Add streams XREADGROUP and XACK example. (#1832)

* Removed stream delete command to allow consumer group example to work.

* Adds stream consumer group example.

* Adds stream consumer group example code.

* Update README.md

Co-authored-by: Leibale Eidelman <leibale1998@gmail.com>

examples/README.md

@@ -19,6 +19,7 @@ This folder contains example scripts showing how to use Node Redis in different
 | `stream-consumer.js`        | Reads entries from a [Redis Stream](https://redis.io/topics/streams-intro) using the blocking `XREAD` command                                       |
 | `time-series.js`            | Create, populate and query timeseries data with [Redis Timeseries](https://redistimeseries.io)                                                      |
 | `topk.js`                   | Use the [RedisBloom](https://redisbloom.io) TopK to track the most frequently seen items.                                                           |
+| `stream-consumer-group.js`  | Reads entties from a [Redis Stream](https://redis.io/topics/streams-intro) as part of a consumer group using the blocking `XREADGROUP` command      |
 
 ## Contributing
 

examples/stream-consumer-group.js

@@ -0,0 +1,104 @@
+// A sample stream consumer using the blocking variant of XREADGROUP.
+// This consumer works in collaboration with other instances of itself
+// in the same consumer group such that the group as a whole receives
+// every entry from the stream.
+//
+// This consumes entries from a stream created by stream-producer.js
+//
+// Run this as follows:
+//
+// $ node stream-consumer-group.js <consumerName>
+//
+// Run multiple instances with different values of <consumerName>
+// to see them processing the stream as a group:
+//
+// $ node stream-consumer-group.js consumer1
+//
+// In another terminal:
+//
+// $ node stream-consumer-group.js consumer2
+
+import { createClient, commandOptions } from 'redis';
+
+async function streamConsumerGroup() {
+  const client = createClient();
+
+  if (process.argv.length !== 3) {
+    console.log(`usage: node stream-consumer-group.js <consumerName>`);
+    process.exit(1);
+  }
+
+  const consumerName = process.argv[2];
+
+  await client.connect();
+
+  // Create the consumer group (and stream) if needed...
+  try {
+    await client.xGroupCreate('mystream', 'myconsumergroup', '0', {
+      MKSTREAM: true
+    });
+    console.log('Created consumer group.');
+  } catch (e) {
+    console.log('Consumer group already exists, skipped creation.');
+  }
+
+  console.log(`Starting consumer ${consumerName}.`);
+
+  while (true) {
+    try {
+      let response = await client.xReadGroup(
+        commandOptions({
+          isolated: true
+        }),
+        'myconsumergroup', 
+        consumerName, [
+          // XREADGROUP can read from multiple streams, starting at a
+          // different ID for each...
+          {
+            key: 'mystream',
+            id: '>' // Next entry ID that no consumer in this group has read
+          }
+        ], {
+          // Read 1 entry at a time, block for 5 seconds if there are none.
+          COUNT: 1,
+          BLOCK: 5000
+        }
+      );
+
+      if (response) {
+        // Response is an array of streams, each containing an array of
+        // entries:
+        //
+        // [
+        //   {
+        //      "name": "mystream",
+        //      "messages": [
+        //        {
+        //          "id": "1642088708425-0",
+        //          "message": {
+        //            "num": "999"
+        //          }
+        //        }
+        //      ]
+        //    }
+        //  ]
+        console.log(JSON.stringify(response));
+
+        // Use XACK to acknowledge successful processing of this
+        // stream entry.
+        const entryId = response[0].messages[0].id;
+        await client.xAck('mystream', 'myconsumergroup', entryId);
+
+        console.log(`Acknowledged processing of entry ${entryId}.`);
+      } else {
+        // Response is null, we have read everything that is
+        // in the stream right now...
+        console.log('No new stream entries.');
+      }
+    } catch (err) {
+      console.error(err);
+    }
+  }
+}
+
+streamConsumerGroup();

examples/stream-producer.js

@@ -6,7 +6,6 @@ async function streamProducer() {
   const client = createClient();
 
   await client.connect();
-  await client.del('mystream');
 
   let num = 0;