look inside url when checking activity origin - #512

The previous assertion that:

> if it's a complicated thing and the `activity.id` doesn't match, I
> think we're fine rejecting the activity

was wrong: at least peertube sends activities that have `url` as an
array of objects.

Notice that this does *not*, in fact, fix #512: the peertube activity
does not contain its short URL (`https://example.com/w/someid`), so
there's no way to confirm that it is the activity we requested.

packages/backend/test/unit/misc/check-against-url.ts

@@ -0,0 +1,51 @@
+/*
+ * SPDX-FileCopyrightText: dakkar and sharkey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { IObject } from '@/core/activitypub/type.js';
+import { describe, expect, test } from '@jest/globals';
+import { assertActivityMatchesUrls } from '@/core/activitypub/misc/check-against-url.js';
+
+function assertOne(activity: IObject) {
+	// return a function so we can use `.toThrow`
+	return () => assertActivityMatchesUrls(activity, ['good']);
+}
+
+describe('assertActivityMatchesUrls', () => {
+	test('id', () => {
+		expect(assertOne({ id: 'bad' })).toThrow(/bad Activity/);
+		expect(assertOne({ id: 'good' })).not.toThrow();
+	});
+
+	test('simple url', () => {
+		expect(assertOne({ url: 'bad' })).toThrow(/bad Activity/);
+		expect(assertOne({ url: 'good' })).not.toThrow();
+	});
+
+	test('array of urls', () => {
+		expect(assertOne({ url: ['bad'] })).toThrow(/bad Activity/);
+		expect(assertOne({ url: ['bad', 'other'] })).toThrow(/bad Activity/);
+		expect(assertOne({ url: ['good'] })).not.toThrow();
+		expect(assertOne({ url: ['bad', 'good'] })).not.toThrow();
+	});
+
+	test('array of objects', () => {
+		expect(assertOne({ url: [{ href: 'bad' }] })).toThrow(/bad Activity/);
+		expect(assertOne({ url: [{ href: 'bad' }, { href: 'other' }] })).toThrow(/bad Activity/);
+		expect(assertOne({ url: [{ href: 'good' }] })).not.toThrow();
+		expect(assertOne({ url: [{ href: 'bad' }, { href: 'good' }] })).not.toThrow();
+	});
+
+	test('mixed array', () => {
+		expect(assertOne({ url: [{ href: 'bad' }, 'other'] })).toThrow(/bad Activity/);
+		expect(assertOne({ url: [{ href: 'bad' }, 'good'] })).not.toThrow();
+		expect(assertOne({ url: ['bad', { href: 'good' }] })).not.toThrow();
+	});
+
+	test('id and url', () => {
+		expect(assertOne({ id: 'other', url: 'bad' })).toThrow(/bad Activity/);
+		expect(assertOne({ id: 'bad', url: 'good' })).not.toThrow();
+		expect(assertOne({ id: 'good', url: 'bad' })).not.toThrow();
+	});
+});