C#•3mo ago

Understanding COM interface references for an ASP.NET REST API...

Hi all, I'm new-ish to Windows, so forgive me but my knowledge of COM is pretty amateur. I'm running a simulation application on a backend server that implements the COM interface IDispatch to create an interface called IRemoteControl like so:

interface IRemoteControl : IDispatch
{
     HRESULT NewModel();
     HRESULT LoadModel(BSTR);
     HRESULT SaveModel(BSTR);
     HRESULT CloseModel();
     HRESULT StartSimulation(BSTR);
     HRESULT StopSimulation();
     HRESULT ResetSimulation(BSTR);
     HRESULT GetValue(BSTR,[out,retval]VARIANT*);
     HRESULT SetValue(BSTR,VARIANT);
     HRESULT Quit();
};

interface IRemoteControl : IDispatch
{
     HRESULT NewModel();
     HRESULT LoadModel(BSTR);
     HRESULT SaveModel(BSTR);
     HRESULT CloseModel();
     HRESULT StartSimulation(BSTR);
     HRESULT StopSimulation();
     HRESULT ResetSimulation(BSTR);
     HRESULT GetValue(BSTR,[out,retval]VARIANT*);
     HRESULT SetValue(BSTR,VARIANT);
     HRESULT Quit();
};

We have a single host machine and expect 4-6 users at a time to be sending messages over an API to start, stop, and reset simulations all running on separate instances of this application on the backend server. I can start the program and manipulate it quite easily in ASP.NET. I import the application's included Type Library DLL as a project dependency, then I can do something like

        [HttpPost("remote-control/create")]
        public IActionResult CreateRemoteControl(string? updatedPath)
        {
RemoteControl remoteControl = new();
return OK();
// Handle other cases, etc.
        }

        [HttpPost("remote-control/create")]
        public IActionResult CreateRemoteControl(string? updatedPath)
        {
RemoteControl remoteControl = new();
return OK();
// Handle other cases, etc.
        }

Whenever I send subsequent calls over a different route to do something like start/stop/reset the simulation, I'm able to do so on the most recently-spawned application instance. However, when multiple users are connected to this server at the same time, I want to be able to assign each user a specific instance of this application, so that subsequent calls only affect that user's instance (so that a user can't send a "reset" message that resets the most recently spawned process, even if it was spawned by another user). I can find the process ID of a spawned RemoteControl object using string currentProcessID = remoteControl.GetCurrentProcessId().ToString();, but I don't know how to use that to restrict commands to specific COM interfaces.

5 Replies

PizzaWizard•3mo ago

Hit the limit on the previous message. Happy to read up and educate myself instead of just waiting for someone to write code for me, but there's a LOT of documentation on COM/OLE, and it's pretty overwhelming for someone who doesn't spend any time in low-level systems/OS programming or C/C++. Would be happy to be pointed in the right direction to get signal from the noise. Thanks!

lycian•3mo ago

Whenever I send subsequent calls over a different route to do something like start/stop/reset the simulation, I'm able to do so on the most recently-spawned application instance.

If the lifetime of the ASP.NET server is tied to the spawned application instances you could easily just keep a map of user:IRemoteControl if I'm understanding your scenario correctly

PizzaWizard•3mo ago

The server will persist across multiple user connections, it essentially never turns off. So do I just give every user a token, and then store that in a dictionary with their remoteControl object? My question would then be, if I wanted to let a user execute a command like remoteControl.StartSimulation() to start a new simulation on their specific instance, I could just pass the user's token and say something like userMap["thisUserToken"] and get back a specific remoteControl object? I was concerned that I would just be passing the reference to the same remoteControl back and forth...

lycian•3mo ago

As long as you new up a new RemoteControl for each UserToken then the references are unique.

static Dictionary<string, IRemoteControl> RemoteControlMapping = new();

[HttpPost("remote-control/create")]
public IActionResult CreateRemoteControl(string userToken)
{
  if (RemoteControlMapping.TryGet(userToken, out var _))
  {
    // handle if it already exists?
  }

  RemoteControlMapping[userToken] = new RemoteControl();
  return OK();
}

static Dictionary<string, IRemoteControl> RemoteControlMapping = new();

[HttpPost("remote-control/create")]
public IActionResult CreateRemoteControl(string userToken)
{
  if (RemoteControlMapping.TryGet(userToken, out var _))
  {
    // handle if it already exists?
  }

  RemoteControlMapping[userToken] = new RemoteControl();
  return OK();
}

roughly that, although you'll probably want some locking/concurrency checks static is important there since it becomes shared. I'm assuming no need for complex DI etc

PizzaWizard•3mo ago

Excellent. This is a very limited-scope application and should only ever have 2-3 simultaneous users and 10ish total users. So trying to keep things as simple as possible (Except of course, for the fact that I'm using a single computer spawning multiple COM applications to act as a backend for a web app and ignoring the stateless part of REST entirely)

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Understanding COM interface references for an ASP.NET REST API...