@Override
                        public void completed(final AsyncExecRuntime result) {
                            LOG.debug("Successfully switched to {}", upgradeProtocol);
                        }
Usually the last HTTP/1.1 request execution handler in the asynchronous
request execution chain that is responsible for execution of
request/response exchanges with the opposite endpoint.

@since 5.0
httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/HttpAsyncMainClientExec.java