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Client Server Program for Primality Checking

Below is an example of a simple client-server program in C. The client sends a number to the server, and the server determines whether the number is prime or not and sends the result back to the client

Server Code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <stdbool.h>

#define PORT 8080

bool is_prime(int num) {
    if (num <= 1) return false;
    for (int i = 2; i * i <= num; i++) {
        if (num % i == 0) return false;
    }
    return true;
}

int main() {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int addrlen = sizeof(address);
    char buffer[1024] = {0};
    char response[1024];

    // Create socket file descriptor
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("Socket failed");
        exit(EXIT_FAILURE);
    }

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    // Bind the socket to the network address and port
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("Bind failed");
        close(server_fd);
        exit(EXIT_FAILURE);
    }

    // Listen for incoming connections
    if (listen(server_fd, 3) < 0) {
        perror("Listen failed");
        close(server_fd);
        exit(EXIT_FAILURE);
    }

    printf("Server is listening on port %d...\n", PORT);

    // Accept a connection
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address, 
                             (socklen_t *)&addrlen)) < 0) {
        perror("Accept failed");
        close(server_fd);
        exit(EXIT_FAILURE);
    }

    // Read data from the client
    read(new_socket, buffer, 1024);
    int number = atoi(buffer);

    // Determine if the number is prime
    if (is_prime(number)) {
        snprintf(response, sizeof(response), "%d is a prime number.", number);
    } else {
        snprintf(response, sizeof(response), "%d is not a prime number.", number);
    }

    // Send the response back to the client
    send(new_socket, response, strlen(response), 0);

    printf("Processed request for number: %d\n", number);

    // Close the sockets
    close(new_socket);
    close(server_fd);

    return 0;
}

Client Code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>

#define PORT 8080

int main() {
    int sock = 0;
    struct sockaddr_in serv_addr;
    char buffer[1024] = {0};
    char input[100];

    // Create socket file descriptor
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        printf("Socket creation error\n");
        return -1;
    }

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);

    // Convert IPv4 and IPv6 addresses from text to binary form
    if (inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr) <= 0) {
        printf("Invalid address/ Address not supported\n");
        return -1;
    }

    // Connect to the server
    if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
        printf("Connection failed\n");
        return -1;
    }

    printf("Enter a number: ");
    scanf("%s", input);

    // Send the number to the server
    send(sock, input, strlen(input), 0);

    // Read the response from the server
    read(sock, buffer, 1024);

    printf("Server: %s\n", buffer);

    // Close the socket
    close(sock);

    return 0;
}

Instructions

  1. Compile the server and client programs:

    gcc -o server server.c
gcc -o client client.c
  2. Start the server:

    ./server
  3. In another terminal, run the client:

    ./client
  4. Enter a number in the client terminal. The server will check if the number is prime and send the result back to the client.

Example Output

Server

Server is listening on port 8080...
Processed request for number: 17

Client

Enter a number: 17
Server: 17 is a prime number.

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