Backend prefetch

backend_prefetch.vcl

# Backend prefetch
vcl 4.1;

import http;

sub vcl_recv {
    // Generate the prefetch URL
    set req.http.X-prefetch = http.prefetch_next_url(prefix = "/.*/dash/[0-9]+-[0-9]+/");
}

sub vcl_backend_fetch {
    if (bereq.http.X-prefetch != "") {
        // Execute prefetch of the next segment
	http.init(0);
        http.req_copy_headers(0);
        http.req_set_method(0, "HEAD");
        http.req_set_url(0, bereq.http.X-prefetch);
        http.req_send_and_finish(0);
    }
}