private static FullHttpResponse newUpgradeResponse() {
        final DefaultFullHttpResponse res = new DefaultFullHttpResponse(
                HTTP_1_1, SWITCHING_PROTOCOLS, Unpooled.EMPTY_BUFFER, /* validateHeaders */ true);
        res.headers().add(HttpHeaderNames.CONNECTION, HttpHeaderValues.UPGRADE);
        res.headers().add(HttpHeaderNames.UPGRADE, Http2CodecUtil.HTTP_UPGRADE_PROTOCOL_NAME);
        return res;
    }
Creates the 101 Switching Protocols response message.
core/src/main/java/com/linecorp/armeria/server/HttpServerUpgradeHandler.java