Expected HTTP 101 response but was '200 OK'

[felislynx-silae]

Hi, I'm trying to connect to SignalR backend but i get response & disconnection like in title:

2025-07-14 17:07:38.934 27586-27662 Connection state: DISCONNECTED
2025-07-14 17:07:38.934 27586-27662 Connection state: CONNECTING
2025-07-14 17:07:38.940 27586-27671 REQUEST: http://backendip/connectionHub/negotiate?patname=Mobile&negotiateVersion=1
                                                                                                    METHOD: POST
                                                                                                    COMMON HEADERS
                                                                                                    -> Accept: application/json
                                                                                                    -> Accept-Charset: UTF-8
                                                                                                    -> Authorization: Bearer redacted
                                                                                                    CONTENT HEADERS
                                                                                                    -> Content-Length: 0
                                                                                                    BODY Content-Type: null
                                                                                                    BODY START

                                                                                                    BODY END
2025-07-14 17:07:39.281 27586-27660 RESPONSE: 200 OK
                                                                                                    METHOD: POST
                                                                                                    FROM: http://backendip/connectionHub/negotiate?patname=Mobile&negotiateVersion=1
                                                                                                    COMMON HEADERS
                                                                                                    -> connection: Keep-Alive
                                                                                                    -> content-type: application/json
                                                                                                    -> date: Mon, 14 Jul 2025 15:07:40 GMT
                                                                                                    -> keep-alive: timeout=15, max=100
                                                                                                    -> server: Apache
                                                                                                    -> transfer-encoding: chunked
                                                                                                    -> vary: Accept-Encoding
                                                                                                    -> x-powered-by: ASP.NET
                                                                                                    BODY Content-Type: application/json
                                                                                                    BODY START
                                                                                                    {"negotiateVersion":1,"connectionId":"vvM1hTE84FtFhdtnlsVOpQ","connectionToken":"L9YsnP8rKZstiUtCxgKDLw","availableTransports":[{"transport":"WebSockets","transferFormats":["Text","Binary"]},{"transport":"ServerSentEvents","transferFormats":["Text"]},{"transport":"LongPolling","transferFormats":["Text","Binary"]}]}
                                                                                                    BODY END
2025-07-14 17:07:39.301 27586-27672 REQUEST: ws://backendip/connectionHub?patname=Mobile&id=L9YsnP8rKZstiUtCxgKDLw
                                                                                                    METHOD: GET
                                                                                                    COMMON HEADERS
                                                                                                    -> Accept: application/json
                                                                                                    -> Accept-Charset: UTF-8
                                                                                                    -> Authorization: Bearer redacted
                                                                                                    CONTENT HEADERS
                                                                                                    -> Connection: Upgrade
                                                                                                    -> Sec-WebSocket-Key: ZWRkMTYyOTIxZDFmNjlhOA==
                                                                                                    -> Sec-WebSocket-Version: 13
                                                                                                    -> Upgrade: websocket
                                                                                                    BODY Content-Type: null
                                                                                                    BODY START

                                                                                                    BODY END
2025-07-14 17:07:39.642 27586-27671 REQUEST ws://backendip/connectionHub?patname=Mobile&id=L9YsnP8rKZstiUtCxgKDLw failed with exception: java.net.ProtocolException: Expected HTTP 101 response but was '200 OK'
2025-07-14 17:07:39.644 27586-27671 Connection state: DISCONNECTED

Any advice?

[lepicekmichal]

This happens when your URL for the SignalR server is incorrect or at least incomplete.
Maybe you missed "/websocket" part (or something similar) at the end? You can also try changing some settings of the connection, in case your server accepts only XY configuration.
Right now, the server is replying to you with a classic HTTP response instead of a WebSocket response.

[felislynx-silae]

@lepicekmichal This is my connection object. It behaves like that for both TransportEnum.WebSockets and TransportEnum.All. Backend team member showed that he connects to this address with his .net code. If i use ws:// instead of http:// it also fails with this message.

val connection = HubConnectionBuilder.create("http://backendip/connectionHub?patname=Mobile") {
        accessToken = generateHeader()
        httpClient =
            HttpClient(OkHttp) {
                engine {
                    config {
                        connectTimeout(30, TimeUnit.SECONDS)
                        readTimeout(30, TimeUnit.SECONDS)
                        writeTimeout(30, TimeUnit.SECONDS)
                    }
                }
                install(WebSockets) {
                    pingIntervalMillis = 20_000
                    maxFrameSize = Long.MAX_VALUE

                }
                install(HttpCookies) {
                    storage = AcceptAllCookiesStorage()
                }
                install(ContentNegotiation) {
                    json(Json {
                        prettyPrint = true
                        isLenient = true
                        ignoreUnknownKeys = true // Often useful
                    })
                }
                install(Logging) {
                    logger = object : Logger {
                        override fun log(message: String) {
                            Log.d("MyLogs", "${message}")
                        }
                    }
                    level = LogLevel.ALL
                }
            }
        transportEnum = TransportEnum.WebSockets
    }

[lepicekmichal]

@felislynx-silae
Alright, I can see you are missing the HttpTimeout plugin (and SSE). Although I'm not sure that should cause your problem.
https://lepicekmichal.github.io/SignalRKore/user-guide/configuration/#custom-http-client

I see you are using Android, so could you try the official Java library? Just so we can pinpoint where the problem is, with my library or with the configuration.