doc(jestream): clarified consumer backoff - also added a test

jetstream/src/jsapi_types.ts

@@ -1005,8 +1005,8 @@ export interface ConsumerUpdateConfig {
    */
   "inactive_threshold"?: Nanos;
   /**
-   * List of durations in nanoseconds format that represents a retry timescale for
-   * NaK'd messages or those being normally retried
+   * List of durations in nanoseconds that represents a retry timescale for
+   * the redelivery of messages
    */
   "backoff"?: Nanos[];
   /**

jetstream/tests/jetstream_test.ts

@@ -38,6 +38,7 @@ import {
 } from "@nats-io/nats-core";
 import {
   assert,
+  assertAlmostEquals,
   assertEquals,
   assertExists,
   assertInstanceOf,
@@ -707,7 +708,8 @@ Deno.test("jetstream - backoff", async () => {
   const { stream, subj } = await initStream(nc);
   const jsm = await jetstreamManager(nc);
 
-  const backoff = [nanos(250), nanos(1000), nanos(3000)];
+  const ms = [250, 1000, 3000];
+  const backoff = ms.map((n) => nanos(n));
   const ci = await jsm.consumers.add(stream, {
     durable_name: "me",
     ack_policy: AckPolicy.Explicit,
@@ -723,10 +725,11 @@ Deno.test("jetstream - backoff", async () => {
   const js = jetstream(nc);
   await js.publish(subj);
 
+  const when: number[] = [];
   const c = await js.consumers.get(stream, "me");
   const iter = await c.consume({
     callback: (m) => {
-      console.log(m.info.redeliveryCount);
+      when.push(Date.now());
       if (m.info.redeliveryCount === 4) {
         iter.stop();
       }
@@ -735,6 +738,58 @@ Deno.test("jetstream - backoff", async () => {
 
   await iter.closed();
 
+  const offset = when.map((n, idx) => {
+    const p = idx > 0 ? idx - 1 : 0;
+    return n - when[p];
+  });
+
+  offset.slice(1).forEach((n, idx) => {
+    assertAlmostEquals(n, ms[idx], 20);
+  });
+
+  await cleanup(ns, nc);
+});
+
+Deno.test("jetstream - redelivery", async () => {
+  const { ns, nc } = await setup(jetstreamServerConf({}));
+  if (await notCompatible(ns, nc, "2.7.2")) {
+    return;
+  }
+
+  const { stream, subj } = await initStream(nc);
+  const jsm = await jetstreamManager(nc);
+
+  const ci = await jsm.consumers.add(stream, {
+    durable_name: "me",
+    ack_policy: AckPolicy.Explicit,
+    max_deliver: 4,
+    ack_wait: nanos(1000),
+  });
+
+  assertEquals(ci.config.max_deliver, 4);
+
+  const js = jetstream(nc);
+  await js.publish(subj);
+
+  const c = await js.consumers.get(stream, "me");
+
+  let redeliveries = 0;
+  const iter = await c.consume({
+    callback: (m) => {
+      if (m.redelivered) {
+        redeliveries++;
+      }
+      if (m.info.redeliveryCount === 4) {
+        setTimeout(() => {
+          iter.stop();
+        }, 2000);
+      }
+    },
+  });
+
+  await iter.closed();
+  assertEquals(redeliveries, 3);
+
   await cleanup(ns, nc);
 });