feat(jetstream): PersistMode for stream configurations

jetstream/src/internal_mod.ts

@@ -179,6 +179,7 @@ export {
   AckPolicy,
   DeliverPolicy,
   DiscardPolicy,
+  PersistMode,
   PubHeaders,
   ReplayPolicy,
   RetentionPolicy,

jetstream/src/jsapi_types.ts

@@ -188,6 +188,12 @@ export type StreamConfig = StreamUpdateConfig & {
    * Enables the ability to send atomic batches to the stream
    */
   "allow_atomic": boolean;
+
+  /**
+   * Sets the persistence model for the stream - the default is PersistMode.Default.
+   * This is a 2.12 feature.
+   */
+  "persist_mode": PersistMode;
 };
 
 /**
@@ -504,6 +510,26 @@ export const StoreCompression = {
 export type StoreCompression =
   typeof StoreCompression[keyof typeof StoreCompression];
 
+export const PersistMode = {
+  /**
+   * All writes are committed and stream data is synced to disk before the publish
+   * acknowledgement is sent.
+   * This is the default mode, and provides the strongest data durability guarantee.
+   */
+  Default: "default",
+  /**
+   * Writes to the stream are committed, but writes to the disk are asynchronously synced.
+   * The publish acknowledgement is sent before the sync to the disk is complete.
+   * This could result in data-loss if the server crashes before the sync is completed, however
+   * with an R3+ stream, the replication provides in-flight redundancy to reduce the likelihood of
+   * this occurring with distinct fault domains.
+   * This can significantly increase the publish throughput.
+   */
+  Async: "async",
+};
+
+export type PersistMode = typeof PersistMode[keyof typeof PersistMode];
+
 /**
  * Options for StreamAPI info requests
  */

jetstream/src/mod.ts

@@ -26,6 +26,7 @@ export {
   JetStreamApiError,
   JetStreamError,
   JsHeaders,
+  PersistMode,
   PubHeaders,
   ReplayPolicy,
   RepublishHeaders,

jetstream/tests/streams_test.ts

@@ -19,7 +19,12 @@ import {
   notCompatible,
   setup,
 } from "test_helpers";
-import { AckPolicy, jetstream, jetstreamManager } from "../src/mod.ts";
+import {
+  AckPolicy,
+  jetstream,
+  jetstreamManager,
+  PersistMode,
+} from "../src/mod.ts";
 
 import { assertEquals, assertExists, assertRejects } from "@std/assert";
 import { initStream } from "./jstest_util.ts";
@@ -167,3 +172,41 @@ Deno.test("streams - first_seq fails if wrong server", async () => {
 
   await cleanup(ns, nc);
 });
+
+Deno.test("streams - persist mode", async () => {
+  const { ns, nc } = await setup(jetstreamServerConf({}));
+  if (await notCompatible(ns, nc, "2.12.0")) {
+    return;
+  }
+
+  const jsm = await jetstreamManager(nc);
+
+  let si = await jsm.streams.add({
+    name: "A",
+    subjects: ["a"],
+    persist_mode: PersistMode.Default,
+  });
+  assertEquals(si.config.persist_mode, undefined);
+  let md = si.config.metadata || {};
+  assertEquals(md["_nats.req.level"], "0");
+
+  si = await jsm.streams.add({
+    name: "B",
+    subjects: ["b"],
+    persist_mode: PersistMode.Async,
+  });
+  assertEquals(si.config.persist_mode, PersistMode.Async);
+  md = si.config.metadata || {};
+  assertEquals(md["_nats.req.level"], "2");
+
+  await assertRejects(
+    () => {
+      // @ts-expect-error: testing server rejection
+      return jsm.streams.update("B", { persist_mode: PersistMode.Default });
+    },
+    Error,
+    "can not change persist mode",
+  );
+
+  await cleanup(ns, nc);
+});