feat(realtime): add metadata to realtime user broadcast push

packages/core/realtime-js/src/lib/serializer.ts

@@ -10,13 +10,18 @@ export type Msg<T> = {
 
 export default class Serializer {
   HEADER_LENGTH = 1
-  META_LENGTH = 4
-  USER_BROADCAST_PUSH_META_LENGTH = 5
+  USER_BROADCAST_PUSH_META_LENGTH = 6
   KINDS = { userBroadcastPush: 3, userBroadcast: 4 }
   BINARY_ENCODING = 0
   JSON_ENCODING = 1
   BROADCAST_EVENT = 'broadcast'
 
+  allowedMetadataKeys: string[] = []
+
+  constructor(allowedMetadataKeys?: string[] | null) {
+    this.allowedMetadataKeys = allowedMetadataKeys ?? []
+  }
+
   encode(msg: Msg<{ [key: string]: any }>, callback: (result: ArrayBuffer | string) => any) {
     if (
       msg.event === this.BROADCAST_EVENT &&
@@ -41,57 +46,58 @@ export default class Serializer {
   }
 
   private _encodeBinaryUserBroadcastPush(message: Msg<{ event: string } & { [key: string]: any }>) {
-    const topic = message.topic
-    const ref = message.ref ?? ''
-    const joinRef = message.join_ref ?? ''
-    const userEvent = message.payload.event
     const userPayload = message.payload?.payload ?? new ArrayBuffer(0)
-
-    const metaLength =
-      this.USER_BROADCAST_PUSH_META_LENGTH +
-      joinRef.length +
-      ref.length +
-      topic.length +
-      userEvent.length
-
-    const header = new ArrayBuffer(this.HEADER_LENGTH + metaLength)
-    let view = new DataView(header)
-    let offset = 0
-
-    view.setUint8(offset++, this.KINDS.userBroadcastPush) // kind
-    view.setUint8(offset++, joinRef.length)
-    view.setUint8(offset++, ref.length)
-    view.setUint8(offset++, topic.length)
-    view.setUint8(offset++, userEvent.length)
-    view.setUint8(offset++, this.BINARY_ENCODING)
-    Array.from(joinRef, (char) => view.setUint8(offset++, char.charCodeAt(0)))
-    Array.from(ref, (char) => view.setUint8(offset++, char.charCodeAt(0)))
-    Array.from(topic, (char) => view.setUint8(offset++, char.charCodeAt(0)))
-    Array.from(userEvent, (char) => view.setUint8(offset++, char.charCodeAt(0)))
-
-    var combined = new Uint8Array(header.byteLength + userPayload.byteLength)
-    combined.set(new Uint8Array(header), 0)
-    combined.set(new Uint8Array(userPayload), header.byteLength)
-
-    return combined.buffer
+    return this._encodeUserBroadcastPush(message, this.BINARY_ENCODING, userPayload)
   }
 
   private _encodeJsonUserBroadcastPush(message: Msg<{ event: string } & { [key: string]: any }>) {
+    const userPayload = message.payload?.payload ?? {}
+    const encoder = new TextEncoder()
+    const encodedUserPayload = encoder.encode(JSON.stringify(userPayload)).buffer
+    return this._encodeUserBroadcastPush(message, this.JSON_ENCODING, encodedUserPayload)
+  }
+
+  private _encodeUserBroadcastPush(
+    message: Msg<{ event: string } & { [key: string]: any }>,
+    encodingType: number,
+    encodedPayload: ArrayBuffer
+  ) {
     const topic = message.topic
     const ref = message.ref ?? ''
     const joinRef = message.join_ref ?? ''
     const userEvent = message.payload.event
-    const userPayload = message.payload?.payload ?? {}
 
-    const encoder = new TextEncoder() // Encodes to UTF-8
-    const encodedUserPayload = encoder.encode(JSON.stringify(userPayload)).buffer
+    // Filter metadata based on allowed keys
+    const rest = this.allowedMetadataKeys
+      ? this._pick(message.payload, this.allowedMetadataKeys)
+      : {}
+
+    const metadata = Object.keys(rest).length === 0 ? '' : JSON.stringify(rest)
+
+    // Validate lengths don't exceed uint8 max value (255)
+    if (joinRef.length > 255) {
+      throw new Error(`joinRef length ${joinRef.length} exceeds maximum of 255`)
+    }
+    if (ref.length > 255) {
+      throw new Error(`ref length ${ref.length} exceeds maximum of 255`)
+    }
+    if (topic.length > 255) {
+      throw new Error(`topic length ${topic.length} exceeds maximum of 255`)
+    }
+    if (userEvent.length > 255) {
+      throw new Error(`userEvent length ${userEvent.length} exceeds maximum of 255`)
+    }
+    if (metadata.length > 255) {
+      throw new Error(`metadata length ${metadata.length} exceeds maximum of 255`)
+    }
 
     const metaLength =
       this.USER_BROADCAST_PUSH_META_LENGTH +
       joinRef.length +
       ref.length +
       topic.length +
-      userEvent.length
+      userEvent.length +
+      metadata.length
 
     const header = new ArrayBuffer(this.HEADER_LENGTH + metaLength)
     let view = new DataView(header)
@@ -102,15 +108,17 @@ export default class Serializer {
     view.setUint8(offset++, ref.length)
     view.setUint8(offset++, topic.length)
     view.setUint8(offset++, userEvent.length)
-    view.setUint8(offset++, this.JSON_ENCODING)
+    view.setUint8(offset++, metadata.length)
+    view.setUint8(offset++, encodingType)
     Array.from(joinRef, (char) => view.setUint8(offset++, char.charCodeAt(0)))
     Array.from(ref, (char) => view.setUint8(offset++, char.charCodeAt(0)))
     Array.from(topic, (char) => view.setUint8(offset++, char.charCodeAt(0)))
     Array.from(userEvent, (char) => view.setUint8(offset++, char.charCodeAt(0)))
+    Array.from(metadata, (char) => view.setUint8(offset++, char.charCodeAt(0)))
 
-    var combined = new Uint8Array(header.byteLength + encodedUserPayload.byteLength)
+    var combined = new Uint8Array(header.byteLength + encodedPayload.byteLength)
     combined.set(new Uint8Array(header), 0)
-    combined.set(new Uint8Array(encodedUserPayload), header.byteLength)
+    combined.set(new Uint8Array(encodedPayload), header.byteLength)
 
     return combined.buffer
   }
@@ -185,4 +193,11 @@ export default class Serializer {
   private _isArrayBuffer(buffer: any): boolean {
     return buffer instanceof ArrayBuffer || buffer?.constructor?.name === 'ArrayBuffer'
   }
+
+  private _pick(obj: Record<string, any> | null | undefined, keys: string[]): Record<string, any> {
+    if (!obj || typeof obj !== 'object') {
+      return {}
+    }
+    return Object.fromEntries(Object.entries(obj).filter(([key]) => keys.includes(key)))
+  }
 }