Accessing the API / event hubs via my own .NET client app

PowerShell Universal
1

This I know is a vague question, but just looking for idea of possibilities before I investigate further.

Basically I want to have my own .NET client app (helper app) probably written in VB.NET which will be installed on a client machine (outside my own network!) which will then collect information such as disk space, error information etc etc and I want to then be able to send it to my powershell universal instance hosted (location to be determined, but perhaps Azure or any IIS / linux hosting platform) so I can then have dashboards to visualize the information for each client I have the client / helper app installed on.

I know you provide a Event Hub client app, but I don’t want to use that, I would prefer an SDK or way to use same functionality in my own app?

Finally if possible in that app I would want it to have similar functionality to the even hub client in that I can send a “command” from powershell universal sever to a specific client to invoke an action.

In principle is this doable?

2

This is possible. You’ll need to install the SignalR client in your app. Here’s the connection logic. It just connects up to the hub. It uses a different hub if authentication is enabled.


            var url = "eventhub";
            if (clientConnection.AppToken != null || clientConnection.UseDefaultCredentials)
            {
                url = "autheventhub";
            }

            var connection = new HubConnectionBuilder()
                .ConfigureLogging(logging =>
                {
                    logging.AddSerilog();
                    logging.SetMinimumLevel(LogLevel.Debug);
                })
                .WithUrl($"{clientConnection.Url}/{url}?group={clientConnection.Hub}", options =>
                {
                    if (clientConnection.AppToken != null)
                    {
                        options.AccessTokenProvider = () => Task.FromResult(clientConnection.AppToken)!;
                    }

                    if (handler != null)
                        options.HttpMessageHandlerFactory = _ => handler;

                    options.UseDefaultCredentials = clientConnection.UseDefaultCredentials;
                    
                    options.Headers.Add("PSUComputerName", Environment.MachineName);
                    options.Headers.Add("PSUUserName", Environment.UserName);
                    options.Headers.Add("PSUDomainName", Environment.UserDomainName);
                })
                .WithAutomaticReconnect(new RetryPolicy())
                .Build();

When it receives a “Module” message, it will invoke the command. This method will get the name of the command. The data is a PSSerialized string.

connection.On(clientConnection.Hub + "Module", (string command, string data, bool returnResult) => eventHubExecutor.ExecuteCommand(clientConnection.Hub, command , data, returnResult));

Here’s some psuedocode. PS expects the ExecuteCommand method to return immediately with an execution ID. If not, the hub will only let one command run at a time.

    public string ExecuteCommand(string hub, string command, string data, bool returnResult)
    {
        Log.Information($"Received event on hub {hub}.");

        var executionId = Guid.NewGuid().ToString();

        _ = Task.Run(() =>
        {
                var item = PSSerializer.Deserialize(data);
// run command 
                    _output[executionId] = output;    
         }
        return executionId;
    }

After executing the command, it will then attempt to get a result back for the command.

connection.On("GetResult", (string eventId) => eventHubExecutor.GetResult(eventId));

It will need to access the _output collection and return the result.

    public string GetResult(string executionId)
    {
        if (!_output.TryGetValue(executionId, out var result))
        {
            return "running";
        }

        _output.TryRemove(executionId, out _);
        return result;
    }

Hope that helps!

3

Hi Adam, thank you so much for that detailed reply, much appreciated.

So this would cover the part of being able to send commands and get a response. But what about just sending information from “my client” app to the powershell universal instance to be able to record customer information etc? I would just send results and diagnostic information in one go so to speak, so it would just contain an GUID / ID to indicate which client and then other data which I would store to view in dashboard etc

4

Sending info back to PSU would likely be done via an API and not an event hub. It’s arguably a bit simpler because you don’t need a web socket connection and could have your client app just make an HTTP request.

Currently, event hubs don’t have a push mechanism. It wouldn’t be too hard to implement on our end, but it would be very similar to what API endpoints already provide.

5

okay cool. Do you have any sample apps or code snippets showing how to both authenticate to and then send data to PSU using websocket etc?