添加WebSockets支持

WebSockets是一种通过HTTP创建基于双向流的通道的技术。

要通过Varnish运行WebSockets，您需要通过管道传输请求并复制升级和连接标头，如下所示：

sub vcl_recv {
    if (req.http.upgrade ~ "(?i)websocket") {
        return (pipe);
    }
}

sub vcl_pipe {
    if (req.http.upgrade) {
        set bereq.http.upgrade = req.http.upgrade;
        set bereq.http.connection = req.http.connection;
    }
}