Open a Linux Networking Socket

tinytcp.cpp

/**
 * Simple TCP Server example.
 */

#include <iostream>
#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <signal.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

using namespace std;


int net_listen(uint16_t port)
{
    char port_str[8];
    struct addrinfo hints;
    struct addrinfo *result;
    struct addrinfo *cur_ai;
    int s;
    int optval = 1;
    int sfd = -1;
    int backlog = 50;

    // Convert port to string
    sprintf(port_str, "%d", port);
    port_str[5] = '\0';

    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_canonname = NULL;
    hints.ai_addr = NULL;
    hints.ai_next = NULL;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_family = AF_UNSPEC;
    hints.ai_flags = AI_PASSIVE; // Bind to all addresses

    s = getaddrinfo(NULL, port_str, &hints, &result);
    if (s != 0) {
        fprintf(stderr, "ERROR: Cannot get address info for listen\n");
        return 0;
    }

    for (cur_ai = result; cur_ai != NULL; cur_ai = cur_ai->ai_next) {
        sfd = socket(cur_ai->ai_family, cur_ai->ai_socktype, cur_ai->ai_protocol);
        if (sfd == -1) {
            continue; // On error, try next address
        }

        if (setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval))) {
            close(sfd);
            freeaddrinfo(result);
            return -1;
        }

        if (bind(sfd, cur_ai->ai_addr, cur_ai->ai_addrlen) == 0) {
            break; // Success
        }

        // Bind failed, close socket and try next address
        close(sfd);
    }

    freeaddrinfo(result);

    if (listen(sfd, backlog) == -1) {
        return -1;
    }

    return (cur_ai == NULL) ? -1 : sfd;
}


int main() {
    printf("Listening on 8080\n");
    int cfd;
    unsigned int addrlen;
    struct sockaddr_storage claddr;
    int sfd = net_listen(8080);
    char addrstr[256];
    char host[NI_MAXHOST];
    char service[NI_MAXSERV];
    const char *msg = "Hello, and goodbye\n";

    signal(SIGPIPE, SIG_IGN); // Disable SIGPIPE for broken sockets

    while(1) {
        addrlen = sizeof(struct sockaddr_storage);
        cfd = accept(sfd, (struct sockaddr *) &claddr, &addrlen);
        if (cfd == -1) {
            fprintf(stderr, "Could not accept client connection\n");
            return 1;
        }

        if (getnameinfo((struct sockaddr *) &claddr, addrlen, host, NI_MAXHOST, service, NI_MAXSERV, 0) == 0) {
            printf("Connection from %s:%s\n", host, service);
        } else {
            printf("Connection from UNKNOWN\n");
        }


        write(cfd, msg, strlen(msg));

        close(cfd);
    }

    printf("Done\n");
    return 0;
}