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

README.md

@@ -491,7 +491,13 @@ on. The exit code is non-zero if any ML data request failed.
 only, because the bundled decoder (`jpeg-js`) decodes only JPEG. A non-JPEG
 image (PNG, HEIC) or a video is reported as `skipped` (unsupported format), kept
 distinct from a `failed` repair, and does not affect the exit code; a genuine
-failure still exits non-zero.
+failure still exits non-zero. 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
+for the file. So a file another account owns, in an album shared with you, is
+skipped by both thumbnail helpers without being fetched, and the fixer skips a
+file whose recorded thumbnail size is 0 or unknown. Otherwise the fixer lowers
+the quality and size of the thumbnail until it fits, and skips the file if even
+the smallest does not.
 
 ### Backup layout
 

TODO.md

@@ -18,6 +18,13 @@ Tag v1.0.0.
 
 # Completed Steps
 
+- 2026-09-23: Stopped `helper fix-missing-thumbnails` retrying files the server
+  always refuses (issue 109). Both thumbnail helpers skip a file another account
+  owns without fetching it. The fixer skips a file whose recorded thumbnail size
+  is 0 or unknown before downloading it, and otherwise tries smaller encodings
+  (720 px quality 50 down to 160 px quality 20) until the encrypted thumbnail is
+  no larger than that size, skipping the file if none fits.
+
 - 2026-09-23: Tested the live-photo hash check's error paths (issue 117). Tests
   download a live photo whose ZIP names an unknown compression method, one whose
   ZIP has no image entry and one with no video entry, and check that nothing is

src/cli-commands.ts

@@ -495,7 +495,7 @@ export const fixMissingThumbnailsCommand = async (
             ctx.stderr.write(`  Skipped: ${skipped}\n`);
             ctx.stderr.write(`  Failed:  ${failed}\n`);
             if (skipped > 0) {
-                ctx.stderr.write("\nSkipped (unsupported format):\n");
+                ctx.stderr.write("\nSkipped:\n");
                 for (const r of results.filter((r) => r.status === "skipped")) {
                     ctx.stderr.write(
                         `  ${r.fileID}\t${r.title}\t${r.reason}\n`,

src/thumbnails.ts

@@ -7,8 +7,21 @@ import { ApiError } from "./api/client.js";
 import { encryptBlob, toBase64 } from "./crypto/index.js";
 import type { EnteFile } from "./model/types.js";
 
-const THUMB_MAX_DIMENSION = 720;
-const THUMB_JPEG_QUALITY = 50;
+// The server refuses a thumbnail larger than the one it already records for the
+// file (`thumbnail.size`, the encrypted size), so these encodings are tried
+// from largest to smallest and the first that fits is uploaded.
+const THUMB_ENCODINGS = [
+    { maxDimension: 720, quality: 50 },
+    { maxDimension: 720, quality: 30 },
+    { maxDimension: 480, quality: 30 },
+    { maxDimension: 320, quality: 20 },
+    { maxDimension: 160, quality: 20 },
+];
+
+// The server accepts a new thumbnail only from the file's owner, so files other
+// people own in albums shared with this account are never checked or repaired.
+const NOT_OWNED_REASON =
+    "owned by another account (only the owner can replace its thumbnail)";
 
 export interface MissingThumbnailInfo {
     fileID: number;
@@ -19,11 +32,12 @@ export interface MissingThumbnailInfo {
 
 // Three outcomes, not two. "fixed": a thumbnail was generated and uploaded.
 // "failed": something went wrong (download, encode, upload) and the file still
-// has no thumbnail. "skipped": the file is a format this helper cannot
-// regenerate — a video, or an image that is not a baseline JPEG. Skipped is a
-// deliberate, expected outcome, not an error (issue #17): the repair path is
-// JPEG-only because `jpeg-js` is, and a PNG or HEIC is left for a format-aware
-// tool rather than reported as a failure.
+// has no thumbnail. "skipped": the server would refuse any thumbnail for the
+// file or this helper cannot regenerate it — a file another account owns, a
+// recorded thumbnail size nothing fits within, a video, or an image that is
+// not a baseline JPEG. Skipped is a deliberate, expected outcome, not an error
+// (issue #17): the repair path is JPEG-only because `jpeg-js` is, and a PNG or
+// HEIC is left for a format-aware tool rather than reported as a failure.
 export type ThumbnailFixStatus = "fixed" | "skipped" | "failed";
 
 export interface ThumbnailFixResult {
@@ -45,6 +59,7 @@ export type ProgressCallback = (message: string) => void;
 // exists, so it is logged and the file is left unreported. That distinction is
 // what stops `fix-missing-thumbnails` from regenerating and uploading over
 // thumbnails that were fine all along while the CDN was briefly returning 500s.
+// Files another account owns are logged as skipped and not checked.
 export const listMissingThumbnails = async (
     lib: Library,
     client: Client,
@@ -52,6 +67,7 @@ export const listMissingThumbnails = async (
 ): Promise<MissingThumbnailInfo[]> => {
     const log = onProgress ?? (() => {});
     const api = client.getApiClient();
+    const { userID } = client.whoami();
     const missing: MissingThumbnailInfo[] = [];
     const seen = new Set<number>();
 
@@ -60,6 +76,13 @@ export const listMissingThumbnails = async (
         for (const photo of album.photos.list()) {
             if (seen.has(photo.fileID)) continue;
             seen.add(photo.fileID);
+            const file = lib.getFile(album.collectionID, photo.fileID);
+            if (file && file.ownerID !== userID) {
+                log(
+                    `[${album.name}] Skipping ${photo.title}: ${NOT_OWNED_REASON}`,
+                );
+                continue;
+            }
             try {
                 const stream = await api.getThumbnailStream(photo.fileID);
                 const reader = stream.getReader();
@@ -135,17 +158,13 @@ const resizeRGBA = (
     return dst;
 };
 
-const generateThumbnail = (fileBytes: Uint8Array): Uint8Array => {
-    const decoded = jpeg.decode(fileBytes, {
-        useTArray: true,
-        formatAsRGBA: true,
-    });
+const generateThumbnail = (
+    decoded: { data: Uint8Array; width: number; height: number },
+    maxDimension: number,
+    quality: number,
+): Uint8Array => {
     const { width: srcW, height: srcH } = decoded;
-    const scale = Math.min(
-        THUMB_MAX_DIMENSION / srcW,
-        THUMB_MAX_DIMENSION / srcH,
-        1,
-    );
+    const scale = Math.min(maxDimension / srcW, maxDimension / srcH, 1);
     const dstW = Math.round(srcW * scale);
     const dstH = Math.round(srcH * scale);
 
@@ -158,7 +177,7 @@ const generateThumbnail = (fileBytes: Uint8Array): Uint8Array => {
 
     const encoded = jpeg.encode(
         { data: pixels, width: dstW, height: dstH },
-        THUMB_JPEG_QUALITY,
+        quality,
     );
     return new Uint8Array(encoded.data);
 };
@@ -171,14 +190,35 @@ const generateThumbnail = (fileBytes: Uint8Array): Uint8Array => {
 const isJpeg = (bytes: Uint8Array): boolean =>
     bytes.length >= 2 && bytes[0] === 0xff && bytes[1] === 0xd8;
 
-// The reason a file cannot have a JPEG thumbnail regenerated for it from its
-// metadata alone, before any bytes are fetched, or undefined when it might. A
-// non-image (video, live photo) is unsupported outright; a still image still
-// has to be checked against its actual bytes once downloaded.
-const unsupportedByType = (file: EnteFile): string | undefined => {
+// The reason a file cannot have a JPEG thumbnail regenerated for it, known from
+// its record alone before any bytes are fetched, or undefined when it might. A
+// still image still has to be checked against its actual bytes once
+// downloaded.
+const reasonToSkip = (file: EnteFile, userID: number): string | undefined => {
+    if (file.ownerID !== userID) {
+        return NOT_OWNED_REASON;
+    }
     if (file.metadata.fileType !== "image") {
         return `unsupported file type: ${file.metadata.fileType} (only JPEG images can be regenerated)`;
     }
+    if (!file.thumbnail.size) {
+        return `recorded thumbnail size is ${file.thumbnail.size ?? "unknown"} (the server refuses a thumbnail larger than the one it records)`;
+    }
+    return undefined;
+};
+
+// Encrypt the largest encoding of the decoded image whose ciphertext is no
+// larger than `maxSize`, or return undefined when even the smallest is larger.
+const encryptThumbnailWithin = (
+    decoded: { data: Uint8Array; width: number; height: number },
+    key: Uint8Array,
+    maxSize: number,
+): { header: Uint8Array; ciphertext: Uint8Array } | undefined => {
+    for (const { maxDimension, quality } of THUMB_ENCODINGS) {
+        const thumbJpeg = generateThumbnail(decoded, maxDimension, quality);
+        const encrypted = encryptBlob(thumbJpeg, key);
+        if (encrypted.ciphertext.length <= maxSize) return encrypted;
+    }
     return undefined;
 };
 
@@ -197,6 +237,7 @@ export const fixMissingThumbnails = async (
     const log = onProgress ?? (() => {});
     const results: ThumbnailFixResult[] = [];
     const api = client.getApiClient();
+    const { userID } = client.whoami();
 
     // Resolve each requested fileID to its file record and owning album by
     // enumerating the library, each file taken from the first album that holds
@@ -237,18 +278,19 @@ export const fixMissingThumbnails = async (
         const { file, collectionName } = entry;
         const title = file.metadata.title;
 
-        const typeReason = unsupportedByType(file);
-        if (typeReason) {
-            log(`[${collectionName}] Skipping ${title}: ${typeReason}`);
+        const skipReason = reasonToSkip(file, userID);
+        if (skipReason) {
+            log(`[${collectionName}] Skipping ${title}: ${skipReason}`);
             results.push({
                 fileID,
                 title,
                 collection: collectionName,
                 status: "skipped",
-                reason: typeReason,
+                reason: skipReason,
             });
             continue;
         }
+        const maxSize = file.thumbnail.size!;
 
         try {
             const photo = lib.photos.byID({ fileID });
@@ -277,12 +319,28 @@ export const fixMissingThumbnails = async (
             }
 
             log(`[${collectionName}] Generating thumbnail for ${title}...`);
-            const thumbJpeg = generateThumbnail(fileBytes);
+            const decoded = jpeg.decode(fileBytes, {
+                useTArray: true,
+                formatAsRGBA: true,
+            });
+            const fitting = encryptThumbnailWithin(decoded, file.key, maxSize);
+            if (!fitting) {
+                const reason = `no thumbnail encoding fits the recorded thumbnail size of ${maxSize} bytes`;
+                log(`[${collectionName}] Skipping ${title}: ${reason}`);
+                results.push({
+                    fileID,
+                    title,
+                    collection: collectionName,
+                    status: "skipped",
+                    reason,
+                });
+                continue;
+            }
+            const { header, ciphertext } = fitting;
 
             log(
-                `[${collectionName}] Encrypting and uploading thumbnail (${thumbJpeg.length} bytes)...`,
+                `[${collectionName}] Uploading thumbnail (${ciphertext.length} bytes)...`,
             );
-            const { header, ciphertext } = encryptBlob(thumbJpeg, file.key);
             const md5 = createHash("md5").update(ciphertext).digest("base64");
             const { objectKey, url } = await api.getUploadURL(
                 ciphertext.length,

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", () => {