fix error stuck

src/attacker.ts

@@ -135,6 +135,12 @@ export class Attacker {
     return null;
   }
 
+  async close() {
+    return new Promise<void>((done) => {
+      this.socket.close(done);
+    });
+  }
+
   async attack(): Promise<string> {
     this.socket = dgram.createSocket('udp4');
     let err: string = null;
@@ -157,6 +163,7 @@ export class Attacker {
     });
     for (const step of AttackRoutine) {
       if (this.error) {
+        await this.close();
         return `Error: ${this.error.toString()}`;
       }
       err = await this.performStep(step);
@@ -164,9 +171,7 @@ export class Attacker {
         break;
       }
     }
-    await new Promise<void>((done) => {
-      this.socket.close(done);
-    });
+    await this.close();
     return err;
   }
 }