Get SslHandler by name for ALPN in HttpClientChannelInitializer (#2488)

Switch to accessing the SslHandler by name in client ALPN.
This should always return the SslHandler for remote endpoint.
If we don't do this, the pipeline will always return the first SslHandler in the pipeline.
When talking through a TLS enabled forward proxy there may be more than one SslHandler present in the pipeline.
This change ensures that we always get the SslHandler for the remote HTTP
endpoint and not an intermediary, ensuring we set the correct negotiated protocol.

Fixes #2480

reactor-netty-http/src/main/java/reactor/netty/http/client/HttpClientConfig.java

@@ -839,27 +839,30 @@ static final class H2OrHttp11Codec extends ChannelInboundHandlerAdapter {
 
 		@Override
 		public void channelActive(ChannelHandlerContext ctx) {
-			SslHandler sslHandler = ctx.pipeline().get(SslHandler.class);
-			if (sslHandler == null) {
-				throw new IllegalStateException("Cannot determine negotiated application-level protocol.");
-			}
-			String protocol = sslHandler.applicationProtocol() != null ? sslHandler.applicationProtocol() : ApplicationProtocolNames.HTTP_1_1;
-			if (log.isDebugEnabled()) {
-				log.debug(format(ctx.channel(), "Negotiated application-level protocol [" + protocol + "]"));
-			}
-			if (ApplicationProtocolNames.HTTP_2.equals(protocol)) {
-				configureHttp2Pipeline(ctx.channel().pipeline(), acceptGzip, decoder, http2Settings, observer);
-			}
-			else if (ApplicationProtocolNames.HTTP_1_1.equals(protocol)) {
-				configureHttp11Pipeline(ctx.channel().pipeline(), acceptGzip, decoder, metricsRecorder, uriTagValue);
-			}
-			else {
-				throw new IllegalStateException("unknown protocol: " + protocol);
-			}
+			ChannelHandler handler = ctx.pipeline().get(NettyPipeline.SslHandler);
+			if (handler instanceof SslHandler) {
+				SslHandler sslHandler = (SslHandler) handler;
 
-			ctx.fireChannelActive();
+				String protocol = sslHandler.applicationProtocol() != null ? sslHandler.applicationProtocol() : ApplicationProtocolNames.HTTP_1_1;
+				if (log.isDebugEnabled()) {
+					log.debug(format(ctx.channel(), "Negotiated application-level protocol [" + protocol + "]"));
+				}
+				if (ApplicationProtocolNames.HTTP_2.equals(protocol)) {
+					configureHttp2Pipeline(ctx.channel().pipeline(), acceptGzip, decoder, http2Settings, observer);
+				}
+				else if (ApplicationProtocolNames.HTTP_1_1.equals(protocol)) {
+					configureHttp11Pipeline(ctx.channel().pipeline(), acceptGzip, decoder, metricsRecorder, uriTagValue);
+				}
+				else {
+					throw new IllegalStateException("unknown protocol: " + protocol);
+				}
 
-			ctx.channel().pipeline().remove(this);
+				ctx.fireChannelActive();
+
+				ctx.channel().pipeline().remove(this);
+			} else {
+				throw new IllegalStateException("Cannot determine negotiated application-level protocol.");
+			}
 		}
 	}