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// shunt - write suppression
//
// Remembers when each (set, address) element expires in the kernel so a
// repeated DNS answer does not rewrite an element that is still fresh.
//
// SPDX-License-Identifier: GPL-3.0-or-later
// Copyright (c) 2026 Dirk Brenken <dev@brenken.org>
export function create(entry_ttl) {
let exp = {};
// A write is due when it moves the expiry by at least half of the
// lifetime it carries, in either direction: an answer with a long TTL
// extends an element that has aged past half, a short one cuts an
// element that poll or an earlier answer left long. Anything closer is
// a rewrite the kernel would not notice.
function due(set, addr, now, ttl) {
let k = `${set}/${addr}`;
let t = ttl ?? entry_ttl;
let e = now + t;
let cur = exp[k];
let d = (cur == null) ? t : (e > cur) ? e - cur : cur - e;
if (d * 2 < t)
return false;
exp[k] = e;
return true;
}
function prune(now) {
let n = 0;
for (let k in exp) {
if (now >= exp[k]) {
delete exp[k];
n++;
}
}
return n;
}
// Dropped wholesale when the table had to be re-created: the kernel has
// no elements any more, so every pair is due again regardless of age.
function reset() {
exp = {};
}
function size() {
return length(keys(exp));
}
return { due, prune, reset, size };
};
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