fix(download): disable uTP to prevent ENOBUFS socket exhaustion crashes

src/download/engine.test.ts

@@ -110,4 +110,19 @@ describe("TorrentEngine macOS port-5350 fix (#22)", () => {
     expect(result?.total).toBe(0);
     engine.destroy();
   });
+
+  it("passes utp:false so utp-native does not exhaust UDP buffers or crash on unhandled bind errors", async () => {
+    const { TorrentEngine } = await import("./engine");
+    const engine = new TorrentEngine();
+    engine.add(
+      "test-id",
+      "magnet:?xt=urn:btih:0000000000000000000000000000000000000000",
+      "/downloads",
+      {},
+    );
+    engine.destroy();
+    expect(constructorCalls).toHaveLength(1);
+    expect(constructorCalls[0]).toMatchObject({ utp: false });
+  });
 });
+

src/download/engine.ts

@@ -71,7 +71,21 @@ export class TorrentEngine {
       // the app the moment a download starts. NAT-PMP can never succeed
       // on macOS because the port is permanently taken, so disable it
       // and let UPnP handle NAT traversal instead.
-      const opts = process.platform === "darwin" ? { natPmp: false } : {};
+      //
+      // Disable uTP across all platforms:
+      // WebTorrent's uTP implementation relies on `utp-native`, which allocates
+      // an independent UDP socket for every outgoing connection attempt. Under
+      // peer discovery churn, this rapidly exhausts socket buffer space and
+      // ephemeral ports (leading to WSAENOBUFS / ENOBUFS: "no buffer space available").
+      // Furthermore, when `utp-native` fails to bind, it emits an unhandled 'error'
+      // on an internal EventEmitter with no listeners, crashing the process as an
+      // uncaught exception. Disabling uTP forces WebTorrent to use standard TCP
+      // connections, which are supported by 100% of BitTorrent clients and operate
+      // reliably without socket buffer exhaustion.
+      const opts = {
+        utp: false,
+        ...(process.platform === "darwin" ? { natPmp: false } : {}),
+      };
       this.client = new WebTorrent(opts);
       this.client.on("error", () => {});
       this.applyThrottle();