Powershell via Ajax returning string (or nothing) in .NET MVC project

Question

I am working on dashboard that shows live details about a set of machines. I have the below for my Powershell

param([string] $server)


    $services = Get-WmiObject win32_service -ComputerName $server | Select -Property  Name, ExitCode, State, Status
    $disk = get-WmiObject win32_logicaldisk -Computername $server | Select-Object -Property DeviceID, @{n="Size";e={[math]::Round($_.Size/1GB,2)}},@{n="FreeSpace";e={[math]::Round($_.FreeSpace/1GB,2)}} 
    $cpu = Get-WmiObject win32_processor -ComputerName $server | Measure-Object -property LoadPercentage -Average | Select Average


$server_summary = @{
    services = $services
    disk = $disk
    cpu = $cpu
}

$json = $server_summary | ConvertTo-Json

return $json

I have the below for my c# function

public JsonResult test (string server)
    {
        string script = ControllerContext.HttpContext.Server.MapPath("~/Content/Powershell/Get-Server-Summary.ps1");
        string cmd = script + " -server '" + server + "'";

        using (var ps = PowerShell.Create())
        {
            ps.AddScript(cmd);
            var results = ps.Invoke();


            return Json(results);
        }

    }

In the script section of my HMTL I have

function test(server) {
        $.ajax({
            type: "POST",
            url: '@Url.Action("test")',
            dataType: "json",
            data: "{'server':" + "'" + server + "'}",
            contentType: "application/json; charset=utf-8",
            success: function (data) {


            },
            error: function (xhr, ajaxOptions, thrownError) {
                alert('Error getting stats for ' + server + '.');
            },

            complete: function () {

            }
        });
    }
$(document).ready(function(){
   test('server_name');
});

Even though I have converted the result to JSON before returning to the results to the application, I receive and empty string.

Am I missing something? I was able to get results with a slightly different function, but it returns incorrect results.

I will post that in the comments because I have too much code to post my question...

The results on the server side look like the below. You can see that I am getting one result, which is a string containing all the json.

It was hard to get the screenshot in time. But you can see the value is there, It is just REALLY buried... Do I really need to parse through all of this? There isn't a function for this already?

`foreach (var result in results) { output = result.ToString(); }` in my C# function returns incorrect results — gregnnylf94, Dec 19 '18 at 17:06
When you debug, what does `results` contain in the server-side code? Is the PowerShell operation asynchronous at all? Can you convert `results` to a simple custom type and return that object instead? In your browser's debugging tools, what is the raw content returned from the server? — David, Dec 19 '18 at 17:10
@David I've added to the Q. But to clarify I do get "Correct" results, it is just being converted from JSON to a string somewhere along the lines. But I converted it twice, or could that be the problem? I converted to JSON once in Powershell, then once before passing it back through ajax. — gregnnylf94, Dec 19 '18 at 17:28
The question says you're getting an empty string in the response client-side, but that last comment suggests you're getting a string of JSON data. Which is it? As for "converting it twice", that doesn't make much sense. It really sounds like the object being returned by `ps.Invoke()` may not be exactly what you expect it to be, and a good approach to that (as well as to prevent unnecessary data from being exposed by your API) is to create a simple object (even an anonymous one) which returns only and exactly what you want to return from your API. That's probably worth a try. — David, Dec 19 '18 at 17:34
What your PowerShell script returns already _is_ JSON text, so you shouldn't pass it to a `Json()` constructor - it seems that the JSON string is then considered a JSON string _value_, to which escaping is applied. — mklement0, Dec 19 '18 at 17:46
@mklement0 That makes sense, but when I pass the results from powershell without converting to JSON, I get an array with one element containing a hashtable reference. Which once passed back through ajax returns a `A circular reference was detected while serializing an object of type 'System.Management.Automation.PSP` error. I'm still working through it. — gregnnylf94, Dec 19 '18 at 17:54
@Daivd I am getting two variations. If I convert the results to JSON in Powershell, when passed back through ajax (from c#) `return Json(value)` is required. This converts my JSON to a single string. If I don't convert in Powershell I get the error mentioned in previous comment. I found `ConvertTo-Json` gives you a Json string which you then can pipe to `ConvterFrom-Json` which returns a JSON object. When this gets passed to C# I can see all my expected results in the Debugger, but I still get the `circular reference` error. I'm understanding it doesnt like the PSObjects but idk how to convert — gregnnylf94, Dec 19 '18 at 20:16
Solution is to convert results to JSON in Powershell. Pass the JSON string to C#. In C# convert the `PSObject` to a `string`. Then convert that string into an `object`. The exact code I used in C# `var results = ps.Invoke()[0].ToString(); JavaScriptSerializer j = new JavaScriptSerializer(); object json = j.Deserialize(results, typeof(object)); return Json(json);` Which I found https://stackoverflow.com/questions/22870624/convert-json-string-to-json-object-c-sharp" — gregnnylf94, Dec 19 '18 at 21:50

score 2 · Accepted Answer · answered Dec 19 '18 at 22:10

Your PowerShell script already returns a JSON string, due to use of ConvertTo-Json.

As you state, the next step, in your C# code, is to extract that string from the System.Collections.ObjectModel.Collection<System.Management.Automation.PSObject instance that PowerShell.Invoke() returns:

 string json = ps.Invoke()[0].ToString();

The final step is to use that string as-is as your method's result data, via the Content() method - there is no need to deserialize the string first only to re-serialize it with the Json() method:

return Content(json, "application/json");

Note that you'll have to change your method's return type from JsonResult to ContentResult.

This approach comes courtesy of this answer.

Powershell via Ajax returning string (or nothing) in .NET MVC project

1 Answers1