Set the HOST header in Http2ClientInitializer when trying to start an…

… upgrade request (#9177)

Motivation:

The io.netty.example.http2.helloworld.client.Http2Client example should work in the h2c (HTTP2 cleartext - non-TLS) mode, which is the default for this example unless you set a -Dssl VM param. As we do not set the HOST header some servers do reject the upgrade request.

Modifications:

Set the HOST header

Result:

Fixes #9115.

example/src/main/java/io/netty/example/http2/helloworld/client/Http2ClientInitializer.java

@@ -22,6 +22,7 @@
 import io.netty.handler.codec.http.DefaultFullHttpRequest;
 import io.netty.handler.codec.http.HttpClientCodec;
 import io.netty.handler.codec.http.HttpClientUpgradeHandler;
+import io.netty.handler.codec.http.HttpHeaderNames;
 import io.netty.handler.codec.http.HttpMethod;
 import io.netty.handler.codec.http.HttpVersion;
 import io.netty.handler.codec.http2.DefaultHttp2Connection;
@@ -36,6 +37,8 @@
 import io.netty.handler.ssl.ApplicationProtocolNegotiationHandler;
 import io.netty.handler.ssl.SslContext;
 
+import java.net.InetSocketAddress;
+
 import static io.netty.handler.logging.LogLevel.INFO;
 
 /**
@@ -130,10 +133,20 @@ private void configureClearText(SocketChannel ch) {
      * A handler that triggers the cleartext upgrade to HTTP/2 by sending an initial HTTP request.
      */
     private final class UpgradeRequestHandler implements ChannelInboundHandler {
+
         @Override
         public void channelActive(ChannelHandlerContext ctx) throws Exception {
             DefaultFullHttpRequest upgradeRequest =
                     new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET, "/");
+
+            // Set HOST header as the remote peer may require it.
+            InetSocketAddress remote = (InetSocketAddress) ctx.channel().remoteAddress();
+            String hostString = remote.getHostString();
+            if (hostString == null) {
+                hostString = remote.getAddress().getHostAddress();
+            }
+            upgradeRequest.headers().set(HttpHeaderNames.HOST, hostString + ':' + remote.getPort());
+
             ctx.writeAndFlush(upgradeRequest);
 
             ctx.fireChannelActive();