From 0c88df619afe084b6e5d2a2088a0a75718bcf70e Mon Sep 17 00:00:00 2001
From: Lucas Barrena <lucasbarrena98@gmail.com>
Date: Thu, 6 Jul 2023 19:29:48 -0300
Subject: [PATCH] Add peer.remoteContiguousLength

---
 lib/replicator.js     | 12 +++++++-
 test/remote-length.js | 68 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+), 1 deletion(-)
 create mode 100644 test/remote-length.js

diff --git a/lib/replicator.js b/lib/replicator.js
index f5bcebbf..704fa03c 100644
--- a/lib/replicator.js
+++ b/lib/replicator.js
@@ -325,6 +325,10 @@ class Peer {
     replicator._ifAvailable++
   }
 
+  get remoteContiguousLength () {
+    return this.remoteBitfield.findFirst(false, 0)
+  }
+
   getMaxInflight () {
     const stream = this.stream.rawStream
     if (!stream.udx) return Math.min(this.inflightRange[1], this.inflightRange[0] * 3)
@@ -680,8 +684,12 @@ class Peer {
 
   onrange ({ drop, start, length }) {
     const has = drop === false
+    const rangeStart = this.remoteBitfield.findFirst(!has, start)
+    const rangeLength = length - (rangeStart - start)
 
-    this.remoteBitfield.setRange(start, length, has)
+    if (rangeLength > 0) {
+      this.remoteBitfield.setRange(rangeStart, rangeLength, has)
+    }
 
     if (drop === false) this._update()
   }
@@ -912,6 +920,8 @@ class Peer {
   }
 
   _maybeWant (start, length = 1) {
+    if (start + length <= this.remoteContiguousLength) return
+
     let i = Math.floor(start / DEFAULT_SEGMENT_SIZE)
     const n = Math.ceil((start + length) / DEFAULT_SEGMENT_SIZE)
 
diff --git a/test/remote-length.js b/test/remote-length.js
new file mode 100644
index 00000000..967a50b6
--- /dev/null
+++ b/test/remote-length.js
@@ -0,0 +1,68 @@
+const test = require('brittle')
+const { create, replicate } = require('./helpers')
+
+test('basic peer remote contiguous length', async function (t) {
+  t.plan(2)
+
+  const a = await create()
+  const b = await create(a.key)
+
+  replicate(a, b, t)
+
+  await a.append('a')
+  await b.get(0)
+  await new Promise(resolve => setTimeout(resolve, 100))
+  t.is(getPeer(a, b).remoteContiguousLength, 1)
+
+  await a.append('b')
+  await b.get(1)
+  await new Promise(resolve => setTimeout(resolve, 100))
+  t.is(getPeer(a, b).remoteContiguousLength, 2)
+})
+
+test('peer remote contiguous length', async function (t) {
+  t.plan(3)
+
+  const a = await create()
+  const b = await create(a.key)
+
+  replicate(a, b, t)
+
+  await a.append('a')
+  await b.get(0)
+  await new Promise(resolve => setTimeout(resolve, 100))
+  t.is(getPeer(a, b).remoteContiguousLength, 1)
+
+  await a.append(['d', 'e'])
+  await b.get(2)
+  await new Promise(resolve => setTimeout(resolve, 100))
+  t.is(getPeer(a, b).remoteContiguousLength, 1)
+
+  await b.get(1)
+  await new Promise(resolve => setTimeout(resolve, 100))
+  t.is(getPeer(a, b).remoteContiguousLength, 3)
+})
+
+test('peer truncates the remote contiguous length', async function (t) {
+  t.plan(2)
+
+  const a = await create()
+  const b = await create(a.key)
+
+  replicate(a, b, t)
+
+  await a.append(['a', 'b'])
+  await b.get(0)
+  await b.get(1)
+  await new Promise(resolve => setTimeout(resolve, 100))
+  t.is(getPeer(a, b).remoteContiguousLength, 2)
+
+  await a.truncate(1)
+  await new Promise(resolve => setTimeout(resolve, 100))
+  t.is(getPeer(a, b).remoteContiguousLength, 1)
+})
+
+// "A" wants to know if "B" is finished syncing, so find the corresponding peer
+function getPeer (a, b) {
+  return a.replicator.peers.find(peer => peer.remotePublicKey.equals(b.replicator.peers[0].stream.publicKey))
+}