README.md

@@ -626,6 +626,13 @@ exits 1, or 3 when the server no longer accepts the saved session (see "Session
 handling"). `--cache-dir` overrides where the cache lives; without it each
 account gets its own directory under the per-user cache path.
 
+An ID given to `files --collection`, `get`, `get-thumb` or
+`helper fix-missing-thumbnails --file` is written in decimal digits, no larger
+than 9007199254740991. Anything else, such as `0x10`, `1e3` or `-1`, is refused
+before any request with one line, `Invalid file ID: <arg>` or
+`Invalid collection ID: <arg>`, and exit status 1. One bad `--file` ID refuses
+the whole command, so nothing is fixed.
+
 `get` and `get-thumb` resolve the file by ID directly, so `--collection` is
 accepted for backward compatibility but ignored. For a live photo, `get` writes
 its image and its video, each named after the title with its own extension, as

TODO.md

@@ -25,6 +25,15 @@ declares one.
 
 # Completed Steps
 
+- 2026-10-14: `files --collection`, `get`, `get-thumb` and
+  `helper fix-missing-thumbnails --file` take an ID only when it is written in
+  decimal digits and is a safe integer (issue 185). Before, `Number()` read
+  `0x10` as 16, `1e3` as 1000 and an empty string as 0, and `--file` dropped an
+  ID it could not read without a word. Anything else now prints
+  `Invalid file ID: <arg>` or `Invalid collection ID: <arg>` and exits 1 before
+  any request; one bad `--file` ID fails the whole command. `parseID` in
+  `src/cli-commands.ts` does the check for all four.
+
 - 2026-10-06: The README says how to run `quak backup` from cron (issue 170):
   log in once as the job's user, a crontab with a backup every night and
   `--verify` on Sundays appending to a log file, and the `HOME` and

src/cli-commands.ts

@@ -97,6 +97,20 @@ const requireSession = (ctx: CliContext): Client | undefined => {
     return client;
 };
 
+// `text` as an ID, or undefined after telling the user it is not one. An ID is
+// written in decimal digits and is a safe integer; `Number()` alone would read
+// `0x10` as 16, `1e3` as 1000 and "" as 0.
+const parseID = (
+    ctx: CliContext,
+    kind: "file" | "collection",
+    text: string,
+): number | undefined => {
+    const id = Number(text);
+    if (/^[0-9]+$/.test(text) && Number.isSafeInteger(id)) return id;
+    ctx.stderr.write(`Invalid ${kind} ID: ${text}\n`);
+    return undefined;
+};
+
 // A library client that omits `fetchMLData`, so the point commands below do not
 // kick the library's background ML backfill: they read metadata, or fetch one
 // file's content, and exit. `backup` and `backup-metadata` handle ML on their
@@ -247,11 +261,8 @@ export const filesCommand = async (
     await init();
     const client = requireSession(ctx);
     if (!client) return 3;
-    const collectionID = Number(opts.collection);
+    const collectionID = parseID(ctx, "collection", opts.collection);
-    if (!Number.isFinite(collectionID)) {
+    if (collectionID === undefined) return 1;
-        ctx.stderr.write("Invalid collection ID\n");
-        return 1;
-    }
 
     const lib = await openReadLibrary(ctx, client);
     try {
@@ -289,11 +300,8 @@ export const getCommand = async (
     await init();
     const client = requireSession(ctx);
     if (!client) return 3;
-    const fileID = Number(fileIDStr);
+    const fileID = parseID(ctx, "file", fileIDStr);
-    if (!Number.isFinite(fileID)) {
+    if (fileID === undefined) return 1;
-        ctx.stderr.write("Invalid file ID\n");
-        return 1;
-    }
 
     const lib = await openReadLibrary(ctx, client);
     try {
@@ -347,11 +355,8 @@ export const getThumbCommand = async (
     await init();
     const client = requireSession(ctx);
     if (!client) return 3;
-    const fileID = Number(fileIDStr);
+    const fileID = parseID(ctx, "file", fileIDStr);
-    if (!Number.isFinite(fileID)) {
+    if (fileID === undefined) return 1;
-        ctx.stderr.write("Invalid file ID\n");
-        return 1;
-    }
 
     const lib = await openReadLibrary(ctx, client);
     try {
@@ -516,15 +521,19 @@ export const fixMissingThumbnailsCommand = async (
     await init();
     const client = requireSession(ctx);
     if (!client) return 3;
+    // One bad --file ID fails the whole command, before anything is fetched.
+    let fileIDs: number[] = [];
+    for (const text of opts.file ?? []) {
+        const fileID = parseID(ctx, "file", text);
+        if (fileID === undefined) return 1;
+        fileIDs.push(fileID);
+    }
     const lib = await openReadLibrary(ctx, client);
     try {
         // Refresh first so files added since the cache was written are found;
         // a failed refresh throws.
         await lib.fresh();
-        let fileIDs: number[];
+        if (fileIDs.length === 0) {
-        if (opts.file && opts.file.length > 0) {
-            fileIDs = opts.file.map(Number).filter(Number.isFinite);
-        } else {
             ctx.stderr.write("Scanning for missing thumbnails...\n");
             const missing = await listMissingThumbnails(lib, client, (msg) => {
                 if (!opts.json) ctx.stderr.write(msg + "\n");