validate-localname.cpp

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

int main( int argc, char *argv[] )
{
    if (argc != 2) {
        fprintf(stderr, "Usage validate-localname <hostname>\n");
        return EXIT_FAILURE;
    }
    char *hostname = argv[1];

    struct addrinfo *res;
    struct addrinfo hints;

    const char* probePort = "5051"; // We can perhaps pick a port from the port-range in resources?

    memset(&hints, 0, sizeof(struct addrinfo));
    if (getaddrinfo(hostname, probePort, &hints, &res) != 0) {
        fprintf(stderr, "Unknown hostname '%s'\n", hostname);
        return EXIT_FAILURE;
    }

    int sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
    if (sockfd < 0) {
        fprintf(stderr, "Cannot open socket\n");
        return EXIT_FAILURE;
    }

    if (bind(sockfd, res->ai_addr, res->ai_addrlen) < 0) {
        fprintf(stderr, "Cannot bind on hostname '%s'\n", hostname);
        return EXIT_FAILURE;
    }

    printf("Hostname '%s' is valid!\n", hostname);

    close(sockfd);
    return 0;
}