Added fallback to ipv4 if ipv6 is not supported

server_ws.hpp

@@ -363,7 +363,7 @@ namespace SimpleWeb {
       std::unique_lock<std::mutex> lock(start_stop_mutex);
 
       asio::ip::tcp::endpoint endpoint;
-      if(config.address.size() > 0)
+      if(!config.address.empty())
         endpoint = asio::ip::tcp::endpoint(make_address(config.address), config.port);
       else
         endpoint = asio::ip::tcp::endpoint(asio::ip::tcp::v6(), config.port);
@@ -375,7 +375,17 @@ namespace SimpleWeb {
 
       if(!acceptor)
         acceptor = std::unique_ptr<asio::ip::tcp::acceptor>(new asio::ip::tcp::acceptor(*io_service));
-      acceptor->open(endpoint.protocol());
+      try {
+        acceptor->open(endpoint.protocol());
+      }
+      catch(const system_error &error) {
+        if(error.code() == asio::error::address_family_not_supported && config.address.empty()) {
+          endpoint = asio::ip::tcp::endpoint(asio::ip::tcp::v4(), config.port);
+          acceptor->open(endpoint.protocol());
+        }
+        else
+          throw;
+      }
       acceptor->set_option(asio::socket_base::reuse_address(config.reuse_address));
       if(config.fast_open) {
 #if defined(__linux__) && defined(TCP_FASTOPEN)