Skip thumbnail repairs the server always refuses (closes #109)

The server accepts a new thumbnail only from the file's owner and only when
it is no larger than the thumbnail size it records. Both thumbnail helpers
now skip files another account owns without fetching them. The fixer skips
a file whose recorded thumbnail size is 0 or unknown before downloading it,
and otherwise tries smaller encodings until the encrypted thumbnail fits,
skipping the file if none does.

Model: opus-5-5

test/thumbnails/thumbnails.test.ts

@@ -215,6 +215,9 @@ const buildThumbMock = async (opts?: {
             thumbnail: {
                 decryptionHeader: toBase64(sodium.randombytes_buf(24)),
             },
+            // The encrypted size of the thumbnail the server records; large
+            // enough here that the default encoding fits.
+            info: { thumbSize: 1_000_000 },
             updationTime: TEST_TIME,
         };
     };
@@ -446,6 +449,32 @@ const openLib = (client: Client): Promise<Library> =>
         precacheOriginals: false,
     });
 
+/** The mock's raw record for one file, for a test to change before login. */
+const rawFile = (m: ThumbMockState, fileID: number): Record<string, unknown> =>
+    m.filesByCollection[1]!.find((f) => f.id === fileID)!;
+
+/** Replace the original the mock serves for one file. */
+const replaceOriginal = (
+    m: ThumbMockState,
+    fileID: number,
+    body: Uint8Array,
+): void => {
+    const push = sodium.crypto_secretstream_xchacha20poly1305_init_push(
+        m.fileKeys[fileID]!,
+    );
+    m.fileCiphertexts[fileID] =
+        sodium.crypto_secretstream_xchacha20poly1305_push(
+            push.state,
+            body,
+            null,
+            sodium.crypto_secretstream_xchacha20poly1305_TAG_FINAL,
+        );
+    rawFile(m, fileID).file = { decryptionHeader: toBase64(push.header) };
+};
+
+const isOriginalDownload = (url: string): boolean =>
+    url.includes("files.ente.io") || url.includes("/files/download/");
+
 const login = (fetch: typeof globalThis.fetch, retry?: RetryOptions) =>
     Client.login({
         email: TEST_EMAIL,
@@ -581,6 +610,33 @@ describe("listMissingThumbnails", () => {
         // Should still be 2, not 4 (each file checked only once)
         expect(missing.length).toBe(2);
     });
+
+    it("skips a file another account owns without fetching its thumbnail", async () => {
+        const otherMock = await buildThumbMock();
+        rawFile(otherMock, 102).ownerID = 7;
+        const logs: string[] = [];
+        const counted = countingFetch(
+            buildThumbFetch(otherMock),
+            (url) => url.includes("thumbnails.ente.io") && url.includes("102"),
+        );
+        const client = await login(counted.fetch);
+        const lib = await openLib(client);
+
+        const missing = await listMissingThumbnails(lib, client, (msg) =>
+            logs.push(msg),
+        );
+        lib.close();
+
+        expect(missing.map((m) => m.fileID)).toEqual([101]);
+        expect(counted.matched()).toBe(0);
+        expect(
+            logs.some(
+                (l) =>
+                    l.includes("Skipping file-102.jpg") &&
+                    l.includes("another account"),
+            ),
+        ).toBe(true);
+    });
 });
 
 describe("fixMissingThumbnails", () => {
@@ -688,6 +744,93 @@ describe("fixMissingThumbnails", () => {
         expect(fixMock.uploadedThumbnails.length).toBe(1);
         expect(fixMock.uploadedThumbnails[0]!.fileID).toBe(101);
     });
+
+    it("skips a file another account owns without downloading it", async () => {
+        // The server accepts a thumbnail only from the file's owner.
+        const fixMock = await buildThumbMock();
+        rawFile(fixMock, 101).ownerID = 7;
+        const counted = countingFetch(
+            buildThumbFetch(fixMock),
+            isOriginalDownload,
+        );
+        const client = await login(counted.fetch);
+        const lib = await openLib(client);
+
+        const results = await fixMissingThumbnails(lib, client, [101]);
+        lib.close();
+
+        expect(results[0]!.status).toBe("skipped");
+        expect(results[0]!.reason).toContain("another account");
+        expect(counted.matched()).toBe(0);
+        expect(fixMock.uploadedThumbnails.length).toBe(0);
+    });
+
+    it("skips a file whose recorded thumbnail size is 0 without downloading it", async () => {
+        // The server refuses a thumbnail larger than the one it records, and
+        // no thumbnail is 0 bytes.
+        const fixMock = await buildThumbMock();
+        rawFile(fixMock, 101).info = { thumbSize: 0 };
+        const counted = countingFetch(
+            buildThumbFetch(fixMock),
+            isOriginalDownload,
+        );
+        const client = await login(counted.fetch);
+        const lib = await openLib(client);
+
+        const results = await fixMissingThumbnails(lib, client, [101]);
+        lib.close();
+
+        expect(results[0]!.status).toBe("skipped");
+        expect(results[0]!.reason).toContain("recorded thumbnail size is 0");
+        expect(counted.matched()).toBe(0);
+        expect(fixMock.uploadedThumbnails.length).toBe(0);
+    });
+
+    it("re-encodes smaller until the thumbnail fits the recorded size", async () => {
+        // A noisy 400x300 JPEG, which the default encoding (quality 50, not
+        // resized because it is under 720 px) cannot compress below the size
+        // recorded here: one byte less than that encoding's ciphertext.
+        const fixMock = await buildThumbMock();
+        const w = 400;
+        const h = 300;
+        const noisy = new Uint8Array(
+            jpegJs.encode(
+                {
+                    data: sodium.randombytes_buf(w * h * 4),
+                    width: w,
+                    height: h,
+                },
+                90,
+            ).data,
+        );
+        replaceOriginal(fixMock, 101, noisy);
+        const decoded = jpegJs.decode(noisy, {
+            useTArray: true,
+            formatAsRGBA: true,
+        });
+        const defaultSize =
+            jpegJs.encode(decoded, 50).data.length +
+            sodium.crypto_secretstream_xchacha20poly1305_ABYTES;
+        const recordedSize = defaultSize - 1;
+        rawFile(fixMock, 101).info = { thumbSize: recordedSize };
+
+        const client = await login(buildThumbFetch(fixMock));
+        const lib = await openLib(client);
+
+        const results = await fixMissingThumbnails(lib, client, [101]);
+        lib.close();
+
+        expect(results[0]!.status).toBe("fixed");
+        const upload = fixMock.uploadedThumbnails[0]!;
+        expect(upload.ciphertext.length).toBeLessThanOrEqual(recordedSize);
+        const decrypted = decryptBlob(
+            upload.ciphertext,
+            fromBase64(upload.decryptionHeader),
+            fixMock.fileKeys[101]!,
+        );
+        expect(decrypted[0]).toBe(0xff);
+        expect(decrypted[1]).toBe(0xd8);
+    });
 });
 
 describe("Client.getApiClient", () => {