Detect stale tcp connections to relay

Enable nostr-tools' internal stale tcp connection detection

docs/transport.md

@@ -85,6 +85,23 @@ to `now` in `disconnect()`. Any incoming message with `time < lastProcessedTimes
 dropped. This prevents the relay from re-delivering messages that were already handled before a
 disconnect.
 
+### Keepalive
+
+`RelayClient` creates its `SimplePool` with `enablePing: true`. This enables nostr-tools'
+built-in heartbeat: every 29 seconds the pool pings each connected relay and expects a
+response within 20 seconds. In Node.js this uses native WebSocket ping/pong frames; in
+browsers (where the WebSocket API doesn't expose ping) it falls back to sending a dummy
+subscription request and waiting for EOSE.
+
+If a relay fails to respond, nostr-tools closes the WebSocket, which fires the subscription
+`onclose` callback, which emits `"disconnect"` on `RelayClient`, which triggers the
+connection manager's existing reconnect loop. This detects "zombie" TCP connections where the
+socket appears open but the relay is unreachable.
+
+Additionally, if a `publishMessage()` call fails (all relays reject the event),
+`RelayClient` emits `"disconnect"` alongside the thrown error. This ensures the reconnect
+loop starts immediately rather than waiting for the next ping cycle.
+
 ### Sequence numbers
 
 `nextSequence()` starts at a random offset in the safe integer range and increments by 2. This

packages/core/src/relay-client.ts

@@ -46,6 +46,8 @@ export class RelayClient extends EventEmitter {
   private messageQueue: MessageQueue;
   private readyTimeoutId: ReturnType<typeof setTimeout> | null = null;
 
+  private disconnecting: boolean = false;
+
   private sequence: number = Math.floor(
     Math.random() * (Number.MAX_SAFE_INTEGER - 500_000),
   );
@@ -72,7 +74,7 @@ export class RelayClient extends EventEmitter {
       logNetworkActivity: true,
       ...config,
     };
-    this.pool = pool ?? new SimplePool();
+    this.pool = pool ?? new SimplePool({ enablePing: true });
     this.sharedPool = pool !== undefined;
 
     this.messageQueue = new MessageQueue({
@@ -120,11 +122,19 @@ export class RelayClient extends EventEmitter {
     return !this.config.pairedPublicKey.every((byte) => byte === 0);
   }
 
+  private emitDisconnect(error: Error): void {
+    if (this.disconnecting) return;
+    this.disconnecting = true;
+    this.emit("disconnect", error);
+  }
+
   async connect(): Promise<void> {
     if (this.config.logNetworkActivity) {
       debug(Scope.Relay, `Connecting to relay...`);
     }
 
+    this.disconnecting = false;
+
     if (this.lastProcessedTimestamp === 0) {
       this.lastProcessedTimestamp = Math.floor(Date.now() / 1000) - 2;
     }
@@ -150,7 +160,7 @@ export class RelayClient extends EventEmitter {
             if (this.config.logNetworkActivity) {
               debug(Scope.Relay, `Subscription closed: ${reasons.join(", ")}`);
             }
-            this.emit("disconnect", new Error("Subscription closed"));
+            this.emitDisconnect(new Error("Subscription closed"));
           },
         },
       );
@@ -251,6 +261,9 @@ export class RelayClient extends EventEmitter {
           error,
         );
       }
+      this.emitDisconnect(
+        error instanceof Error ? error : new Error(`Publish failed: ${error}`),
+      );
       throw error;
     }
   }
@@ -330,7 +343,7 @@ export class RelayClient extends EventEmitter {
   }
 
   isConnected(): boolean {
-    return true;
+    return this.subscription !== null;
   }
 
   private netlog(