HTTPCLIENT-2261 - Enable HTTP/2 CONNECT tunneling for HTTP/2 clients through HTTP/2 proxies

Wire HTTP/2 tunnel establishment into InternalH2ConnPool for tunneled routes by using H2OverH2TunnelSupport to convert an existing proxy HTTP/2 connection into a stream-backed tunnel session

Author: arturobernalg

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

@@ -250,6 +250,19 @@ public void cancelled() {
                     public void completed(final AsyncExecRuntime execRuntime) {
                         final HttpHost proxy = route.getProxyHost();
                         tracker.connectProxy(proxy, route.isSecure() && !route.isTunnelled());
+                        if (route.isTunnelled() && execRuntime instanceof InternalH2AsyncExecRuntime) {
+                            if (route.getHopCount() > 2) {
+                                asyncExecCallback.failed(new HttpException("Proxy chains are not supported"));
+                                return;
+                            }
+                            if (LOG.isDebugEnabled()) {
+                                LOG.debug("{} H2 tunnel to target already established by connection pool", exchangeId);
+                            }
+                            tracker.tunnelTarget(false);
+                            if (route.isLayered()) {
+                                tracker.layerProtocol(route.isSecure());
+                            }
+                        }
                         if (LOG.isDebugEnabled()) {
                             LOG.debug("{} connected to proxy", exchangeId);
                         }

httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/H2AsyncClientBuilder.java

@@ -840,9 +840,12 @@ public CloseableHttpAsyncClient build() {
                 new H2AsyncMainClientExec(httpProcessor),
                 ChainElement.MAIN_TRANSPORT.name());
 
+        final HttpProcessor proxyConnectHttpProcessor =
+                new DefaultHttpProcessor(new RequestTargetHost(), new RequestUserAgent(userAgentCopy));
+
         execChainDefinition.addFirst(
                 new AsyncConnectExec(
-                        new DefaultHttpProcessor(new RequestTargetHost(), new RequestUserAgent(userAgentCopy)),
+                        proxyConnectHttpProcessor,
                         proxyAuthStrategyCopy,
                         schemePortResolver != null ? schemePortResolver : DefaultSchemePortResolver.INSTANCE,
                         authCachingDisabled),
@@ -971,7 +974,18 @@ public CloseableHttpAsyncClient build() {
         }
 
         final MultihomeConnectionInitiator connectionInitiator = new MultihomeConnectionInitiator(ioReactor, dnsResolver);
-        final InternalH2ConnPool connPool = new InternalH2ConnPool(connectionInitiator, host -> null, tlsStrategyCopy);
+        final InternalH2ConnPool connPool = new InternalH2ConnPool(
+                connectionInitiator,
+                host -> null,
+                tlsStrategyCopy,
+                ioEventHandlerFactory,
+                proxyConnectHttpProcessor,
+                proxyAuthStrategyCopy,
+                schemePortResolver != null ? schemePortResolver : DefaultSchemePortResolver.INSTANCE,
+                authCachingDisabled,
+                authSchemeRegistryCopy,
+                credentialsProviderCopy,
+                defaultRequestConfig);
         connPool.setConnectionConfigResolver(connectionConfigResolver);
 
         List<Closeable> closeablesCopy = closeables != null ? new ArrayList<>(closeables) : null;

httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/InternalH2AsyncClient.java

@@ -108,11 +108,7 @@ HttpRoute determineRoute(
             final HttpHost httpHost,
             final HttpRequest request,
             final HttpClientContext clientContext) throws HttpException {
-        final HttpRoute route = routePlanner.determineRoute(httpHost, request, clientContext);
-        if (route.isTunnelled()) {
-            throw new HttpException("HTTP/2 tunneling not supported");
-        }
-        return route;
+        return routePlanner.determineRoute(httpHost, request, clientContext);
     }
 
 }