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

3 files changed, 228 insertions, 0 deletions

diff --git a/src/script/lua_api/CMakeLists.txt b/src/script/lua_api/CMakeLists.txt
index 1a78580e6..55bbf934b 100644
--- a/src/script/lua_api/CMakeLists.txt
+++ b/src/script/lua_api/CMakeLists.txt
@@ -8,6 +8,7 @@ set(common_SCRIPT_LUA_API_SRCS
 	${CMAKE_CURRENT_SOURCE_DIR}/l_itemstackmeta.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/l_mapgen.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/l_metadata.cpp
+	${CMAKE_CURRENT_SOURCE_DIR}/l_modchannels.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/l_nodemeta.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/l_nodetimer.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/l_noise.cpp
diff --git a/src/script/lua_api/l_modchannels.cpp b/src/script/lua_api/l_modchannels.cpp
new file mode 100644
index 000000000..ac28e2ada
--- /dev/null
+++ b/src/script/lua_api/l_modchannels.cpp
@@ -0,0 +1,161 @@
+/*
+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 <cassert>
+#include <log.h>
+#include "lua_api/l_modchannels.h"
+#include "l_internal.h"
+#include "modchannels.h"
+
+int ModApiChannels::l_mod_channel_join(lua_State *L)
+{
+	if (!lua_isstring(L, 1))
+		return 0;
+
+	std::string channel = luaL_checkstring(L, 1);
+	if (channel.empty())
+		return 0;
+
+	getGameDef(L)->joinModChannel(channel);
+	ModChannel *channelObj = getGameDef(L)->getModChannel(channel);
+	assert(channelObj);
+	ModChannelRef::create(L, channelObj);
+
+	int object = lua_gettop(L);
+	lua_pushvalue(L, object);
+	return 1;
+}
+
+void ModApiChannels::Initialize(lua_State *L, int top)
+{
+	API_FCT(mod_channel_join);
+}
+
+/*
+ * ModChannelRef
+ */
+
+ModChannelRef::ModChannelRef(ModChannel *modchannel) : m_modchannel(modchannel)
+{
+}
+
+int ModChannelRef::l_leave(lua_State *L)
+{
+	ModChannelRef *ref = checkobject(L, 1);
+	ModChannel *channel = getobject(ref);
+	if (!channel)
+		return 0;
+
+	getGameDef(L)->leaveModChannel(channel->getName());
+	// Channel left, invalidate the channel object ptr
+	// This permits to invalidate every object action from Lua because core removed
+	// channel consuming link
+	ref->m_modchannel = nullptr;
+	return 0;
+}
+
+int ModChannelRef::l_send_all(lua_State *L)
+{
+	ModChannelRef *ref = checkobject(L, 1);
+	ModChannel *channel = getobject(ref);
+	if (!channel || !channel->canWrite())
+		return 0;
+
+	// @TODO serialize message
+	std::string message = luaL_checkstring(L, 2);
+
+	getGameDef(L)->sendModChannelMessage(channel->getName(), message);
+	return 0;
+}
+
+int ModChannelRef::l_is_writeable(lua_State *L)
+{
+	ModChannelRef *ref = checkobject(L, 1);
+	ModChannel *channel = getobject(ref);
+	if (!channel)
+		return 0;
+
+	lua_pushboolean(L, channel->canWrite());
+	return 1;
+}
+void ModChannelRef::Register(lua_State *L)
+{
+	lua_newtable(L);
+	int methodtable = lua_gettop(L);
+	luaL_newmetatable(L, className);
+	int metatable = lua_gettop(L);
+
+	lua_pushliteral(L, "__metatable");
+	lua_pushvalue(L, methodtable);
+	lua_settable(L, metatable); // hide metatable from lua getmetatable()
+
+	lua_pushliteral(L, "__index");
+	lua_pushvalue(L, methodtable);
+	lua_settable(L, metatable);
+
+	lua_pushliteral(L, "__gc");
+	lua_pushcfunction(L, gc_object);
+	lua_settable(L, metatable);
+
+	lua_pop(L, 1); // Drop metatable
+
+	luaL_openlib(L, 0, methods, 0); // fill methodtable
+	lua_pop(L, 1);			// Drop methodtable
+}
+
+void ModChannelRef::create(lua_State *L, ModChannel *channel)
+{
+	ModChannelRef *o = new ModChannelRef(channel);
+	*(void **)(lua_newuserdata(L, sizeof(void *))) = o;
+	luaL_getmetatable(L, className);
+	lua_setmetatable(L, -2);
+}
+
+int ModChannelRef::gc_object(lua_State *L)
+{
+	ModChannelRef *o = *(ModChannelRef **)(lua_touserdata(L, 1));
+	delete o;
+	return 0;
+}
+
+ModChannelRef *ModChannelRef::checkobject(lua_State *L, int narg)
+{
+	luaL_checktype(L, narg, LUA_TUSERDATA);
+
+	void *ud = luaL_checkudata(L, narg, className);
+	if (!ud)
+		luaL_typerror(L, narg, className);
+
+	return *(ModChannelRef **)ud; // unbox pointer
+}
+
+ModChannel *ModChannelRef::getobject(ModChannelRef *ref)
+{
+	return ref->m_modchannel;
+}
+
+// clang-format off
+const char ModChannelRef::className[] = "ModChannelRef";
+const luaL_Reg ModChannelRef::methods[] = {
+	luamethod(ModChannelRef, leave),
+	luamethod(ModChannelRef, is_writeable),
+	luamethod(ModChannelRef, send_all),
+	{0, 0},
+};
+// clang-format on
diff --git a/src/script/lua_api/l_modchannels.h b/src/script/lua_api/l_modchannels.h
new file mode 100644
index 000000000..dbbf11a05
--- /dev/null
+++ b/src/script/lua_api/l_modchannels.h
@@ -0,0 +1,66 @@
+/*
+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.
+*/
+
+#pragma once
+
+#include "lua_api/l_base.h"
+#include "config.h"
+
+class ModChannel;
+
+class ModApiChannels : public ModApiBase
+{
+private:
+	// mod_channel_join(name)
+	static int l_mod_channel_join(lua_State *L);
+
+public:
+	static void Initialize(lua_State *L, int top);
+};
+
+class ModChannelRef : public ModApiBase
+{
+public:
+	ModChannelRef(ModChannel *modchannel);
+	~ModChannelRef() = default;
+
+	static void Register(lua_State *L);
+	static void create(lua_State *L, ModChannel *channel);
+
+	// leave()
+	static int l_leave(lua_State *L);
+
+	// send(message)
+	static int l_send_all(lua_State *L);
+
+	// is_writeable()
+	static int l_is_writeable(lua_State *L);
+
+private:
+	// garbage collector
+	static int gc_object(lua_State *L);
+
+	static ModChannelRef *checkobject(lua_State *L, int narg);
+	static ModChannel *getobject(ModChannelRef *ref);
+
+	ModChannel *m_modchannel = nullptr;
+
+	static const char className[];
+	static const luaL_Reg methods[];
+};