fix: throw an error when started listening before app is boostrapped

src/consumer/kafkaConsumer.ts

@@ -18,7 +18,7 @@
 
 import vm from "vm";
 
-import { Inject, Injectable } from "@nestjs/common";
+import { Inject, Injectable, OnApplicationBootstrap } from "@nestjs/common";
 import {
   CustomTransportStrategy,
   MessageHandler,
@@ -37,9 +37,14 @@ import { IKafkaConsumerSerializedOptions } from "./interfaces";
 import { KafkaConsumerMessageHandler } from "./kafkaConsumerMessageHandler";
 
 @Injectable()
-export class KafkaConsumer extends Server implements CustomTransportStrategy {
+export class KafkaConsumer
+  extends Server
+  implements CustomTransportStrategy, OnApplicationBootstrap
+{
   public readonly transportId = KafkaConsumerTransportId;
 
+  private applicationBootstrapped = false;
+
   private readonly messageHandlersMap: Map<
     string,
     Map<string, MessageHandler>
@@ -62,9 +67,24 @@ export class KafkaConsumer extends Server implements CustomTransportStrategy {
   }
 
   public listen(callback: (error?: unknown) => void): void {
+    if (!this.applicationBootstrapped) {
+      const errorMessage =
+        "Application is not bootstrapped. " +
+        "Ensure that you have called app.listen() " +
+        "before calling app.startAllMicroservices(). " +
+        "The listen method was invoked before the application finished bootstrapping.";
+
+      this.logger.error(errorMessage);
+      return callback(new Error(errorMessage));
+    }
+
     this.start().then(callback).catch(callback);
   }
 
+  public onApplicationBootstrap(): void {
+    this.applicationBootstrapped = true;
+  }
+
   private addMessageHandlerToMap(
     connectionName: string,
     topics: string[],