fix: separate resource previews from downloads

src/App.test.tsx

@@ -53,12 +53,17 @@ class SuccessfulParserWorker implements WorkerPort {
   onerror: ((event: ErrorEvent) => void) | null = null;
   terminated = false;
   lastMessage: WorkerRequest | undefined;
+  readonly messages: WorkerRequest[] = [];
   lastTransfer: Transferable[] = [];
 
-  constructor(private readonly packageResult?: OneNotePackageDto) {}
+  constructor(
+    private readonly packageResult?: OneNotePackageDto,
+    private readonly resourcePage = false
+  ) {}
 
   postMessage(message: WorkerRequest, transfer: Transferable[] = []): void {
     this.lastMessage = message;
+    this.messages.push(message);
     this.lastTransfer = transfer;
     queueMicrotask(() => {
       if (message.type === 'parse-one') {
@@ -84,7 +89,18 @@ class SuccessfulParserWorker implements WorkerPort {
           page: {
             ...page,
             id: message.pageId,
-            blocks: [
+            blocks: this.resourcePage
+              ? [
+                  {
+                    kind: 'image',
+                    id: 'image-1',
+                    resourceId: 'resource-image',
+                    filename: 'large.png',
+                    isBackground: false,
+                    layout: {},
+                  },
+                ]
+              : [
                   {
                     kind: 'text',
                     id: 'text-1',
@@ -105,6 +121,35 @@ class SuccessfulParserWorker implements WorkerPort {
             diagnostics: [],
           },
         });
+      } else if (message.type === 'get-resource') {
+        if (message.intent === 'preview') {
+          this.respond({
+            type: 'failure',
+            requestId: message.requestId,
+            error: {
+              code: 'resource-not-available',
+              message:
+                'This image can be downloaded but is not approved for automatic preview.',
+              recoverable: true,
+            },
+          });
+        } else {
+          this.respond({
+            type: 'resource',
+            requestId: message.requestId,
+            sessionId: message.sessionId,
+            resource: {
+              id: message.resourceId,
+              kind: 'image',
+              filename: 'large.png',
+              extension: 'png',
+              mediaType: 'image/png',
+              browserRenderable: false,
+              size: 4,
+              bytes: Uint8Array.of(1, 2, 3, 4).buffer,
+            },
+          });
+        }
       } else if (message.type === 'export-session') {
         this.respond({
           type: 'export-artifact',
@@ -231,6 +276,54 @@ describe('OneNoteApplication', () => {
     expect(click).toHaveBeenCalledOnce();
   });
 
+  it('requests a rejected preview separately from an explicit image download', async () => {
+    const user = userEvent.setup();
+    const worker = new SuccessfulParserWorker(undefined, true);
+    vi.spyOn(URL, 'createObjectURL').mockReturnValue('blob:local-image');
+    const click = vi
+      .spyOn(HTMLAnchorElement.prototype, 'click')
+      .mockImplementation(() => undefined);
+    render(
+      <OneNoteApplication
+        createWorkerClient={() => new OneNoteWorkerClient(() => worker)}
+      />
+    );
+
+    await user.upload(
+      screen.getByLabelText('Choose OneNote files'),
+      new File([new Uint8Array([1, 2, 3])], 'Section.one')
+    );
+
+    expect(
+      await screen.findByText(/not approved for automatic preview/i)
+    ).toBeVisible();
+    expect(worker.messages).toContainEqual(
+      expect.objectContaining({
+        type: 'get-resource',
+        resourceId: 'resource-image',
+        intent: 'preview',
+      })
+    );
+    expect(
+      worker.messages.some(
+        (message) =>
+          message.type === 'get-resource' && message.intent === 'download'
+      )
+    ).toBe(false);
+
+    await user.click(
+      screen.getByRole('button', { name: 'Download original image' })
+    );
+    expect(worker.messages).toContainEqual(
+      expect.objectContaining({
+        type: 'get-resource',
+        resourceId: 'resource-image',
+        intent: 'download',
+      })
+    );
+    expect(click).toHaveBeenCalledOnce();
+  });
+
   it('opens a dropped OneNote package through the local worker', async () => {
     const notebook: OneNotePackageDto = {
       format: 'onepkg',

src/App.tsx

@@ -308,7 +308,7 @@ export function OneNoteApplication({
     }
   };
 
-  const loadSelectedResource = useCallback(
+  const previewSelectedResource = useCallback(
     async (resourceId: string): Promise<OneNoteResourcePayloadDto> => {
       const client = activeClient.current;
       if (!client || state.phase !== 'loaded') {
@@ -317,7 +317,7 @@ export function OneNoteApplication({
           'The local parser session is no longer available.'
         );
       }
-      const response = await client.getResource(
+      const response = await client.getResourcePreview(
         state.source.sessionId,
         resourceId,
         state.source.kind === 'onepkg' ? selectedSectionId : undefined
@@ -335,7 +335,25 @@ export function OneNoteApplication({
 
   const downloadSelectedResource = useCallback(
     async (resourceId: string, suggestedName?: string): Promise<void> => {
-      const resource = await loadSelectedResource(resourceId);
+      const client = activeClient.current;
+      if (!client || state.phase !== 'loaded') {
+        throw new WorkerClientError(
+          'session-not-available',
+          'The local parser session is no longer available.'
+        );
+      }
+      const response = await client.getResourceDownload(
+        state.source.sessionId,
+        resourceId,
+        state.source.kind === 'onepkg' ? selectedSectionId : undefined
+      );
+      if (response.type === 'failure') {
+        throw new WorkerClientError(
+          response.error.code,
+          response.error.message
+        );
+      }
+      const resource = response.resource;
       const filename = safeDownloadFilename(
         resource.filename ??
           suggestedName ??
@@ -343,7 +361,7 @@ export function OneNoteApplication({
       );
       downloadBrowserFile(resource.bytes, resource.mediaType, filename);
     },
-    [loadSelectedResource]
+    [selectedSectionId, state]
   );
 
   const exportLoadedSource = useCallback(
@@ -464,7 +482,7 @@ export function OneNoteApplication({
               error={
                 pageState.phase === 'error' ? pageState.message : undefined
               }
-              loadResource={loadSelectedResource}
+              previewResource={previewSelectedResource}
               downloadResource={downloadSelectedResource}
             />
           </div>

src/worker/onenote.client.test.ts

@@ -114,19 +114,59 @@ describe('OneNoteWorkerClient', () => {
     );
   });
 
-  it('requests a lazy resource from the retained parser session', async () => {
+  it('marks an automatic resource request as preview-only', async () => {
     const worker = new FakeWorker();
     const client = new OneNoteWorkerClient(() => worker);
-    const result = client.getResource('session-1', 'resource-2', 'section-3');
+    const result = client.getResourcePreview(
+      'session-1',
+      'resource-2',
+      'section-3'
+    );
 
     expect(worker.lastMessage).toEqual({
       type: 'get-resource',
       requestId: 'resource-1',
       sessionId: 'session-1',
       resourceId: 'resource-2',
+      intent: 'preview',
       sectionId: 'section-3',
     });
 
+    const bytes = Uint8Array.of(1, 2, 3).buffer;
+    worker.respond({
+      type: 'resource',
+      requestId: 'resource-1',
+      sessionId: 'session-1',
+      resource: {
+        id: 'resource-2',
+        kind: 'image',
+        filename: 'image.png',
+        mediaType: 'image/png',
+        browserRenderable: true,
+        size: 3,
+        bytes,
+      },
+    });
+
+    await expect(result).resolves.toMatchObject({
+      type: 'resource',
+      resource: { bytes },
+    });
+  });
+
+  it('marks an explicit resource request as a download', async () => {
+    const worker = new FakeWorker();
+    const client = new OneNoteWorkerClient(() => worker);
+    const result = client.getResourceDownload('session-1', 'resource-2');
+
+    expect(worker.lastMessage).toEqual({
+      type: 'get-resource',
+      requestId: 'resource-1',
+      sessionId: 'session-1',
+      resourceId: 'resource-2',
+      intent: 'download',
+    });
+
     const bytes = Uint8Array.of(1, 2, 3).buffer;
     worker.respond({
       type: 'resource',

src/worker/onenote.client.ts

@@ -8,6 +8,7 @@ import type {
   WorkerCabinetPart,
   WorkerExportFormat,
   WorkerFailure,
+  WorkerResourceIntent,
   WorkerResponse,
 } from './worker-protocol.js';
 
@@ -148,10 +149,27 @@ export class OneNoteWorkerClient {
     });
   }
 
-  getResource(
+  getResourcePreview(
     sessionId: string,
     resourceId: string,
     sectionId?: string
+  ): Promise<ResourceWorkerResponse> {
+    return this.getResource(sessionId, resourceId, 'preview', sectionId);
+  }
+
+  getResourceDownload(
+    sessionId: string,
+    resourceId: string,
+    sectionId?: string
+  ): Promise<ResourceWorkerResponse> {
+    return this.getResource(sessionId, resourceId, 'download', sectionId);
+  }
+
+  private getResource(
+    sessionId: string,
+    resourceId: string,
+    intent: WorkerResourceIntent,
+    sectionId?: string
   ): Promise<ResourceWorkerResponse> {
     if (this.terminated) {
       return Promise.reject(
@@ -173,6 +191,7 @@ export class OneNoteWorkerClient {
         requestId,
         sessionId,
         resourceId,
+        intent,
         ...(sectionId === undefined ? {} : { sectionId }),
       });
     });

src/worker/onenote.worker.ts

@@ -168,14 +168,19 @@ async function handleRequest(data: WorkerRequest): Promise<void> {
       const resource = session.resources.get(
         workerResourceKey(data.resourceId, data.sectionId)
       );
-      const payload = resource ? resourcePayload(resource) : undefined;
+      const payload = resource
+        ? resourcePayload(resource, data.intent)
+        : undefined;
       if (!payload) {
         workerScope.postMessage({
           type: 'failure',
           requestId: data.requestId,
           error: {
             code: 'resource-not-available',
-            message: 'The selected embedded resource is not available.',
+            message:
+              data.intent === 'preview' && resource
+                ? 'This image can be downloaded but is not approved for automatic preview.'
+                : 'The selected embedded resource is not available.',
             recoverable: true,
           },
         });

src/worker/parser-adapter.test.ts

@@ -43,7 +43,7 @@ describe('worker parser adapter', () => {
     expect(result.resources).toHaveLength(1);
     const resource = [...result.resources.values()][0]!;
     expect(result.resources.get(workerResourceKey(resource.id))).toBe(resource);
-    const payload = resourcePayload(resource);
+    const payload = resourcePayload(resource, 'preview');
     expect(payload).toMatchObject({
       kind: 'image',
       mediaType: 'image/png',
@@ -55,6 +55,45 @@ describe('worker parser adapter', () => {
     );
   });
 
+  it('rejects unsafe previews before copying while preserving explicit downloads', () => {
+    const source = Uint8Array.of(1, 2, 3, 4);
+    const rejected = {
+      id: 'rejected-image',
+      kind: 'image' as const,
+      sourceJcid: 1,
+      extension: 'png',
+      mediaType: 'image/png',
+      browserRenderable: false,
+      size: source.byteLength,
+      blob: { source, offset: 0, size: source.byteLength },
+      availability: 'available' as const,
+    };
+
+    expect(resourcePayload(rejected, 'preview')).toBeUndefined();
+    expect(resourcePayload(rejected, 'download')).toMatchObject({
+      id: 'rejected-image',
+      browserRenderable: false,
+      bytes: source.buffer,
+    });
+  });
+
+  it('rejects an oversized preview before allocating its declared payload', () => {
+    const source = Uint8Array.of(0x89, 0x50, 0x4e, 0x47);
+    const oversized = {
+      id: 'oversized-image',
+      kind: 'image' as const,
+      sourceJcid: 1,
+      extension: 'png',
+      mediaType: 'image/png',
+      browserRenderable: true,
+      size: 32 * 1024 * 1024 + 1,
+      blob: { source, offset: 0, size: 32 * 1024 * 1024 + 1 },
+      availability: 'available' as const,
+    };
+
+    expect(resourcePayload(oversized, 'preview')).toBeUndefined();
+  });
+
   it('opens a real ONEPKG and addresses page IDs without rewriting them', async () => {
     const result = await openPackageForWorker(
       fixtureBytes('../../tests/fixtures/joplin-test.onepkg.base64'),

src/worker/parser-adapter.ts

@@ -22,7 +22,8 @@ import {
   type CabSetPart,
   type OneNotePackageOpenOptions,
 } from '../onenote/onepkg/index.js';
-import type { WorkerFailure } from './worker-protocol.js';
+import { DEFAULT_BROWSER_IMAGE_SAFETY_LIMITS } from '../onenote/image-safety.js';
+import type { WorkerFailure, WorkerResourceIntent } from './worker-protocol.js';
 
 export interface ParsedWorkerSection {
   section: OneNoteSectionDto;
@@ -95,10 +96,21 @@ export function workerResourceKey(
 }
 
 export function resourcePayload(
-  resource: OneNoteResource
+  resource: OneNoteResource,
+  intent: WorkerResourceIntent
 ): OneNoteResourcePayloadDto | undefined {
   const blob = resource.blob;
   if (resource.availability !== 'available' || !blob) return undefined;
+  if (
+    intent === 'preview' &&
+    (resource.kind !== 'image' ||
+      !resource.browserRenderable ||
+      (resource.mediaType !== 'image/png' &&
+        resource.mediaType !== 'image/jpeg') ||
+      blob.size > DEFAULT_BROWSER_IMAGE_SAFETY_LIMITS.maxBytes)
+  ) {
+    return undefined;
+  }
   const bytes = new ArrayBuffer(blob.size);
   new Uint8Array(bytes).set(
     blob.source.subarray(blob.offset, blob.offset + blob.size)

src/worker/worker-protocol.ts

@@ -13,6 +13,8 @@ export interface WorkerCabinetPart {
 export type WorkerExportFormat =
   'static-zip' | 'json' | 'text' | 'markdown' | 'html';
 
+export type WorkerResourceIntent = 'preview' | 'download';
+
 export interface WorkerExportArtifact {
   filename: string;
   mediaType: string;
@@ -45,6 +47,7 @@ export type WorkerRequest =
       requestId: string;
       sessionId: string;
       resourceId: string;
+      intent: WorkerResourceIntent;
       sectionId?: string;
     }
   | {