Accept small metadata files (.sfv, .nfo, .nzb) without retry loops

SFV checksum verification files are legitimately tiny (~128 bytes) but were
rejected by the "suspicious small download" detection, causing infinite
"Direktlink erneuern" retry loops that blocked package extraction.

- Add KNOWN_SMALL_FILE_RE for .sfv, .nfo, .nzb, .md5, .sha1, .sha256, .crc,
  .txt, .url, .lnk, .srr file extensions
- Skip suspicious-small-download rejection for known small files when they
  match their expected size (or have no size expectation)
- Skip tiny-download error detection for known small metadata files
- Add test: verifies .sfv file downloads without retries and completes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main/download-manager.ts

@@ -131,6 +131,9 @@ const PREALLOC_RESUME_MISMATCH_THRESHOLD_BYTES = 1024 * 1024;
 
 const LARGE_BINARY_FILE_RE = /\.(?:part\d+\.rar|rar|r\d{2,3}|zip(?:\.\d+)?|7z(?:\.\d+)?|tar|gz|bz2|xz|iso|mkv|mp4|avi|mov|wmv|m4v|ts|m2ts|webm|mp3|flac|aac|wav)$/i;
 
+/** Files that are legitimately tiny (< 5 KB) and should NOT be rejected as suspicious. */
+const KNOWN_SMALL_FILE_RE = /\.(?:sfv|nfo|nzb|md5|sha1|sha256|crc|txt|url|lnk|srr)$/i;
+
 function expectedMinBytes(totalBytes: number | null | undefined, strict: boolean): number {
   if (!totalBytes || totalBytes <= 0) {
     return 10240;
@@ -437,6 +440,13 @@ function shouldRejectSuspiciousSmallDownload(
   const size = Math.max(0, Math.floor(Number(fileSizeOnDisk) || 0));
   const expected = Number.isFinite(expectedTotal || NaN) ? Math.max(0, Math.floor(expectedTotal || 0)) : 0;
   const binaryLike = isLargeBinaryLikePath(filePath || fileName);
+  const name = path.basename(String(filePath || fileName || ""));
+
+  // Known small files (e.g. .sfv, .nfo) are legitimately tiny — never reject them
+  // as long as they received the expected number of bytes (or we have no expectation).
+  if (KNOWN_SMALL_FILE_RE.test(name) && (expected <= 0 || size >= expected)) {
+    return false;
+  }
 
   if (size <= 0) {
     return expected > 0 || binaryLike;
@@ -9340,8 +9350,13 @@ export class DownloadManager extends EventEmitter {
         }
 
         // Detect tiny error-response files (e.g. hoster returning "Forbidden" with HTTP 200).
-        // No legitimate file-hoster download is < 512 bytes.
+        // No legitimate file-hoster download is < 512 bytes, EXCEPT known small metadata
+        // files like .sfv (checksum verification), .nfo (release info), etc.
         if (written > 0 && written < 512) {
+          const knownSmallFile = KNOWN_SMALL_FILE_RE.test(item.fileName || effectiveTargetPath);
+          if (knownSmallFile && ((!item.totalBytes || item.totalBytes <= 0) || written >= item.totalBytes)) {
+            logger.info(`Kleine Metadaten-Datei akzeptiert (${written} B): ${item.fileName || effectiveTargetPath}`);
+          } else {
             let snippet = "";
             try {
               snippet = await fs.promises.readFile(effectiveTargetPath, "utf8");
@@ -9368,6 +9383,7 @@ export class DownloadManager extends EventEmitter {
               throw new Error(`Download zu klein (${written} B) – Hoster-Fehlerseite?${snippet ? ` Inhalt: "${snippet}"` : ""}`);
             }
           }
+        }
 
         const completionValidation = validateDownloadedFileCompletion({
           actualBytes: written,

tests/download-manager.test.ts

@@ -6140,6 +6140,65 @@ describe("download manager", () => {
     }
   });
 
+  it("accepts small .sfv metadata files without rejecting them as suspicious", async () => {
+    const root = fs.mkdtempSync(path.join(os.tmpdir(), "rd-dm-"));
+    tempDirs.push(root);
+    // SFV content is just CRC32 checksums — legitimately tiny
+    const sfvContent = Buffer.from("archive.part1.rar 1A2B3C4D\narchive.part2.rar 5E6F7A8B\n", "utf8");
+
+    const server = http.createServer((req, res) => {
+      res.statusCode = 200;
+      res.setHeader("Content-Length", String(sfvContent.length));
+      res.end(sfvContent);
+    });
+
+    server.listen(0, "127.0.0.1");
+    await once(server, "listening");
+    const address = server.address();
+    if (!address || typeof address === "string") throw new Error("server address unavailable");
+    const directUrl = `http://127.0.0.1:${address.port}/checksum.sfv`;
+
+    globalThis.fetch = async (input: RequestInfo | URL, init?: RequestInit): Promise<Response> => {
+      const url = typeof input === "string" ? input : input instanceof URL ? input.toString() : input.url;
+      if (url.includes("/unrestrict/link")) {
+        return new Response(
+          JSON.stringify({ download: directUrl, filename: "archive.sfv", filesize: sfvContent.length }),
+          { status: 200, headers: { "Content-Type": "application/json" } }
+        );
+      }
+      return originalFetch(input, init);
+    };
+
+    try {
+      const manager = new DownloadManager(
+        {
+          ...defaultSettings(),
+          token: "rd-token",
+          outputDir: path.join(root, "downloads"),
+          extractDir: path.join(root, "extract"),
+          autoExtract: false,
+          autoReconnect: false
+        },
+        emptySession(),
+        createStoragePaths(path.join(root, "state"))
+      );
+
+      manager.addPackages([{ name: "sfv-test", links: ["https://dummy/sfv-file"] }]);
+      await manager.start();
+      await waitFor(() => !manager.getSnapshot().session.running, 15000);
+
+      const item = Object.values(manager.getSnapshot().session.items)[0];
+      expect(item?.status).toBe("completed");
+      expect(item?.retries).toBe(0);
+      expect(fs.existsSync(item.targetPath)).toBe(true);
+      const onDisk = fs.readFileSync(item.targetPath);
+      expect(onDisk.length).toBe(sfvContent.length);
+    } finally {
+      server.close();
+      await once(server, "close");
+    }
+  });
+
   it("limits AllDebrid rapidgator starts to one active task by default", async () => {
     const root = fs.mkdtempSync(path.join(os.tmpdir(), "rd-dm-"));
     tempDirs.push(root);