@Override
            public void channelActive(ChannelHandlerContext ctx) throws Exception {
                final DefaultFullHttpRequest upgradeRequest =
                        new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.HEAD, "/");
                ctx.writeAndFlush(upgradeRequest);

                ctx.fireChannelActive();

                // Done with this handler, remove it from the pipeline.
                ctx.pipeline().remove(this);

                configureEndOfPipeline(ctx.pipeline());
            }
A handler that triggers the cleartext upgrade to HTTP/2 by sending an initial HTTP request.
thrift/thrift0.13/src/test/java/com/linecorp/armeria/server/thrift/AbstractTHttp2Client.java