// SERWER
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define PORT_NUMBER 12345
#define BUFFER_SIZE 256

int main()
{
    int server_socket, client_socket, address_length, pid;
    struct sockaddr_in server_address, client_address;
    char buffer[BUFFER_SIZE];

    // create server socket
    server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket == -1) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    // set server address
    memset(&server_address, 0, sizeof(server_address));
    server_address.sin_family = AF_INET;
    server_address.sin_port = htons(PORT_NUMBER);
    server_address.sin_addr.s_addr = INADDR_ANY;

    // bind server socket to address
    if (bind(server_socket, (struct sockaddr *)&server_address, sizeof(server_address)) == -1) {
        perror("bind");
        exit(EXIT_FAILURE);
    }

    // listen for incoming connections
    if (listen(server_socket, 5) == -1) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

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

    while (1) {
        // accept incoming connection
        address_length = sizeof(client_address);
        client_socket = accept(server_socket, (struct sockaddr *)&client_address, &address_length);
        if (client_socket == -1) {
            perror("accept");
            continue;
        }

        // fork new process to handle client request
        pid = fork();
        if (pid == -1) {
            perror("fork");
            exit(EXIT_FAILURE);
        } else if (pid == 0) { // child process
            // close server socket in child process
            close(server_socket);

            // read message from client
            memset(buffer, 0, BUFFER_SIZE);
            if (read(client_socket, buffer, BUFFER_SIZE) == -1) {
                perror("read");
                exit(EXIT_FAILURE);
            }
            printf("Received message: %s\n", buffer);

            // send response to client
            if (write(client_socket, "Message received", 16) == -1) {
                perror("write");
                exit(EXIT_FAILURE);
            }

            // close client socket in child process
            close(client_socket);

            // exit child process
            exit(EXIT_SUCCESS);
        } else { // parent process
            // close client socket in parent process
            close(client_socket);
        }
    }

    // close server socket
    close(server_socket);

    return 0;
}

// KLIENT
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

#define SERVER_ADDRESS "localhost"
#define PORT_NUMBER 12345
#define BUFFER_SIZE 256

int main()
{
    int client_socket, result;
    struct sockaddr_in server_address;
    struct hostent *server;
    char buffer[BUFFER_SIZE];

    // resolve server hostname
    server = gethostbyname(SERVER_ADDRESS);
    if (server == NULL) {
        fprintf(stderr, "Error: no such host: %s\n", SERVER_ADDRESS);
        exit(EXIT_FAILURE);
    }

    // create client socket
    client_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (client_socket == -1) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    // set server address
    memset(&server_address, 0, sizeof(server_address));
    server_address.sin_family = AF_INET;
    memcpy(&server_address.sin_addr.s_addr, server->h_addr, server->h_length);
    server_address.sin_port = htons(PORT_NUMBER);

    // connect to server
    result = connect(client_socket, (struct sockaddr *)&server_address, sizeof(server_address));
    if (result == -1) {
        perror("connect");
        exit(EXIT_FAILURE);
    }

    // send message to server
    if (write(client_socket, "Hello, server", 14) == -1) {
        perror("write");
        exit(EXIT_FAILURE);
    }

    // read response from server
    memset(buffer, 0, BUFFER_SIZE);
    if (read(client_socket, buffer, BUFFER_SIZE) == -1) {
        perror("read");
        exit(EXIT_FAILURE);
    }
    printf("Received response: %s\n", buffer);

    // close client socket
    close(client_socket);

    return 0;
}