dnsmasq: a resolver tool and event (ADR 0044/0046)

The mesh's resolver is more than config after all. Tools: dnsmasq_names (what
this node answers, from the generated wildcard file) and dnsmasq_resolve (resolve
a name through this node's own resolver — the check that wildcard-resolution
actually answers). Event: it watches the wildcard file and emits
module.dnsmasq.name.added/.removed as machines' names become resolvable here —
DNS having propagated to this node, distinct from the mesh's node.* events.
Typechecks; manifest parses.

modules/dnsmasq/index.ts

@@ -0,0 +1,38 @@
+// dnsmasq's events. The resolver's answered set changes whenever the mesh rewrites the wildcard file
+// and restarts it — a machine joined the private network or left it. This watches that file and
+// announces, from the resolver's own vantage, that a name became (or stopped being) resolvable on
+// this node: DNS having actually propagated here, distinct from the mesh's own node.* events.
+//
+// Emits (novox/hq ADR 0046/0047):
+//   module.dnsmasq.name.added    — this node's resolver now answers a machine's name
+//   module.dnsmasq.name.removed  — it no longer does
+
+import { emit } from "@novox/mesh-sdk/events";
+import { DnsmasqClient } from "./client.js";
+
+const dnsmasq = DnsmasqClient.fromEnv();
+
+// name -> address, primed silently so a restart does not re-announce every name it already answered.
+const known = new Map<string, string>();
+let primed = false;
+
+async function poll(): Promise<void> {
+  const now = new Map((await dnsmasq.answeredNames()).map((a) => [a.name, a.address]));
+  if (primed) {
+    for (const [name, address] of now) {
+      if (!known.has(name)) await emit("module.dnsmasq.name.added", { name, address });
+    }
+    for (const [name] of known) {
+      if (!now.has(name)) await emit("module.dnsmasq.name.removed", { name });
+    }
+  }
+  known.clear();
+  for (const [name, address] of now) known.set(name, address);
+  primed = true;
+}
+
+const run = (): void => void poll().catch((err) => console.error(`[dnsmasq] ${err}`));
+setInterval(run, 30_000);
+run();
+
+console.log("[dnsmasq] watching the resolver's answered names");