don't destroy consumer when there are pending messages

examples/redis-pending/index.js

@@ -0,0 +1,58 @@
+"use strict";
+
+// Adapted from: https://github.com/moleculerjs/moleculer-channels/issues/74
+
+const { ServiceBroker } = require("moleculer");
+const ChannelsMiddleware = require("../../types").Middleware;
+const broker = new ServiceBroker({
+	namespace: "test",
+	nodeID: "test1",
+	transporter: "TCP",
+	middlewares: [
+		ChannelsMiddleware({
+			adapter: "redis://127.0.0.1:6379"
+		})
+	]
+});
+
+const serviceSchema = {
+	name: "subscriber",
+	channels: {
+		"order.created": {
+			group: "mygroup",
+			redis: {
+				minIdleTime: 1000,
+				claimInterval: 1,
+				startID: "0"
+			},
+			maxRetries: 100,
+			handler(payload) {
+				this.logger.info("Received order.created event", payload);
+				throw new Error();
+			}
+		}
+	}
+};
+broker.createService(serviceSchema);
+
+// Start the Moleculer broker
+broker.start().then(async () => {
+	try {
+		broker.repl();
+
+		for (let i = 0; i < 10; i++) {
+			await broker.sendToChannel("order.created", { id: i, items: "test" });
+
+			await broker.Promise.delay(100);
+		}
+
+		await broker.destroyService("subscriber");
+
+		setTimeout(() => {
+			broker.logger.info("Recreate service");
+			broker.createService(serviceSchema);
+		}, 10000);
+	} catch (error) {
+		console.log(error);
+	}
+});

src/adapters/redis.js

@@ -505,15 +505,32 @@ class RedisAdapter extends BaseAdapter {
 									})
 									.then(() => {
 										const pubClient = this.clients.get(this.pubName);
-										// 1. Delete consumer from the consumer group
-										// 2. Do NOT destroy the consumer group
-										// https://redis.io/commands/XGROUP
-										return pubClient.xgroup(
-											"DELCONSUMER",
-											chan.name, // Stream Name
-											chan.group, // Consumer Group
-											chan.id // Consumer ID
-										);
+										return pubClient
+											.xpending(
+												chan.name,
+												chan.group,
+												"-", // Start
+												"+", // End
+												10 // Max reported entries
+											)
+											.then(pending => {
+												if (pending.length !== 0) {
+													// Don't destroy the consumer group if there are pending messages
+													// It might come back online in the future and process the messages
+													// More info: https://github.com/moleculerjs/moleculer-channels/issues/74
+													return;
+												}
+
+												// 1. Delete consumer from the consumer group
+												// 2. Do NOT destroy the consumer group
+												// https://redis.io/commands/XGROUP
+												return pubClient.xgroup(
+													"DELCONSUMER",
+													chan.name, // Stream Name
+													chan.group, // Consumer Group
+													chan.id // Consumer ID
+												);
+											});
 									})
 									.then(() => resolve())
 									.catch(err => reject(err));