Add a 'supportsDownloading' browser option to gate saving/downloading

Introduces a 'supportsDownloading' browser option (defaulting to false)
that lets embedders disable the save/download paths entirely. When
disabled:
  - the toolbar and secondary-toolbar download buttons are hidden;
  - PDFViewerApplication.{download,save,downloadOrSave} and the
    "beforeunload" save prompt bail out early;
  - the BaseDownloadManager helpers (download, downloadData,
    openOrDownloadData) and the Firefox/generic _triggerDownload
    implementations no-op.

test/integration/viewer_spec.mjs

@@ -1455,6 +1455,72 @@ describe("PDF viewer", () => {
     });
   });
 
+  describe("Save/download disabled when supportsDownloading is false", () => {
+    let pages;
+
+    beforeEach(async () => {
+      pages = await loadAndWait(
+        "tracemonkey.pdf",
+        ".textLayer .endOfContent",
+        null,
+        null,
+        { supportsDownloading: false }
+      );
+    });
+
+    afterEach(async () => {
+      await closePages(pages);
+    });
+
+    it("must hide the download buttons and skip save/download", async () => {
+      await Promise.all(
+        pages.map(async ([browserName, page]) => {
+          await page.waitForSelector("#downloadButton", { hidden: true });
+          await waitAndClick(page, "#secondaryToolbarToggleButton");
+          await page.waitForSelector("#secondaryDownload", { hidden: true });
+
+          const triggered = await page.evaluate(async () => {
+            const app = window.PDFViewerApplication;
+            const calls = [];
+            const saveDocument = app.pdfDocument.saveDocument.bind(
+              app.pdfDocument
+            );
+            app.pdfDocument.saveDocument = (...args) => {
+              calls.push("saveDocument");
+              return saveDocument(...args);
+            };
+
+            // Each bail-out path dispatches a TESTING-only "downloadskipped"
+            // event, so we can deterministically wait for all four attempts to
+            // run to completion.
+            let skipped = 0;
+            const allSkipped = new Promise(resolve => {
+              app.eventBus.on("downloadskipped", function listener() {
+                if (++skipped === 4) {
+                  app.eventBus.off("downloadskipped", listener);
+                  resolve();
+                }
+              });
+            });
+
+            await app.download();
+            await app.save();
+            await app.downloadOrSave();
+            app.eventBus.dispatch("download", { source: null });
+            await allSkipped;
+
+            return { calls, skipped, downloadManager: app.downloadManager };
+          });
+          expect(triggered.downloadManager)
+            .withContext(`In ${browserName}`)
+            .toBeNull();
+          expect(triggered.calls).withContext(`In ${browserName}`).toEqual([]);
+          expect(triggered.skipped).withContext(`In ${browserName}`).toBe(4);
+        })
+      );
+    });
+  });
+
   describe("Pinch-zoom", () => {
     let pages;
 

web/app.js

@@ -385,6 +385,7 @@ const PDFViewerApplication = {
         maxCanvasPixels: x => parseInt(x, 10),
         spreadModeOnLoad: x => parseInt(x, 10),
         supportsCaretBrowsingMode: x => x === "true",
+        supportsDownloading: x => x === "true",
         viewerCssTheme: x => parseInt(x, 10),
         forcePageColors: x => x === "true",
         pageColorsBackground: x => x,
@@ -434,7 +435,16 @@ const PDFViewerApplication = {
       ignoreDestinationZoom: AppOptions.get("ignoreDestinationZoom"),
     }));
 
-    const downloadManager = (this.downloadManager = new DownloadManager());
+    const supportsDownloading = AppOptions.get("supportsDownloading");
+    const downloadManager = (this.downloadManager = supportsDownloading
+      ? new DownloadManager()
+      : null);
+    if (appConfig.secondaryToolbar?.downloadButton) {
+      appConfig.secondaryToolbar.downloadButton.hidden = !supportsDownloading;
+    }
+    if (appConfig.toolbar?.download) {
+      appConfig.toolbar.download.hidden = !supportsDownloading;
+    }
 
     const findController = (this.findController = new PDFFindController({
       linkService,
@@ -1311,6 +1321,13 @@ const PDFViewerApplication = {
   },
 
   async download() {
+    if (!this.downloadManager) {
+      if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("TESTING")) {
+        this.eventBus.dispatch("downloadskipped", { source: this });
+      }
+      return;
+    }
+
     let data;
     try {
       data = await (this.pdfDocument
@@ -1323,6 +1340,13 @@ const PDFViewerApplication = {
   },
 
   async save() {
+    if (!this.downloadManager) {
+      if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("TESTING")) {
+        this.eventBus.dispatch("downloadskipped", { source: this });
+      }
+      return;
+    }
+
     if (this._saveInProgress) {
       return;
     }
@@ -1354,6 +1378,13 @@ const PDFViewerApplication = {
   },
 
   async downloadOrSave() {
+    if (!this.downloadManager) {
+      if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("TESTING")) {
+        this.eventBus.dispatch("downloadskipped", { source: this });
+      }
+      return;
+    }
+
     // In the Firefox case, this method MUST always trigger a download.
     // When the user is closing a modified and unsaved document, we display a
     // prompt asking for saving or not. In case they save, we must wait for
@@ -2442,6 +2473,9 @@ const PDFViewerApplication = {
     if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("TESTING")) {
       return;
     }
+    if (!this.downloadManager) {
+      return;
+    }
     if (!this.pdfDocument) {
       return;
     }

web/app_options.js

@@ -102,6 +102,11 @@ const defaultOptions = {
     value: true,
     kind: OptionKind.BROWSER,
   },
+  supportsDownloading: {
+    /** @type {boolean} */
+    value: true,
+    kind: OptionKind.BROWSER,
+  },
   supportsIntegratedFind: {
     /** @type {boolean} */
     value: false,

web/pdf_attachment_viewer.js

@@ -126,7 +126,7 @@ class PDFAttachmentViewer extends BaseTreeViewer {
         : fallbackContent;
 
       if (content) {
-        this.downloadManager.openOrDownloadData(content, filename);
+        this.downloadManager?.openOrDownloadData(content, filename);
       }
     };
 

web/pdf_outline_viewer.js

@@ -155,7 +155,10 @@ class PDFOutlineViewer extends BaseTreeViewer {
         const content = await linkService.getAttachmentContent(attachmentId);
 
         if (content) {
-          this.downloadManager.openOrDownloadData(content, attachment.filename);
+          this.downloadManager?.openOrDownloadData(
+            content,
+            attachment.filename
+          );
         }
       };