[FEAT] start a watcher at a specific revision

FIX #650

jetstream/kv.ts

@@ -748,6 +748,9 @@ export class Bucket implements KV, KvRemove {
     const subj = cc.filter_subject!;
     const copts = consumerOpts(cc);
     copts.bindStream(this.stream);
+    if (opts.resumeFromRevision && opts.resumeFromRevision > 0) {
+      copts.startSequence(opts.resumeFromRevision);
+    }
     copts.orderedConsumer();
     copts.callback((err, jm) => {
       if (err) {

jetstream/tests/kv_test.ts

@@ -1945,3 +1945,24 @@ Deno.test("kv - compression", async () => {
   assertEquals(status.compression, false);
   await cleanup(ns, nc);
 });
+
+Deno.test("kv - watch start at", async () => {
+  const { ns, nc } = await setup(jetstreamServerConf());
+  const js = nc.jetstream();
+  const kv = await js.views.kv("a");
+  await kv.put("a", "1");
+  await kv.put("b", "2");
+  await kv.put("c", "3");
+
+  const iter = await kv.watch({ resumeFromRevision: 2 });
+  await (async () => {
+    for await (const o of iter) {
+      // expect first key to be "b"
+      assertEquals(o.key, "b");
+      assertEquals(o.revision, 2);
+      break;
+    }
+  })();
+
+  await cleanup(ns, nc);
+});

jetstream/types.ts

@@ -1135,6 +1135,12 @@ export type KvWatchOptions = {
    * Specify what to include in the watcher, by default all last values.
    */
   include?: KvWatchInclude;
+  /**
+   * Starts watching at the specified revision. This is intended for watchers
+   * that have restarted watching and have maintained some state of where they are
+   * in the watch.
+   */
+  resumeFromRevision?: number;
 };
 
 export interface RoKV {