Server4.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "Ws2_32.lib")

/*
 * Predefined time-zone offset table relative to Malaysia Standard Time (MST, UTC+8).
 * - Each time zone is mapped to its corresponding offset from MST.
 */
struct timezone_offset {
    const char *zone;
    int offset; /* Offset in hours from Malaysia Standard Time */
};

const struct timezone_offset tz_table[] = {
    {"PST", -16},  /* Pacific Standard Time (GMT-8 relative to MST+8) */
    {"MST", -15},  /* Mountain Standard Time (GMT-7 relative to MST+8) */
    {"CST", -14},  /* Central Standard Time (GMT-6 relative to MST+8) */
    {"EST", -13},  /* Eastern Standard Time (GMT-5 relative to MST+8) */
    {"GMT", -8},   /* Greenwich Mean Time (GMT+0 relative to MST+8) */
    {"CET", -7},   /* Central European Time (GMT+1 relative to MST+8) */
    {"MSK", -5},   /* Moscow Time (GMT+3 relative to MST+8) */
    {"JST", +1},   /* Japan Standard Time (GMT+9 relative to MST+8) */
    {"AEDT", +3},  /* Australian Eastern Daylight Time (GMT+11 relative to MST+8) */
    {NULL, 0}      /* Sentinel value to mark the end of the table */
};

/*
 * Function to find the offset for a given time zone relative to MST.
 * - If the time zone is valid, returns the corresponding offset in hours.
 * - If the time zone is invalid, returns INT_MIN as an error flag.
 */
int find_timezone_offset(const char *zone) {
    for (int i = 0; tz_table[i].zone != NULL; i++) {
        if (strcmp(tz_table[i].zone, zone) == 0) {
            return tz_table[i].offset;
        }
    }
    return INT_MIN; /* Invalid time zone */
}

/*
 * Function to get the current time in a specific time zone relative to MST.
 * - Adjusts the time based on the given offset from MST.
 * - Formats the adjusted time as a string.
 */
void get_time_in_timezone(char *buffer, size_t buffer_size, int offset) {
    time_t now = time(NULL);         /* Get the current time */
    now += offset * 3600;            /* Adjust time by offset (in seconds) */
    struct tm *local_time = localtime(&now); /* Convert to adjusted time as local time */

    /* Format the date and time into the provided buffer */
    strftime(buffer, buffer_size, "%A, %d %B %Y %H:%M:%S\r\n", local_time);
}

int main(void) {
    /*
     * Initialize WinSock.
     * - Required for using sockets on Windows.
     * - MAKEWORD(2, 2) specifies version 2.2 of the API.
     */
    WSADATA wsa_data;
    if (WSAStartup(MAKEWORD(2, 2), &wsa_data) != 0) {
        fprintf(stderr, "Failed to initialize WinSock.\n");
        return 1;
    }

    /*
     * Create a listening socket.
     * - Configured for TCP/IP communication (SOCK_STREAM).
     */
    SOCKET listen_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (listen_socket == INVALID_SOCKET) {
        fprintf(stderr, "Socket creation failed: %d\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }

    /*
     * Configure the server's address and port.
     * - Use designated initializers for clarity and maintainability.
     */
    struct sockaddr_in server_addr = {
        .sin_family = AF_INET,
        .sin_port = htons(8080), /* Convert port to network byte order */
        .sin_addr.s_addr = INADDR_ANY /* Bind to all network interfaces */
    };

    /*
     * Bind the listening socket to the specified address and port.
     */
    if (bind(listen_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) == SOCKET_ERROR) {
        fprintf(stderr, "Bind failed: %d\n", WSAGetLastError());
        closesocket(listen_socket);
        WSACleanup();
        return 1;
    }

    /*
     * Start listening for incoming connection requests.
     * - SOMAXCONN allows the maximum number of pending connections.
     */
    if (listen(listen_socket, SOMAXCONN) == SOCKET_ERROR) {
        fprintf(stderr, "Listen failed: %d\n", WSAGetLastError());
        closesocket(listen_socket);
        WSACleanup();
        return 1;
    }

    printf("[DEBUG] Server4 (Malaysia Time): Waiting for a client to connect...\n");

    /*
     * Accept a client connection.
     * - If `accept()` fails, clean up and exit.
     */
    SOCKET client_socket = accept(listen_socket, NULL, NULL);
    if (client_socket == INVALID_SOCKET) {
        fprintf(stderr, "Accept failed: %d\n", WSAGetLastError());
        closesocket(listen_socket);
        WSACleanup();
        return 1;
    }
    printf("[DEBUG] Client connected.\n");

    char buffer[1024];
    for (;;) {
        /*
         * Receive data from the client.
         * - If `recv()` returns <= 0, the client has disconnected.
         */
        int n = recv(client_socket, buffer, (int)(sizeof(buffer) - 1), 0);
        if (n <= 0) {
            printf("[DEBUG] Client disconnected.\n");
            break;
        }

        buffer[n] = '\0'; /* Null-terminate the received string */

        /*
         * Check for the "Time <zone>" command.
         * - Extract the time zone from the command.
         * - Return the current time in the specified time zone.
         */
        if (strncmp(buffer, "Time ", 5) == 0) {
            char zone[64];
            sscanf(buffer + 5, "%63s", zone); /* Extract the time zone */
            int offset = find_timezone_offset(zone);

            if (offset != INT_MIN) {
                char time_response[256];
                get_time_in_timezone(time_response, sizeof(time_response), offset);
                send(client_socket, time_response, (int)strlen(time_response), 0);
            } else {
                const char *error_msg = "Error: Invalid time zone.\r\n";
                send(client_socket, error_msg, (int)strlen(error_msg), 0);
            }
            continue;
        }

        /*
         * Check for the "Exit Server" command.
         * - If received, terminate the connection and server.
         */
        if (strcmp(buffer, "Exit Server") == 0) {
            printf("[DEBUG] 'Exit Server' command received. Shutting down.\n");
            break;
        }

        /*
         * Send an error message for unrecognized commands.
         */
        const char *error_msg = "Error: Unrecognized command. Use 'Time <zone>' or 'Exit Server'.\r\n";
        send(client_socket, error_msg, (int)strlen(error_msg), 0);
    }

    /*
     * Cleanup resources before exiting.
     * - Close the client and listening sockets.
     * - Terminate WinSock.
     */
    closesocket(client_socket);
    closesocket(listen_socket);
    WSACleanup();

    printf("[DEBUG] Server4 (Malaysia Time) shutdown complete.\n");
    return 0;
}