brotli.vcl

sub vcl_recv {
    if(req.http.Accept-Encoding ~ "br") {
        set req.http.X-brotli = "true";
    }
}

sub vcl_hash {
    if(req.http.X-brotli == "true") {
        hash_data("br");
    }
}

sub vcl_hit {
    if(req.http.X-brotli == "true") {
        if(obj.ttl <= 0 && obj.grace > 0){
            set req.http.X-brotli-bgfetch = "true";
        }
    }
}

sub vcl_backend_fetch {
    if(req.http.X-brotli == "true") {
        if(req.http.X-brotli-bgfetch == "true") {
            set bereq.http.accept-encoding = "br";

            # we don't want a 304, so clear out last modified and etag
            unset bereq.http.if-modified-since;
            unset bereq.http.if-none-match;
        }
    }

    unset bereq.http.X-brotli;
    unset bereq.http.X-brotli-bgfetch;
}

sub vcl_backend_response {
    # blah blah
    # set your default ttls here
    beresp.ttl = 1y;

    if(req.http.X-brotli == "true") {
        if(req.http.X-brotli-bgfetch != "true") {
            beresp.ttl = 0;
            beresp.grace = 1h;
        }
    }
}