From 35dfde838be2dd50ee37d420f87a0cac917e621c Mon Sep 17 00:00:00 2001
From: Hazelnoot <acomputerdog@gmail.com>
Date: Sun, 25 May 2025 12:34:09 -0400
Subject: add function diffArraysSimple for more efficient change detection

---
 .../backend/src/core/FederatedInstanceService.ts   | 18 +++------
 packages/backend/src/misc/diff-arrays.ts           | 44 ++++++++++++++++++++++
 2 files changed, 50 insertions(+), 12 deletions(-)

(limited to 'packages/backend/src')

diff --git a/packages/backend/src/core/FederatedInstanceService.ts b/packages/backend/src/core/FederatedInstanceService.ts
index eb634b1d68..34df10f0ff 100644
--- a/packages/backend/src/core/FederatedInstanceService.ts
+++ b/packages/backend/src/core/FederatedInstanceService.ts
@@ -14,7 +14,7 @@ import { UtilityService } from '@/core/UtilityService.js';
 import { bindThis } from '@/decorators.js';
 import type { GlobalEvents } from '@/core/GlobalEventService.js';
 import { Serialized } from '@/types.js';
-import { diffArrays } from '@/misc/diff-arrays.js';
+import { diffArrays, diffArraysSimple } from '@/misc/diff-arrays.js';
 
 @Injectable()
 export class FederatedInstanceService implements OnApplicationShutdown {
@@ -99,11 +99,11 @@ export class FederatedInstanceService implements OnApplicationShutdown {
 
 	private syncCache(before: Serialized<MiMeta | undefined>, after: Serialized<MiMeta>): void {
 		const changed =
-			hasDiff(before?.blockedHosts, after.blockedHosts) ||
-			hasDiff(before?.silencedHosts, after.silencedHosts) ||
-			hasDiff(before?.mediaSilencedHosts, after.mediaSilencedHosts) ||
-			hasDiff(before?.federationHosts, after.federationHosts) ||
-			hasDiff(before?.bubbleInstances, after.bubbleInstances);
+			diffArraysSimple(before?.blockedHosts, after.blockedHosts) ||
+			diffArraysSimple(before?.silencedHosts, after.silencedHosts) ||
+			diffArraysSimple(before?.mediaSilencedHosts, after.mediaSilencedHosts) ||
+			diffArraysSimple(before?.federationHosts, after.federationHosts) ||
+			diffArraysSimple(before?.bubbleInstances, after.bubbleInstances);
 
 		if (changed) {
 			// We have to clear the whole thing, otherwise subdomains won't be synced.
@@ -134,9 +134,3 @@ export class FederatedInstanceService implements OnApplicationShutdown {
 		this.dispose();
 	}
 }
-
-function hasDiff(before: string[] | null | undefined, after: string[] | null | undefined): boolean {
-	const { added, removed } = diffArrays(before, after);
-	return added.length > 0 || removed.length > 0;
-}
-
diff --git a/packages/backend/src/misc/diff-arrays.ts b/packages/backend/src/misc/diff-arrays.ts
index b3879cc996..b50ca1d4f7 100644
--- a/packages/backend/src/misc/diff-arrays.ts
+++ b/packages/backend/src/misc/diff-arrays.ts
@@ -56,3 +56,47 @@ export function diffArrays<T>(dataBefore: T[] | null | undefined, dataAfter: T[]
 	// data NEITHER before nor after => no change
 	return { added: [], removed: [] };
 }
+
+/**
+ * Checks for any difference between two snapshots of data.
+ * Null, undefined, and empty arrays are supported, and duplicate values are ignored.
+ * The inputs are treated as un-ordered, so a re-ordering of the same data will NOT be considered a change.
+ * @param dataBefore Array containing data before the change
+ * @param dataAfter Array containing data after the change
+ */
+export function diffArraysSimple<T>(dataBefore: T[] | null | undefined, dataAfter: T[] | null | undefined): boolean {
+	const before = dataBefore ? new Set(dataBefore) : null;
+	const after = dataAfter ? new Set(dataAfter) : null;
+
+	if (before?.size && after?.size) {
+		// different size => changed
+		if (before.size !== after.size) return true;
+
+		// removed => changed
+		for (const host of before) {
+			// delete operation removes duplicates to speed up the "after" loop
+			if (!after.delete(host)) {
+				return true;
+			}
+		}
+
+		// added => changed
+		for (const host of after) {
+			if (!before.has(host)) {
+				return true;
+			}
+		}
+
+		// identical values => no change
+		return false;
+	}
+
+	// before and NOT after => change
+	if (before?.size) return true;
+
+	// after and NOT before => change
+	if (after?.size) return true;
+
+	// NEITHER before nor after => no change
+	return false;
+}
-- 
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