Implement mod communication channels (#6351)

Implement network communication for channels

* Implement ModChannel manager server side to route incoming messages from clients to other clients
* Add signal handler switch on client & ModChannelMgr on client to handle channels
* Add Lua API bindings + client packet sending + unittests
* Implement server message sending
* Add callback from received message handler to Lua API using registration method

src/modchannels.cpp

@@ -0,0 +1,152 @@
+/*
+Minetest
+Copyright (C) 2017 nerzhul, Loic Blot <loic.blot@unix-experience.fr>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#include "modchannels.h"
+#include <algorithm>
+#include <cassert>
+#include "util/basic_macros.h"
+
+bool ModChannel::registerConsumer(u16 peer_id)
+{
+
+	// ignore if peer_id already joined
+	if (CONTAINS(m_client_consumers, peer_id))
+		return false;
+
+	m_client_consumers.push_back(peer_id);
+	return true;
+}
+
+bool ModChannel::removeConsumer(u16 peer_id)
+{
+	bool found = false;
+	auto peer_removal_fct = [peer_id, &found](u16 p) {
+		if (p == peer_id)
+			found = true;
+
+		return p == peer_id;
+	};
+
+	m_client_consumers.erase(
+			std::remove_if(m_client_consumers.begin(),
+					m_client_consumers.end(), peer_removal_fct),
+			m_client_consumers.end());
+
+	return found;
+}
+
+bool ModChannel::canWrite() const
+{
+	return m_state == MODCHANNEL_STATE_READ_WRITE;
+}
+
+void ModChannel::setState(ModChannelState state)
+{
+	assert(state != MODCHANNEL_STATE_INIT);
+
+	m_state = state;
+}
+
+bool ModChannelMgr::channelRegistered(const std::string &channel) const
+{
+	return m_registered_channels.find(channel) != m_registered_channels.end();
+}
+
+ModChannel *ModChannelMgr::getModChannel(const std::string &channel)
+{
+	if (!channelRegistered(channel))
+		return nullptr;
+
+	return m_registered_channels[channel].get();
+}
+
+bool ModChannelMgr::canWriteOnChannel(const std::string &channel) const
+{
+	const auto channel_it = m_registered_channels.find(channel);
+	if (channel_it == m_registered_channels.end()) {
+		return false;
+	}
+
+	return channel_it->second->canWrite();
+}
+
+void ModChannelMgr::registerChannel(const std::string &channel)
+{
+	m_registered_channels[channel] =
+			std::unique_ptr<ModChannel>(new ModChannel(channel));
+}
+
+bool ModChannelMgr::setChannelState(const std::string &channel, ModChannelState state)
+{
+	if (!channelRegistered(channel))
+		return false;
+
+	auto channel_it = m_registered_channels.find(channel);
+	channel_it->second->setState(state);
+
+	return true;
+}
+
+bool ModChannelMgr::removeChannel(const std::string &channel)
+{
+	if (!channelRegistered(channel))
+		return false;
+
+	m_registered_channels.erase(channel);
+	return true;
+}
+
+bool ModChannelMgr::joinChannel(const std::string &channel, u16 peer_id)
+{
+	if (!channelRegistered(channel))
+		registerChannel(channel);
+
+	return m_registered_channels[channel]->registerConsumer(peer_id);
+}
+
+bool ModChannelMgr::leaveChannel(const std::string &channel, u16 peer_id)
+{
+	if (!channelRegistered(channel))
+		return false;
+
+	// Remove consumer from channel
+	bool consumerRemoved = m_registered_channels[channel]->removeConsumer(peer_id);
+
+	// If channel is empty, remove it
+	if (m_registered_channels[channel]->getChannelPeers().empty()) {
+		removeChannel(channel);
+	}
+	return consumerRemoved;
+}
+
+void ModChannelMgr::leaveAllChannels(u16 peer_id)
+{
+	for (auto &channel_it : m_registered_channels)
+		channel_it.second->removeConsumer(peer_id);
+}
+
+static std::vector<u16> empty_channel_list;
+const std::vector<u16> &ModChannelMgr::getChannelPeers(const std::string &channel) const
+{
+	const auto &channel_it = m_registered_channels.find(channel);
+	if (channel_it == m_registered_channels.end())
+		return empty_channel_list;
+
+	return channel_it->second->getChannelPeers();
+}