server.c

#include <sys/types.h>
#include <sys/socket.h> // listen()
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <unistd.h> // close()
#include <string.h> // memset()
#include <errno.h>
#include <stdio.h>

#include "server.h"

int create_tcp_server(const char* hostname, const char* servname)
{
    int socket;

    if ((socket = create_socket_stream(hostname, servname)) < 0)
        return -1;

    if (listen(socket, 5) < 0) {    /* (Socket, Waiting list size) */
        perror("listen");
        close(socket);
        return -1;
    }
    
    return socket;
}

int create_socket_stream(const char* hostname, const char* servname)
{
    struct addrinfo hints;
    struct addrinfo *result, *rp;
    int sfd, s;

    memset(&hints, 0, sizeof(struct addrinfo)); /* init hints */
    hints.ai_flags = AI_PASSIVE;                /* Not only loopback if hostname is null */
    hints.ai_family = AF_INET;                  /* AF_UNSPEC/AF_INET/AF_INET6 */
    hints.ai_socktype = SOCK_STREAM;            /* STREAM(TCP), DGRAM(UDP), SEQPACKET(?) */
    hints.ai_protocol = 0;                      /* Any protocol */
    hints.ai_canonname = NULL;
    hints.ai_addr = NULL;
    hints.ai_next = NULL;

    s = getaddrinfo(hostname, servname, &hints, &result);
    if (s != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
        return -1;
    }

    for (rp = result; rp != NULL; rp = rp->ai_next) {

        sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
        
        if (sfd == -1) {
            perror("socket");
            continue;
        }

        int optvalue = 1;
        setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &optvalue, sizeof(optvalue));

        if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0) {
            break;  /* Success */
        } else {
            fprintf(stderr, "Warning: failed to bind to address %s, service: %s (%m).\n", inet_ntoa(((const struct sockaddr_in*)(rp->ai_addr))->sin_addr), servname);
        }

        close(sfd);
    }
    freeaddrinfo(result);   /* No longer needed */

    if (rp == NULL) {   /* No address succeeded */
        fprintf(stderr, "Error: Could not bind\n");
        return -1;
    }

    return sfd;
}