## server.c
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char const *argv[]) {
    if (argc > 2)
        return 128;

    int serv_sock, connect_sock, port = 13172;
    char *msg = "Hello from server process.";
    struct sockaddr_in address;
    char buf[1024] = { 0 };
    if (argc == 2)
        port = atoi(argv[1]);

    if ((serv_sock = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket");
        return 1;
    }

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

    if (bind(serv_sock, (struct sockaddr*) &address, sizeof(address)) < 0) {
        perror("bind");
        return 1;
    }

    if (listen(serv_sock, 1) < 0) {
        perror("listen");
        return 1;
    }

    struct sockaddr_in peer;
    int size = sizeof(struct sockaddr_in);
    if ((connect_sock = accept(serv_sock, (struct sockaddr *) &peer, (socklen_t*) &size) < 0)) {
        perror("accept");
        return 1;
    }

    printf("Read %d byte\n", read(connect_sock, buf, 1024));
    fflush(stdout);
    printf("Message: %s\n", buf);
    send(connect_sock, msg, strlen(msg), 0);
    shutdown(connect_sock, 0);
    shutdown(serv_sock, 0);

    return 0;
}

## client
#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, char const *argv[]) {
    if (argc > 2)
        return 128;

    int sock, port = 13172;
    struct sockaddr_in server;
    char *msg = "Hello from client process.";
    char buf[1024] = { 0 };
    if (argc == 2)
        port = atoi(argv[1]);

    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket");
        return 1;
    }

    server.sin_family = AF_INET;
    server.sin_port = htons(port);
    if ((inet_pton(AF_INET, "127.0.0.1", &server.sin_addr)) <= 0)
        return 1;

    if ((connect(sock, (struct sockaddr *) &server, sizeof(server))) < 0) {
        perror("connect");
        return 1;
    }

    printf("Sent %d byte\n", send(sock, msg, strlen(msg), 0));
    fflush(stdout);
    int n = read(sock, buf, 1024);
    printf("Message: %s", buf);
    shutdown(sock, 0);

}