Fix "Connection: Upgrade" case, close #3606

This is a temporary workaround.
The proper fix would have to be in Netty.

gatling-http-client/src/main/java/io/gatling/http/client/impl/FixedWebSocketClientHandshaker13.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2011-2018 GatlingCorp (https://gatling.io)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.gatling.http.client.impl;
+
+import io.netty.handler.codec.http.FullHttpRequest;
+import io.netty.handler.codec.http.HttpHeaderNames;
+import io.netty.handler.codec.http.HttpHeaders;
+import io.netty.handler.codec.http.websocketx.WebSocketClientHandshaker13;
+import io.netty.handler.codec.http.websocketx.WebSocketVersion;
+import io.netty.util.AsciiString;
+
+import java.net.URI;
+
+public class FixedWebSocketClientHandshaker13 extends WebSocketClientHandshaker13 {
+
+  private static final AsciiString WS_UPGRADE = new AsciiString("Upgrade");
+
+  public FixedWebSocketClientHandshaker13(URI webSocketURL, String subprotocol, boolean allowExtensions, HttpHeaders customHeaders, int maxFramePayloadLength) {
+    super(webSocketURL, WebSocketVersion.V13, subprotocol, allowExtensions, customHeaders, maxFramePayloadLength);
+  }
+
+  @Override
+  protected FullHttpRequest newHandshakeRequest() {
+    FullHttpRequest handshakeRequest = super.newHandshakeRequest();
+    handshakeRequest.headers().set(HttpHeaderNames.CONNECTION, WS_UPGRADE);
+    return handshakeRequest;
+  }
+}

gatling-http-client/src/main/java/io/gatling/http/client/impl/WebSocketHandler.java

@@ -16,6 +16,8 @@
 
 package io.gatling.http.client.impl;
 
+import java.io.IOException;
+
 import io.gatling.http.client.HttpClientConfig;
 import io.gatling.http.client.WebSocketListener;
 import io.gatling.http.client.impl.request.WritableRequest;
@@ -29,8 +31,6 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.IOException;
-
 public class WebSocketHandler extends ChannelDuplexHandler {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(WebSocketHandler.class);
@@ -86,9 +86,8 @@ public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise)
         WritableRequest request = WritableRequestBuilder.buildRequest(tx.request, ctx.alloc(), config, false);
 
         handshaker =
-          WebSocketClientHandshakerFactory.newHandshaker(
+          new FixedWebSocketClientHandshaker13(
             tx.request.getUri().toJavaNetURI(),
-            WebSocketVersion.V13,
             tx.request.getWsSubprotocol(),
             true,
             request.getRequest().headers(),