3 Copyright (C) 2010-2013 celeron55, Perttu Ahola <celeron55@gmail.com>
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU Lesser General Public License as published by
7 the Free Software Foundation; either version 2.1 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public License along
16 with this program; if not, write to the Free Software Foundation, Inc.,
17 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
26 #include "serialization.h" // For SER_FMT_VER_INVALID
27 #include "content/mods.h"
28 #include "inventorymanager.h"
29 #include "content/subgames.h"
30 #include "tileanimation.h" // TileAnimationParams
31 #include "particles.h" // ParticleParams
32 #include "network/peerhandler.h"
33 #include "network/address.h"
34 #include "util/numeric.h"
35 #include "util/thread.h"
36 #include "util/basic_macros.h"
37 #include "util/metricsbackend.h"
38 #include "serverenvironment.h"
39 #include "clientiface.h"
40 #include "chatmessage.h"
41 #include "translation.h"
46 #include <unordered_set>
51 class IWritableItemDefManager;
53 class IWritableCraftDefManager;
60 struct PlayerHPChangeReason;
61 class IRollbackManager;
62 struct RollbackAction;
64 class ServerScripting;
65 class ServerEnvironment;
66 struct SimpleSoundSpec;
74 class ServerModManager;
75 class ServerInventoryManager;
78 enum ClientDeletionReason {
87 std::string sha1_digest; // base64-encoded
88 bool no_announce; // true: not announced in TOCLIENT_ANNOUNCE_MEDIA (at player join)
90 MediaInfo(const std::string &path_="",
91 const std::string &sha1_digest_=""):
93 sha1_digest(sha1_digest_),
99 struct ServerSoundParams
110 float max_hear_distance = 32 * BS;
113 std::string to_player = "";
114 std::string exclude_player = "";
116 v3f getPos(ServerEnvironment *env, bool *pos_exists) const;
119 struct ServerPlayingSound
121 ServerSoundParams params;
122 SimpleSoundSpec spec;
123 std::unordered_set<session_t> clients; // peer ids
127 MinimapType type = MINIMAP_TYPE_OFF;
134 // structure for everything getClientInfo returns, for convenience
141 u8 major, minor, patch;
142 std::string vers_string, lang_code;
145 class Server : public con::PeerHandler, public MapEventReceiver,
150 NOTE: Every public method should be thread-safe
154 const std::string &path_world,
155 const SubgameSpec &gamespec,
156 bool simple_singleplayer_mode,
159 ChatInterface *iface = nullptr,
160 std::string *on_shutdown_errmsg = nullptr
163 DISABLE_CLASS_COPY(Server);
167 // This is mainly a way to pass the time to the server.
168 // Actual processing is done in an another thread.
169 void step(float dtime);
170 // This is run by ServerThread and does the actual processing
171 void AsyncRunStep(bool initial_step=false);
173 PlayerSAO* StageTwoClientInit(session_t peer_id);
179 void handleCommand(NetworkPacket* pkt);
181 void handleCommand_Null(NetworkPacket* pkt) {};
182 void handleCommand_Deprecated(NetworkPacket* pkt);
183 void handleCommand_Init(NetworkPacket* pkt);
184 void handleCommand_Init2(NetworkPacket* pkt);
185 void handleCommand_ModChannelJoin(NetworkPacket *pkt);
186 void handleCommand_ModChannelLeave(NetworkPacket *pkt);
187 void handleCommand_ModChannelMsg(NetworkPacket *pkt);
188 void handleCommand_RequestMedia(NetworkPacket* pkt);
189 void handleCommand_ClientReady(NetworkPacket* pkt);
190 void handleCommand_GotBlocks(NetworkPacket* pkt);
191 void handleCommand_PlayerPos(NetworkPacket* pkt);
192 void handleCommand_DeletedBlocks(NetworkPacket* pkt);
193 void handleCommand_InventoryAction(NetworkPacket* pkt);
194 void handleCommand_ChatMessage(NetworkPacket* pkt);
195 void handleCommand_Damage(NetworkPacket* pkt);
196 void handleCommand_PlayerItem(NetworkPacket* pkt);
197 void handleCommand_Respawn(NetworkPacket* pkt);
198 void handleCommand_Interact(NetworkPacket* pkt);
199 void handleCommand_RemovedSounds(NetworkPacket* pkt);
200 void handleCommand_NodeMetaFields(NetworkPacket* pkt);
201 void handleCommand_InventoryFields(NetworkPacket* pkt);
202 void handleCommand_FirstSrp(NetworkPacket* pkt);
203 void handleCommand_SrpBytesA(NetworkPacket* pkt);
204 void handleCommand_SrpBytesM(NetworkPacket* pkt);
205 void handleCommand_HaveMedia(NetworkPacket *pkt);
207 void ProcessData(NetworkPacket *pkt);
209 void Send(NetworkPacket *pkt);
210 void Send(session_t peer_id, NetworkPacket *pkt);
212 // Helper for handleCommand_PlayerPos and handleCommand_Interact
213 void process_PlayerPos(RemotePlayer *player, PlayerSAO *playersao,
216 // Both setter and getter need no envlock,
217 // can be called freely from threads
218 void setTimeOfDay(u32 time);
221 Shall be called with the environment locked.
222 This is accessed by the map, which is inside the environment,
223 so it shouldn't be a problem.
225 void onMapEditEvent(const MapEditEvent &event);
227 // Connection must be locked when called
228 std::string getStatusString();
229 inline double getUptime() const { return m_uptime_counter->get(); }
231 // read shutdown state
232 inline bool isShutdownRequested() const { return m_shutdown_state.is_requested; }
234 // request server to shutdown
235 void requestShutdown(const std::string &msg, bool reconnect, float delay = 0.0f);
237 // Returns -1 if failed, sound handle on success
239 s32 playSound(const SimpleSoundSpec &spec, const ServerSoundParams ¶ms,
240 bool ephemeral=false);
241 void stopSound(s32 handle);
242 void fadeSound(s32 handle, float step, float gain);
245 std::set<std::string> getPlayerEffectivePrivs(const std::string &name);
246 bool checkPriv(const std::string &name, const std::string &priv);
247 void reportPrivsModified(const std::string &name=""); // ""=all
248 void reportInventoryFormspecModified(const std::string &name);
249 void reportFormspecPrependModified(const std::string &name);
251 void setIpBanned(const std::string &ip, const std::string &name);
252 void unsetIpBanned(const std::string &ip_or_name);
253 std::string getBanDescription(const std::string &ip_or_name);
255 void notifyPlayer(const char *name, const std::wstring &msg);
256 void notifyPlayers(const std::wstring &msg);
258 void spawnParticle(const std::string &playername,
259 const ParticleParameters &p);
261 u32 addParticleSpawner(const ParticleSpawnerParameters &p,
262 ServerActiveObject *attached, const std::string &playername);
264 void deleteParticleSpawner(const std::string &playername, u32 id);
266 bool dynamicAddMedia(std::string filepath, u32 token,
267 const std::string &to_player, bool ephemeral);
269 ServerInventoryManager *getInventoryMgr() const { return m_inventory_mgr.get(); }
270 void sendDetachedInventory(Inventory *inventory, const std::string &name, session_t peer_id);
272 // Envlock and conlock should be locked when using scriptapi
273 ServerScripting *getScriptIface(){ return m_script; }
275 // actions: time-reversed list
276 // Return value: success/failure
277 bool rollbackRevertActions(const std::list<RollbackAction> &actions,
278 std::list<std::string> *log);
280 // IGameDef interface
282 virtual IItemDefManager* getItemDefManager();
283 virtual const NodeDefManager* getNodeDefManager();
284 virtual ICraftDefManager* getCraftDefManager();
285 virtual u16 allocateUnknownNodeId(const std::string &name);
286 IRollbackManager *getRollbackManager() { return m_rollback; }
287 virtual EmergeManager *getEmergeManager() { return m_emerge; }
288 virtual ModMetadataDatabase *getModStorageDatabase() { return m_mod_storage_database; }
290 IWritableItemDefManager* getWritableItemDefManager();
291 NodeDefManager* getWritableNodeDefManager();
292 IWritableCraftDefManager* getWritableCraftDefManager();
294 virtual const std::vector<ModSpec> &getMods() const;
295 virtual const ModSpec* getModSpec(const std::string &modname) const;
296 static std::string getBuiltinLuaPath();
297 virtual std::string getWorldPath() const { return m_path_world; }
299 inline bool isSingleplayer() const
300 { return m_simple_singleplayer_mode; }
302 inline void setAsyncFatalError(const std::string &error)
303 { m_async_fatal_error.set(error); }
304 inline void setAsyncFatalError(const LuaError &e)
306 setAsyncFatalError(std::string("Lua: ") + e.what());
309 bool showFormspec(const char *name, const std::string &formspec, const std::string &formname);
310 Map & getMap() { return m_env->getMap(); }
311 ServerEnvironment & getEnv() { return *m_env; }
314 u32 hudAdd(RemotePlayer *player, HudElement *element);
315 bool hudRemove(RemotePlayer *player, u32 id);
316 bool hudChange(RemotePlayer *player, u32 id, HudElementStat stat, void *value);
317 bool hudSetFlags(RemotePlayer *player, u32 flags, u32 mask);
318 bool hudSetHotbarItemcount(RemotePlayer *player, s32 hotbar_itemcount);
319 void hudSetHotbarImage(RemotePlayer *player, const std::string &name);
320 void hudSetHotbarSelectedImage(RemotePlayer *player, const std::string &name);
322 Address getPeerAddress(session_t peer_id);
324 void setLocalPlayerAnimations(RemotePlayer *player, v2s32 animation_frames[4],
326 void setPlayerEyeOffset(RemotePlayer *player, const v3f &first, const v3f &third);
328 void setSky(RemotePlayer *player, const SkyboxParams ¶ms);
329 void setSun(RemotePlayer *player, const SunParams ¶ms);
330 void setMoon(RemotePlayer *player, const MoonParams ¶ms);
331 void setStars(RemotePlayer *player, const StarParams ¶ms);
333 void setClouds(RemotePlayer *player, const CloudParams ¶ms);
335 void overrideDayNightRatio(RemotePlayer *player, bool do_override, float brightness);
337 void setLighting(RemotePlayer *player, const Lighting &lighting);
339 void RespawnPlayer(session_t peer_id);
341 /* con::PeerHandler implementation. */
342 void peerAdded(con::Peer *peer);
343 void deletingPeer(con::Peer *peer, bool timeout);
345 void DenySudoAccess(session_t peer_id);
346 void DenyAccess(session_t peer_id, AccessDeniedCode reason,
347 const std::string &custom_reason = "", bool reconnect = false);
348 void acceptAuth(session_t peer_id, bool forSudoMode);
349 void DisconnectPeer(session_t peer_id);
350 bool getClientConInfo(session_t peer_id, con::rtt_stat_type type, float *retval);
351 bool getClientInfo(session_t peer_id, ClientInfo &ret);
353 void printToConsoleOnly(const std::string &text);
355 void HandlePlayerHPChange(PlayerSAO *sao, const PlayerHPChangeReason &reason);
356 void SendPlayerHP(PlayerSAO *sao);
357 void SendPlayerBreath(PlayerSAO *sao);
358 void SendInventory(PlayerSAO *playerSAO, bool incremental);
359 void SendMovePlayer(session_t peer_id);
360 void SendPlayerSpeed(session_t peer_id, const v3f &added_vel);
361 void SendPlayerFov(session_t peer_id);
363 void SendMinimapModes(session_t peer_id,
364 std::vector<MinimapMode> &modes,
367 void sendDetachedInventories(session_t peer_id, bool incremental);
369 virtual bool registerModStorage(ModMetadata *storage);
370 virtual void unregisterModStorage(const std::string &name);
372 bool joinModChannel(const std::string &channel);
373 bool leaveModChannel(const std::string &channel);
374 bool sendModChannelMessage(const std::string &channel, const std::string &message);
375 ModChannel *getModChannel(const std::string &channel);
377 // Send block to specific player only
378 bool SendBlock(session_t peer_id, const v3s16 &blockpos);
380 // Get or load translations for a language
381 Translations *getTranslationLanguage(const std::string &lang_code);
383 static ModMetadataDatabase *openModStorageDatabase(const std::string &world_path);
385 static ModMetadataDatabase *openModStorageDatabase(const std::string &backend,
386 const std::string &world_path, const Settings &world_mt);
388 static bool migrateModStorageDatabase(const GameParams &game_params,
389 const Settings &cmd_args);
391 // Lua files registered for init of async env, pair of modname + path
392 std::vector<std::pair<std::string, std::string>> m_async_init_files;
394 // Data transferred into async envs at init time
395 std::unique_ptr<PackedValue> m_async_globals_data;
400 // Environment mutex (envlock)
401 std::mutex m_env_mutex;
404 friend class EmergeThread;
405 friend class RemoteClient;
406 friend class TestServerShutdownState;
408 struct ShutdownState {
409 friend class TestServerShutdownState;
411 bool is_requested = false;
412 bool should_reconnect = false;
416 void trigger(float delay, const std::string &msg, bool reconnect);
417 void tick(float dtime, Server *server);
418 std::wstring getShutdownTimerMessage() const;
419 bool isTimerRunning() const { return m_timer > 0.0f; }
421 float m_timer = 0.0f;
424 struct PendingDynamicMediaCallback {
425 std::string filename; // only set if media entry and file is to be deleted
427 std::unordered_set<session_t> waiting_players;
430 // The standard library does not implement std::hash for pairs so we have this:
432 size_t operator() (const std::pair<v3s16, u16> &p) const {
433 return std::hash<v3s16>()(p.first) ^ p.second;
437 typedef std::unordered_map<std::pair<v3s16, u16>, std::string, SBCHash> SerializedBlockCache;
441 void SendMovement(session_t peer_id);
442 void SendHP(session_t peer_id, u16 hp);
443 void SendBreath(session_t peer_id, u16 breath);
444 void SendAccessDenied(session_t peer_id, AccessDeniedCode reason,
445 const std::string &custom_reason, bool reconnect = false);
446 void SendAccessDenied_Legacy(session_t peer_id, const std::wstring &reason);
447 void SendDeathscreen(session_t peer_id, bool set_camera_point_target,
448 v3f camera_point_target);
449 void SendItemDef(session_t peer_id, IItemDefManager *itemdef, u16 protocol_version);
450 void SendNodeDef(session_t peer_id, const NodeDefManager *nodedef,
451 u16 protocol_version);
453 /* mark blocks not sent for all clients */
454 void SetBlocksNotSent(std::map<v3s16, MapBlock *>& block);
457 virtual void SendChatMessage(session_t peer_id, const ChatMessage &message);
458 void SendTimeOfDay(session_t peer_id, u16 time, f32 time_speed);
460 void SendLocalPlayerAnimations(session_t peer_id, v2s32 animation_frames[4],
461 f32 animation_speed);
462 void SendEyeOffset(session_t peer_id, v3f first, v3f third);
463 void SendPlayerPrivileges(session_t peer_id);
464 void SendPlayerInventoryFormspec(session_t peer_id);
465 void SendPlayerFormspecPrepend(session_t peer_id);
466 void SendShowFormspecMessage(session_t peer_id, const std::string &formspec,
467 const std::string &formname);
468 void SendHUDAdd(session_t peer_id, u32 id, HudElement *form);
469 void SendHUDRemove(session_t peer_id, u32 id);
470 void SendHUDChange(session_t peer_id, u32 id, HudElementStat stat, void *value);
471 void SendHUDSetFlags(session_t peer_id, u32 flags, u32 mask);
472 void SendHUDSetParam(session_t peer_id, u16 param, const std::string &value);
473 void SendSetSky(session_t peer_id, const SkyboxParams ¶ms);
474 void SendSetSun(session_t peer_id, const SunParams ¶ms);
475 void SendSetMoon(session_t peer_id, const MoonParams ¶ms);
476 void SendSetStars(session_t peer_id, const StarParams ¶ms);
477 void SendCloudParams(session_t peer_id, const CloudParams ¶ms);
478 void SendOverrideDayNightRatio(session_t peer_id, bool do_override, float ratio);
479 void SendSetLighting(session_t peer_id, const Lighting &lighting);
480 void broadcastModChannelMessage(const std::string &channel,
481 const std::string &message, session_t from_peer);
484 Send a node removal/addition event to all clients except ignore_id.
485 Additionally, if far_players!=NULL, players further away than
486 far_d_nodes are ignored and their peer_ids are added to far_players
488 // Envlock and conlock should be locked when calling these
489 void sendRemoveNode(v3s16 p, std::unordered_set<u16> *far_players = nullptr,
490 float far_d_nodes = 100);
491 void sendAddNode(v3s16 p, MapNode n,
492 std::unordered_set<u16> *far_players = nullptr,
493 float far_d_nodes = 100, bool remove_metadata = true);
495 void sendMetadataChanged(const std::unordered_set<v3s16> &positions,
496 float far_d_nodes = 100);
498 // Environment and Connection must be locked when called
499 // `cache` may only be very short lived! (invalidation not handeled)
500 void SendBlockNoLock(session_t peer_id, MapBlock *block, u8 ver,
501 u16 net_proto_version, SerializedBlockCache *cache = nullptr);
503 // Sends blocks to clients (locks env and con on its own)
504 void SendBlocks(float dtime);
506 bool addMediaFile(const std::string &filename, const std::string &filepath,
507 std::string *filedata = nullptr, std::string *digest = nullptr);
508 void fillMediaCache();
509 void sendMediaAnnouncement(session_t peer_id, const std::string &lang_code);
510 void sendRequestedMedia(session_t peer_id,
511 const std::vector<std::string> &tosend);
512 void stepPendingDynMediaCallbacks(float dtime);
514 // Adds a ParticleSpawner on peer with peer_id (PEER_ID_INEXISTENT == all)
515 void SendAddParticleSpawner(session_t peer_id, u16 protocol_version,
516 const ParticleSpawnerParameters &p, u16 attached_id, u32 id);
518 void SendDeleteParticleSpawner(session_t peer_id, u32 id);
520 // Spawns particle on peer with peer_id (PEER_ID_INEXISTENT == all)
521 void SendSpawnParticle(session_t peer_id, u16 protocol_version,
522 const ParticleParameters &p);
524 void SendActiveObjectRemoveAdd(RemoteClient *client, PlayerSAO *playersao);
525 void SendActiveObjectMessages(session_t peer_id, const std::string &datas,
526 bool reliable = true);
527 void SendCSMRestrictionFlags(session_t peer_id);
533 void HandlePlayerDeath(PlayerSAO* sao, const PlayerHPChangeReason &reason);
534 void DeleteClient(session_t peer_id, ClientDeletionReason reason);
535 void UpdateCrafting(RemotePlayer *player);
536 bool checkInteractDistance(RemotePlayer *player, const f32 d, const std::string &what);
538 void handleChatInterfaceEvent(ChatEvent *evt);
540 // This returns the answer to the sender of wmessage, or "" if there is none
541 std::wstring handleChat(const std::string &name, std::wstring wmessage_input,
542 bool check_shout_priv = false, RemotePlayer *player = nullptr);
543 void handleAdminChat(const ChatEventChat *evt);
545 // When called, connection mutex should be locked
546 RemoteClient* getClient(session_t peer_id, ClientState state_min = CS_Active);
547 RemoteClient* getClientNoEx(session_t peer_id, ClientState state_min = CS_Active);
549 // When called, environment mutex should be locked
550 std::string getPlayerName(session_t peer_id);
551 PlayerSAO *getPlayerSAO(session_t peer_id);
554 Get a player from memory or creates one.
555 If player is already connected, return NULL
556 Does not verify/modify auth info and password.
558 Call with env and con locked.
560 PlayerSAO *emergePlayer(const char *name, session_t peer_id, u16 proto_version);
562 void handlePeerChanges();
568 std::string m_path_world;
569 // Subgame specification
570 SubgameSpec m_gamespec;
571 // If true, do not allow multiple players and hide some multiplayer
573 bool m_simple_singleplayer_mode;
574 u16 m_max_chatmessage_length;
575 // For "dedicated" server list flag
577 Settings *m_game_settings = nullptr;
579 // Thread can set; step() will throw as ServerError
580 MutexedVariable<std::string> m_async_fatal_error;
583 float m_liquid_transform_timer = 0.0f;
584 float m_liquid_transform_every = 1.0f;
585 float m_masterserver_timer = 0.0f;
586 float m_emergethread_trigger_timer = 0.0f;
587 float m_savemap_timer = 0.0f;
588 IntervalLimiter m_map_timer_and_unload_interval;
591 ServerEnvironment *m_env = nullptr;
593 // Reference to the server map until ServerEnvironment is initialized
594 // after that this variable must be a nullptr
595 ServerMap *m_startup_server_map = nullptr;
598 std::shared_ptr<con::Connection> m_con;
601 BanManager *m_banmanager = nullptr;
603 // Rollback manager (behind m_env_mutex)
604 IRollbackManager *m_rollback = nullptr;
607 EmergeManager *m_emerge = nullptr;
610 // Envlock and conlock should be locked when using Lua
611 ServerScripting *m_script = nullptr;
613 // Item definition manager
614 IWritableItemDefManager *m_itemdef;
616 // Node definition manager
617 NodeDefManager *m_nodedef;
619 // Craft definition manager
620 IWritableCraftDefManager *m_craftdef;
623 std::unique_ptr<ServerModManager> m_modmgr;
625 std::unordered_map<std::string, Translations> server_translations;
630 // A buffer for time steps
631 // step() increments and AsyncRunStep() run by m_thread reads it.
632 float m_step_dtime = 0.0f;
633 std::mutex m_step_dtime_mutex;
635 // The server mainly operates in this thread
636 ServerThread *m_thread = nullptr;
641 // Timer for sending time of day over network
642 float m_time_of_day_send_timer = 0.0f;
647 ClientInterface m_clients;
651 Queues stuff from peerAdded() and deletingPeer() to
654 std::queue<con::PeerChange> m_peer_change_queue;
656 std::unordered_map<session_t, std::string> m_formspec_state_data;
662 ShutdownState m_shutdown_state;
664 ChatInterface *m_admin_chat;
665 std::string m_admin_nick;
667 // if a mod-error occurs in the on_shutdown callback, the error message will
668 // be written into this
669 std::string *const m_on_shutdown_errmsg;
672 Map edit event queue. Automatically receives all map edits.
673 The constructor of this class registers us to receive them through
676 NOTE: Should these be moved to actually be members of
681 Queue of map edits from the environment for sending to the clients
682 This is behind m_env_mutex
684 std::queue<MapEditEvent*> m_unsent_map_edit_queue;
686 If a non-empty area, map edit events contained within are left
687 unsent. Done at map generation time to speed up editing of the
688 generated area, as it will be sent anyway.
689 This is behind m_env_mutex
691 VoxelArea m_ignore_map_edit_events_area;
693 // media files known to server
694 std::unordered_map<std::string, MediaInfo> m_media;
696 // pending dynamic media callbacks, clients inform the server when they have a file fetched
697 std::unordered_map<u32, PendingDynamicMediaCallback> m_pending_dyn_media;
698 float m_step_pending_dyn_media_timer = 0.0f;
703 std::unordered_map<s32, ServerPlayingSound> m_playing_sounds;
704 s32 m_next_sound_id = 0; // positive values only
707 std::unordered_map<std::string, ModMetadata *> m_mod_storages;
708 ModMetadataDatabase *m_mod_storage_database = nullptr;
709 float m_mod_storage_save_timer = 10.0f;
711 // CSM restrictions byteflag
712 u64 m_csm_restriction_flags = CSMRestrictionFlags::CSM_RF_NONE;
713 u32 m_csm_restriction_noderange = 8;
715 // ModChannel manager
716 std::unique_ptr<ModChannelMgr> m_modchannel_mgr;
719 std::unique_ptr<ServerInventoryManager> m_inventory_mgr;
721 // Global server metrics backend
722 std::unique_ptr<MetricsBackend> m_metrics_backend;
725 MetricCounterPtr m_uptime_counter;
726 MetricGaugePtr m_player_gauge;
727 MetricGaugePtr m_timeofday_gauge;
728 MetricGaugePtr m_lag_gauge;
729 MetricCounterPtr m_aom_buffer_counter[2]; // [0] = rel, [1] = unrel
730 MetricCounterPtr m_packet_recv_counter;
731 MetricCounterPtr m_packet_recv_processed_counter;
732 MetricCounterPtr m_map_edit_event_counter;
736 Runs a simple dedicated server loop.
738 Shuts down when kill is set to true.
740 void dedicated_server_loop(Server &server, bool &kill);