From 2856d0989a2499fefd93db6bd2ca4bb5432417b9 Mon Sep 17 00:00:00 2001
From: Jonas <jonas@freesources.org>
Date: Wed, 21 Jun 2023 15:50:39 +0200
Subject: [PATCH] Add y.js helpers to decode awareness messages

Signed-off-by: Jonas <jonas@freesources.org>
---
 src/helpers/yjs.js | 41 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/src/helpers/yjs.js b/src/helpers/yjs.js
index bc83c1e30a5..d843bc0b7e0 100644
--- a/src/helpers/yjs.js
+++ b/src/helpers/yjs.js
@@ -20,8 +20,21 @@
  *
  */
 
-import { encodeArrayBuffer, decodeArrayBuffer } from '../helpers/base64.js'
+import { encodeArrayBuffer, decodeArrayBuffer } from './base64.js'
 import { Doc, encodeStateAsUpdate, applyUpdate } from 'yjs'
+import * as decoding from 'lib0/decoding.js'
+
+export const yjsMessageTypes = {
+	sync: 0,
+	awareness: 1,
+	awarenessQuery: 3,
+}
+
+export const yjsMessageSyncTypes = {
+	step1: 0,
+	step2: 1,
+	update: 3,
+}
 
 /**
  *
@@ -42,3 +55,29 @@ export function applyDocumentState(ydoc, documentState, origin) {
 	const update = decodeArrayBuffer(documentState)
 	applyUpdate(ydoc, update, origin)
 }
+
+/**
+ * @param {string} update - base64 encoded Y.js message
+ */
+export function getMessageType(update) {
+	const decoder = decoding.createDecoder(update)
+	return decoding.readVarUint(decoder)
+}
+
+/**
+ * @param {string} update - base64 encoded Y.js message
+ */
+export function getAwarenessMessageClientIds(update) {
+	const decoder = decoding.createDecoder(update)
+	const type = decoding.readVarUint(decoder)
+	if (type !== yjsMessageTypes.awareness) {
+		return []
+	}
+
+	const len = decoding.readVarUint(decoder)
+	const clientIds = []
+	for (let i = 0; i < len; i++) {
+		clientIds.push(decoding.readVarUint(decoder))
+	}
+	return clientIds
+}