v4(), ifaddr));
        sock.set_option(boost::asio::ip::multicast::outbound_interface(ifaddr));

        for (auto i = 0u; i < 5u; ++i) {
          sock.async_send_to(boost::asio::buffer("Hello!"s), mcast_ep, yield);

          timer.expires_after(1s);
          timer.async_wait(yield);
        }

        sock.set_option(
            boost::asio::ip::multicast::leave_group(mcast_ep.address().to_v4(), ifaddr));
      }
    }
  });

  boost::asio::spawn(ctx, [&sock](auto&& yield) {
    char buf[1024];
    boost::asio::ip::udp::endpoint sender_ep{};
    for (;;) {
      const auto len = sock.async_receive_from(boost::asio::buffer(buf), sender_ep, yield);
      std::cout << sender_ep.address() << "> " << std::string_view{buf, len} << std::endl;
    }
  });

  ctx.run();
}