Fix(backend): ActivityPubでのHTMLへのシリアライズを修正 (#13752)

* devモードでもActivityPub系エンドポイントへアクセスできるように

* ActivityPubでのHTMLのシリアライズを修正

* ハードコードしていたurlを`httpUrl`へ修正

* テストの追加

3 files changed, 27 insertions, 3 deletions

diff --git a/packages/backend/src/core/MfmService.ts b/packages/backend/src/core/MfmService.ts
index 2fb731201b..9786f8b8bb 100644
--- a/packages/backend/src/core/MfmService.ts
+++ b/packages/backend/src/core/MfmService.ts
@@ -6,7 +6,7 @@
 import { URL } from 'node:url';
 import { Inject, Injectable } from '@nestjs/common';
 import * as parse5 from 'parse5';
-import { Window } from 'happy-dom';
+import { Window, XMLSerializer } from 'happy-dom';
 import { DI } from '@/di-symbols.js';
 import type { Config } from '@/config.js';
 import { intersperse } from '@/misc/prelude/array.js';
@@ -247,6 +247,8 @@ export class MfmService {
 
 		const doc = window.document;
 
+		const body = doc.createElement('p');
+
 		function appendChildren(children: mfm.MfmNode[], targetElement: any): void {
 			if (children) {
 				for (const child of children.map(x => (handlers as any)[x.type](x))) targetElement.appendChild(child);
@@ -457,8 +459,8 @@ export class MfmService {
 			},
 		};
 
-		appendChildren(nodes, doc.body);
+		appendChildren(nodes, body);
 
-		return `<p>${doc.body.innerHTML}</p>`;
+		return new XMLSerializer().serializeToString(body);
 	}
 }
diff --git a/packages/backend/test/unit/MfmService.ts b/packages/backend/test/unit/MfmService.ts
index f613fe9c7c..fd4a03413b 100644
--- a/packages/backend/test/unit/MfmService.ts
+++ b/packages/backend/test/unit/MfmService.ts
@@ -39,6 +39,12 @@ describe('MfmService', () => {
 			const output = '<p>foo <i>bar</i></p>';
 			assert.equal(mfmService.toHtml(mfm.parse(input)), output);
 		});
+
+		test('escape', () => {
+			const input = '```\n<p>Hello, world!</p>\n```';
+			const output = '<p><pre><code>&lt;p&gt;Hello, world!&lt;/p&gt;</code></pre></p>';
+			assert.equal(mfmService.toHtml(mfm.parse(input)), output);
+		});
 	});
 
 	describe('fromHtml', () => {
diff --git a/packages/frontend/vite.config.local-dev.ts b/packages/frontend/vite.config.local-dev.ts
index 460787fd05..f9dff13b15 100644
--- a/packages/frontend/vite.config.local-dev.ts
+++ b/packages/frontend/vite.config.local-dev.ts
@@ -51,6 +51,22 @@ const devConfig = {
 			'/_info_card_': httpUrl,
 			'/bios': httpUrl,
 			'/cli': httpUrl,
+			'/inbox': httpUrl,
+			'/notes': {
+				target: httpUrl,
+				headers: {
+					'Accept': 'application/activity+json',
+				},
+			},
+			'/users': {
+				target: httpUrl,
+				headers: {
+					'Accept': 'application/activity+json',
+				},
+			},
+			'/.well-known': {
+				target: httpUrl,
+			},
 		},
 	},
 	build: {