fix(libreoffice): render scrolled workbooks in full for SinglePageSheets

2026-08-17 04:32:15 +01:00 · 2026-08-12 21:34:10 +02:00
parent dc61c3631e
commit 8d327a5196
5 changed files with 468 additions and 0 deletions
--- a/pkg/modules/libreoffice/api/singlepagesheets.go
+++ b/pkg/modules/libreoffice/api/singlepagesheets.go
@@ -0,0 +1,230 @@
+package api
+
+import (
+	"archive/zip"
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+)
+
+// topLeftCellAttr matches the topLeftCell attribute that an OOXML worksheet
+// uses (on <sheetView> and, for frozen panes, <pane>) to store the cell that
+// was at the top-left of the window when the workbook was saved.
+var topLeftCellAttr = regexp.MustCompile(` topLeftCell="[^"]*"`)
+
+// maxDecompressedWorksheet bounds how much a single worksheet may decompress to
+// while rewriting it. It guards against a decompression bomb and keeps memory
+// predictable. A worksheet larger than this is left untouched, so a pathological
+// workbook falls back to the original file rather than being rewritten.
+const maxDecompressedWorksheet = 128 << 20 // 128 MiB
+
+// resetCalcScrollPosition returns a path to a copy of inputPath whose worksheet
+// scroll positions have been reset to the top-left cell, or inputPath unchanged
+// when the reset does not apply or cannot be performed safely.
+//
+// LibreOffice's SinglePageSheets export starts each single page at the sheet's
+// saved topLeftCell, dropping every row and column above and to the left of it.
+// A workbook saved scrolled away from A1 therefore renders truncated. Removing
+// the attribute before the conversion makes the whole used range render.
+// See https://github.com/gotenberg/gotenberg/issues/1222.
+//
+// The function never fails the conversion. On a non-xlsx input, a workbook that
+// carries no scroll position, or any read, rewrite or validation error, it
+// returns the original path so a malformed rewrite can never reach LibreOffice.
+func resetCalcScrollPosition(ctx context.Context, logger *slog.Logger, inputPath string) string {
+	// Resolve the extension to a literal so the sanitized filename is never
+	// derived from the (user-controlled) upload name.
+	var ext string
+	switch strings.ToLower(filepath.Ext(inputPath)) {
+	case ".xlsx":
+		ext = ".xlsx"
+	case ".xlsm":
+		ext = ".xlsm"
+	default:
+		return inputPath
+	}
+
+	src, err := os.ReadFile(inputPath)
+	if err != nil {
+		logger.WarnContext(ctx, fmt.Sprintf("reset calc scroll position: read input: %s; using the original file", err))
+		return inputPath
+	}
+
+	out, changed, err := stripWorksheetScrollPosition(src)
+	if err != nil {
+		logger.WarnContext(ctx, fmt.Sprintf("reset calc scroll position: %s; using the original file", err))
+		return inputPath
+	}
+	if !changed {
+		// The common case: nothing was saved scrolled, so nothing to do.
+		return inputPath
+	}
+
+	// A rewrite that dropped, renamed or corrupted an entry must never reach
+	// LibreOffice; fall back to the original workbook if it does not round-trip.
+	if err = validateWorkbook(src, out); err != nil {
+		logger.WarnContext(ctx, fmt.Sprintf("reset calc scroll position: %s; using the original file", err))
+		return inputPath
+	}
+
+	// Write the sanitized copy alongside the input, inside the request working
+	// directory that LibreOffice already reads from. The pattern is constant,
+	// so the resulting name carries no user-controlled path component.
+	dst, err := os.CreateTemp(filepath.Dir(inputPath), "singlepagesheets-*"+ext)
+	if err != nil {
+		logger.WarnContext(ctx, fmt.Sprintf("reset calc scroll position: create sanitized file: %s; using the original file", err))
+		return inputPath
+	}
+	defer dst.Close()
+
+	_, err = dst.Write(out)
+	if err != nil {
+		_ = os.Remove(dst.Name())
+		logger.WarnContext(ctx, fmt.Sprintf("reset calc scroll position: write sanitized file: %s; using the original file", err))
+		return inputPath
+	}
+
+	logger.DebugContext(ctx, "reset calc scroll position: cleared worksheet topLeftCell for SinglePageSheets export")
+	return dst.Name()
+}
+
+// stripWorksheetScrollPosition rewrites the worksheet XML entries of an xlsx
+// workbook, removing the topLeftCell attribute, and reports whether anything
+// changed. Every non-worksheet entry, and every worksheet that does not carry
+// the attribute, is copied byte-for-byte without recompression.
+func stripWorksheetScrollPosition(src []byte) ([]byte, bool, error) {
+	reader, err := zip.NewReader(bytes.NewReader(src), int64(len(src)))
+	if err != nil {
+		return nil, false, fmt.Errorf("open workbook: %w", err)
+	}
+
+	var buf bytes.Buffer
+	writer := zip.NewWriter(&buf)
+	changed := false
+
+	for _, file := range reader.File {
+		rewritten, ok, err := rewriteWorksheet(file)
+		if err != nil {
+			return nil, false, err
+		}
+
+		if ok {
+			// Recompress only the worksheets that actually changed.
+			header := file.FileHeader
+			header.Method = zip.Deflate
+			w, err := writer.CreateHeader(&header)
+			if err != nil {
+				return nil, false, fmt.Errorf("write worksheet %q: %w", file.Name, err)
+			}
+			_, err = w.Write(rewritten)
+			if err != nil {
+				return nil, false, fmt.Errorf("write worksheet %q: %w", file.Name, err)
+			}
+			changed = true
+			continue
+		}
+
+		err = copyZipEntry(writer, file)
+		if err != nil {
+			return nil, false, err
+		}
+	}
+
+	err = writer.Close()
+	if err != nil {
+		return nil, false, fmt.Errorf("finalize workbook: %w", err)
+	}
+	if !changed {
+		return nil, false, nil
+	}
+	return buf.Bytes(), true, nil
+}
+
+// rewriteWorksheet returns file's contents with topLeftCell removed, and
+// whether file is a worksheet that carried the attribute. A worksheet without
+// the attribute, or any other entry, returns ok false so the caller copies it
+// verbatim.
+func rewriteWorksheet(file *zip.File) ([]byte, bool, error) {
+	if !strings.HasPrefix(file.Name, "xl/worksheets/") || !strings.HasSuffix(strings.ToLower(file.Name), ".xml") {
+		return nil, false, nil
+	}
+
+	rc, err := file.Open()
+	if err != nil {
+		return nil, false, fmt.Errorf("open worksheet %q: %w", file.Name, err)
+	}
+	defer rc.Close()
+
+	// Read at most maxDecompressedWorksheet+1 bytes so a decompression bomb
+	// cannot exhaust memory; a genuine overflow aborts the rewrite.
+	data, err := io.ReadAll(io.LimitReader(rc, maxDecompressedWorksheet+1))
+	if err != nil {
+		return nil, false, fmt.Errorf("read worksheet %q: %w", file.Name, err)
+	}
+	if len(data) > maxDecompressedWorksheet {
+		return nil, false, fmt.Errorf("worksheet %q exceeds %d bytes", file.Name, maxDecompressedWorksheet)
+	}
+
+	if !bytes.Contains(data, []byte("topLeftCell")) {
+		return nil, false, nil
+	}
+	return topLeftCellAttr.ReplaceAll(data, nil), true, nil
+}
+
+// copyZipEntry writes file into writer without decompressing and recompressing
+// it, preserving its exact bytes.
+func copyZipEntry(writer *zip.Writer, file *zip.File) error {
+	w, err := writer.CreateRaw(&file.FileHeader)
+	if err != nil {
+		return fmt.Errorf("copy entry %q: %w", file.Name, err)
+	}
+	rc, err := file.OpenRaw()
+	if err != nil {
+		return fmt.Errorf("open entry %q: %w", file.Name, err)
+	}
+	_, err = io.Copy(w, rc)
+	if err != nil {
+		return fmt.Errorf("copy entry %q: %w", file.Name, err)
+	}
+	return nil
+}
+
+// validateWorkbook checks that out reopens as a zip holding exactly the same
+// entry names as src, rejecting a rewrite that lost, renamed or added an entry
+// or produced a broken central directory. The entry payloads themselves are
+// not re-read: unchanged entries are copied byte-for-byte from a workbook that
+// already parsed, and rewritten worksheets are produced by the standard library
+// writer, so re-decompressing everything would only add a decompression-bomb
+// surface without catching a failure this transform can introduce.
+func validateWorkbook(src, out []byte) error {
+	original, err := zip.NewReader(bytes.NewReader(src), int64(len(src)))
+	if err != nil {
+		return fmt.Errorf("reopen original workbook: %w", err)
+	}
+	rewritten, err := zip.NewReader(bytes.NewReader(out), int64(len(out)))
+	if err != nil {
+		return fmt.Errorf("reopen rewritten workbook: %w", err)
+	}
+
+	if len(rewritten.File) != len(original.File) {
+		return fmt.Errorf("entry count changed from %d to %d", len(original.File), len(rewritten.File))
+	}
+
+	names := make(map[string]struct{}, len(original.File))
+	for _, file := range original.File {
+		names[file.Name] = struct{}{}
+	}
+	for _, file := range rewritten.File {
+		_, ok := names[file.Name]
+		if !ok {
+			return fmt.Errorf("unexpected entry %q", file.Name)
+		}
+	}
+	return nil
+}