From 77a378dc64e1c539ee9325e717bd03cce766fb8e Mon Sep 17 00:00:00 2001
From: Kevin Jahns <kevin.jahns@pm.me>
Date: Mon, 6 Jul 2020 18:11:40 +0200
Subject: [PATCH] implement modifyAwarenessState

---
 awareness.js | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/awareness.js b/awareness.js
index 4849a32..98ff372 100644
--- a/awareness.js
+++ b/awareness.js
@@ -80,7 +80,7 @@ export class Awareness extends Observable {
     clearInterval(this._checkInterval)
   }
   /**
-   * @return {Object<string,Object>|null}
+   * @return {Object<string,any>|null}
    */
   getLocalState () {
     return this.states.get(this.doc.clientID) || null
@@ -125,7 +125,7 @@ export class Awareness extends Observable {
   }
   /**
    * @param {string} field
-   * @param {Object} value
+   * @param {any} value
    */
   setLocalStateField (field, value) {
     const state = this.getLocalState()
@@ -192,6 +192,33 @@ export const encodeAwarenessUpdate = (awareness, clients, states = awareness.sta
   return encoding.toUint8Array(encoder)
 }
 
+/**
+ * Modify the content of an awareness update before re-encoding it to an awareness update.
+ *
+ * This might be useful when you have a central server that wants to ensure that clients
+ * cant hijack somebody elses identity.
+ *
+ * @param {Uint8Array} update
+ * @param {function(any):any} modify
+ * @return {Uint8Array}
+ */
+export const modifyAwarenessUpdate = (update, modify) => {
+  const decoder = decoding.createDecoder(update)
+  const encoder = encoding.createEncoder()
+  const len = decoding.readVarUint(decoder)
+  encoding.writeVarUint(encoder, len)
+  for (let i = 0; i < len; i++) {
+    const clientID = decoding.readVarUint(decoder)
+    const clock = decoding.readVarUint(decoder)
+    const state = JSON.parse(decoding.readVarString(decoder))
+    const modifiedState = modify(state)
+    encoding.writeVarUint(encoder, clientID)
+    encoding.writeVarUint(encoder, clock)
+    encoding.writeVarString(encoder, JSON.stringify(modifiedState))
+  }
+  return encoding.toUint8Array(encoder)
+}
+
 /**
  * @param {Awareness} awareness
  * @param {Uint8Array} update