Part 3: Multiplayer WebSocket Game server written in C using libuv & libwebsockets & Cocos2d-x-HTML5

In this file all the game logic is happening ,

1. Start game loop timer.
2. Establish the client connection.  
3. The WebSocket request received from client connection.
4. The connection is kept in hash map. 
5. From the game loop response back to the client after processing the data.
6. Updates other clients about the current client . 

Main assumptions on event driven servers , the requests must be received none stop and be able to none block it on any conditions,
Remember no threads here per connection .
Each request will call callback function that the server must handle asynchronously.
The client and the server have pre defined simple protocol which defined and inform both sides
about the state they are in .
This is the state protocol used in this tutorial :

0 : login
1 : login success acknowledgment
2 : send move request
3 : response move acknowledgment
4 : other player register
5 : other player movment
6 : delete user from client
7 : gem scatter
8 : gem eat and score increment 
9 : gem eat and score increment acknowledgment
game_handler.c 

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/******************************************************* Copyright (C) 2016 meiry242@gmail.com This file is part of http://www.gamedevcraft.com . Author : Meir yanovich ********************************************************/ #include "game_handler.h" #include "simplog.h" extern int debug_level; connection_num_as_id = 0; Hashmap *users_map_main = NULL; //Array *gems_array = NULL; uv_timer_t timeout_watcher; static bool str_eq(void *key_a, void *key_b) { return !strcmp((const char *)key_a, (const char *)key_b); } /* use djb hash unless we find it inadequate */ static int str_hash_fn(void *str) { uint32_t hash = 5381; char *p; for (p = str; p && *p; p++) { hash = ((hash << 5) + hash) + *p; } return (int)hash; } static int c = 0; //generate random gems in the game bool generate_random_gems(int num_of_gems, gem_types gem_type) { if (gems_array == NULL) { gems_array = arrayCreate(); } int array_size = arraySize(gems_array); //960, 640 for (int i = array_size; i < (array_size+num_of_gems); i++) { struct gem_data *gemdata = malloc(sizeof * gemdata); //r = (rand() % (max + 1 - min)) + min int rw = (rand() % (900 + 1 - 50)) + 50; //returns a pseudo-random integer between x resolution size 0 -> width int rh = (rand() % (600 + 1 - 50)) + 50; //returns a pseudo-random integer between x resolution size 0 -> height lwsl_notice("c:%d type:%d width %d height %d\n", c, gem_type, rw, rh); gemdata->type = gem_type; gemdata->x = rw; gemdata->y = rh; gemdata->collide_with_player = false; arrayAdd(gems_array, gemdata); c++; } return true; } struct session_holder_data * set_session_holder_data(bool(*cp)(void*, void*, void*), struct per_session_data__apigataway *_pss) { struct session_holder_data *session_holder_data_tmp = malloc(sizeof * session_holder_data_tmp); session_holder_data_tmp->found = false; session_holder_data_tmp->current_session_player_id = _pss->player_id; session_holder_data_tmp->players_session_holder = arrayCreate(); hashmapForEach(users_map_main, cp, session_holder_data_tmp); return session_holder_data_tmp; } void send_response(cJSON *_root_respose,struct per_session_data__apigataway *_other_p_session, struct per_session_data__apigataway *_pss) { unsigned char response_to_other_client[LWS_PRE + 1024]; unsigned char *p_response_to_other_client = &response_to_other_client[LWS_PRE]; char* resp_json = cJSON_Print(_root_respose); int n = sprintf((char *)p_response_to_other_client, "%s", resp_json); lwsl_notice("send_response to client [%s] %s\n", _other_p_session->player_name, resp_json); LOG_PRINT("send_response to client [%s] %s\n", _other_p_session->player_name, resp_json); //lwsl_notice("[%s] send response to client [%s] from server on registrator: %s \n", _pss->player_name, _other_p_session->player_name, p_response_to_other_client); //LOG_PRINT("[%s] send response to client [%s] from server on registrator: %s \n", _pss->player_name, _other_p_session->player_name, p_response_to_other_client); //each player has its own copy of libwebsockets (lws in short ) wsi , whitch is the player channel + session pointer int m = lws_write(_other_p_session->player_wsi, p_response_to_other_client, n, LWS_WRITE_BINARY); if (m < n) { lwsl_err("ERROR %d writing to di socket on registrator\n", sizeof(response_to_other_client)); LOG_PRINT("ERROR %d writing to di socket on movment\n", sizeof(response_to_other_client)); } } //preper inform about this user which is dead ( disconnected from the game ) static bool user_is_dead_cp(void* key, void* value, void* context) { struct session_holder_data *session_holder_data_tmp = (struct session_holder_data *)context; //It is not the current user //lwsl_notice("key: '%s' current_session_player_id: '%s'\n", (char *)key, (char *)session_holder_data_tmp->current_session_player_id); if (strcmp(key, session_holder_data_tmp->current_session_player_id) != 0) { //set the holder arrayAdd(session_holder_data_tmp->players_session_holder, (struct per_session_data__apigataway *)value); } return true; } //check and handle other users static bool check_other_users_cp(void* key, void* value, void* context) { struct session_holder_data *session_holder_data_tmp = (struct session_holder_data *)context; //It is not the current user //lwsl_notice("key: '%s' current_session_player_id: '%s'\n", (char *)key, (char *)session_holder_data_tmp->current_session_player_id); if (strcmp(key, session_holder_data_tmp->current_session_player_id) != 0) { //set the holder arrayAdd(session_holder_data_tmp->players_session_holder, (struct per_session_data__apigataway *)value); } return true; } //check and handle other movments static bool check_other_users_movment_cp(void* key, void* value, void* context) { struct session_holder_data *session_holder_data_tmp = (struct session_holder_data *)context; //It is not the current user //lwsl_notice("key: '%s' current_session_player_id: '%s'\n", (char *)key, (char *)session_holder_data_tmp->current_session_player_id); //LOG_PRINT("key: '%s' current_session_player_id: '%s'\n", (char *)key, (char *)session_holder_data_tmp->current_session_player_id); if (strcmp(key, session_holder_data_tmp->current_session_player_id) != 0) { //set the holder arrayAdd(session_holder_data_tmp->players_session_holder, (struct per_session_data__apigataway *)value); } return true; } //check and handle other score update static bool check_other_users_gemscore_cp(void* key, void* value, void* context) { struct session_holder_data *session_holder_data_tmp = (struct session_holder_data *)context; //It is not the current user //lwsl_notice("key: '%s' current_session_player_id: '%s'\n", (char *)key, (char *)session_holder_data_tmp->current_session_player_id); //LOG_PRINT("key: '%s' current_session_player_id: '%s'\n", (char *)key, (char *)session_holder_data_tmp->current_session_player_id); if (strcmp(key, session_holder_data_tmp->current_session_player_id) != 0) { //set the holder arrayAdd(session_holder_data_tmp->players_session_holder, (struct per_session_data__apigataway *)value); } return true; } //response to every 100ms game loop tick static bool response_to_client_cp(void* key, void* value, void* context) { bool doInvokeResponse = false; int hash_map_size = hashmapSize(users_map_main); if (hash_map_size > 0) { //when response is created there is need to define buffer to hold the response //libwebsokets way there need for pedding left:LWS_PRE struct per_session_data__apigataway *pss = (struct per_session_data__apigataway *)hashmapGet(users_map_main, (char *)key); char* resp_jsont = cJSON_Print(pss->user_json_respose); //lwsl_notice("INSIDE RESPONSE_TO_CLIENT_CP pss->user_json_respose: %s \n", resp_jsont); //LOG_PRINT("INSIDE RESPONSE_TO_CLIENT_CP pss->user_json_respose: %s \n", resp_jsont); //first on registretion the server scatter the gems if (pss->status == 0 && pss->done_srv_update == true) { cJSON *root_respose = build_gems_scatter_json(pss); doInvokeResponse = true; pss->user_json_respose = root_respose; char* resp_json = cJSON_Print(pss->user_json_respose); lwsl_notice("Response to client gems from server: %s \n",resp_json); send_response_to_current_player(pss); } //response json by state of the user //state 1 registretion : if (pss->status == 0 && pss->done_srv_update == true) { //update it to 1 so registretion will invoked only once per conneting user pss->status =1; cJSON *root_respose = build_player_json_registrator(pss); doInvokeResponse = true; //check if there is other players that registed beside you int user_hash_size = hashmapSize(users_map_main); //lwsl_notice("response_to_client_cp : user_hash_size: %d \n", user_hash_size); if (user_hash_size > 1) { struct session_holder_data *session_holder_data_tmp = set_session_holder_data(check_other_users_cp, pss); //now we have the others users which we need to update the current user //preper the other players session structures cJSON* players; int i = 0; int size = arraySize(session_holder_data_tmp->players_session_holder); if (size > 0) { players = cJSON_CreateArray(); while (i < size) { struct per_session_data__apigataway *other_p_session = arrayGet(session_holder_data_tmp->players_session_holder, i); //build json of player cJSON* player = build_player_json_registrator(other_p_session); cJSON_InsertItemInArray(players, i, player); //send current player to other players //change only for this response the json to: "4 : other player" int status = cJSON_GetObjectItem(root_respose, "status")->valueint; //BUG in cJSON need to update also valuedouble when updating valueint //https://sourceforge.net/p/cjson/discussion/998969/thread/813ba29b/ cJSON_GetObjectItem(root_respose, "status")->valueint = 4; cJSON_GetObjectItem(root_respose, "status")->valuedouble = 4; //send to client send_response(root_respose,other_p_session,pss); //set back the original status cJSON_GetObjectItem(root_respose, "status")->valueint = status; cJSON_GetObjectItem(root_respose, "status")->valuedouble = status; // Move to next. i++; } cJSON_AddItemToObject(root_respose, "players", players); arrayFree(session_holder_data_tmp->players_session_holder); free(session_holder_data_tmp); } } pss->user_json_respose = root_respose; } else if (pss->status == 2 && pss->done_srv_update == true) //movment state { pss->status =3; //aprove movment state //for current session doInvokeResponse = true; cJSON *root_respose = build_player_json_movment(pss); //lwsl_notice("RESPONSE START pss->request_from_client_buf Movment 2: %s \n", pss->request_from_client_buf); //LOG_PRINT("RESPONSE START pss->request_from_client_buf Movmente 2: %s \n", pss->request_from_client_buf); if (pss->collision_status == 8) { //gem eat and score increment acknowledgment pss->collision_status = 9; root_respose = build_gems_score_json(pss); lwsl_notice("RESPONSE MIDELL pss->collision_status: %d \n", pss->collision_status); LOG_PRINT("RESPONSE MIDELL pss->collision_status: %d \n", pss->collision_status); } //lwsl_notice("RESPONSE pss->request_from_client_buf Movment 2: %s \n", pss->request_from_client_buf); //LOG_PRINT("RESPONSE pss->request_from_client_buf Movmente 2: %s \n", pss->request_from_client_buf); int user_hash_size = hashmapSize(users_map_main); //lwsl_notice("response_to_client_cp : user_hash_size: %d \n", user_hash_size); if (user_hash_size > 1) { //create tmp game users session data holder struct session_holder_data *session_holder_data_tmp = set_session_holder_data(check_other_users_movment_cp, pss); int i = 0; //check if there are more users then current player int size = arraySize(session_holder_data_tmp->players_session_holder); if (size > 0) { while (i < size) { struct per_session_data__apigataway *other_p_session = arrayGet(session_holder_data_tmp->players_session_holder, i); //send current player to other players //change the status only for this response the json status param to: "4 : other player" int status = cJSON_GetObjectItem(root_respose, "status")->valueint; //BUG in cJSON need to update also valuedouble when updating valueint //https://sourceforge.net/p/cjson/discussion/998969/thread/813ba29b/ cJSON_GetObjectItem(root_respose, "status")->valueint = 5; cJSON_GetObjectItem(root_respose, "status")->valuedouble = 5; char* resp_json = cJSON_Print(root_respose); //send to client send_response(root_respose, other_p_session, pss); //set back the original status cJSON_GetObjectItem(root_respose, "status")->valueint = status; cJSON_GetObjectItem(root_respose, "status")->valuedouble = status; // Move to next. i++; } //clean arrayFree(session_holder_data_tmp->players_session_holder); free(session_holder_data_tmp); } } //save the letest response pss->user_json_respose = root_respose; } //now invoke to the current session of the current player if (doInvokeResponse) { send_response_to_current_player(pss); } } return true; } //send respomse to current session player void send_response_to_current_player(struct per_session_data__apigataway *_pss) { unsigned char response_to_client[LWS_PRE + 1024]; unsigned char *p_response_to_clientout = &response_to_client[LWS_PRE]; char* resp_json = cJSON_Print(_pss->user_json_respose); int n = sprintf((char *)p_response_to_clientout, "%s", resp_json); //lwsl_notice("Response to client from server: %s \n", p_response_to_clientout); //LOG_PRINT("Response to client from server: %s \n", p_response_to_clientout); //each player has its own copy of libwebsockets (lws in short ) wsi , witch is the player channel + session pointer int m = lws_write(_pss->player_wsi, p_response_to_clientout, n, LWS_WRITE_BINARY); if (m < n) { lwsl_err("ERROR %d writing to di socket\n", sizeof(response_to_client)); LOG_PRINT("ERROR %d writing to di socket\n", sizeof(response_to_client)); } //reset values for next tick in the game loop memset(_pss->player_seq, 0, sizeof(_pss->player_seq)); _pss->player_seq_index = 0; _pss->collision_status = 0; } //scatter the gems void scatter_gems() { generate_random_gems(1, SIMPLE); //generate_random_gems(3, BOMB); } //all sessions to the game will be invoked via this function //this function is the GAME LOGIC static void game_loop_cb(uv_timer_t* handle #if UV_VERSION_MAJOR == 0 , int status #endif ) { ASSERT(handle != NULL); ASSERT(1 == uv_is_active((uv_handle_t*)handle)); int after = hashmapSize(users_map_main); if (hashmapSize(users_map_main)>0) { hashmapForEach(users_map_main, &response_to_client_cp, users_map_main); } } //main ws api function , which is called each time client invoke API int callback_wsapi(struct lws *wsi, enum lws_callback_reasons reason, void *user, void *in, size_t len) { if (users_map_main == NULL) { users_map_main = hashmapCreate(10, str_hash_fn, str_eq); } //char *resp_json; unsigned char response_to_client[LWS_PRE + 1024]; struct per_session_data__apigataway *pss = (struct per_session_data__apigataway *)user; unsigned char *p_response_to_clientout = &response_to_client[LWS_PRE]; int n; switch (reason) { case LWS_CALLBACK_PROTOCOL_INIT: { srand((unsigned int)time(NULL)); //Scatter gems scatter_gems(); uv_timer_init(lws_uv_getloop(lws_get_context(wsi), 0),&timeout_watcher); //every 100ms uv_timer_start(&timeout_watcher, game_loop_cb, 1000, 100); break; } case LWS_CALLBACK_ESTABLISHED: { pss->recive_all_from_client = 0; pss->player_wsi = malloc(sizeof pss->player_wsi); pss->player_wsi = wsi; pss->player_seq_index = 0; pss->score = 0; pss->bomb_gems = arrayCreate(); pss->simple_gems = arrayCreate(); connection_num_as_id++; break; } case LWS_CALLBACK_SERVER_WRITEABLE: { //get request from client and parse json //lwsl_notice("pss->request_from_client_buf 2: %s \n", pss->request_from_client_buf); cJSON * root = cJSON_Parse(pss->request_from_client_buf); int status = cJSON_GetObjectItem(root, "status")->valueint; switch (status) { case 0: //Registration { pss->done_srv_update = false; pss->player_name = cJSON_GetObjectItem(root, "player_name")->valuestring; pss->status = status; pss->player_id = generateId(); pss->utc_timestemp = (long long)time(NULL); char* end_player_pos_x = cJSON_GetObjectItem(root, "end_player_pos_x")->valuestring; char* end_player_pos_y = cJSON_GetObjectItem(root, "end_player_pos_y")->valuestring; pss->end_player_pos_x = end_player_pos_x; pss->end_player_pos_y = end_player_pos_y; pss->done_srv_update = true; //set the user in the users repostory on succesfull registretion hashmapPut(users_map_main, pss->player_id, pss); int after = hashmapSize(users_map_main); lwsl_notice("Registration : hashmapSize size :%d , \n", after); break; } case 2: //Movment { //MEIRY need to update hashmap lwsl_notice("pss->request_from_client_buf Movment : %s \n", pss->request_from_client_buf); LOG_PRINT("pss->request_from_client_buf Movmente : %s \n", pss->request_from_client_buf); pss->done_srv_update = false; int collision_status = cJSON_GetObjectItem(root, "collision_status")->valueint; pss->collision_status = collision_status; pss->counter++; //lwsl_notice("Movment : pss->player_seq_index :%d , \n", pss->player_seq_index); char* player_x = cJSON_GetObjectItem(root, "player_x")->valuestring; char* player_y = cJSON_GetObjectItem(root, "player_y")->valuestring; //lwsl_notice("Movmentplayer_x:%s\n", player_x); //lwsl_notice("Movmentplayer_y:%s\n", player_y); char* end_player_pos_x = cJSON_GetObjectItem(root, "end_player_pos_x")->valuestring; char* end_player_pos_y = cJSON_GetObjectItem(root, "end_player_pos_y")->valuestring; char* player_seq = cJSON_GetObjectItem(root, "player_seq")->valuestring; //int stop_player = cJSON_GetObjectItem(root, "stop_player")->valueint; int status = cJSON_GetObjectItem(root, "status")->valueint; pss->player_x_r[pss->player_seq_index] = player_x; pss->player_y_r[pss->player_seq_index] = player_y; pss->player_seq[pss->player_seq_index] = player_seq; //lwsl_notice("Movment : pss->player_seq_index :%d , \n", pss->player_seq_index); pss->player_seq_index++; pss->status =2; pss->utc_timestemp = (long long)time(NULL); //for tracking pss->end_player_pos_x = end_player_pos_x; pss->end_player_pos_y = end_player_pos_y; lwsl_notice("MIDEL pss->request_from_client_buf Movment : %s \n", pss->request_from_client_buf); LOG_PRINT("MIDEL pss->request_from_client_buf Movmente : %s \n", pss->request_from_client_buf); if (pss->collision_status == 8) { lwsl_notice("INSIDE 1 pss->request_from_client_buf Movment : %s \n", pss->request_from_client_buf); LOG_PRINT("INSIDE 1 pss->request_from_client_buf Movmente : %s \n", pss->request_from_client_buf); int score = cJSON_GetObjectItem(root, "score")->valueint; cJSON *simple_gems = cJSON_GetObjectItem(root, "simple_gems"); for (int i = 0; i < cJSON_GetArraySize(simple_gems); i++) { struct gem_data *gemdata = malloc(sizeof * gemdata); cJSON * itemX = cJSON_GetArrayItem(simple_gems, i); ++i; cJSON * itemY = cJSON_GetArrayItem(simple_gems, i); gemdata->x = itemX->valueint; gemdata->y = itemY->valueint; gemdata->type = SIMPLE; gemdata->collide_with_player = true; arrayAdd(pss->simple_gems, gemdata); } cJSON *bomb_gems = cJSON_GetObjectItem(root, "bomb_gems"); for (int i = 0; i < cJSON_GetArraySize(bomb_gems); i++) { struct gem_data *gemdata = malloc(sizeof * gemdata); cJSON * itemX = cJSON_GetArrayItem(bomb_gems, i); ++i; cJSON * itemY = cJSON_GetArrayItem(bomb_gems, i); gemdata->x = itemX->valueint; gemdata->y = itemY->valueint; gemdata->type = BOMB; gemdata->collide_with_player = true; arrayAdd(pss->bomb_gems, gemdata); } pss->score = score; pss->collision_utc_timestemp = (long long)cJSON_GetObjectItem(root, "utc_timestemp")->valuedouble; //for tracking lwsl_notice("INSIDE 2 pss->request_from_client_buf Movment : %s \n", pss->request_from_client_buf); LOG_PRINT("INSIDE 2 pss->request_from_client_buf Movmente : %s \n", pss->request_from_client_buf); } lwsl_notice("END pss->request_from_client_buf Movment : %s \n", pss->request_from_client_buf); LOG_PRINT("END pss->request_from_client_buf Movmente : %s \n", pss->request_from_client_buf); //pss->stop_player = stop_player; pss->done_srv_update = true; struct per_session_data__apigataway *pssTmp = hashmapPut(users_map_main, pss->player_id, pss); if(pssTmp->collision_status == 8) { lwsl_notice("INSIDE HASHMAPPUT pssTmp->request_from_client_buf Movment : %s \n", pssTmp->request_from_client_buf); LOG_PRINT("INSIDE HASHMAPPUT pssTmp->request_from_client_buf Movmente : %s \n", pssTmp->request_from_client_buf); } break; } default: lwsl_notice("Invalid status \n"); } break; } case LWS_CALLBACK_RECEIVE: { if (len < 1) { break; } //lwsl_notice("Request from server: %s \n", (const char *)in); pss->binary = lws_frame_is_binary(wsi); //memcpy(&pss->request_from_client_buf[LWS_PRE], in, len); memcpy(&pss->request_from_client_buf, in, len); //lwsl_notice("pss->request_from_client_buf: %s \n", pss->request_from_client_buf); pss->recive_all_from_client = 1; //Only invoke callback back to client when baby client is ready to eat lws_callback_on_writable(wsi); break; } /* * this just demonstrates how to use the protocol filter. If you won't * study and reject connections based on header content, you don't need * to handle this callback */ case LWS_CALLBACK_FILTER_PROTOCOL_CONNECTION: //dump_handshake_info(wsi); /* you could return non-zero here and kill the connection */ break; /* * this just demonstrates how to handle * LWS_CALLBACK_WS_PEER_INITIATED_CLOSE and extract the peer's close * code and auxiliary data. You can just not handle it if you don't * have a use for this. */ case LWS_CALLBACK_WS_PEER_INITIATED_CLOSE: { lwsl_notice("LWS_CALLBACK_WS_PEER_INITIATED_CLOSE: len %d\n", len); for (n = 0; n < (int)len; n++) { lwsl_notice(" %d: 0x%02X\n", n, ((unsigned char *)in)[n]); } //update it to 6 which is this user is capot pss->status =6; //we will use the registrator json , as only the status and the id is all it matters int user_hash_size = hashmapSize(users_map_main); //lwsl_notice("response_to_client_cp : user_hash_size: %d \n", user_hash_size); if (user_hash_size > 1) { struct session_holder_data *session_holder_data_tmp = set_session_holder_data(user_is_dead_cp, pss); //now we have the others users which we need to update the current user //preper the other players session structures int i = 0; int size = arraySize(session_holder_data_tmp->players_session_holder); if (size > 0) { while (i < size) { struct per_session_data__apigataway *other_p_session = arrayGet(session_holder_data_tmp->players_session_holder, i); //send current player to other players int status = cJSON_GetObjectItem(pss->user_json_respose, "status")->valueint; //BUG in cJSON need to update also valuedouble when updating valueint //https://sourceforge.net/p/cjson/discussion/998969/thread/813ba29b/ cJSON_GetObjectItem(pss->user_json_respose, "status")->valueint = 6; cJSON_GetObjectItem(pss->user_json_respose, "status")->valuedouble = 6; send_response(pss->user_json_respose, other_p_session, pss); // Move to next. i++; } arrayFree(session_holder_data_tmp->players_session_holder); free(session_holder_data_tmp); } } //send to self char* resp_json = cJSON_Print(pss->user_json_respose); int n = sprintf((char *)p_response_to_clientout, "%s", resp_json); //lwsl_notice("Response to client from server: %s \n", p_response_to_clientout); //LOG_PRINT("Response to client from server: %s \n", p_response_to_clientout); //each player has its own copy of libwebsockets (lws in short ) wsi , witch is the player channel + session pointer int m = lws_write(pss->player_wsi, p_response_to_clientout, n, LWS_WRITE_BINARY); if (m < n) { lwsl_err("ERROR %d writing to di socket\n", sizeof(response_to_client)); LOG_PRINT("ERROR %d writing to di socket\n", sizeof(response_to_client)); } //handle user that disconnected //remove from users hash hashmapRemove(users_map_main, pss->player_id); int hash_map_size = hashmapSize(users_map_main); lwsl_notice("User %s disconnected: %s hashmap:%d \n", pss->player_name, pss->player_id, hash_map_size); LOG_PRINT("User %s disconnected: %s hashmap:%d \n", pss->player_name, pss->player_id, hash_map_size); //no players on the server reset gems if (hash_map_size == 0) { if (gems_array != NULL) { int array_size = arraySize(gems_array); int i = 0; while (i < array_size) { lwsl_notice("clear count gem element ii:%d \n", i); struct gem_data* gd = arrayRemove(gems_array, i); int array_size1 = arraySize(gems_array); lwsl_notice("clear gem element ii:%d x:%d y:%d type:%d \n", i, gd->x, gd->y,gd->type); free(gd); array_size--; } //build again the gems scatter_gems(); } } break; } default: break; } return 0; }

I will explain the important Sections of the code , not in descending order,
But in the order of execution

Line 331: This is the main function we defined in the previous PART 2 .
This is the entry point in which all request will be captured .
Line 336 : init the hashmap which will hold all of our connections ( clients )
Lines 339 - 341 : init the session data structure , the one we defined in PART 2
in the protocols array

The big switch of web sockets connection States ,
each connection has state on his life cycle on each state callback will fire ,
this big switch will handle those callback by name

Lines 346 - 354:  LWS_CALLBACK_PROTOCOL_INIT 
This state will be called only ONCE  per session Usually good place to init stuff .we init here the Game Loop timer 
Lines 356 - 366: LWS_CALLBACK_ESTABLISHED
This state called when client connected to the server for the first time , called once per connection We allocate the session data structure and the basic parameters.
Lines 368 -  384: LWS_CALLBACK_SERVER_WRITEABLE: 
This callback will write back to the client , ONLY when the client ready to receive the response .
Lines 375 - 392: when client request registration , which means client hold the 0 state .
collect all data from the client request which arrived as JSON  format in to the session data structure.
Lines 393 - 422: when client request is movement , ( client is moving ) . which means client hold the 2 state . collect all data from the client request which arrived as JSON  format in to the session data structure.
Lines 425 - 483: collision detection code which is not implemented fully . so you can ignore it.
Lines 486 - 500: LWS_CALLBACK_RECEIVE:
Client request frames that are receiving . can be called several times per request .
Line 493: mark as binary request type
Line 499: libwebsockets API that command the server to send replay only when the client is ready to receive it .
Lines 518 - 600: LWS_CALLBACK_WS_PEER_INITIATED_CLOSE
When client connection is close for example when browser tab in which the game running is closed
When network is stop working , when game is closed and so on .
This callback will trigger , init we will clean the client connection from the main hashmap that holding the connections and do some memory cleaning . 
And inform OTHER PLAYERS that this current player has disconnected from the game .
Lines 527 - 558 : set this current player state to 6 which means this player is dead.
Lines 531 - 557 : send response to other players and inform them about the dead player.
Line 573: remove current player from the users hashmap 

The event driven programming is usually involve event that is fired on every event occurred .
And in this server is there is no exception , we using callback functions . allot .

Lines 147 - 284 : response_to_client_cp 
This callback function will be called each game loop tick every time there is a need to response to clients . It will response to clients based on states the client handled is in .
Lines 162 - 220: build response on registration state , inform others about new user joined to the game Lines 221 -277:response to build response on movement state , inform others about new user joined to the game Lines 281:response to current connection ( current player ) .
Lines 314 -229: game_loop_cb
The game loop which will fire every 100ms , this will simulate the client game loop
And check the game logic , and response according to game events back to the clients 



Continue to PART 4 where we examine the client side