Modern way to bind a socket to a port

README.md

Simple function that takes a socket type and a port, and returns a new socket of that type, bound to that port on the wildcard address (on either IPv4 or IPv6).

This is the modern way to create a socket that will accept connections from other hosts. You use it like that:

int my_socket = bound_socket(SOCK_DGRAM, 8080);
if (my_socket == -1) {
  // Failed to get (or bind) socket
}

Note: if it doesn't compile, you may need to define the feature flags for getaddrinfo or change the standard.

socket.c

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

int bound_socket(int socktype, uint16_t port) {
    char port_str [8];
    struct addrinfo hints;
    struct addrinfo *result, *rp;
    
    /* Get the possible bind addresses */
    
    memset(&hints, 0x00, sizeof (struct addrinfo));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = socktype;
    hints.ai_flags = AI_PASSIVE;
    
    sprintf(port_str, "%u", port);
    
    if (getaddrinfo(NULL, port_str, &hints, &result))
        return -1;
    
    /* Try to bind to each address until one works */
    
    for (rp = result; rp != NULL; rp = rp->ai_next) {
        int sock = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
        if (sock == -1) continue;
        
        if (bind(sock, rp->ai_addr, rp->ai_addrlen) == 0) {
            freeaddrinfo(result);
            return sock;
        }
        
        close(sock);
    }
    
    /* Couldn't bind */
    
    freeaddrinfo(result);
    return -1;
}