Fix #56: StreamBuf parser hang on non-xdr:wsDr drawing root

lib/xlsx/xform/drawing/drawing-xform.js

@@ -53,14 +53,24 @@ class DrawingXform extends BaseXform {
     switch (node.name) {
       case this.tag:
         this.reset();
+        this._rootTag = undefined;
         this.model = {
           anchors: [],
         };
         break;
       default:
-        this.parser = this.map[node.name];
-        if (this.parser) {
-          this.parser.parseOpen(node);
+        // If we have not yet opened a model, this is the root element of a
+        // drawing file with a non-standard namespace (e.g. not xdr:wsDr).
+        // Capture the actual root tag so parseClose can signal loop-exit when
+        // the corresponding close tag arrives, preventing a StreamBuf hang.
+        if (!this.model) {
+          this._rootTag = node.name;
+          this.model = {anchors: []};
+        } else {
+          this.parser = this.map[node.name];
+          if (this.parser) {
+            this.parser.parseOpen(node);
+          }
         }
         break;
     }
@@ -85,6 +95,13 @@ class DrawingXform extends BaseXform {
       case this.tag:
         return false;
       default:
+        // Return false (loop-exit signal) when the actual root element closes,
+        // even if it used a non-standard namespace instead of xdr:wsDr.
+        // Without this, the StreamBuf for-await loop exhausts all SAX events
+        // and blocks waiting for stream data that never arrives (issue #56).
+        if (name === this._rootTag) {
+          return false;
+        }
         // could be some unrecognised tags
         return true;
     }

spec/integration/issues/issue-56-streambuf-non-xdr-root.spec.js

@@ -0,0 +1,45 @@
+const fs = require('fs');
+const JSZip = require('jszip');
+
+const ExcelJS = verquire('exceljs');
+
+// Regression test for protobi/exceljs#56: StreamBuf parser hangs when a
+// workbook drawing file uses a root element other than <xdr:wsDr>.
+//
+// Root cause: DrawingXform.parseClose() only returned the loop-exit signal
+// (false) when the close tag matched exactly `xdr:wsDr`. Any other close tag
+// fell to `default: return true`, keeping the BaseXform for-await loop alive
+// until the underlying stream was exhausted — which never happens with
+// StreamBuf unless the caller explicitly ends it.
+//
+// Fix: capture the actual root tag in parseOpen() and also return false when
+// that tag closes.
+
+function buildFixture() {
+  const srcBuf = fs.readFileSync('./spec/integration/data/test-issue-1575.xlsx');
+  const unknownTag = '<some:other xmlns:some="http://example.com/unknown-drawing-ns"/>';
+
+  return JSZip.loadAsync(srcBuf).then(zip =>
+    zip.files['xl/drawings/drawing1.xml'].async('string').then(originalXml => {
+      const openStart = originalXml.indexOf('<xdr:wsDr');
+      const openEnd = originalXml.indexOf('>', openStart);
+      const modifiedXml =
+        originalXml.substring(0, openStart) + unknownTag + originalXml.substring(openEnd + 1);
+
+      zip.file('xl/drawings/drawing1.xml', modifiedXml);
+      return zip.generateAsync({type: 'nodebuffer'});
+    })
+  );
+}
+
+describe('github issues', () => {
+  it('issue 56 - StreamBuf hang on drawing with non-xdr:wsDr root element', () => {
+    const wb = new ExcelJS.Workbook();
+    return buildFixture()
+      .then(buf => wb.xlsx.load(buf))
+      .then(() => {
+        // Arriving here means the parser exited cleanly — no StreamBuf hang.
+        expect(true).to.equal(true);
+      });
+  }).timeout(5000);
+});