refactoring

Resolve #7779

packages/backend/src/misc/detect-url-mime.ts

@@ -0,0 +1,15 @@
+import { createTemp } from './create-temp';
+import { downloadUrl } from './download-url';
+import { detectType } from './get-file-info';
+
+export async function detectUrlMime(url: string) {
+	const [path, cleanup] = await createTemp();
+
+	try {
+		await downloadUrl(url, path);
+		const { mime } = await detectType(path);
+		return mime;
+	} finally {
+		cleanup();
+	}
+}