SmolChat/server.c

// server.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <signal.h>
#include <pthread.h>
#include <sqlite3.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <crypt.h>
#include <errno.h>
#include <openssl/ssl.h>
#include <openssl/err.h>
#include <ctype.h>

#define MAX_CLIENTS 500
#define MAX_USERNAME 32
#define MAX_PASSWORD 64
#define MAX_MESSAGE 1024
#define MAX_ROOMS 100
#define MAX_BANNED_WORDS 50
#define CONFIG_PATH "server.conf"
#define MAX_MESSAGES_PER_MINUTE 60

typedef enum
{
    USER_REGULAR,
    USER_MODERATOR,
    USER_ADMIN
} UserRole;

typedef struct
{
    int socket;
    char username[MAX_USERNAME];
    char current_room[MAX_USERNAME];
    UserRole role;
    time_t last_activity;
    int message_count;
    time_t last_message_reset;
    time_t last_message_time;
} Client;

typedef struct
{
    char name[MAX_USERNAME];
    char description[256];
    Client *members[MAX_CLIENTS];
    int member_count;
    int is_private;
    char password[MAX_PASSWORD];
} Room;

typedef struct
{
    int port;
    char default_room[MAX_USERNAME];
    int max_clients;
    int allow_room_creation;
    char banned_words[MAX_BANNED_WORDS][32];
    int banned_word_count;

    /* new config options */
    char motd[256];
    char admins[32][MAX_USERNAME];
    int admin_count;
    int max_message_length;
    int max_rooms;
} ServerConfig;

sqlite3 *database;
Client clients[MAX_CLIENTS];
Room rooms[MAX_ROOMS];
ServerConfig config;
pthread_mutex_t clients_mutex = PTHREAD_MUTEX_INITIALIZER;
int server_socket;
FILE *log_file;
Room global_rooms[MAX_ROOMS] = {0};
int active_room_count = 0;

SSL_CTX *ssl_ctx;

/* Forward declarations to avoid implicit declaration / conflicting type errors */
void safe_strcpy(char *dest, const char *src, size_t size);
void safe_strcat(char *dest, const char *src, size_t size);

void server_log(const char *level, const char *message)
{
    time_t now = time(NULL);
    char *date = ctime(&now);
    date[strlen(date) - 1] = '\0';

    printf("\033[34m[%s] %s: %s\033[0m\n", date, level, message);

    if (log_file)
    {
        fprintf(log_file, "[%s] %s: %s\n", date, level, message);
        fflush(log_file);
    }
}

int is_word_banned(const char *message)
{
    for (int i = 0; i < config.banned_word_count; i++)
    {
        if (strcasestr(message, config.banned_words[i]))
        {
            return 1;
        }
    }
    return 0;
}

/* small helper: trim leading/trailing whitespace in-place */
static void trim(char *s) {
    if (!s) return;
    // trim leading
    while (*s && isspace((unsigned char)*s)) memmove(s, s+1, strlen(s));
    // trim trailing
    size_t len = strlen(s);
    while (len > 0 && isspace((unsigned char)s[len-1])) s[--len] = '\0';
}

void parse_config()
{
    /* set sensible defaults */
    strcpy(config.default_room, "lobby");
    config.port = 8888;
    config.max_clients = MAX_CLIENTS;
    config.allow_room_creation = 1;
    config.banned_word_count = 0;
    config.motd[0] = '\0';
    config.admin_count = 0;
    config.max_message_length = MAX_MESSAGE; /* fallback to compile-time */
    config.max_rooms = MAX_ROOMS;

    FILE *file = fopen(CONFIG_PATH, "r");
    if (!file)
    {
        server_log("WARN", "No config file found. Using defaults.");
        return;
    }

    char line[512];
    while (fgets(line, sizeof(line), file))
    {
        trim(line);
        if (line[0] == '#' || line[0] == ';' || line[0] == '\0') continue; /* comment/empty */

        char key[128], value[384];
        if (sscanf(line, "%127[^=]=%383[^\n]", key, value) == 2)
        {
            trim(key);
            trim(value);

            if (strcasecmp(key, "port") == 0) {
                config.port = atoi(value);
            } else if (strcasecmp(key, "default_room") == 0) {
                safe_strcpy(config.default_room, value, sizeof(config.default_room));
            } else if (strcasecmp(key, "max_clients") == 0) {
                config.max_clients = atoi(value);
                if (config.max_clients < 1) config.max_clients = 1;
                if (config.max_clients > MAX_CLIENTS) config.max_clients = MAX_CLIENTS;
            } else if (strcasecmp(key, "allow_room_creation") == 0) {
                config.allow_room_creation = (strcasecmp(value, "true") == 0 || strcmp(value, "1") == 0);
            } else if (strcasecmp(key, "banned_words") == 0) {
                config.banned_word_count = 0;
                char *tok = strtok(value, ",");
                while (tok && config.banned_word_count < MAX_BANNED_WORDS) {
                    trim(tok);
                    strncpy(config.banned_words[config.banned_word_count++], tok, 31);
                    config.banned_words[config.banned_word_count-1][31] = '\0';
                    tok = strtok(NULL, ",");
                }
            } else if (strcasecmp(key, "motd") == 0) {
                safe_strcpy(config.motd, value, sizeof(config.motd));
            } else if (strcasecmp(key, "admins") == 0) {
                config.admin_count = 0;
                char *tok = strtok(value, ",");
                while (tok && config.admin_count < (int)(sizeof(config.admins)/sizeof(config.admins[0]))) {
                    trim(tok);
                    strncpy(config.admins[config.admin_count++], tok, MAX_USERNAME-1);
                    config.admins[config.admin_count-1][MAX_USERNAME-1] = '\0';
                    tok = strtok(NULL, ",");
                }
            } else if (strcasecmp(key, "max_message_length") == 0) {
                config.max_message_length = atoi(value);
                if (config.max_message_length < 16) config.max_message_length = 16;
                if (config.max_message_length > MAX_MESSAGE) config.max_message_length = MAX_MESSAGE;
            } else if (strcasecmp(key, "max_rooms") == 0) {
                config.max_rooms = atoi(value);
                if (config.max_rooms < 1) config.max_rooms = 1;
                if (config.max_rooms > MAX_ROOMS) config.max_rooms = MAX_ROOMS;
            }
        }
    }
    fclose(file);

    char buf[256];
    snprintf(buf, sizeof(buf), "Config loaded: port=%d default_room=%s max_clients=%d max_message_length=%d",
             config.port, config.default_room, config.max_clients, config.max_message_length);
    server_log("INFO", buf);
}

Room *find_or_create_room(const char *room_name, const char *password, Client *creator)
{
    for (int i = 0; i < active_room_count; i++)
    {
        if (strcmp(global_rooms[i].name, room_name) == 0)
        {
            if (global_rooms[i].is_private && strcmp(global_rooms[i].password, password) != 0)
            {
                return NULL; // Incorrect password
            }
            return &global_rooms[i];
        }
    }

    if (active_room_count < MAX_ROOMS &&
        (config.allow_room_creation || (creator && creator->role >= USER_MODERATOR)))
    {
        pthread_mutex_lock(&clients_mutex); /* protect global_rooms modifications */
        Room *new_room = &global_rooms[active_room_count++];

        /* initialize the new room but do NOT add members here.
           Membership must be managed by the caller under clients_mutex
           to avoid races/duplicate entries. */
        memset(new_room, 0, sizeof(Room));
        strncpy(new_room->name, room_name, MAX_USERNAME - 1);
        new_room->name[MAX_USERNAME - 1] = '\0';
        strncpy(new_room->password, password, MAX_PASSWORD - 1);
        new_room->password[MAX_PASSWORD - 1] = '\0';
        new_room->is_private = (password && password[0] != '\0');
        new_room->member_count = 0;
        pthread_mutex_unlock(&clients_mutex);

        char log_msg[256];
        snprintf(log_msg, sizeof(log_msg),
                 "Room created: %s by user %s",
                 room_name, creator ? creator->username : "system");
        server_log("ROOM", log_msg);

        return new_room;
    }

    return NULL;
}

// Add these safe room membership helpers to avoid duplicates
void add_client_to_room(Room *room, Client *client) {
    if (!room || !client) return;
    pthread_mutex_lock(&clients_mutex);
    // avoid duplicates
    for (int i = 0; i < room->member_count; i++) {
        if (room->members[i] == client) {
            pthread_mutex_unlock(&clients_mutex);
            return;
        }
    }
    if (room->member_count < MAX_CLIENTS) {
        room->members[room->member_count++] = client;
    }
    pthread_mutex_unlock(&clients_mutex);
}

void remove_client_from_room(Room *room, Client *client) {
    if (!room || !client) return;
    pthread_mutex_lock(&clients_mutex);
    for (int i = 0; i < room->member_count; i++) {
        if (room->members[i] == client) {
            memmove(&room->members[i], &room->members[i + 1],
                    (room->member_count - i - 1) * sizeof(Client *));
            room->member_count--;
            break;
        }
    }
    pthread_mutex_unlock(&clients_mutex);
}

void broadcast_room_message(Room *room, const char *message, Client *sender) {
    if (!room || !sender) return;

    // Don't broadcast commands
    if (message[0] == '/') return;

    char formatted_message[MAX_MESSAGE];
    snprintf(formatted_message, sizeof(formatted_message),
             "[%s] %s: %s\n", room->name, sender->username, message);

    pthread_mutex_lock(&clients_mutex);
    
    // First verify sender is still in room
    int sender_in_room = 0;
    for (int i = 0; i < room->member_count; i++) {
        if (room->members[i] == sender && room->members[i]->socket > 0) {
            sender_in_room = 1;
            break;
        }
    }

    if (!sender_in_room) {
        pthread_mutex_unlock(&clients_mutex);
        return;
    }

    // Now broadcast to room members (skip sender so messages are not echoed back)
    for (int i = 0; i < room->member_count; i++) {
        Client *client = room->members[i];
        if (!client || client->socket <= 0) continue;

        // skip duplicates of the same client pointer in the list
        int duplicate = 0;
        for (int k = 0; k < i; k++) {
            if (room->members[k] == client) { duplicate = 1; break; }
        }
        if (duplicate) continue;

        if (client == sender) continue; /* do not echo to sender */

        ssize_t sent = send(client->socket, formatted_message, 
                           strlen(formatted_message), MSG_NOSIGNAL);

        if (sent <= 0) {
            /* Handle disconnected client: remove from members list while holding mutex */
            if (errno == EPIPE || errno == ECONNRESET || sent == -1) {
                close(client->socket);
                client->socket = 0;
                memmove(&room->members[i], &room->members[i + 1], 
                        (room->member_count - i - 1) * sizeof(Client*));
                room->member_count--;
                i--; /* adjust index after removal */
            }
        }
    }

    pthread_mutex_unlock(&clients_mutex);
    server_log("MESSAGE", formatted_message);
}

int authenticate_user(const char *username, const char *password)
{
    sqlite3_stmt *stmt;
    const char *query = "SELECT password FROM users WHERE username = ?";

    sqlite3_prepare_v2(database, query, -1, &stmt, 0);
    sqlite3_bind_text(stmt, 1, username, -1, SQLITE_STATIC);

    int authenticated = 0;
    if (sqlite3_step(stmt) == SQLITE_ROW)
    {
        const char *stored_hash = (const char *)sqlite3_column_text(stmt, 0);
        const char *computed_hash = crypt(password, stored_hash);
        authenticated = (computed_hash && strcmp(computed_hash, stored_hash) == 0);
    }

    sqlite3_finalize(stmt);
    return authenticated;
}

int register_user(const char *username, const char *password)
{
    sqlite3_stmt *stmt;

    // Check if user already exists
    const char *check_query = "SELECT username FROM users WHERE username = ?";
    sqlite3_prepare_v2(database, check_query, -1, &stmt, 0);
    sqlite3_bind_text(stmt, 1, username, -1, SQLITE_STATIC);

    if (sqlite3_step(stmt) == SQLITE_ROW)
    {
        sqlite3_finalize(stmt);
        return 0; // User already exists
    }
    sqlite3_finalize(stmt);

    // Generate salt and hash password
    char salt[32];
    snprintf(salt, sizeof(salt), "$6$%08x%08x", rand(), rand());
    char *hashed_password = crypt(password, salt);

    // Insert new user
    const char *insert_query = "INSERT INTO users (username, password, role) VALUES (?, ?, ?)";
    sqlite3_prepare_v2(database, insert_query, -1, &stmt, 0);
    sqlite3_bind_text(stmt, 1, username, -1, SQLITE_STATIC);
    sqlite3_bind_text(stmt, 2, hashed_password, -1, SQLITE_STATIC);
    sqlite3_bind_int(stmt, 3, USER_REGULAR);

    int result = sqlite3_step(stmt) == SQLITE_DONE;
    sqlite3_finalize(stmt);
    return result;
}

void *handle_client(void *arg)
{
    Client *client = (Client *)arg;
    char buffer[MAX_MESSAGE];
    int read_size;

    char welcome[MAX_MESSAGE];
    snprintf(welcome, sizeof(welcome),
             "Welcome, %s! You are in room %s",
             client->username, client->current_room);
    send(client->socket, welcome, strlen(welcome), 0);

    // Find default room and add client
    Room *default_room = NULL;
    for (int i = 0; i < active_room_count; i++) {
        if (strcmp(global_rooms[i].name, "lobby") == 0) {
            default_room = &global_rooms[i];
            break;
        }
    }

    if (default_room) {
        add_client_to_room(default_room, client);

        strncpy(client->current_room, "lobby", MAX_USERNAME);
        
        char join_msg[MAX_MESSAGE];
        snprintf(join_msg, sizeof(join_msg), "%s joined the chat", client->username);
        broadcast_room_message(default_room, join_msg, client);

        /* send MOTD to the new client if configured */
        if (config.motd[0]) {
            char motd_msg[512];
            snprintf(motd_msg, sizeof(motd_msg), "MOTD: %s\n", config.motd);
            send(client->socket, motd_msg, strlen(motd_msg), 0);
        }
    }

    while ((read_size = recv(client->socket, buffer, MAX_MESSAGE, 0)) > 0)
    {
        /* enforce configured max message length */
        if (config.max_message_length > 0 && read_size > config.max_message_length) {
            const char *err = "Your message is too long and was discarded.\n";
            send(client->socket, err, strlen(err), 0);
            continue;
        }

        buffer[read_size] = '\0';

        char log_msg[MAX_MESSAGE + 100];
        snprintf(log_msg, sizeof(log_msg),
                 "Received from %s: %s", client->username, buffer);
        server_log("RECV", log_msg);

        // Server: Inside handle_client()
        server_log("DEBUG", "Received message");
        printf("Message from %s: %s\n", client->username, buffer);

        if (strncmp(buffer, "/join ", 6) == 0)
        {
            char room_name[MAX_USERNAME] = {0};
            char password[MAX_PASSWORD] = {0};
            sscanf(buffer + 6, "%s %s", room_name, password);

            Room *room = find_or_create_room(room_name, password, client);
            if (room) {
                // Remove client from current room (if present) - notify before modifying
                Room *old_room = NULL;
                int old_index = -1;
                for (int i = 0; i < active_room_count; i++) {
                    if (strcmp(global_rooms[i].name, client->current_room) == 0) {
                        old_room = &global_rooms[i];
                        break;
                    }
                }

                if (old_room) {
                    for (int j = 0; j < old_room->member_count; j++) {
                        if (old_room->members[j] == client) {
                            // Notify old room before removing (don't hold mutex during broadcast)
                            char leave_msg[MAX_MESSAGE];
                            snprintf(leave_msg, sizeof(leave_msg), "%s left the room", client->username);
                            broadcast_room_message(old_room, leave_msg, client);

                            // remove safely using helper
                            remove_client_from_room(old_room, client);
                            break;
                        }
                    }
                }

                // Check if client is already in the new room
                int already_in_room = 0;
                for (int i = 0; i < room->member_count; i++) {
                    if (room->members[i] == client) {
                        already_in_room = 1;
                        break;
                    }
                }

                if (!already_in_room) {
                    // Add to new room safely (avoids duplicates)
                    add_client_to_room(room, client);

                    safe_strcpy(client->current_room, room_name, MAX_USERNAME);

                    // Notify new room (do not hold mutex while broadcasting)
                    char join_msg[MAX_MESSAGE];
                    snprintf(join_msg, sizeof(join_msg), "%s joined the room", client->username);
                    broadcast_room_message(room, join_msg, client);
                }

                // Send confirmation to client
                char confirm_msg[MAX_MESSAGE];
                snprintf(confirm_msg, sizeof(confirm_msg), "You joined room: %s\n", room_name);
                send(client->socket, confirm_msg, strlen(confirm_msg), 0);
            } else {
                const char *error_msg = "Could not join room. It might be private or full.\n";
                send(client->socket, error_msg, strlen(error_msg), 0);
            }
        }
        else if (strcmp(buffer, "/rooms") == 0)
        {
            char room_list[MAX_MESSAGE] = "Available Rooms:\n";
            for (int i = 0; i < active_room_count; i++)
            {
                char room_info[128];
                snprintf(room_info, sizeof(room_info),
                         "- %s (Members: %d)\n",
                         global_rooms[i].name, global_rooms[i].member_count);
                strcat(room_list, room_info);
            }
            send(client->socket, room_list, strlen(room_list), 0);
        }
        else
        {
            Room *current_room = NULL;
            for (int i = 0; i < active_room_count; i++)
            {
                if (strcmp(global_rooms[i].name, client->current_room) == 0)
                {
                    current_room = &global_rooms[i];
                    break;
                }
            }

            if (current_room)
            {
                if (is_word_banned(buffer))
                {
                    const char *warning = "Your message contains banned words and was not sent.";
                    send(client->socket, warning, strlen(warning), 0);
                    continue;
                }
                // Server: Before broadcasting
                server_log("DEBUG", "Broadcasting message");
                printf("Broadcasting message: %s\n", buffer);

                // Rate limiting
                if (time(NULL) - client->last_message_time >= 60) {
                    client->message_count = 0;
                    client->last_message_time = time(NULL);
                }
                
                if (client->message_count >= MAX_MESSAGES_PER_MINUTE) {
                    const char *rate_limit_msg = "Rate limit exceeded. Please wait.\n";
                    send(client->socket, rate_limit_msg, strlen(rate_limit_msg), 0);
                    continue;
                }
                client->message_count++;

                broadcast_room_message(current_room, buffer, client);
            }
        }
    }

    server_log("DISCONNECT", client->username);
    close(client->socket);
    client->socket = 0;
    return NULL;
}

void send_private_message(Client *sender, const char *recipient_name, const char *message) {
    pthread_mutex_lock(&clients_mutex);
    for (int i = 0; i < MAX_CLIENTS; i++) {
        if (clients[i].socket != 0 && strcmp(clients[i].username, recipient_name) == 0) {
            char formatted_message[MAX_MESSAGE];
            snprintf(formatted_message, sizeof(formatted_message),
                     "[PM from %s]: %s", sender->username, message);
            send(clients[i].socket, formatted_message, strlen(formatted_message), 0);
            
            // Send confirmation to sender
            snprintf(formatted_message, sizeof(formatted_message),
                     "[PM to %s]: %s", recipient_name, message);
            send(sender->socket, formatted_message, strlen(formatted_message), 0);
            pthread_mutex_unlock(&clients_mutex);
            return;
        }
    }
    pthread_mutex_unlock(&clients_mutex);
    
    // User not found
    char error_msg[MAX_MESSAGE];
    snprintf(error_msg, sizeof(error_msg), "User '%s' not found or offline.\n", recipient_name);
    send(sender->socket, error_msg, strlen(error_msg), 0);
}

int init_database()
{
    int rc = sqlite3_open("chat.db", &database);
    if (rc)
    {
        server_log("ERROR", "Cannot open database");
        return 0;
    }

    const char *tables[] = {
        "CREATE TABLE IF NOT EXISTS users ("
        "username TEXT PRIMARY KEY, "
        "password TEXT, "
        "role INTEGER);",
        
        "CREATE TABLE IF NOT EXISTS rooms ("
        "name TEXT PRIMARY KEY,"
        "description TEXT,"
        "is_private INTEGER,"
        "password TEXT);",
        
        "CREATE TABLE IF NOT EXISTS messages ("
        "id INTEGER PRIMARY KEY AUTOINCREMENT,"
        "room TEXT,"
        "sender TEXT,"
        "content TEXT,"
        "timestamp INTEGER,"
        "FOREIGN KEY(room) REFERENCES rooms(name),"
        "FOREIGN KEY(sender) REFERENCES users(username));"
    };

    char *err_msg = 0;
    for (int i = 0; i < sizeof(tables)/sizeof(tables[0]); i++) {
        int rc = sqlite3_exec(database, tables[i], 0, 0, &err_msg);
        if (rc != SQLITE_OK) {
            char error_message[256];
            snprintf(error_message, sizeof(error_message), "Database error: %s", err_msg);
            server_log("ERROR", error_message);
            sqlite3_free(err_msg);
            return 0;
        }
    }

    // Create default room if it doesn't exist
    const char *default_room_query = 
        "INSERT OR IGNORE INTO rooms (name, description, is_private) "
        "VALUES ('lobby', 'Default chat room', 0);";
    
    sqlite3_exec(database, default_room_query, 0, 0, &err_msg);
    return 1;
}

volatile sig_atomic_t server_running = 1;

void handle_shutdown(int signal) {
    server_running = 0;
    server_log("INFO", "Shutting down server...");
    
    // Close all client connections
    pthread_mutex_lock(&clients_mutex);
    for (int i = 0; i < MAX_CLIENTS; i++) {
        if (clients[i].socket != 0) {
            close(clients[i].socket);
        }
    }
    pthread_mutex_unlock(&clients_mutex);
    
    // Close server socket
    close(server_socket);
    
    // Close database connection
    sqlite3_close(database);
    
    // Close log file
    if (log_file) {
        fclose(log_file);
    }
    
    exit(0);
}

// Add these safe string functions
void safe_strcpy(char *dest, const char *src, size_t size) {
    if (!dest || !src || size == 0) return;
    strncpy(dest, src, size - 1);
    dest[size - 1] = '\0';
}

void safe_strcat(char *dest, const char *src, size_t size) {
    if (!dest || !src || size == 0) return;
    size_t current_len = strlen(dest);
    if (current_len >= size - 1) return;
    strncpy(dest + current_len, src, size - current_len - 1);
    dest[size - 1] = '\0';
}

int main() {
    srand(time(NULL));  // Initialize random number generator
    log_file = fopen("server.log", "a");
    parse_config();
    init_database();

    struct sockaddr_in server_addr, client_addr;
    socklen_t client_addr_len = sizeof(client_addr);

    server_socket = socket(AF_INET, SOCK_STREAM, 0);
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(config.port);

    int yes = 1;
    if (setsockopt(server_socket, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes)) == -1) {
        server_log("ERROR", "Failed to set socket options");
        return 1;
    }

    if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        server_log("ERROR", "Bind failed");
        return 1;
    }

    if (listen(server_socket, MAX_CLIENTS) < 0) {
        server_log("ERROR", "Listen failed");
        return 1;
    }

    server_log("INFO", "Server initialized. Waiting for connections...");

    // Initialize default room
    Room *default_room = &global_rooms[active_room_count++];
    strncpy(default_room->name, "lobby", MAX_USERNAME);
    default_room->description[0] = '\0';
    default_room->is_private = 0;
    default_room->password[0] = '\0';
    default_room->member_count = 0;

    server_log("INFO", "Default room 'lobby' initialized");

    signal(SIGINT, handle_shutdown);
    signal(SIGTERM, handle_shutdown);

    while (server_running)
    {
        int client_socket = accept(server_socket,
                                   (struct sockaddr *)&client_addr,
                                   &client_addr_len);

        char client_ip[INET_ADDRSTRLEN];
        inet_ntop(AF_INET, &client_addr.sin_addr, client_ip, sizeof(client_ip));
        server_log("INFO", "Client connected");
        printf("Client connected from %s:%d\n", client_ip, ntohs(client_addr.sin_port));

        // Read the combined username and password
        char credentials[MAX_USERNAME + MAX_PASSWORD + 10]; // Extra space for command
        ssize_t recv_len = recv(client_socket, credentials, sizeof(credentials) - 1, 0);
        if (recv_len <= 0) {
            close(client_socket);
            continue;
        }
        credentials[recv_len] = '\0';

        // Parse command, username and password
        char command[10];
        char username[MAX_USERNAME];
        char password[MAX_PASSWORD];
        
        if (sscanf(credentials, "%9s %31s %63s", command, username, password) != 3) {
            const char *error_msg = "Invalid format. Use: LOGIN username password or REGISTER username password\n";
            send(client_socket, error_msg, strlen(error_msg), 0);
            close(client_socket);
            continue;
        }

        if (strcmp(command, "REGISTER") == 0) {
            if (register_user(username, password)) {
                const char *success_msg = "Registration successful. Please login.\n";
                send(client_socket, success_msg, strlen(success_msg), 0);
            } else {
                const char *error_msg = "Registration failed. Username may already exist.\n";
                send(client_socket, error_msg, strlen(error_msg), 0);
            }
            close(client_socket);
            continue;
        } else if (strcmp(command, "LOGIN") == 0) {
            if (authenticate_user(username, password)) {
                server_log("INFO", "Authentication successful");
                const char *success_msg = "Authentication successful\n";
                send(client_socket, success_msg, strlen(success_msg), 0);

                pthread_mutex_lock(&clients_mutex);
                int slot_found = 0;
                for (int i = 0; i < MAX_CLIENTS; i++) {
                    if (clients[i].socket == 0) {
                        clients[i].socket = client_socket;
                        safe_strcpy(clients[i].username, username, MAX_USERNAME);
                        safe_strcpy(clients[i].current_room, config.default_room, MAX_USERNAME);
                        clients[i].role = USER_REGULAR;
                        clients[i].last_activity = time(NULL);
                        clients[i].message_count = 0;
                        clients[i].last_message_time = time(NULL);

                        pthread_t thread;
                        if (pthread_create(&thread, NULL, handle_client, &clients[i]) != 0) {
                            server_log("ERROR", "Failed to create client thread");
                            clients[i].socket = 0;
                            close(client_socket);
                        } else {
                            pthread_detach(thread);
                            slot_found = 1;
                        }
                        break;
                    }
                }
                pthread_mutex_unlock(&clients_mutex);

                if (!slot_found) {
                    server_log("ERROR", "Server full");
                    const char *error_msg = "Server is full\n";
                    send(client_socket, error_msg, strlen(error_msg), 0);
                    close(client_socket);
                }
            } else {
                server_log("WARN", "Authentication failed");
                const char *error_msg = "Authentication failed: Invalid credentials\n";
                send(client_socket, error_msg, strlen(error_msg), 0);
                close(client_socket);
            }
        } else {
            const char *error_msg = "Invalid command. Use LOGIN or REGISTER\n";
            send(client_socket, error_msg, strlen(error_msg), 0);
            close(client_socket);
        }
    }

    sqlite3_close(database);
    return 0;
}