Fix cache bug in iterator.nextv()

iterator.js

@@ -76,10 +76,18 @@ class Iterator extends AbstractIterator {
  }
  }
 
- // TODO (v2): read from cache first?
  async _nextv (size, options) {
  this[kFirst] = false
 
+ // If next() was called then empty the cache first
+ if (this[kPosition] < this[kCache].length) {
+ const length = Math.min(size, this[kCache].length - this[kPosition])
+ const chunk = this[kCache].slice(this[kPosition], this[kPosition] + length)
+
+ this[kPosition] += length
+ return chunk
+ }
+
  // Avoid iterator_nextv() call if end was already reached
  if ((this[kState][0] & STATE_ENDED) !== 0) {
  return []

test/iterator-test.js

@@ -37,3 +37,37 @@ test('iterator optimized for seek', async function (t) {
  await ite.close()
  return db.close()
 })
+
+// TODO: move to abstract-level
+for (const slice of [false, true]) {
+ test(`nextv() after next() respects cache (slice=${slice})`, async function (t) {
+ const db = testCommon.factory()
+
+ await db.open()
+ await db.batch()
+ .put('a', 'value')
+ .put('b', 'value')
+ .put('c', 'value')
+ .put('d', 'value')
+ .write()
+
+ const it = db.iterator()
+
+ // Two called are needed to populate the cache
+ t.same(await it.next(), ['a', 'value'], 'entry a ok')
+ t.same(await it.next(), ['b', 'value'], 'entry b ok')
+ t.is(it.cached, 2)
+
+ if (slice) {
+ t.same(await it.nextv(1), [['c', 'value']], 'entries ok (1)')
+ t.same(await it.nextv(1), [['d', 'value']], 'entries ok (2)')
+ t.same(await it.nextv(1), [], 'empty')
+ } else {
+ t.same(await it.nextv(10), [['c', 'value'], ['d', 'value']], 'entries ok')
+ t.same(await it.nextv(10), [], 'empty')
+ }
+
+ await it.close()
+ return db.close()
+ })
+}