Unable to connect to the Flask-SocketIO server

[MikeEmbedded]

Hi,

I am new to C# and .NET. I installed SocketIoClient 4.0.1 to my project using NuGet.

I added code te print debug messages and have next debug print when I try to call SocketIoClient.ConnectAsync():

bug: SocketIOClient.Session.WebSocket.WebSocketSession[0]
[WebSocket?] 5
dbug: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
Sending Text message...
dbug: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
Sent Text message.
dbug: SocketIOClient.SocketIO[0]
Session connected
dbug: SocketIOClient.SocketIO[0]
Transport upgraded
fail: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
Failed to receive message
fail: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
System.ArgumentException: Value does not fall within the expected range.
at SocketIOClient.Protocol.WebSocket.WebSocketAdapter.ReceiveAsync(CancellationToken cancellationToken)

How can I know what is wrong?

I use .NET8.0

[MikeEmbedded]

I downloaded source code of SocketIOClient and used it in my project. Now ConnectAsync() stuck in different place:

dbug: SocketIOClient.SocketIO[0]
ConnectCoreAsync attempt 1 / 10
dbug: SocketIOClient.SocketIO[0]
Creating session...
dbug: SocketIOClient.SocketIO[0]
Session created: HttpSession
dbug: SocketIOClient.SocketIO[0]
Session connecting...
dbug: SocketIOClient.SocketIO[0]
Waiting for socket.io connection result...
dbug: SocketIOClient.Protocol.Http.HttpAdapter[0]
[Polling?] (null)
dbug: SocketIOClient.Session.Http.HttpSession[0]
[Polling?] 0{"sid":"y5-6hFu34OSeJRW4AAAQ","upgrades":["websocket"],"pingTimeout":20000,"pingInterval":25000,"maxPayload":1000000}
dbug: SocketIOClient.SocketIO[0]
Session connected
dbug: SocketIOClient.Protocol.Http.HttpAdapter[0]
[Polling?] 40/socket.io,
dbug: SocketIOClient.Session.Http.HttpSession[0]
[Polling?] OK
dbug: SocketIOClient.Session.Http.HttpSession[0]
Deliver message to SocketIO, Type: Opened
dbug: SocketIOClient.SocketIO[0]
Transport upgrading...
dbug: SocketIOClient.SocketIO[0]
Creating session...
dbug: SocketIOClient.SocketIO[0]
Session created: WebSocketSession
dbug: SocketIOClient.SocketIO[0]
Session connecting...
dbug: SocketIOClient.Session.WebSocket.WebSocketSession[0]
[WebSocket?] 5
dbug: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
Sending Text message...
dbug: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
Sent Text message.
dbug: SocketIOClient.SocketIO[0]
Session connected
dbug: SocketIOClient.SocketIO[0]
Transport upgraded

How can I find the problem?

[doghappy]

I have just released a new version 4.0.2. the issue should be fixed. Please let me know if the issue still exists.

[MikeEmbedded]

Hi,

thank you for your answer and update.

I downloaded the latest source code and no success. ConnectAsync() stucks same place.

I use SocketIO client with these connect options:

SocketIOConnectOptions.Transport = SocketIOClient.Common.TransportProtocol.Polling;
SocketIOConnectOptions.Path = "socket.io";
SocketIOConnectOptions.EIO = EngineIO.V4;

Info about server:
Flask-SocketIO 5.3.6
python-socketio 5.14.2
python-engineio 4.12.3
async_mode = eventlet

Hope this helps

[doghappy]

Based on my testing, the Python implementation of Socket.IO appears to have a slight incompatibility with this library and fails to upgrade to the WebSocket transport automatically. Therefore, I recommend using the following configuration to disable the AutoUpgrade.

Here are my test code:

python server:

from flask import Flask
from flask_socketio import SocketIO, emit

app = Flask(__name__)

socketio = SocketIO(app, async_mode='threading')

@socketio.on('test-req')
def handle_my_event(data):
    print('received:', data)
    emit('test-res', {
        'status': 'ok',
        'echo': data
    })

if __name__ == '__main__':
    socketio.run(app, host='0.0.0.0', port=5001)

c# client:

var io = new SocketIO(new Uri("http://localhost:5001"), new SocketIOOptions
{
    AutoUpgrade = false,
    // ^^^^^ HIGHLIGHT
    Transport = TransportProtocol.WebSocket,
    Reconnection = false
});
io.On("test-res", handler =>
{
    Console.WriteLine(handler.RawText);
    return Task.CompletedTask;
});
await io.ConnectAsync();
Console.WriteLine("Connected");
await io.EmitAsync("test-req", ["hello"]);
await Task.Delay(1000);

await io.DisconnectAsync();

client output:

Connected
["test-res",{"status":"ok","echo":"hello"}]

[MikeEmbedded]

It still gives an error:

dbug: SocketIOClient.SocketIO[0]
ConnectCoreAsync attempt 1 / 1
dbug: SocketIOClient.SocketIO[0]
Creating session...
dbug: SocketIOClient.SocketIO[0]
Session created: WebSocketSession
dbug: SocketIOClient.SocketIO[0]
Session connecting...
dbug: SocketIOClient.SocketIO[0]
Waiting for socket.io connection result...
dbug: SocketIOClient.Session.WebSocket.WebSocketSession[0]
[WebSocket?] 0{"sid":"IXs9IhF0qK0G9Nb5AABi","upgrades":[],"pingTimeout":20000,"pingInterval":25000,"maxPayload":1000000}
dbug: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
Sending Text message...
dbug: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
Sent Text message.
dbug: SocketIOClient.Session.WebSocket.WebSocketSession[0]
Deliver message to SocketIO, Type: Opened
dbug: SocketIOClient.SocketIO[0]
Session connected
dbug: SocketIOClient.Session.WebSocket.WebSocketSession[0]
[WebSocket?] 44/socket.io,"Unable to connect"
fail: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
Failed to receive message
fail: SocketIOClient.Protocol.WebSocket.WebSocketAdapter[0]
System.Text.Json.JsonReaderException: '/' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 0.
at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan1 bytes) at System.Text.Json.Utf8JsonReader.ConsumeValue(Byte marker) at System.Text.Json.Utf8JsonReader.ReadFirstToken(Byte first) at System.Text.Json.Utf8JsonReader.ReadSingleSegment() at System.Text.Json.Utf8JsonReader.Read() at System.Text.Json.JsonDocument.Parse(ReadOnlySpan1 utf8JsonSpan, JsonReaderOptions readerOptions, MetadataDb& database, StackRowStack& stack)
at System.Text.Json.JsonDocument.Parse(ReadOnlyMemory`1 utf8Json, JsonReaderOptions readerOptions, Byte[] extraRentedArrayPoolBytes, PooledByteBufferWriter extraPooledByteBufferWriter, Boolean allowDuplicateProperties)
at System.T

it throws an exception in WebSocketAdapter.cs await OnNextAsync(protocolMessage).ConfigureAwait(false); with

protocolMessage.Text = "44/socket.io,"Unable to connect""

and in exception OnDisconnected() is null. Am I doing something worng? I am not an experiensed in C#, sorry

catch (Exception e)
{
logger.LogError("Failed to receive message");
logger.LogError(e.ToString());
OnDisconnected(); // ----------------null--------------------------
throw;
}

Thank you.

[doghappy]

From the logs, it appears that the server returned an error, which is likely caused by incorrect credentials. If the correct credentials are provided, the server should not return 44/socket.io,"Unable to connect", and this issue can be avoided.

In addition, this library has a large number of automated test cases, but they are primarily written against the JavaScript server implementation. Since you are using Python, there may be slight differences in the server behavior, which could result in this edge case not being covered.

I really appreciate you providing such detailed information. I have fixed the deserialization issue, and you can build from the latest code. I will release a new version as soon as possible.

[doghappy]

Apologies, the new version has been released.

[MikeEmbedded]

Thank you. I will try to know more about credentials.