connection_check.cpp

#include <sys/socket.h>
#include <netinet/tcp.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <iostream>
#include <cerrno>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <curl/curl.h>
#include <ifaddrs.h>
#include <net/if.h>

bool check_connection(char* ifname, char* test_server){
  CURL *curl = curl_easy_init();
  CURLcode res;
  if(curl){
    curl_easy_setopt(curl, CURLOPT_URL, test_server);
    curl_easy_setopt(curl, CURLOPT_INTERFACE, ifname);
    curl_easy_setopt(curl, CURLOPT_NOBODY, 1L);
    curl_easy_setopt(curl, CURLOPT_TIMEOUT, 1L);
    res = curl_easy_perform(curl);
  }

  curl_easy_cleanup(curl);
  return (res == CURLE_OK);
}

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

  if(argc < 2){
    printf("Need a argument to be test server\n");
    exit(EXIT_FAILURE);
  }

  struct ifaddrs *ifaddr, *ifa;
  if(getifaddrs(&ifaddr) == -1){
    perror("getifaddrs()");
    exit(EXIT_FAILURE);
  }

  for(ifa = ifaddr; ifa != nullptr ; ifa = ifa->ifa_next) {
    bool has_it = false;
    if(ifa->ifa_addr->sa_family == AF_PACKET){
      has_it = check_connection(ifa->ifa_name, argv[1]);
    } else {
      continue;
    }
    printf("%*s: %s\n",
             IFNAMSIZ,
             ifa->ifa_name,
             has_it ? "[Route to internet]" : "[-----------------]"
      );

  }
  freeifaddrs(ifaddr);

	exit(EXIT_SUCCESS);
}