CODEWITHSUNDEEP
c#flasksignalr
Ponnu Kutty
Ponnu Kutty

Reputation: 11

Can I connect to flask server from SignalR client

I have created a flask server using Python. My server is listening on 127.0.0.1.

I have created a SignalR client in C# and trying to connect to the above server. I am getting the following error on client side.

Error Opening Connection:Microsoft.AspNet.SignalR.Client.HttpClientException: StatusCode: 404, ReasonPhrase: 'NOT FOUND', Version: 1.1, Content: System.Net.Http.HttpConnection+HttpConnectionResponseContent, Headers: { Date: Tue, 18 Jun 2019 04:11:55 GMT Content-Type: text/html Content-Length: 232 } at Microsoft.AspNet.SignalR.Client.Http.DefaultHttpClient.<>c__DisplayClass5_0.b__1(HttpResponseMessage responseMessage) in //src/Microsoft.AspNet.SignalR.Client/Http/DefaultHttpClient.cs:line 95 at Microsoft.AspNet.SignalR.TaskAsyncHelper.TaskRunners2.<>c__DisplayClass3_0.<RunTask>b__0(Task1 t) in //src/Microsoft.AspNet.SignalR.Core/TaskAsyncHelper.cs:line 1280

Unhandled Exception: System.InvalidOperationException: Data cannot be sent because the connection is in the disconnected state. Call start before sending any data. at Microsoft.AspNet.SignalR.Client.Connection.Send(String data) in //src/Microsoft.AspNet.SignalR.Client/Connection.cs:line 815 at Microsoft.AspNet.SignalR.Client.Hubs.HubProxy.Invoke[TResult,TProgress](String method, Action`1 onProgress, Object[] args) in //src/Microsoft.AspNet.SignalR.Client/Hubs/HubProxy.cs:line 184 at Microsoft.AspNet.SignalR.Client.Hubs.HubProxy.Invoke(String method, Object[] args) in /_/src/Microsoft.AspNet.SignalR.Client/Hubs/HubProxy.cs:line 71

On server side I see: 127.0.0.1 - - [2019-06-18 09:41:55] "GET /signalr/negotiate?clientProtocol=2.1&connectionData=[%7B%22Name%22:%22main%22%7D] HTTP/1.1" 404

When I connect from IE browser, it is working fine.

hubConnection = new HubConnection("http://127.0.0.1:5000/", true);
IHubProxy myHub = hubConnection.CreateHubProxy("main");
hubConnection.Start(new LongPollingTransport()).ContinueWith(task =>
  {
     if (task.IsFaulted)
        {
           Console.WriteLine("Error Opening Connection:{0}", task.Exception.GetBaseException());
        }
     else
        {
             Console.WriteLine("Connected");
                 }
        }).Wait();

Can somebody tell me if it is actually possible to connect from SignalR client to a flask server? If so, what has to be corrected?

Upvotes: 1

Views: 988

Answers (1)

hmelende
hmelende

Reputation: 1

I was able to do something like this indirectly using SSE to get the SignalR message to Flask (caveat emptor: this is not production code it is only to do a POC):

  1. I hosted a .NET SignalR Hub (easy to do as per these instructions just be sure to change the .NET Core version to whatever you have, I have 5.0 VS 2019: https://learn.microsoft.com/en-us/aspnet/core/tutorials/signalr?view=aspnetcore-5.0&tabs=visual-studio).
  2. I was able to connect to this hub using Python and the signalrcore chat example: https://pypi.org/project/signalrcore
  3. On my Flask web app, I then used SSE to allow my Python server code to receive a SignalR message then pass it onto my Flask code: https://medium.com/code-zen/python-generator-and-html-server-sent-events-3cdf14140e56
  4. The example in #3 above uses a call to "print" that just prints the message but in order to pass onto SSE I used a thread-safe Queue and I overrode with my own "myprint" function as follows:

Python:

from queue import Queue
from threading import Thread
messageQueue = Queue()
    
def myprint(*values: object):
    messageQueue.put(values)

So from the example in #3 above in the function eventStream() instead of just "Poll data from the database" you would have:

def eventStream():
        while True:
            # Check concurrent queue
            messages = messageQueue.get()
            yield "data: {}\n\n".format(messages)

And in my html I have something like this where I use a Bootstrap toast-popup (https://getbootstrap.com/docs/5.0/components/toasts/) to show the message came in to the browser:

<script>
$(document).ready(function(){
        // From https://medium.com/code-zen/python-generator-and-html-server-sent-events-3cdf14140e56
        var toastWorking = document.getElementById('toast-popup');
        var eventSource = new EventSource("/stream");
        eventSource.onmessage = function(e) {
          var toast = new bootstrap.Toast(toastWorking)
          var today  = new Date();
          document.getElementById("toast-popup-small-display").innerHTML = today.toLocaleTimeString(); //today.toLocaleDateString("en-US", options)
          document.getElementById("toast-popup-message").innerHTML = e.data;
          //alert(e.data)

          toast.show('show');
        };
</script>

Good luck

Upvotes: 0

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