download 기능 수정

packages/backend/src/services/onlyOffice.ts

@@ -1,5 +1,6 @@
 import { config } from '../config.js';
 import type { SessionDoc } from '../types/session.js';
+import { overwriteDocument } from './sessionStore.js';
 import { signOnlyOfficePayload } from '../utils/jwt.js';
 
 export function buildEditorConfig(doc: SessionDoc, userId: string) {
@@ -49,6 +50,59 @@ export function buildEditorConfig(doc: SessionDoc, userId: string) {
   };
 }
 
+/** Prefer the internal Document Server base when the backend fetches the file. */
+export function toInternalOnlyOfficeUrl(raw: string): string {
+  try {
+    const target = new URL(raw);
+    const publicBase = new URL(config.onlyOfficeUrl);
+    const internalBase = new URL(config.onlyOfficeInternalUrl);
+    if (
+      target.host === publicBase.host ||
+      target.host === internalBase.host
+    ) {
+      target.protocol = internalBase.protocol;
+      target.host = internalBase.host;
+    }
+    return target.toString();
+  } catch {
+    return raw;
+  }
+}
+
+/**
+ * Download an OnlyOffice-produced file URL and overwrite the session document
+ * (converting back to the original extension when needed).
+ */
+export async function persistDocumentFromUrl(
+  doc: SessionDoc,
+  fileUrl: string,
+  filetype?: string,
+): Promise<Buffer> {
+  const fetchUrl = toInternalOnlyOfficeUrl(fileUrl);
+  const downloaded = await fetch(fetchUrl);
+  if (!downloaded.ok) {
+    throw new Error(`download_failed_${downloaded.status}`);
+  }
+
+  let buffer: Buffer = Buffer.from(await downloaded.arrayBuffer());
+  const returnedType = (filetype ?? doc.fileType).toLowerCase();
+
+  if (returnedType !== doc.fileType) {
+    const converted = await convertToOriginalFormat(
+      fetchUrl,
+      returnedType,
+      doc.fileType,
+    );
+    if (!converted) {
+      throw new Error(`convert_failed:${returnedType}->${doc.fileType}`);
+    }
+    buffer = Buffer.from(converted);
+  }
+
+  await overwriteDocument(doc, buffer, doc.fileType);
+  return buffer;
+}
+
 export async function convertToOriginalFormat(
   sourceUrl: string,
   fromExt: string,