Insert Server Name Indication (SNI) only for hostnames, not for IP addresses

Author: jakjinak

websocketpp/transport/asio/security/tls.hpp

@@ -234,16 +234,21 @@ class connection : public lib::enable_shared_from_this<connection> {
     void pre_init(init_handler callback) {
         // TODO: is this the best way to check whether this function is 
         //       available in the version of OpenSSL being used?
-        // TODO: consider case where host is an IP address
 #if OPENSSL_VERSION_NUMBER >= 0x90812f
         if (!m_is_server) {
             // For clients on systems with a suitable OpenSSL version, set the
             // TLS SNI hostname header so connecting to TLS servers using SNI
             // will work.
-            long res = SSL_set_tlsext_host_name(
-                get_socket().native_handle(), m_uri->get_host().c_str());
-            if (!(1 == res)) {
-                callback(socket::make_error_code(socket::error::tls_failed_sni_hostname));
+            auto host = m_uri->get_host();
+            lib::asio::error_code ec_addr;
+            boost::asio::ip::address addr = boost::asio::ip::make_address(host, ec_addr);
+            if (ec_addr) {
+                // The SNI applies only to DNS host names, not for IP addresses
+                long res = SSL_set_tlsext_host_name(
+                    get_socket().native_handle(), host.c_str());
+                if (!(1 == res)) {
+                    callback(socket::make_error_code(socket::error::tls_failed_sni_hostname));
+                }
             }
         }
 #endif