server: reduce dead instance detection to 7 days

CALCKEY.md

@@ -124,3 +124,4 @@
 	- 384e8c49b738f576ba8843296de6cebf01c1b247: server: allow to like own gallery posts
 	- 4c5aa9e53887cca5561fcec6ab0754e018f589a5: server: allow to like own pages
 	- 923c93da1228458dd65be47483c198a1a9191bcf: use await for notes.countBy
+	- ca90cedba0a0704b503c2778694230f5a7dfbace: server: reduce dead instance detection to 7 days

packages/backend/src/misc/skipped-instances.ts

@@ -0,0 +1,54 @@
+import { Brackets } from 'typeorm';
+import { fetchMeta } from '@/misc/fetch-meta.js';
+import { Instances } from '@/models/index.js';
+import { Instance } from '@/models/entities/instance.js';
+import { DAY } from '@/const.js';
+
+// Threshold from last contact after which an instance will be considered
+// "dead" and should no longer get activities delivered to it.
+const deadThreshold = 7 * DAY;
+
+/**
+ * Returns the subset of hosts which should be skipped.
+ * 
+ * @param hosts array of punycoded instance hosts
+ * @returns array of punycoed instance hosts that should be skipped (subset of hosts parameter)
+ */
+export async function skippedInstances(hosts: Array<Instace['host']>): Array<Instance['host']> {
+	// first check for blocked instances since that info may already be in memory
+	const { blockedHosts } = await fetchMeta();
+
+	const skipped = hosts.filter(host => blockedHosts.includes(host));
+	// if possible return early and skip accessing the database
+	if (skipped.length === hosts.length) return hosts;	
+
+	const deadTime = new Date(Date.now() - deadThreshold);
+
+	return skipped.concat(
+		await Instances.createQueryBuilder('instance')
+			.where('instance.host in (:...hosts)', {
+				// don't check hosts again that we already know are suspended
+				// also avoids adding duplicates to the list
+				hosts: hosts.filter(host => !skipped.includes(host)),
+			})
+			.andWhere(new Brackets(qb => { qb
+				.where('instance.isSuspended')
+				.orWhere('instance.lastCommunicatedAt < :deadTime', { deadTime });
+			}))
+			.select('host')
+			.getRawMany()
+	);
+}
+
+/**
+ * Returns whether a specific host (punycoded) should be skipped.
+ * Convenience wrapper around skippedInstances which should only be used if there is a single host to check.
+ * If you have multiple hosts, consider using skippedInstances instead to do a bulk check.
+ *
+ * @param host punycoded instance host
+ * @returns whether the given host should be skipped
+ */
+export async function shouldSkipInstance(host: Instance['host']): boolean {
+	const skipped = await skippedInstances([host]);
+	return skipped.length > 0;
+}