StructParents entry isn't required on pages with no tagged contents (bug 1855641)

src/core/struct_tree.js

@@ -158,7 +158,7 @@ class StructTreeRoot {
     newRefs.push({ ref: structTreeRootRef, data: buffer.join("") });
   }
 
-  async canUpdateStructTree({ pdfManager, newAnnotationsByPage }) {
+  async canUpdateStructTree({ pdfManager, xref, newAnnotationsByPage }) {
     if (!this.ref) {
       warn("Cannot update the struct tree: no root reference.");
       return false;
@@ -180,17 +180,18 @@ class StructTreeRoot {
       warn("Cannot update the struct tree: nums isn't an array.");
       return false;
     }
+    const numberTree = new NumberTree(parentTree, xref);
 
-    const { numPages } = pdfManager.catalog;
     for (const pageIndex of newAnnotationsByPage.keys()) {
-      const { pageDict, ref: pageRef } = await pdfManager.getPage(pageIndex);
+      const { pageDict } = await pdfManager.getPage(pageIndex);
-      if (!(pageRef instanceof Ref)) {
+      if (!pageDict.has("StructParents")) {
-        warn(`Cannot save the struct tree: page ${pageIndex} has no ref.`);
+        // StructParents is required when the content stream has some tagged
-        return false;
+        // contents but a page can just have tagged annotations.
+        continue;
       }
       const id = pageDict.get("StructParents");
-      if (!Number.isInteger(id) || id < 0 || id >= numPages) {
+      if (!Number.isInteger(id) || !Array.isArray(numberTree.get(id))) {
-        warn(`Cannot save the struct tree: page ${pageIndex} has no id.`);
+        warn(`Cannot save the struct tree: page ${pageIndex} has a wrong id.`);
         return false;
       }
     }
@@ -202,7 +203,7 @@ class StructTreeRoot {
         elements,
         xref: this.dict.xref,
         pageDict,
-        parentTree,
+        numberTree,
       });
 
       for (const element of elements) {
@@ -312,6 +313,7 @@ class StructTreeRoot {
 
     for (const [pageIndex, elements] of newAnnotationsByPage) {
       const { ref: pageRef } = await pdfManager.getPage(pageIndex);
+      const isPageRef = pageRef instanceof Ref;
       for (const {
         accessibilityData,
         ref,
@@ -364,7 +366,10 @@ class StructTreeRoot {
         const objDict = new Dict(xref);
         tagDict.set("K", objDict);
         objDict.set("Type", objr);
-        objDict.set("Pg", pageRef);
+        if (isPageRef) {
+          // Pg is optional.
+          objDict.set("Pg", pageRef);
+        }
         objDict.set("Obj", ref);
 
         buffer.length = 0;
@@ -378,7 +383,7 @@ class StructTreeRoot {
     return nextKey + 1;
   }
 
-  static #collectParents({ elements, xref, pageDict, parentTree }) {
+  static #collectParents({ elements, xref, pageDict, numberTree }) {
     const idToElement = new Map();
     for (const element of elements) {
       if (element.structTreeParentId) {
@@ -388,11 +393,12 @@ class StructTreeRoot {
     }
 
     const id = pageDict.get("StructParents");
-    const numberTree = new NumberTree(parentTree, xref);
+    if (!Number.isInteger(id)) {
-    const parentArray = numberTree.get(id);
-    if (!Array.isArray(parentArray)) {
       return;
     }
+    // The parentArray type has already been checked by the caller.
+    const parentArray = numberTree.get(id);
+
     const updateElement = (kid, pageKid, kidRef) => {
       const element = idToElement.get(kid);
       if (element) {

src/core/worker.js

@@ -576,6 +576,7 @@ class WorkerMessageHandler {
           } else if (
             await _structTreeRoot.canUpdateStructTree({
               pdfManager,
+              xref,
               newAnnotationsByPage,
             })
           ) {

test/unit/api_spec.js

@@ -2297,7 +2297,7 @@ describe("api", function () {
       await loadingTask.destroy();
     });
 
-    it("write a new stamp annotation in a tagged pdf, save and check that the structure tree", async function () {
+    it("write a new stamp annotation in a tagged pdf, save and check the structure tree", async function () {
       if (isNodeJS) {
         pending("Cannot create a bitmap from Node.js.");
       }
@@ -2349,6 +2349,76 @@ describe("api", function () {
       await loadingTask.destroy();
     });
 
+    it("write a new stamp annotation in a tagged pdf, save, repeat and check the structure tree", async function () {
+      if (isNodeJS) {
+        pending("Cannot create a bitmap from Node.js.");
+      }
+
+      const TEST_IMAGES_PATH = "../images/";
+      const filename = "firefox_logo.png";
+      const path = new URL(TEST_IMAGES_PATH + filename, window.location).href;
+
+      const response = await fetch(path);
+      const blob = await response.blob();
+      let loadingTask, pdfDoc;
+      let data = buildGetDocumentParams("empty.pdf");
+
+      for (let i = 1; i <= 2; i++) {
+        const bitmap = await createImageBitmap(blob);
+        loadingTask = getDocument(data);
+        pdfDoc = await loadingTask.promise;
+        pdfDoc.annotationStorage.setValue("pdfjs_internal_editor_0", {
+          annotationType: AnnotationEditorType.STAMP,
+          rect: [10 * i, 10 * i, 20 * i, 20 * i],
+          rotation: 0,
+          bitmap,
+          bitmapId: "im1",
+          pageIndex: 0,
+          structTreeParentId: null,
+          accessibilityData: {
+            type: "Figure",
+            alt: `Hello World ${i}`,
+          },
+        });
+
+        data = await pdfDoc.saveDocument();
+        await loadingTask.destroy();
+      }
+
+      loadingTask = getDocument(data);
+      pdfDoc = await loadingTask.promise;
+      const page = await pdfDoc.getPage(1);
+      const tree = await page.getStructTree();
+
+      expect(tree).toEqual({
+        children: [
+          {
+            role: "Figure",
+            children: [
+              {
+                type: "annotation",
+                id: "pdfjs_internal_id_18R",
+              },
+            ],
+            alt: "Hello World 1",
+          },
+          {
+            role: "Figure",
+            children: [
+              {
+                type: "annotation",
+                id: "pdfjs_internal_id_26R",
+              },
+            ],
+            alt: "Hello World 2",
+          },
+        ],
+        role: "Root",
+      });
+
+      await loadingTask.destroy();
+    });
+
     it("write a new stamp annotation in a non-tagged pdf, save and check that the structure tree", async function () {
       if (isNodeJS) {
         pending("Cannot create a bitmap from Node.js.");