Server1.c

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

/*
 * Reverse and Uppercase Function:
 * - Reverses the given string in-place.
 * - Converts all alphabetical characters to uppercase.
 *
 * This function demonstrates efficient string manipulation by
 * processing the string directly in memory.
 */
void reverse_and_uppercase(char *str) {
    size_t len = strlen(str);

    /* Reverse the string in-place */
    for (size_t i = 0; i < len / 2; i++) {
        char temp = str[i];
        str[i] = str[len - 1 - i];
        str[len - 1 - i] = temp;
    }

    /* Convert alphabets to uppercase */
    for (size_t i = 0; i < len; i++) {
        if (isalpha((unsigned char)str[i])) {
            str[i] = (char)toupper((unsigned char)str[i]);
        }
    }
}

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).
     * - If the creation fails, print an error and exit.
     */
    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 the bind operation fails, the server cannot proceed.
     */
    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 listening fails, the server cannot accept connections.
     */
    if (listen(listen_socket, SOMAXCONN) == SOCKET_ERROR) {
        fprintf(stderr, "Listen failed: %d\n", WSAGetLastError());
        closesocket(listen_socket);
        WSACleanup();
        return 1;
    }

    printf("[INFO] Server1: 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("[INFO] 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 */

        /*
         * Process the received message:
         * - Reverse the string and convert it to uppercase.
         */
        reverse_and_uppercase(buffer);

        /* Send the processed string back to the client */
        send(client_socket, buffer, (int)strlen(buffer), 0);
    }

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

    printf("[DEBUG] Server1 shutdown complete.\n");
    return 0;
}