Add y.js helpers to decode awareness messages

Signed-off-by: Jonas <[email protected]>

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
+}