diff --git a/client/lib/source/ws-source.ts b/client/lib/source/ws-source.ts
index 1dcbb51..53b757d 100644
--- a/client/lib/source/ws-source.ts
+++ b/client/lib/source/ws-source.ts
@@ -1,17 +1,18 @@
-import { Observable, Subject } from 'rxjs'
+import { Observable } from 'rxjs'
+import { map } from 'rxjs/operators'
 import { webSocket, WebSocketSubject, WebSocketSubjectConfig } from 'rxjs/webSocket'
 import { Update } from '../types'
 import { Source } from './source'
 
 export class WebsocketSource<T> implements Source<T> {
-  private websocket$: WebSocketSubject<Update<T>> | undefined
+  private websocket$: WebSocketSubject<RPCResponse<Update<T>>> | undefined
 
   constructor (
     private readonly url: string,
   ) { }
 
   watch$ (): Observable<Update<T>> {
-    const fullConfig: WebSocketSubjectConfig<Update<T>> = {
+    const fullConfig: WebSocketSubjectConfig<RPCResponse<Update<T>>> = {
       url: this.url,
       openObserver: {
         next: () => {
@@ -20,6 +21,51 @@ export class WebsocketSource<T> implements Source<T> {
       },
     }
     this.websocket$ = webSocket(fullConfig)
-    return this.websocket$
+    return this.websocket$.pipe(
+      map(res => {
+        if (isRpcSuccess(res)) return res.result
+        if (isRpcError(res)) throw new RpcError(res.error)
+      }),
+    ) as Observable<Update<T>>
   }
 }
+
+interface RPCBase {
+  jsonrpc: '2.0'
+}
+
+export interface RPCSuccess<T> extends RPCBase {
+  result: T
+}
+
+export interface RPCError extends RPCBase {
+  error: {
+    code: number // 34 means unauthenticated
+    message: string
+    data: {
+      details: string
+    }
+  }
+}
+
+export type RPCResponse<T> = RPCSuccess<T> | RPCError
+
+function isRpcError<Error, Result> (arg: { error: Error } | { result: Result}): arg is { error: Error } {
+  return !!(arg as any).error
+}
+
+function isRpcSuccess<Error, Result> (arg: { error: Error } | { result: Result}): arg is { result: Result } {
+  return !!(arg as any).result
+}
+
+class RpcError {
+  code: number
+  message: string
+  details: string
+
+  constructor (e: RPCError['error']) {
+    this.code = e.code
+    this.message = e.message
+    this.details = e.data.details
+  }
+}
\ No newline at end of file