From 443335fa73c57e9ca4b0cd13931799e030872892 Mon Sep 17 00:00:00 2001
From: Bartosz Sypytkowski <b.sypytkowski@gmail.com>
Date: Thu, 2 May 2024 08:10:04 +0200
Subject: [PATCH 1/2] missing state vector should be usable for update encoding

---
 tests/doc.tests.js | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/tests/doc.tests.js b/tests/doc.tests.js
index bb94819d..c5df310b 100644
--- a/tests/doc.tests.js
+++ b/tests/doc.tests.js
@@ -327,3 +327,45 @@ export const testSyncDocsEvent = async _tc => {
   t.assert(!ydoc.isSynced)
   t.assert(ydoc.whenSynced !== oldWhenSynced)
 }
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMissingStateVector = tc => {
+  const d1 = new Y.Doc()
+  d1.clientID = 1
+  const m1 = d1.getMap('test')
+  /** @type {any[]} */
+  const updates = []
+  d1.on('update', (update) => {
+    updates.push(update)
+  })
+  m1.set('a', '1')
+  m1.set('b', '2')
+  m1.set('c', '3')
+  m1.set('d', '4')
+  m1.set('e', '5')
+
+  // we only apply second half of the updates
+  const second = updates.slice(3)
+
+  const d2 = new Y.Doc()
+  d2.clientID = 2
+  const m2 = d2.getMap('test')
+
+  for (let u of second) {
+    Y.applyUpdate(d2, u)
+  }
+  let json = m2.toJSON()
+  t.compare(json, {})
+
+  // a missing state vector should mark the beginning of missing updates
+  const missingSV = /** @type {Map<number, number>} */ (d2.store.pendingStructs?.missing)
+  //t.compare(missingSV, new Map([[1, 0]]))
+
+  // exchange all updates from missing state vector onwards
+  const update = Y.encodeStateAsUpdate(d1, Y.encodeStateVector(missingSV))
+  Y.applyUpdate(d2, update)
+  json = m2.toJSON()
+  t.compare(json, {'a':'1','b':'2','c':'3','d':'4','e':'5'})
+}
\ No newline at end of file

From 27299f7746a69dbc59354cd027069c502cdaddf2 Mon Sep 17 00:00:00 2001
From: Bartosz Sypytkowski <b.sypytkowski@gmail.com>
Date: Thu, 2 May 2024 08:17:06 +0200
Subject: [PATCH 2/2] fix: initialize missing state vector with 0 for new
 client

---
 src/utils/encoding.js | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/utils/encoding.js b/src/utils/encoding.js
index 08a9602d..1d84d495 100644
--- a/src/utils/encoding.js
+++ b/src/utils/encoding.js
@@ -265,7 +265,10 @@ const integrateStructs = (transaction, store, clientsStructRefs) => {
    */
   const updateMissingSv = (client, clock) => {
     const mclock = missingSV.get(client)
-    if (mclock == null || mclock > clock) {
+    if (mclock === undefined) {
+      // we never seen that client before
+      missingSV.set(client, 0)
+    } else if (mclock > clock) {
       missingSV.set(client, clock)
     }
   }