Implement streaming file download for backup route

- Enhanced the backup server route to support streaming of large backup files using Node.js streams.
- Improved error handling for file access and added appropriate HTTP responses for missing parameters and inaccessible files.
- Updated response headers to include content length and type for better client handling.

src/routes/backup/+server.ts

@@ -1,9 +1,12 @@
 import { env } from '$env/dynamic/private';
+import { createReadStream } from 'node:fs';
 import fs from 'node:fs/promises';
 import path from 'node:path';
+import { Readable } from 'node:stream';
+import type { RequestHandler } from './$types';
 
-// GET /backup?file=nombre.bak -> descarga el archivo físico desde BACKUP_PATH
-export const GET = async ({ url }: { url: URL }) => {
+// GET /backup?file=nombre.bak -> descarga el archivo físico desde BACKUP_PATH (streaming; soporta archivos muy grandes)
+export const GET: RequestHandler = async ({ url, request }) => {
     const fileName = url.searchParams.get('file');
     if (!fileName) {
         return new Response('Missing file parameter', { status: 400 });
@@ -28,14 +31,20 @@ export const GET = async ({ url }: { url: URL }) => {
             console.error('Backup path is not a regular file:', filePath);
             return new Response('Backup file not found or inaccessible', { status: 404 });
         }
-        console.log('Serving backup file from', filePath);
-        const data = await fs.readFile(filePath);
+        console.log('Serving backup file from', filePath, 'size', st.size);
+        const nodeStream = createReadStream(filePath, { highWaterMark: 1024 * 1024 });
+        request.signal.addEventListener('abort', () => {
+            nodeStream.destroy();
+        });
+        const body = Readable.toWeb(nodeStream) as unknown as ReadableStream<Uint8Array>;
         const headers = new Headers();
         headers.set('Content-Type', 'application/octet-stream');
         headers.set('Content-Disposition', `attachment; filename="${fileName}"`);
-        return new Response(data, { status: 200, headers });
-    } catch (e: any) {
-        console.error('Error serving backup file:', e?.message ?? e);
+        headers.set('Content-Length', String(st.size));
+        return new Response(body, { status: 200, headers });
+    } catch (e: unknown) {
+        const msg = e instanceof Error ? e.message : String(e);
+        console.error('Error serving backup file:', msg);
         return new Response('Backup file not found or inaccessible', { status: 404 });
     }
 };