always select latest batch for now

lib/replicator.js

@@ -1749,6 +1749,17 @@ class Peer {
     return false
   }
 
+  _addLastRangeBatch(r, start, end) {
+    const { WANT_BATCH } = w
+
+    const next = this.core.bitfield.findLast(false, end - 1)
+    if (next === -1 || next < start) return false
+
+    const b = (next - (next & (WANT_BATCH - 1))) / WANT_BATCH
+
+    return r.addBatch(b)
+  }
+
   _populateRangeBatches(r) {
     const { WANT_BATCH } = w
     for (let i = r.batches.length - 1; i >= 0; i--) {
@@ -1764,10 +1775,13 @@ class Peer {
       r.removeBatch(b)
     }
 
-    while (r.batches.length < 3) {
-      const end = r.end === -1 ? this.core.state.length : r.end
-      if (end <= r.start) return
+    const end = r.end === -1 ? this.core.state.length : r.end
+    if (end <= r.start) return
 
+    // always keep the last batch in the range selected
+    if (r.batches.length < 3) this._addLastRangeBatch(r, r.start, end)
+
+    while (r.batches.length < 3) {
       const len = end - r.start
       const off = r.start + (r.linear ? 0 : Math.floor(Math.random() * len))
 

test/replicate.js

@@ -11,6 +11,7 @@ const {
 } = require('./helpers')
 const { makeStreamPair } = require('./helpers/networking.js')
 const crypto = require('hypercore-crypto')
+const { once } = require('events')
 const Hypercore = require('../')
 
 const DEBUG = false
@@ -2863,6 +2864,49 @@ test('delayed updateAll clears timer after reorg skip', async function (t) {
   t.is(r._updateAllBump, null, 'timer handle should be cleared after firing')
 })
 
+test('small wants - range request stall', async function (t) {
+  t.plan(3)
+  Hypercore.enable(Hypercore.SMALL_WANTS)
+  t.teardown(() => Hypercore.enable(0))
+
+  const core = await create(t)
+  const blockLength = 20_000
+  await core.append(Array(blockLength).fill('a'))
+  t.is(core.length, blockLength, 'length is set')
+
+  let i = 0
+  while (i < blockLength) {
+    await core.clear(i, i + 1)
+    i += 2
+  }
+
+  const peer = await create(t, core.key)
+  const uploaded = once(core, 'upload')
+  replicate(core, peer, t)
+
+  peer.download({ start: 0, end: blockLength }).done()
+  await uploaded
+
+  let tries = 100 // Usually < ~10-20 tries but padding for slow CI machines
+
+  const targetBlock = blockLength - 1
+  while (tries-- > 0) {
+    const h = await peer.has(blockLength - 1)
+
+    if (h) {
+      t.pass('got block near end')
+      break
+    }
+
+    await new Promise((resolve) => setTimeout(resolve, 10))
+  }
+
+  t.comment('tries', tries)
+
+  const value = await peer.get(targetBlock)
+  t.alike(value, b4a.from('a'), 'got nth - 1 block')
+})
+
 test('delayed updateAll timer doesnt keep event loop alive', async function (t) {
   const core = await create(t)