Computer Systems Fundamentals

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

int main(void) {

    // create a IPv4 TCP/IP socket
    int sock_fd = socket(AF_INET, SOCK_STREAM, 0);

    struct addrinfo hints = {
        .ai_family = AF_INET,        /* IPv4 only */
        .ai_socktype = SOCK_STREAM,  /* TCP */
    };

    // we wish to connect to port 1521 on our local machine
    // first convert it to a struct addrinfo

    struct addrinfo *a;
    int s = getaddrinfo("localhost", "1521", &hints, &a);
    if (s != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
        return 1;
    }

    // then try to establish a connection
    if (connect(sock_fd, a->ai_addr, a->ai_addrlen) == -1) {
        perror("connect");
        exit(2);
    }

    char *message = "My name is Ingo Montoya";
    printf("SENDING: %s\n", message);

    write(sock_fd, message, strlen(message));

    char response[1000];
    int n_bytes = read(sock_fd, response, (sizeof response) - 1);
    response[n_bytes] = '\0';
    printf("RESPONSE WAS: %s\n", response);

    close(sock_fd);

    return 0;
}

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

int main(int argc, char **argv) {

    // create a IPv4 TCP/IP socket
    int sock_fd = socket(AF_INET, SOCK_STREAM, 0);

    struct addrinfo hints = {
        .ai_family = AF_INET,
        .ai_socktype = SOCK_STREAM,
        .ai_flags = AI_PASSIVE,
    };

    // we wish to wait for connections on port 1521 on our local machine
    // first convert it to a struct addrinfo
    struct addrinfo *a;
    int s = getaddrinfo(NULL, "1521", &hints, &a);
    if (s != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
        exit(1);
    }

    // attach the address to the socket
    if (bind(sock_fd, a->ai_addr, a->ai_addrlen) != 0) {
        perror("bind()");
        return 1;
    }

    // specify the maximum number of connections that can be queued for the socket
    if (listen(sock_fd, 16) != 0) {
        perror("listen()");
        return 1;
    }

    printf("Waiting for connection\n");
    int client_fd;
    while ((client_fd = accept(sock_fd, NULL, NULL)) >= 0) {

        // a real server might spawn a client process here to handle the connection
        // so it can accept another connection immediately

        printf("Connection made: client_fd=%d\n", client_fd);

        char message[1024];
        int n_bytes = read(client_fd, message, (sizeof message) - 1);
        message[n_bytes] = '\0';
        printf("READ %d BYTES: %s\n", n_bytes, message);

        char response[1024];
        snprintf(response, sizeof response, "%d bytes received \n", n_bytes);
        printf("SENDING: %s\n", response);
        write(client_fd, response, strlen(response));
        close(client_fd);
    }

    close(sock_fd);

    return 0;
}