📅 fix: Render Dotted Date Formats in Parsed Spreadsheets

packages/api/src/files/documents/crud.spec.ts

@@ -214,6 +214,29 @@ describe('Document Parser', () => {
     await expect(parseDocument({ file })).resolves.toBeDefined();
   });
 
+  test('parseDocument() renders dates with dotted number formats instead of serials', async () => {
+    const file = {
+      originalname: 'sample-dotted-dates.xlsx',
+      path: path.join(__dirname, 'sample-dotted-dates.xlsx'),
+      mimetype: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
+    } as Express.Multer.File;
+
+    const document = await parseDocument({ file });
+
+    expect(document.text).toBe(
+      'Dates:\n' +
+        'Format,Value\n' +
+        'dd.mm.yyyy,31.08.2026\n' +
+        'dd.mm,01.09\n' +
+        'd.m.yyyy,7.8.2026\n' +
+        'dd/mm/yyyy,31/08/2026\n' +
+        '"#,##0.00","1,234.50"\n' +
+        '"d. mmmm yyyy ""kl."" hh:mm",31. August 2026 kl. 12:35\n' +
+        'dd\\.mm\\.yyyy,31.08.2026\n' +
+        'hh:mm:ss.0,12:35:00.4\n',
+    );
+  });
+
   test('parseDocument() parses empty xlsx with only sheet name', async () => {
     const file = {
       originalname: 'empty.xlsx',

packages/api/src/files/documents/crud.ts

@@ -3,6 +3,7 @@ import yauzl from 'yauzl';
 import { megabyte, excelMimeTypes, FileSources } from 'librechat-data-provider';
 import type { TextItem } from 'pdfjs-dist/types/src/display/api';
 import type { MistralOCRUploadResult } from '~/types';
+import { fillUnformattedDates } from './spreadsheetDates';
 import { assertSafeZipSize } from './zipSafety';
 
 type FileParseFn = (file: Express.Multer.File) => Promise<string>;
@@ -109,15 +110,16 @@ async function wordDocToText(file: Express.Multer.File): Promise<string> {
 async function excelSheetToText(file: Express.Multer.File): Promise<string> {
   // xlsx CDN build (0.20.x) does not bind fs internally when dynamically imported;
   // readFile() fails with "Cannot access file". read() takes a pre-loaded Buffer instead.
-  const { read, utils } = await import('xlsx');
+  const { read, utils, SSF } = await import('xlsx');
   const data = await fs.promises.readFile(file.path);
   /* Reject zip-bomb XLSX/ODS before SheetJS's internal extractor runs.
    * `.xls` (BIFF/CFB) is not a ZIP — magic-byte check skips the
    * validator for it (yauzl would reject it as malformed anyway). */
   if (data.length >= 4 && data[0] === 0x50 && data[1] === 0x4b) {
     await assertSafeZipSize(data, { name: file.originalname ?? 'spreadsheet' });
   }
-  const workbook = read(data, { type: 'buffer' });
+  const workbook = read(data, { type: 'buffer', cellNF: true });
+  fillUnformattedDates(workbook, SSF);
 
   let text = '';
   for (const sheetName of workbook.SheetNames) {

packages/api/src/files/documents/html.spec.ts

@@ -289,6 +289,17 @@ describe('Office HTML producers', () => {
       expect(html).toContain('Sheet One');
       expect(html).toContain('Second Sheet');
     });
+
+    test('renders dates with dotted number formats instead of serials', async () => {
+      const html = await excelSheetToHtml(readFixture('sample-dotted-dates.xlsx'));
+      expect(html).toContain('31.08.2026');
+      expect(html).toContain('01.09');
+      expect(html).toContain('7.8.2026');
+      expect(html).toContain('31. August 2026 kl. 12:35');
+      expect(html).toContain('12:35:00.4');
+      expect(html).not.toContain('46265');
+      expect(html).not.toContain('46241');
+    });
   });
 
   describe('csvToHtml', () => {

packages/api/src/files/documents/html.ts

@@ -1,6 +1,7 @@
 import yauzl from 'yauzl';
 import { excelMimeTypes, megabyte } from 'librechat-data-provider';
 import { tryLibreOfficePreview } from './libreoffice';
+import { fillUnformattedDates } from './spreadsheetDates';
 import { assertSafeZipSize } from './zipSafety';
 
 /**
@@ -770,7 +771,8 @@ export async function excelSheetToHtml(buffer: Buffer): Promise<string> {
     await assertSafeZipSize(buffer, { name: 'spreadsheet' });
   }
   const XLSX = await import('xlsx');
-  const workbook = XLSX.read(buffer, { type: 'buffer' });
+  const workbook = XLSX.read(buffer, { type: 'buffer', cellNF: true });
+  fillUnformattedDates(workbook, XLSX.SSF);
   const sheets = await renderWorkbookSheets(workbook, XLSX);
   /* The per-sheet HTML from `sheet_to_html` is generally well-formed but we
    * still sanitize it (defense in depth). The chrome (tab strip, banners) is

packages/api/src/files/documents/spreadsheetDates.ts

@@ -0,0 +1,45 @@
+import type { CellObject, WorkBook } from 'xlsx';
+
+/** The subset of SheetJS `SSF` used here; the package types it as `any`. */
+interface SpreadsheetFormatter {
+  is_date(fmt: string): boolean;
+  format(fmt: string, value: number, options?: { date1904?: boolean }): string;
+}
+
+/**
+ * Quote every `.` in a number format so SheetJS treats it as a literal separator.
+ * Skips dots inside `"..."` literals, backslash-escaped dots and `.0` fractional seconds.
+ */
+function quoteFormatDots(fmt: string): string {
+  return fmt.replace(/"[^"]*"|\\.|\.(?!0)/g, (match) => (match === '.' ? '"."' : match));
+}
+
+/**
+ * SheetJS reads `.` in a number format as the start of fractional seconds, so date formats such
+ * as `dd.mm.yyyy` throw while formatting and the cell is left with only its raw serial number.
+ * Renders those cells again with the dots quoted; every other cell keeps what SheetJS produced.
+ * The workbook must have been read with `cellNF: true` so the format is available on `cell.z`.
+ */
+export function fillUnformattedDates(workbook: WorkBook, ssf: SpreadsheetFormatter): void {
+  const date1904 = workbook.Workbook?.WBProps?.date1904 === true;
+  for (const sheetName of workbook.SheetNames) {
+    const worksheet = workbook.Sheets[sheetName];
+    for (const address in worksheet) {
+      if (address.startsWith('!')) {
+        continue;
+      }
+      const cell = worksheet[address] as CellObject;
+      if (cell.t !== 'n' || cell.w != null || typeof cell.v !== 'number') {
+        continue;
+      }
+      if (typeof cell.z !== 'string' || !ssf.is_date(cell.z)) {
+        continue;
+      }
+      try {
+        cell.w = ssf.format(quoteFormatDots(cell.z), cell.v, { date1904 });
+      } catch {
+        /* Keep the raw value when the format still cannot be rendered */
+      }
+    }
+  }
+}