fix: cursors with query and blob lists

Author: kitsonk

blob.test.ts

@@ -464,6 +464,27 @@ Deno.test({
   },
 });
 
+Deno.test({
+  name: "list - with cursor",
+  async fn() {
+    const kv = await setup();
+    await set(kv, ["hello", 1], new Uint8Array([1, 2, 3]));
+    await set(kv, ["hello", 2], new Uint8Array([1, 2, 3]));
+    await set(kv, ["hello", 3], new Uint8Array([1, 2, 3]));
+    await set(kv, ["hello"], new Uint8Array([1, 2, 3]));
+    await set(kv, ["world"], new Uint8Array([1, 2, 3]));
+    const iterator = list(kv, { prefix: ["hello"] }, { limit: 2 });
+    const entries = await Array.fromAsync(iterator);
+    assertEquals(entries.length, 2);
+    const iterator2 = list(kv, { prefix: ["hello"] }, { limit: 2, cursor: iterator.cursor });
+    const entries2 = await Array.fromAsync(iterator2);
+    assertEquals(entries2.length, 1);
+    assertEquals(entries2[0].key, ["hello", 3]);
+    assertEquals(entries2[0].value, { kind: "buffer", size: 3 });
+    return teardown();
+  },
+});
+
 Deno.test({
   name: "list - meta",
   async fn() {

blob_util.ts

@@ -333,13 +333,17 @@ export class BlobListIterator extends AsyncIterator implements
   > {
   #iterator: Deno.KvListIterator<unknown>;
   #count = 0;
+  #cursor?: string;
   #kv: Deno.Kv;
   #limit?: number;
   #options: Deno.KvListOptions;
   #valueKind: "meta" | "bytes" | "blob" | "stream";
 
   get cursor(): string {
-    return this.#iterator.cursor;
+    if (!this.#cursor) {
+      throw new Error("Cannot get cursor before first iteration");
+    }
+    return this.#cursor;
   }
 
   constructor(
@@ -371,6 +375,7 @@ export class BlobListIterator extends AsyncIterator implements
         if (this.#limit && this.#count > this.#limit) {
           break;
         }
+        this.#cursor = this.#iterator.cursor;
         const key: Deno.KvKey = entry.key.slice(0, -1);
         if (this.#valueKind === "meta") {
           return {

query.test.ts

@@ -539,6 +539,32 @@ Deno.test("Query - limit API", async () => {
   db.close();
 });
 
+Deno.test("Query - with cursor", async () => {
+  const db = await Deno.openKv(":memory:");
+  await db
+    .atomic()
+    .set(["a", "b"], { age: 10 })
+    .set(["a", "b", "c"], { age: 10 })
+    .set(["a", "d", "e"], { age: 10 })
+    .set(["a", "d", "f"], { age: 10 })
+    .set(["a", "g"], { age: 20 })
+    .set(["b", "h"], { age: 10 })
+    .commit();
+  const iterator = query(db, { prefix: [] }, { limit: 2 })
+    .where("age", "==", 10)
+    .get();
+  const result = await Array.fromAsync(iterator);
+  assertEquals(result.length, 2);
+  const iterator2 = query(db, { prefix: [] }, { limit: 2, cursor: iterator.cursor })
+    .where("age", "==", 10)
+    .get();
+  const result2 = await Array.fromAsync(iterator2);
+  assertEquals(result2.length, 2);
+  assertEquals(result2[0].key, ["a", "d", "e"]);
+  assertEquals(result2[1].key, ["a", "d", "f"]);
+  db.close();
+});
+
 Deno.test({
   name: "query - blob with limit",
   async fn() {

query.ts

@@ -811,11 +811,15 @@ const AsyncIterator = Object.getPrototypeOf(async function* () {}).constructor;
 class QueryListIterator<T = unknown> extends AsyncIterator implements Deno.KvListIterator<T> {
   #iterator: Deno.KvListIterator<T>;
   #count = 0;
+  #cursor?: string;
   #limit?: number;
   #query: Filter[];
 
   get cursor(): string {
-    return this.#iterator.cursor;
+    if (!this.#cursor) {
+      throw new Error("Cannot get cursor before first iteration");
+    }
+    return this.#cursor;
   }
 
   constructor(
@@ -836,6 +840,7 @@ class QueryListIterator<T = unknown> extends AsyncIterator implements Deno.KvLis
         if (this.#limit && this.#count > this.#limit) {
           return { value: undefined, done: true };
         }
+        this.#cursor = this.#iterator.cursor;
         return { value: entry, done: false };
       }
     }