Live prefetching

prefetch_live.vcl

# Live prefetching

vcl 4.1;

import http;
import kvstore;

sub vcl_init
{
    new limit = kvstore.init();
}

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

    # Only prefetch once per 3s
    if (limit.counter(req.http.X-prefetch, 1, 3s) == 1) {
        http.init(0);
        http.req_copy_headers(0);
        http.req_set_method(0, "HEAD");
        http.req_set_url(0, req.http.X-prefetch);
        http.req_send_and_finish(0);
    }
}