[FEAT] discard_new_per_subject functionality

described in nats-io/nats-architecture-and-design#160 (#373)

nats-base-client/kv.ts

@@ -53,7 +53,7 @@ import {
 import { millis, nanos } from "./jsutil.ts";
 import { QueuedIterator, QueuedIteratorImpl } from "./queued_iterator.ts";
 import { headers, MsgHdrs } from "./headers.ts";
-import { consumerOpts, deferred, ErrorCode } from "./mod.ts";
+import { consumerOpts, deferred, ErrorCode, NatsError } from "./mod.ts";
 import { compare, Feature, parseSemVer } from "./semver.ts";
 import { JetStreamManagerImpl } from "./jsm.ts";
 
@@ -422,8 +422,18 @@ export class Bucket implements KV, KvRemove {
       o.headers = h;
       h.set("Nats-Expected-Last-Subject-Sequence", `${opts.previousSeq}`);
     }
-    const pa = await this.js.publish(this.subjectForKey(ek), data, o);
-    return pa.seq;
+    try {
+      const pa = await this.js.publish(this.subjectForKey(ek), data, o);
+      return pa.seq;
+    } catch (err) {
+      const ne = err as NatsError;
+      if (ne.isJetStreamError()) {
+        ne.message = ne.api_error?.description!;
+        ne.code = `${ne.api_error?.code!}`;
+        return Promise.reject(ne);
+      }
+      return Promise.reject(err);
+    }
   }
 
   async get(

nats-base-client/types.ts

@@ -1760,6 +1760,11 @@ export interface StreamUpdateConfig {
    * When a Stream reach its limits either old messages are deleted or new ones are denied
    */
   discard: DiscardPolicy;
+  /**
+   * Sets the context of the on a per subject basis. Requires {@link DiscardPolicy.New} as the
+   * {@link discard} policy.
+   */
+  discard_new_per_subject: boolean;
   /**
    * Disables acknowledging messages that are received by the Stream.
    */

tests/jsm_test.ts

@@ -1717,3 +1717,53 @@ Deno.test("jsm - list filter", async () => {
   }
   await cleanup(ns, nc);
 });
+
+Deno.test("jsm - discard_new_per_subject option", async () => {
+  const { ns, nc } = await setup(
+    jetstreamServerConf({}, true),
+  );
+
+  if (await notCompatible(ns, nc, "2.9.2")) {
+    return;
+  }
+
+  const jsm = await nc.jetstreamManager();
+
+  // discard policy new is required
+  await assertRejects(
+    async () => {
+      await jsm.streams.add({
+        name: "A",
+        discard_new_per_subject: true,
+        subjects: ["$KV.A.>"],
+        max_msgs_per_subject: 1,
+      });
+    },
+    Error,
+    "discard new per subject requires discard new policy to be set",
+  );
+
+  let si = await jsm.streams.add({
+    name: "KV_A",
+    discard: DiscardPolicy.New,
+    discard_new_per_subject: true,
+    subjects: ["$KV.A.>"],
+    max_msgs_per_subject: 1,
+  });
+  assertEquals(si.config.discard_new_per_subject, true);
+
+  const js = nc.jetstream();
+
+  const kv = await js.views.kv("A", { bindOnly: true });
+  await kv.put("B", Empty);
+  await assertRejects(
+    async () => {
+      (nc as NatsConnectionImpl).options.debug = true;
+      await kv.put("B", Empty);
+    },
+    Error,
+    "maximum messages per subject exceeded",
+  );
+
+  await cleanup(ns, nc);
+});