squeezelite-esp32/components/spotify/cspot/bell/main/platform/linux/MDNSService.cpp

#include <arpa/inet.h>
#include <ifaddrs.h>
#include <net/if.h>
#include <netdb.h>
#include <unistd.h>
#include <cstring>
#include <vector>
#include <mutex>
#include <atomic>

#if __has_include("avahi-client/client.h")
#include <avahi-client/client.h>
#include <avahi-client/publish.h>
#include <avahi-common/alternative.h>
#include <avahi-common/simple-watch.h>
#elif !defined(BELL_DISABLE_AVAHI)
#define BELL_DISABLE_AVAHI
#endif

#include "BellLogger.h"
#include "MDNSService.h"
#include "mdnssvc.h"

using namespace bell;

#ifndef BELL_DISABLE_AVAHI
static void groupHandler(AvahiEntryGroup* g, AvahiEntryGroupState state,
                         AVAHI_GCC_UNUSED void* userdata) {}
#endif

class implMDNSService : public MDNSService {
 private:
#ifndef BELL_DISABLE_AVAHI
  AvahiEntryGroup* avahiGroup;
#endif
  struct mdns_service* service;

 public:
#ifndef BELL_DISABLE_AVAHI
  static AvahiClient* avahiClient;
  static AvahiSimplePoll* avahiPoll;
#endif
  static struct mdnsd* mdnsServer;
  static in_addr_t host;
  static std::atomic<size_t> instances;

  implMDNSService(struct mdns_service* service) : service(service){ instances++; };
#ifndef BELL_DISABLE_AVAHI
  implMDNSService(AvahiEntryGroup* avahiGroup) : avahiGroup(avahiGroup){};
#endif
  void unregisterService();
};

struct mdnsd* implMDNSService::mdnsServer = NULL;
in_addr_t implMDNSService::host = INADDR_ANY;
std::atomic<size_t> implMDNSService::instances = 0;
static std::mutex registerMutex;
#ifndef BELL_DISABLE_AVAHI
AvahiClient* implMDNSService::avahiClient = NULL;
AvahiSimplePoll* implMDNSService::avahiPoll = NULL;
#endif

/**
 * Linux implementation of MDNSService using avahi.
 * @see https://www.avahi.org/doxygen/html/
 **/

void implMDNSService::unregisterService() {
#ifndef BELL_DISABLE_AVAHI
  if (avahiGroup) {
    avahi_entry_group_free(avahiGroup);
    if (!--instances && implMDNSService::avahiClient) {
      avahi_client_free(implMDNSService::avahiClient);
      avahi_simple_poll_free(implMDNSService::avahiPoll);
      implMDNSService::avahiClient = nullptr;
      implMDNSService::avahiPoll = nullptr;
    }
  } else
#endif
  {
    mdns_service_remove(implMDNSService::mdnsServer, service);
    if (!--instances && implMDNSService::mdnsServer) {
     mdnsd_stop(implMDNSService::mdnsServer);
     implMDNSService::mdnsServer = nullptr;
    }
  }  
}

std::unique_ptr<MDNSService> MDNSService::registerService(
    const std::string& serviceName, const std::string& serviceType,
    const std::string& serviceProto, const std::string& serviceHost,
    int servicePort, const std::map<std::string, std::string> txtData) {
  std::lock_guard lock(registerMutex);
#ifndef BELL_DISABLE_AVAHI
  // try avahi first if available
  if (!implMDNSService::avahiPoll) {
    implMDNSService::avahiPoll = avahi_simple_poll_new();
  }

  if (implMDNSService::avahiPoll && !implMDNSService::avahiClient) {
    implMDNSService::avahiClient =
        avahi_client_new(avahi_simple_poll_get(implMDNSService::avahiPoll),
                         AvahiClientFlags(0), NULL, NULL, NULL);
  }
  AvahiEntryGroup* avahiGroup = NULL;

  if (implMDNSService::avahiClient &&
      (avahiGroup = avahi_entry_group_new(implMDNSService::avahiClient,
                                          groupHandler, NULL)) == NULL) {
    BELL_LOG(error, "MDNS", "cannot create service %s", serviceName.c_str());
  }

  if (avahiGroup != NULL) {
    AvahiStringList* avahiTxt = NULL;

    for (auto& [key, value] : txtData) {
      avahiTxt =
          avahi_string_list_add_pair(avahiTxt, key.c_str(), value.c_str());
    }

    std::string type(serviceType + "." + serviceProto);
    int ret = avahi_entry_group_add_service_strlst(
        avahiGroup, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC, (AvahiPublishFlags)0,
        serviceName.c_str(), type.c_str(), NULL, NULL, servicePort, avahiTxt);
    avahi_string_list_free(avahiTxt);

    if (ret >= 0) {
      ret = avahi_entry_group_commit(avahiGroup);
    }

    if (ret < 0) {
      BELL_LOG(error, "MDNS", "cannot run service %s", serviceName.c_str());
      avahi_entry_group_free(avahiGroup);
    } else {
      BELL_LOG(info, "MDNS", "using avahi for %s", serviceName.c_str());
      return std::make_unique<implMDNSService>(avahiGroup);
    }
  }
#endif

  // avahi failed, use build-in server
  struct ifaddrs* ifaddr;

  // get the host address first
  if (serviceHost.size()) {
    struct hostent* h = gethostbyname(serviceHost.c_str());
    if (h) {
      memcpy(&implMDNSService::host, h->h_addr_list[0], 4);
    }
  }

  // try go guess ifaddr if we have nothing as listening to INADDR_ANY usually does not work
  if (implMDNSService::host == INADDR_ANY && getifaddrs(&ifaddr) != -1) {
    for (struct ifaddrs* ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
      if (ifa->ifa_addr == NULL || ifa->ifa_addr->sa_family != AF_INET ||
          !(ifa->ifa_flags & IFF_UP) || !(ifa->ifa_flags & IFF_MULTICAST) ||
          (ifa->ifa_flags & IFF_LOOPBACK))
        continue;

      implMDNSService::host =
          ((struct sockaddr_in*)ifa->ifa_addr)->sin_addr.s_addr;
      break;
    }
    freeifaddrs(ifaddr);
  }

  if (!implMDNSService::mdnsServer) {
    char hostname[256];
    struct in_addr addr;

    // it's the same, but who knows..
    addr.s_addr = implMDNSService::host;
    gethostname(hostname, sizeof(hostname));

    implMDNSService::mdnsServer = mdnsd_start(addr, false);

    if (implMDNSService::mdnsServer) {
      mdnsd_set_hostname(implMDNSService::mdnsServer, hostname, addr);
    }
  }

  if (implMDNSService::mdnsServer) {
    std::vector<const char*> txt;
    std::vector<std::unique_ptr<std::string>> txtStr;

    for (auto& [key, value] : txtData) {
      auto str = make_unique<std::string>(key + "=" + value);
      txtStr.push_back(std::move(str));
      txt.push_back(txtStr.back()->c_str());
    }

    txt.push_back(NULL);
    std::string type(serviceType + "." + serviceProto + ".local");

    BELL_LOG(info, "MDNS", "using built-in mDNS for %s", serviceName.c_str());
    auto service =
        mdnsd_register_svc(implMDNSService::mdnsServer, serviceName.c_str(),
                             type.c_str(), servicePort, NULL, txt.data());

    if (service) return std::make_unique<implMDNSService>(service);
  }

  BELL_LOG(error, "MDNS", "cannot start any mDNS listener for %s",
           serviceName.c_str());
  return nullptr;
}