Enhance XLSX extraction with structured tab-delimited format and escaping

- Add clear sheet separators
- Escape special characters
- Trim trailing empty columns
- Preserve row structure
- Single-pass optimization

lightrag/api/routers/document_routes.py

@@ -1052,27 +1052,110 @@ def _extract_pptx(file_bytes: bytes) -> str:
 
 
 def _extract_xlsx(file_bytes: bytes) -> str:
-    """Extract XLSX content (synchronous).
+    """Extract XLSX content in tab-delimited format with clear sheet separation.
+
+    This function processes Excel workbooks and converts them to a structured text format
+    suitable for LLM prompts and RAG systems. Each sheet is clearly delimited with
+    separator lines, and special characters are escaped to preserve the tab-delimited structure.
+
+    Features:
+    - Each sheet is wrapped with '====================' separators for visual distinction
+    - Special characters (tabs, newlines, backslashes) are escaped to prevent structure corruption
+    - Trailing empty columns are trimmed per row to reduce token waste
+    - Empty rows are preserved as blank lines to maintain row structure
+    - Single-pass optimization for better performance on large spreadsheets
 
     Args:
         file_bytes: XLSX file content as bytes
 
     Returns:
-        str: Extracted text content
+        str: Extracted text content with all sheets in tab-delimited format.
+             Format: Sheet separators, sheet name, then tab-delimited rows.
+
+    Example output:
+        ==================== Sheet: Data ====================
+        Name\tAge\tCity
+        Alice\t30\tNew York
+        Bob\t25\tLondon
+
+        ==================== Sheet: Summary ====================
+        Total\t2
+        ====================
     """
     from openpyxl import load_workbook  # type: ignore
 
     xlsx_file = BytesIO(file_bytes)
     wb = load_workbook(xlsx_file)
-    content = ""
-    for sheet in wb:
-        content += f"Sheet: {sheet.title}\n"
+
+    def escape_cell(cell_value: str | int | float | None) -> str:
+        """Escape characters that would break tab-delimited layout.
+
+        Escape order is critical: backslashes first, then tabs/newlines.
+        This prevents double-escaping issues.
+
+        Args:
+            cell_value: The cell value to escape (can be None, str, int, or float)
+
+        Returns:
+            str: Escaped cell value safe for tab-delimited format
+        """
+        if cell_value is None:
+            return ""
+        text = str(cell_value)
+        # CRITICAL: Escape backslash first to avoid double-escaping
+        return (
+            text.replace("\\", "\\\\")  # Must be first: \ -> \\
+            .replace("\t", "\\t")  # Tab -> \t (visible)
+            .replace("\r\n", "\\n")  # Windows newline -> \n
+            .replace("\r", "\\n")  # Mac newline -> \n
+            .replace("\n", "\\n")  # Unix newline -> \n
+        )
+
+    def escape_sheet_title(title: str) -> str:
+        """Escape sheet title to prevent formatting issues in separators.
+
+        Args:
+            title: Original sheet title
+
+        Returns:
+            str: Sanitized sheet title with tabs/newlines replaced
+        """
+        return str(title).replace("\n", " ").replace("\t", " ").replace("\r", " ")
+
+    content_parts: list[str] = []
+    sheet_separator = "=" * 20
+
+    for idx, sheet in enumerate(wb):
+        if idx > 0:
+            content_parts.append("")  # Blank line between sheets for readability
+
+        # Escape sheet title to handle edge cases with special characters
+        safe_title = escape_sheet_title(sheet.title)
+        content_parts.append(f"{sheet_separator} Sheet: {safe_title} {sheet_separator}")
+
+        # Single-pass optimization: escape and trim in one iteration
         for row in sheet.iter_rows(values_only=True):
-            content += (
-                "\t".join(str(cell) if cell is not None else "" for cell in row) + "\n"
-            )
-        content += "\n"
-    return content
+            row_parts = []
+            last_nonempty_idx = -1
+
+            # Build escaped row while tracking last non-empty cell position
+            for idx, cell in enumerate(row):
+                escaped = escape_cell(cell)
+                row_parts.append(escaped)
+                if escaped != "":
+                    last_nonempty_idx = idx
+
+            # Handle completely empty rows vs rows with data
+            if last_nonempty_idx == -1:
+                # Preserve empty rows as blank lines (maintains row structure)
+                content_parts.append("")
+            else:
+                # Only join up to last non-empty cell (trim trailing empties)
+                content_parts.append("\t".join(row_parts[: last_nonempty_idx + 1]))
+
+    # Final separator for symmetry (makes parsing easier)
+    content_parts.append(sheet_separator)
+    return "\n".join(content_parts)
 
 
 async def pipeline_enqueue_file(