private void doProceedToNextHop(
            final State state,
            final HttpRequest request,
            final AsyncEntityProducer entityProducer,
            final AsyncExecChain.Scope scope,
            final AsyncExecChain chain,
            final AsyncExecCallback asyncExecCallback) {
        final RouteTracker tracker = state.tracker;
        final String exchangeId = scope.exchangeId;
        final HttpRoute route = scope.route;
        final AsyncExecRuntime execRuntime = scope.execRuntime;
        final CancellableDependency operation = scope.cancellableDependency;
        final HttpClientContext clientContext = scope.clientContext;

        final HttpRoute fact = tracker.toRoute();
        final int step = routeDirector.nextStep(route, fact);

        switch (step) {
            case HttpRouteDirector.CONNECT_TARGET:
                operation.setDependency(execRuntime.connectEndpoint(clientContext, new FutureCallback<AsyncExecRuntime>() {

                    @Override
                    public void completed(final AsyncExecRuntime execRuntime) {
                        tracker.connectTarget(route.isSecure());
                        if (LOG.isDebugEnabled()) {
                            LOG.debug("{} connected to target", exchangeId);
                        }
                        proceedToNextHop(state, request, entityProducer, scope, chain, asyncExecCallback);
                    }

                    @Override
                    public void failed(final Exception ex) {
                        asyncExecCallback.failed(ex);
                    }

                    @Override
                    public void cancelled() {
                        asyncExecCallback.failed(new InterruptedIOException());
                    }

                }));
                break;

            case HttpRouteDirector.CONNECT_PROXY:
                operation.setDependency(execRuntime.connectEndpoint(clientContext, new FutureCallback<AsyncExecRuntime>() {

                    @Override
                    public void completed(final AsyncExecRuntime execRuntime) {
                        final HttpHost proxy = route.getProxyHost();
                        tracker.connectProxy(proxy, route.isSecure() && !route.isTunnelled());
                        if (LOG.isDebugEnabled()) {
                            LOG.debug("{} connected to proxy", exchangeId);
                        }
                        proceedToNextHop(state, request, entityProducer, scope, chain, asyncExecCallback);
                    }

                    @Override
                    public void failed(final Exception ex) {
                        asyncExecCallback.failed(ex);
                    }

                    @Override
                    public void cancelled() {
                        asyncExecCallback.failed(new InterruptedIOException());
                    }

                }));
                break;

            case HttpRouteDirector.TUNNEL_TARGET:
                final HttpHost proxy = route.getProxyHost();
                final HttpHost target = route.getTargetHost();
                if (LOG.isDebugEnabled()) {
                    LOG.debug("{} create tunnel", exchangeId);
                }
                createTunnel(state, proxy, target, scope, new AsyncExecCallback() {

                    @Override
                    public AsyncDataConsumer handleResponse(final HttpResponse response, final EntityDetails entityDetails) throws HttpException, IOException {
                        return asyncExecCallback.handleResponse(response, entityDetails);
                    }

                    @Override
                    public void handleInformationResponse(final HttpResponse response) throws HttpException, IOException {
                        asyncExecCallback.handleInformationResponse(response);
                    }

                    @Override
                    public void completed() {
                        if (!execRuntime.isEndpointConnected()) {
                            // Remote endpoint disconnected. Need to start over
                            if (LOG.isDebugEnabled()) {
                                LOG.debug("{} proxy disconnected", exchangeId);
                            }
                            state.tracker.reset();
                        }
                        if (state.challenged) {
                            if (LOG.isDebugEnabled()) {
                                LOG.debug("{} proxy authentication required", exchangeId);
                            }
                            proceedToNextHop(state, request, entityProducer, scope, chain, asyncExecCallback);
                        } else {
                            if (state.tunnelRefused) {
                                if (LOG.isDebugEnabled()) {
                                    LOG.debug("{} tunnel refused", exchangeId);
                                }
                                asyncExecCallback.completed();
                            } else {
                                if (LOG.isDebugEnabled()) {
                                    LOG.debug("{} tunnel to target created", exchangeId);
                                }
                                tracker.tunnelTarget(false);
                                proceedToNextHop(state, request, entityProducer, scope, chain, asyncExecCallback);
                            }
                        }
                    }

                    @Override
                    public void failed(final Exception cause) {
                        execRuntime.markConnectionNonReusable();
                        asyncExecCallback.failed(cause);
                    }

                });
                break;

            case HttpRouteDirector.TUNNEL_PROXY:
                // The most simple example for this case is a proxy chain
                // of two proxies, where P1 must be tunnelled to P2.
                // route: Source -> P1 -> P2 -> Target (3 hops)
                // fact:  Source -> P1 -> Target       (2 hops)
                asyncExecCallback.failed(new HttpException("Proxy chains are not supported"));
                break;

            case HttpRouteDirector.LAYER_PROTOCOL:
                execRuntime.upgradeTls(clientContext, new FutureCallback<AsyncExecRuntime>() {

                    @Override
                    public void completed(final AsyncExecRuntime asyncExecRuntime) {
                        if (LOG.isDebugEnabled()) {
                            LOG.debug("{} upgraded to TLS", exchangeId);
                        }
                        tracker.layerProtocol(route.isSecure());
                        proceedToNextHop(state, request, entityProducer, scope, chain, asyncExecCallback);
                    }

                    @Override
                    public void failed(final Exception ex) {
                        asyncExecCallback.failed(ex);
                    }

                    @Override
                    public void cancelled() {
                        asyncExecCallback.failed(new InterruptedIOException());
                    }

                });
                break;

            case HttpRouteDirector.UNREACHABLE:
                asyncExecCallback.failed(new HttpException("Unable to establish route: " +
                        "planned = " + route + "; current = " + fact));
                break;

            case HttpRouteDirector.COMPLETE:
                if (LOG.isDebugEnabled()) {
                    LOG.debug("{} route fully established", exchangeId);
                }
                proceedConnected(request, entityProducer, scope, chain, asyncExecCallback);
                break;

            default:
                throw new IllegalStateException("Unknown step indicator " + step + " from RouteDirector.");
        }
    }
Request execution handler in the asynchronous request execution chain
that is responsible for establishing connection to the target
origin server as specified by the current connection route.

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