Fix EventEmitter leak

src/socket.ts

@@ -453,9 +453,18 @@ export class FluentSocket extends EventEmitter {
     this.processMessages(protocol.decodeServerStream(this.passThroughStream));
 
     return new Promise<void>((resolve, reject) => {
-      // This may call both resolve and reject, but the ES standard says this is OK
-      this.once(FluentSocketEvent.CONNECTED, () => resolve());
-      this.once(FluentSocketEvent.ERROR, err => reject(err));
+      const onConnected = () => {
+        resolve();
+        // Avoid a memory leak and remove the other listener
+        this.removeListener(FluentSocketEvent.ERROR, onError);
+      };
+      const onError = (err: Error) => {
+        reject(err);
+        // Avoid a memory leak and remove the other listener
+        this.removeListener(FluentSocketEvent.CONNECTED, onConnected);
+      };
+      this.once(FluentSocketEvent.CONNECTED, onConnected);
+      this.once(FluentSocketEvent.ERROR, onError);
     });
   }
 
@@ -483,7 +492,7 @@ export class FluentSocket extends EventEmitter {
         this.onMessage(message);
       }
     } catch (e) {
-      this.close(CloseState.RECONNECT, e);
+      this.close(CloseState.RECONNECT, e as Error);
     }
   }
 

test/test.socket.ts

@@ -60,6 +60,19 @@ describe("FluentSocket", () => {
     sinon.assert.calledOnce(connectStub);
   });
 
+  it("should not preserve error handlers after connect", done => {
+    const {socket, connectStub} = createFluentSocket({disableReconnect: true});
+
+    socket.on(FluentSocketEvent.WRITABLE, () => {
+      expect(socket.listenerCount(FluentSocketEvent.ERROR)).to.equal(0);
+      done();
+    });
+
+    socket.connect();
+
+    sinon.assert.calledOnce(connectStub);
+  });
+
   it("should not block for draining on write by default", done => {
     const {socket, stream, connectStub} = createFluentSocket({
       disableReconnect: true,