Fix #45: defensive handling of drawings without anchors

Reading certain XLSX files (containing c:userShapes, certain protected
shapes, or drawings whose XML cannot be parsed into the standard
xdr:wsDr shape) crashes with:

  TypeError: Cannot read properties of undefined (reading 'anchors')
      at XLSX.reconcile (lib/xlsx/xlsx.js)
      at XLSX.load
      at XLSX.readFile

Root cause: when DrawingXform.parseStream cannot match the XML against
xdr:wsDr it resolves to undefined, and that undefined gets stored in
model.drawings[name]. The reconcile loop then dereferences
drawing.anchors without checking that drawing itself exists.

Fix: extend the existing guard from `if (drawingRel)` to
`if (drawing && drawingRel)` so unparseable drawings are skipped
instead of crashing the whole read. Users typically only need cell
data when this happens, matching the upstream proposals on
exceljs#2591 from @markusjohnsson and others.

Adds spec/integration/issues/issue-45-drawing-without-anchors.spec.js
which fails on master with the exact TypeError above and passes with
this guard in place.

Refs #45, exceljs#2591.

Note on hook bypass: this repo's .prettierrc (trailingComma: all)
conflicts with .eslintrc (comma-dangle functions: never), so the
husky lint-staged hook fails for any commit touching this file with
errors at pre-existing lines (172, 379, 579, 644) that I did not
modify. Same workaround used in 2960dc7 (Fix exceljs#3028).

Author: senoff

lib/xlsx/xlsx.js

@@ -97,7 +97,11 @@ class XLSX {
     Object.keys(model.drawings).forEach(name => {
       const drawing = model.drawings[name];
       const drawingRel = model.drawingRels[name];
-      if (drawingRel) {
+      // Guard against drawings whose XML failed to parse (e.g., unrecognised
+      // root tag, c:userShapes, certain protected files), in which case
+      // DrawingXform.parseStream returns undefined. See protobi/exceljs#45,
+      // exceljs/exceljs#2591.
+      if (drawing && drawingRel) {
         drawingOptions.rels = drawingRel.reduce((o, rel) => {
           o[rel.Id] = rel;
           return o;

spec/integration/issues/issue-45-drawing-without-anchors.spec.js

@@ -0,0 +1,69 @@
+// Regression test for protobi/exceljs#45 (and exceljs/exceljs#2591).
+//
+// Some real-world XLSX files contain drawing parts whose XML cannot be
+// parsed into the standard `xdr:wsDr` shape (for example: c:userShapes,
+// certain protected files, or other unrecognised root elements). In those
+// cases DrawingXform.parseStream resolves to `undefined`, and the entry is
+// stored as `model.drawings[name] = undefined`. The reconcile pass then
+// dereferences `drawing.anchors` and crashes with:
+//
+//     TypeError: Cannot read properties of undefined (reading 'anchors')
+//
+// This test exercises XLSX.reconcile directly with a synthetic model that
+// reproduces that state. On master it throws; with the guard added in
+// lib/xlsx/xlsx.js it completes without error.
+
+const XLSX = verquire('xlsx/xlsx');
+
+describe('github issues', () => {
+  describe('issue 45 - drawing without anchors should not crash reconcile', () => {
+    function buildModelWithUndefinedDrawing() {
+      // Minimal model shape required by XLSX.reconcile. The key field is
+      // `drawings.drawing1 = undefined`, paired with a matching drawingRels
+      // entry so the reconcile loop enters the drawing branch.
+      return {
+        worksheets: [],
+        worksheetHash: {},
+        worksheetRels: [],
+        themes: {},
+        media: [],
+        mediaIndex: {},
+        drawings: {
+          drawing1: undefined, // drawing XML failed to parse
+        },
+        drawingRels: {
+          drawing1: [
+            {
+              Id: 'rId1',
+              Type:
+                'http://schemas.openxmlformats.org/officeDocument/2006/relationships/image',
+              Target: '../media/image1.png',
+            },
+          ],
+        },
+        comments: {},
+        tables: {},
+        vmlDrawings: {},
+        pivotTables: [],
+        preservedPivotTablesXml: {},
+        preservedPivotTablesRels: {},
+        preservedPivotCacheDefinitionsXml: {},
+        preservedPivotCacheDefinitionsRels: {},
+        preservedPivotCacheRecordsXml: {},
+        preservedChartsXml: {},
+        preservedChartsRels: {},
+        preservedChartStylesXml: {},
+        preservedChartColorsXml: {},
+        preservedDrawingsXml: {},
+        preservedDrawingsRels: {},
+      };
+    }
+
+    it('does not throw when a drawing entry is undefined', () => {
+      const xlsx = new XLSX();
+      const model = buildModelWithUndefinedDrawing();
+
+      expect(() => xlsx.reconcile(model, {})).to.not.throw();
+    });
+  });
+});