Adding WebSockets support

WebSockets is a technology for creating a bidirectional stream-based channel over HTTP.

To run WebSockets through Varnish you need to pipe the request and copy the Upgrade header as follows:

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;
    }
}