SignalR WebSockets - Error: There was an error with the transport.

Describe the bug

Hey, I got a problem with WebSockets transport type. Since that, we are using LongPooling for now and it is working okayish. That thing is that if I want to connect to the hub with external application (node/js in browser) I get this error:

Error: Failed to start the connection: Error: There was an error with the transport.

It might be the thing that my server does not support WebSockets transport type, but since we are working on a bash systems I haven’t found solution yet.

This is the list what I thought of that might cause the issue (some things may be missing):

• client/server package versions
• ssl connections
• CORS (well not in a nodejs console app, but in browser)
• endpoints.MapHub<>("...", o => o.Transports = HttpTransportType.WebSockets); - no change
• app.UseWebSockets() manually - no change
• doesn’t matter if it’s executed inside docker container or at localhost
• actually had to use skipNegotiations: true since I get 404
• @aspnet/signalr and @microsoft/signalr differences

To Reproduce

1. dotnet new webapi
2. Startup.cs.

public void ConfigureServices(IServiceCollection services)
{
     services.AddControllers();
     services.AddSignalR();
}

public void Configure(IApplicationBuilder app)
{
     app.UseRouting();
     app.UseEndpoints(endpoints =>
     {
            endpoints.MapControllers();
            endpoints.MapHub<ChatHub>("/hub/chat");
     });
}

1. ChatHub.cs

public class ChatHub : Hub
{
}

1. .csproj should look like this:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <RootNamespace>YOUR_APP_NAME</RootNamespace>
  </PropertyGroup>
  
</Project>

1. Client (I used nodejs) index.js

const signalR = require("@microsoft/signalr");

let connection = new signalR.HubConnectionBuilder()
    .withUrl("http://localhost:5001/hubs/chat", { transport: signalR.HttpTransportType.WebSockets })
    .configureLogging(signalR.LogLevel.Debug)
    .build();

connection.start()
    .then(() => console.log("Connection started"))
    .catch(e => console.log(e));

package.json

{
  "name": "signalr-web-client",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "@microsoft/signalr": "^3.1.3"
  }
}

1. dotnet run
2. node index.js

Further technical details

• dotnet and OS

$ dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   3.1.102
 Commit:    573d158fea

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.15
 OS Platform: Darwin
 RID:         osx.10.15-x64
 Base Path:   /usr/local/share/dotnet/sdk/3.1.102/

Host (useful for support):
  Version: 3.1.2
  Commit:  916b5cba26

.NET Core SDKs installed:
  3.0.100 [/usr/local/share/dotnet/sdk]
  3.1.102 [/usr/local/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.2 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

• node and npm

$ node -v
v12.13.0

$ npm -v
6.12.0

• IDE

JetBrains Rider 2019.2.4
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o