snapcast/server/publishZeroConf/publish_avahi.cpp

/***
    This file is part of snapcast
    Copyright (C) 2014-2022  Johannes Pohl

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
***/

// prototype/interface header file
#include "publish_avahi.hpp"

// local headers
#include "common/aixlog.hpp"

// 3rd party headers

// standard headers
#include <cstdio>
#include <cstdlib>


static constexpr auto LOG_TAG = "Avahi";

static AvahiEntryGroup* group;
static AvahiSimplePoll* simple_poll;
static char* name;

PublishAvahi::PublishAvahi(const std::string& serviceName, boost::asio::io_context& ioc) : PublishmDNS(serviceName, ioc), client_(nullptr), timer_(ioc)
{
    group = nullptr;
    simple_poll = nullptr;
    name = avahi_strdup(serviceName_.c_str());
}


void PublishAvahi::publish(const std::vector<mDNSService>& services)
{
    services_ = services;

    /// Allocate main loop object
    if ((simple_poll = avahi_simple_poll_new()) == nullptr)
    {
        /// TODO: error handling
        LOG(ERROR, LOG_TAG) << "Failed to create simple poll object.\n";
    }

    /// Allocate a new client
    int error;
    client_ = avahi_client_new(avahi_simple_poll_get(simple_poll), AVAHI_CLIENT_IGNORE_USER_CONFIG, client_callback, this, &error);

    /// Check wether creating the client object succeeded
    if (client_ == nullptr)
    {
        LOG(ERROR, LOG_TAG) << "Failed to create client: " << avahi_strerror(error) << "\n";
    }

    poll();
}


void PublishAvahi::poll()
{
    timer_.expires_after(std::chrono::milliseconds(50));
    timer_.async_wait([this](const boost::system::error_code& ec) {
        if (!ec && (avahi_simple_poll_iterate(simple_poll, 0) == 0))
            poll();
    });
}


PublishAvahi::~PublishAvahi()
{
    timer_.cancel();

    if (client_ != nullptr)
        avahi_client_free(client_);

    if (simple_poll != nullptr)
        avahi_simple_poll_free(simple_poll);

    avahi_free(name);
}


void PublishAvahi::entry_group_callback(AvahiEntryGroup* g, AvahiEntryGroupState state, AVAHI_GCC_UNUSED void* userdata)
{
    assert(g == group || group == nullptr);
    group = g;

    /// Called whenever the entry group state changes
    switch (state)
    {
        case AVAHI_ENTRY_GROUP_ESTABLISHED:
            /// The entry group has been established successfully
            LOG(INFO, LOG_TAG) << "Service '" << name << "' successfully established.\n";
            break;

        case AVAHI_ENTRY_GROUP_COLLISION:
        {
            char* n;

            /// A service name collision with a remote service happened. Let's pick a new name
            n = avahi_alternative_service_name(name);
            avahi_free(name);
            name = n;

            LOG(NOTICE, LOG_TAG) << "Service name collision, renaming service to '" << name << "'\n";

            /// And recreate the services
            static_cast<PublishAvahi*>(userdata)->create_services(avahi_entry_group_get_client(g));
            break;
        }

        case AVAHI_ENTRY_GROUP_FAILURE:

            LOG(ERROR, LOG_TAG) << "Entry group failure: " << avahi_strerror(avahi_client_errno(avahi_entry_group_get_client(g))) << "\n";

            /// Some kind of failure happened while we were registering our services
            avahi_simple_poll_quit(simple_poll);
            break;

        case AVAHI_ENTRY_GROUP_UNCOMMITED:
        case AVAHI_ENTRY_GROUP_REGISTERING:;
    }
}

void PublishAvahi::create_services(AvahiClient* c)
{
    assert(c);
    char* n;

    /// If this is the first time we're called, let's create a new entry group if necessary
    if (group == nullptr)
    {
        if ((group = avahi_entry_group_new(c, entry_group_callback, this)) == nullptr)
        {
            LOG(ERROR, LOG_TAG) << "avahi_entry_group_new() failed: " << avahi_strerror(avahi_client_errno(c)) << "\n";
            goto fail;
        }
    }

    /// If the group is empty (either because it was just created, or because it was reset previously, add our entries.
    int ret;
    if (avahi_entry_group_is_empty(group) != 0)
    {
        LOG(INFO, LOG_TAG) << "Adding service '" << name << "'\n";

        /// We will now add two services and one subtype to the entry group
        for (const auto& service : services_)
        {
            if ((ret = avahi_entry_group_add_service(group, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC, AvahiPublishFlags(0), name, service.name_.c_str(), nullptr,
                                                     nullptr, service.port_, static_cast<char*>(nullptr))) < 0)
            {
                if (ret == AVAHI_ERR_COLLISION)
                    goto collision;

                LOG(ERROR, LOG_TAG) << "Failed to add " << service.name_ << " service: " << avahi_strerror(ret) << "\n";
                goto fail;
            }
        }

        /// Add an additional (hypothetic) subtype
        /* if ((ret = avahi_entry_group_add_service_subtype(group, AVAHI_IF_UNSPEC, AVAHI_PROTO_UNSPEC, AvahiPublishFlags(0), name,
           "_printer._tcp",
           NULL, "_magic._sub._printer._tcp") < 0))
                        {
                                fprintf(stderr, "Failed to add subtype _magic._sub._printer._tcp: %s\n", avahi_strerror(ret));
                                goto fail;
                        }
        */
        /// Tell the server to register the service
        if ((ret = avahi_entry_group_commit(group)) < 0)
        {
            LOG(ERROR, LOG_TAG) << "Failed to commit entry group: " << avahi_strerror(ret) << "\n";
            goto fail;
        }
    }

    return;

collision:

    /// A service name collision with a local service happened. Let's pick a new name
    n = avahi_alternative_service_name(name);
    avahi_free(name);
    name = n;

    LOG(INFO, LOG_TAG) << "Service name collision, renaming service to '" << name << "'\n";

    avahi_entry_group_reset(group);

    create_services(c);
    return;

fail:
    avahi_simple_poll_quit(simple_poll);
}


void PublishAvahi::client_callback(AvahiClient* c, AvahiClientState state, AVAHI_GCC_UNUSED void* userdata)
{
    assert(c);

    /// Called whenever the client or server state changes
    switch (state)
    {
        case AVAHI_CLIENT_S_RUNNING:

            /// The server has startup successfully and registered its host name on the network, so it's time to create our services
            static_cast<PublishAvahi*>(userdata)->create_services(c);
            break;

        case AVAHI_CLIENT_FAILURE:

            LOG(ERROR, LOG_TAG) << "Client failure: " << avahi_strerror(avahi_client_errno(c)) << "\n";
            avahi_simple_poll_quit(simple_poll);
            break;

        case AVAHI_CLIENT_S_COLLISION:

            /// Let's drop our registered services. When the server is back
            /// in AVAHI_SERVER_RUNNING state we will register them again with the new host name.

        case AVAHI_CLIENT_S_REGISTERING:

            /// The server records are now being established. This might be caused by a host name change. We need to wait
            /// for our own records to register until the host name is properly esatblished.

            if (group != nullptr)
                avahi_entry_group_reset(group);
            break;

        case AVAHI_CLIENT_CONNECTING:;
    }
}