FirstClient.c

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

/*
 * Thread argument structure.
 * This structure holds the socket used to communicate with the server.
 */
struct thread_args {
    SOCKET sock; /* Socket connected to the server */
};

/*
 * Thread function: Continuously receives messages from the server.
 * - Messages received from the server are displayed in the console.
 * - If the server sends an "Exit Server" message or disconnects, the thread exits.
 *
 * This function runs in its own thread to ensure the client can both
 * send and receive messages simultaneously.
 */
void *receive_thread(void *arg) {
    struct thread_args *t = arg;
    SOCKET sock = t->sock;
    free(t); /* Free dynamically allocated thread arguments */

    char buffer[1024];
    for (;;) {
        /*
         * Receive data from the server.
         * - If `recv()` returns <= 0, the connection has been lost, and the thread exits.
         */
        int n = recv(sock, buffer, (int)(sizeof(buffer) - 1), 0);
        if (n <= 0) {
            printf("[DEBUG] Disconnected from the server.\n");
            exit(0); /* Exit the process */
        }

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

        /*
         * Check for the "Exit Server" command from the server.
         * If received, exit the process.
         */
        if (strcmp(buffer, "Exit Server") == 0) {
            printf("[DEBUG] Server shutdown message received. Exiting.\n");
            exit(0);
        }

        /* Print the received message to the console */
        printf("[RECEIVED] From server/other client: %s\n", buffer);
    }

    return NULL; /* This point is never reached */
}

int main(int argc, char *argv[]) {
    /*
     * Check command-line arguments.
     * - The user must provide the server's IP address as an argument.
     */
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <server_ip>\n", argv[0]);
        return 1;
    }

    /*
     * 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 socket for communicating with the server.
     * - SOCK_STREAM indicates a TCP connection.
     *
    SOCKET sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sock == 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 srv = {
        .sin_family = AF_INET,
        .sin_port = htons(8080) /* Convert port to network byte order */
    };

    /*
     * Convert the server's IP address from string to binary format.
     * - `inet_pton()` returns <= 0 if the conversion fails.
     */
    if (inet_pton(AF_INET, argv[1], &srv.sin_addr) <= 0) {
        fprintf(stderr, "Invalid server address.\n");
        closesocket(sock);
        WSACleanup();
        return 1;
    }

    /*
     * Connect to the server.
     * - If the connection fails, clean up and exit.
     */
    if (connect(sock, (struct sockaddr *)&srv, sizeof(srv)) == SOCKET_ERROR) {
        fprintf(stderr, "Connection to server failed: %d\n", WSAGetLastError());
        closesocket(sock);
        WSACleanup();
        return 1;
    }

    printf("[DEBUG] Connected as FirstClient.\n");

    /*
     * Create a separate thread for receiving messages from the server.
     * - The main thread remains available for user input and sending messages.
     */
    struct thread_args *targs = calloc(1, sizeof(*targs));
    targs->sock = sock;
    pthread_t recv_tid;
    if (pthread_create(&recv_tid, NULL, receive_thread, targs) != 0) {
        fprintf(stderr, "Failed to create receive thread.\n");
        free(targs);
        closesocket(sock);
        WSACleanup();
        return 1;
    }

    /*
     * Main thread handles user input.
     * - Messages typed by the user are sent to the server.
     * - If the user types "Exit Server," the client exits.
     */
    char input[1024];
    while (fgets(input, sizeof(input), stdin)) {
        /*
         * Remove trailing newline character from the input string.
         * - This ensures the server receives a clean message.
         */
        char *nl = strchr(input, '\n');
        if (nl) *nl = '\0';

        /* Send the user's message to the server */
        send(sock, input, (int)strlen(input), 0);

        /*
         * Check for the "Exit Server" command.
         * - If the user types this command, the client exits.
         */
        if (strcmp(input, "Exit Server") == 0) {
            printf("[DEBUG] 'Exit Server' command sent. Exiting.\n");
            break;
        }
    }

    /*
     * Cleanup resources before exiting.
     * - Close the socket and terminate WinSock.
     */
    closesocket(sock);
    WSACleanup();
    return 0;
}