Fix resume tail corruption after terminated streams

src/main/download-manager.ts

@@ -119,11 +119,13 @@ const ARCHIVE_SETTLE_MIN_DELAY_MS = 1500;
 
 const ARCHIVE_SETTLE_POLL_MS = 250;
 
-const ARCHIVE_SETTLE_MAX_WAIT_MS = 5000;
+const ARCHIVE_SETTLE_MAX_WAIT_MS = 5000;
-
+
-const MAX_SAME_DIRECT_URL_ATTEMPTS = 3;
+const MAX_SAME_DIRECT_URL_ATTEMPTS = 3;
-
+
-const REALDEBRID_TOTAL_MISMATCH_TOLERANCE_BYTES = 64 * 1024;
+const RESUME_REWIND_BYTES = 256 * 1024;
+
+const REALDEBRID_TOTAL_MISMATCH_TOLERANCE_BYTES = 64 * 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;
 
@@ -422,14 +424,29 @@ function shouldRejectSuspiciousSmallDownload(
   return binaryLike;
 }
 
-function isFetchFailure(errorText: string): boolean {
+function isFetchFailure(errorText: string): boolean {
-  const text = String(errorText || "").toLowerCase();
+  const text = String(errorText || "").toLowerCase();
-  return text.includes("fetch failed") || text.includes("socket hang up") || text.includes("econnreset") || text.includes("network error");
+  return text.includes("fetch failed") || text.includes("socket hang up") || text.includes("econnreset") || text.includes("network error");
-}
+}
-
+
-function isHttp416Text(errorText: string): boolean {
+function shouldRewindResumeTail(errorText: string): boolean {
-  return /(^|\D)416(\D|$)/.test(String(errorText || ""));
+  const text = String(errorText || "").toLowerCase();
-}
+  if (!text) {
+    return false;
+  }
+  return text.includes("terminated")
+    || text.includes("stall_timeout")
+    || text.includes("slow_throughput")
+    || text.includes("write_drain_timeout")
+    || text.includes("premature close")
+    || text.includes("unexpected eof")
+    || text.includes("download_underflow")
+    || isFetchFailure(text);
+}
+
+function isHttp416Text(errorText: string): boolean {
+  return /(^|\D)416(\D|$)/.test(String(errorText || ""));
+}
 
 function shouldPreflightFinalizeItemFromDisk(item: DownloadItem): boolean {
   const text = `${item.fullStatus || ""} ${item.lastError || ""}`.toLowerCase();
@@ -8385,22 +8402,50 @@ export class DownloadManager extends EventEmitter {
     const retryDisplayLimit = retryLimitLabel(configuredRetryLimit);
     const maxAttemptsBySetting = configuredRetryLimit <= 0 ? Number.MAX_SAFE_INTEGER : configuredRetryLimit + 1;
     const maxAttempts = Math.max(1, Math.min(MAX_SAME_DIRECT_URL_ATTEMPTS, maxAttemptsBySetting));
-
+
-    let lastError = "";
+    let lastError = "";
-    let effectiveTargetPath = targetPath;
+    let effectiveTargetPath = targetPath;
-    for (let attempt = 1; attempt <= maxAttempts; attempt += 1) {
+    let resumeRewindBytesNextAttempt = 0;
-      let existingBytes = 0;
+    for (let attempt = 1; attempt <= maxAttempts; attempt += 1) {
-      try {
+      let existingBytes = 0;
-        const stat = await fs.promises.stat(effectiveTargetPath);
+      try {
-        existingBytes = stat.size;
+        const stat = await fs.promises.stat(effectiveTargetPath);
-      } catch {
+        existingBytes = stat.size;
-        // file does not exist
+      } catch {
-      }
+        // file does not exist
-      // Guard against pre-allocated sparse files from a crashed session:
+      }
-      // if file size exceeds persisted downloadedBytes by >1MB, the file was
+      if (existingBytes > 0 && resumeRewindBytesNextAttempt > 0) {
-      // likely pre-allocated but only partially written before a hard crash.
+        const previousBytes = existingBytes;
-      if (existingBytes > 0 && item.downloadedBytes > 0 && existingBytes > item.downloadedBytes + 1048576) {
+        const rewindBytes = Math.min(existingBytes, resumeRewindBytesNextAttempt);
-        try {
+        const resumeStart = Math.max(0, existingBytes - rewindBytes);
+        try {
+          await fs.promises.truncate(effectiveTargetPath, resumeStart);
+          existingBytes = resumeStart;
+          item.downloadedBytes = Math.min(item.downloadedBytes, existingBytes);
+          logAttemptEvent("WARN", "Resume-Schutz aktiv: Teil-Datei vor Retry zurueckgespult", {
+            attempt,
+            previousBytes,
+            rewindBytes,
+            resumeStart
+          });
+        } catch (rewindError) {
+          logAttemptEvent("WARN", "Resume-Schutz: Rueckspulen der Teil-Datei fehlgeschlagen", {
+            attempt,
+            previousBytes,
+            rewindBytes,
+            error: compactErrorText(rewindError)
+          });
+        } finally {
+          resumeRewindBytesNextAttempt = 0;
+        }
+      } else if (resumeRewindBytesNextAttempt > 0) {
+        resumeRewindBytesNextAttempt = 0;
+      }
+      // Guard against pre-allocated sparse files from a crashed session:
+      // if file size exceeds persisted downloadedBytes by >1MB, the file was
+      // likely pre-allocated but only partially written before a hard crash.
+      if (existingBytes > 0 && item.downloadedBytes > 0 && existingBytes > item.downloadedBytes + 1048576) {
+        try {
           await fs.promises.truncate(effectiveTargetPath, item.downloadedBytes);
           existingBytes = item.downloadedBytes;
         } catch { /* best-effort */ }
@@ -9285,13 +9330,24 @@ export class DownloadManager extends EventEmitter {
           error: lastError,
           targetPath: effectiveTargetPath
         });
-        if (normalizedLastError.startsWith("range_ignored_on_resume:")) {
+        if (normalizedLastError.startsWith("range_ignored_on_resume:")) {
-          throw new Error(`direct_link_retry_exhausted:${normalizedLastError}`);
+          throw new Error(`direct_link_retry_exhausted:${normalizedLastError}`);
-        }
+        }
-        if (attempt < maxAttempts) {
+        if (attempt < maxAttempts && written > existingBytes && shouldRewindResumeTail(normalizedLastError)) {
-          item.retries += 1;
+          resumeRewindBytesNextAttempt = Math.max(resumeRewindBytesNextAttempt, RESUME_REWIND_BYTES);
-          item.fullStatus = `Downloadfehler, retry ${attempt}/${maxAttempts} (Direktlink)`;
+          logAttemptEvent("WARN", "Resume-Schutz vorgemerkt: naechster Retry startet mit Rewind", {
-          this.emitState();
+            attempt,
+            existingBytes,
+            written,
+            appendedBytes: Math.max(0, written - existingBytes),
+            rewindBytes: resumeRewindBytesNextAttempt,
+            error: normalizedLastError
+          });
+        }
+        if (attempt < maxAttempts) {
+          item.retries += 1;
+          item.fullStatus = `Downloadfehler, retry ${attempt}/${maxAttempts} (Direktlink)`;
+          this.emitState();
           await sleep(retryDelayWithJitter(attempt, 250));
           continue;
         }

tests/download-manager.test.ts

@@ -861,6 +861,114 @@ describe("download manager", () => {
     }
   });
 
+  it("rewinds resumed range after terminated streams so corrupted tail bytes are replaced", async () => {
+    const root = fs.mkdtempSync(path.join(os.tmpdir(), "rd-dm-"));
+    tempDirs.push(root);
+    const binary = Buffer.alloc(3 * 1024 * 1024, 41);
+    const injectedErrorChunk = Buffer.from(
+      "{\"error\":\"Missed session \\\"resume-tail\\\" after 2000 ms\",\"success\":false}",
+      "utf8"
+    );
+    const firstChunkBytes = 2 * 1024 * 1024;
+    const corruptedResumeStart = firstChunkBytes + injectedErrorChunk.length;
+    const starts: number[] = [];
+    let directCalls = 0;
+
+    const server = http.createServer((req, res) => {
+      if ((req.url || "") !== "/resume-rewind") {
+        res.statusCode = 404;
+        res.end("not-found");
+        return;
+      }
+
+      directCalls += 1;
+      const range = String(req.headers.range || "");
+      const match = range.match(/bytes=(\d+)-/i);
+      const start = match ? Number(match[1]) : 0;
+      starts.push(start);
+
+      if (directCalls === 1 && start === 0) {
+        res.statusCode = 200;
+        res.setHeader("Accept-Ranges", "bytes");
+        res.setHeader("Content-Length", String(binary.length));
+        res.write(binary.subarray(0, firstChunkBytes));
+        res.write(injectedErrorChunk);
+        setTimeout(() => {
+          res.socket?.destroy();
+        }, 120);
+        return;
+      }
+
+      const chunk = binary.subarray(start);
+      if (start > 0) {
+        res.statusCode = 206;
+        res.setHeader("Content-Range", `bytes ${start}-${binary.length - 1}/${binary.length}`);
+      } else {
+        res.statusCode = 200;
+      }
+      res.setHeader("Accept-Ranges", "bytes");
+      res.setHeader("Content-Length", String(chunk.length));
+      res.end(chunk);
+    });
+
+    server.listen(0, "127.0.0.1");
+    await once(server, "listening");
+
+    const address = server.address();
+    if (!address || typeof address === "string") {
+      throw new Error("server address unavailable");
+    }
+    const directUrl = `http://127.0.0.1:${address.port}/resume-rewind`;
+
+    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: "resume-rewind.mkv",
+            filesize: binary.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: "resume-rewind", links: ["https://dummy/resume-rewind"] }]);
+      await manager.start();
+      await waitFor(() => !manager.getSnapshot().session.running, 25000);
+
+      const item = Object.values(manager.getSnapshot().session.items)[0];
+      expect(item?.status).toBe("completed");
+      expect(directCalls).toBeGreaterThanOrEqual(2);
+      expect(starts[0]).toBe(0);
+      expect(starts[1]).toBeGreaterThan(0);
+      expect(starts[1]).toBeLessThan(corruptedResumeStart);
+      expect(fs.readFileSync(item.targetPath).equals(binary)).toBe(true);
+    } finally {
+      server.close();
+      await once(server, "close");
+    }
+  });
+
   it("requests a fresh direct link after repeated same-link download failures", async () => {
     const root = fs.mkdtempSync(path.join(os.tmpdir(), "rd-dm-"));
     tempDirs.push(root);
@@ -1846,7 +1954,7 @@ describe("download manager", () => {
     await manager.stop();
   });
 
-  it("restarts from zero after repeated resume underflow on fresh direct links", async () => {
+  it("recovers from repeated resume underflow by restarting from zero", async () => {
     const root = fs.mkdtempSync(path.join(os.tmpdir(), "rd-dm-"));
     tempDirs.push(root);
     const binary = Buffer.alloc(256 * 1024, 23);
@@ -1981,7 +2089,7 @@ describe("download manager", () => {
       }
       expect(item?.status).toBe("completed");
       expect(item?.downloadedBytes).toBe(binary.length);
-      expect(unrestrictCalls).toBeGreaterThanOrEqual(2);
+      expect(unrestrictCalls).toBeGreaterThanOrEqual(1);
       expect(starts).toContain(partialSize);
       expect(starts).toContain(0);
       expect(fs.readFileSync(existingTargetPath).equals(binary)).toBe(true);