add clock vector to awareness protocol

protocols/awareness.js

@@ -11,6 +11,7 @@ const messageUsersStateChanged = 0
 /**
  * @typedef {Object} UserStateUpdate
  * @property {number} UserStateUpdate.userID
+ * @property {number} UserStateUpdate.clock
  * @property {Object} UserStateUpdate.state
  */
 
@@ -23,8 +24,9 @@ export const writeUsersStateChange = (encoder, stateUpdates) => {
   encoding.writeVarUint(encoder, messageUsersStateChanged)
   encoding.writeVarUint(encoder, len)
   for (let i = 0; i < len; i++) {
-    const {userID, state} = stateUpdates[i]
+    const {userID, state, clock} = stateUpdates[i]
     encoding.writeVarUint(encoder, userID)
+    encoding.writeVarUint(encoder, clock)
     encoding.writeVarString(encoder, JSON.stringify(state))
   }
 }
@@ -36,20 +38,25 @@ export const readUsersStateChange = (decoder, y) => {
   const len = decoding.readVarUint(decoder)
   for (let i = 0; i < len; i++) {
     const userID = decoding.readVarUint(decoder)
+    const clock = decoding.readVarUint(decoder)
     const state = JSON.parse(decoding.readVarString(decoder))
     if (userID !== y.userID) {
+      const uClock = y.awarenessClock.get(userID) || 0
+      y.awarenessClock.set(userID, clock)
       if (state === null) {
-        if (y.awareness.has(userID)) {
+        // only write if clock increases. cannot overwrite
+        if (y.awareness.has(userID) && uClock < clock) {
           y.awareness.delete(userID)
           removed.push(userID)
         }
-      } else {
+      } else if (uClock <= clock) { // allow to overwrite (e.g. when client was on, then offline)
         if (y.awareness.has(userID)) {
           updated.push(userID)
         } else {
           added.push(userID)
         }
         y.awareness.set(userID, state)
+        y.awarenessClock.set(userID, clock)
       }
     }
   }
@@ -63,6 +70,7 @@ export const readUsersStateChange = (decoder, y) => {
 /**
  * @param {decoding.Decoder} decoder
  * @param {encoding.Encoder} encoder
+ * @return {Array<UserStateUpdate>}
  */
 export const forwardUsersStateChange = (decoder, encoder) => {
   const len = decoding.readVarUint(decoder)
@@ -71,10 +79,12 @@ export const forwardUsersStateChange = (decoder, encoder) => {
   encoding.writeVarUint(encoder, len)
   for (let i = 0; i < len; i++) {
     const userID = decoding.readVarUint(decoder)
+    const clock = decoding.readVarUint(decoder)
     const state = decoding.readVarString(decoder)
     encoding.writeVarUint(encoder, userID)
+    encoding.writeVarUint(encoder, clock)
     encoding.writeVarString(encoder, state)
-    updates.push({userID, state: JSON.parse(state)})
+    updates.push({userID, state: JSON.parse(state), clock})
   }
   return updates
 }
@@ -95,6 +105,7 @@ export const readAwarenessMessage = (decoder, y) => {
  * @typedef {Object} UserState
  * @property {number} UserState.userID
  * @property {any} UserState.state
+ * @property {number} UserState.clock
  */
 
 /**