How to make Async calls generate event for Powershell script?

Question

I'm building event-oriented Powershell scripts. For asynchronous network operations, I usually use Begin/End calls such as BeginAcceptTcpClient / EndAcceptTcpClient for a System.Net.Sockets.TcpListener object. These calls use an IAsyncResult object to reference the asynchronous operation.

To generate events that can be easily used by Powershell and mixed with native Powershell events, I use the New-ScriptblockCallback function provided by Microsoft.

function New-ScriptblockCallback {
  param (
    [parameter(Mandatory = $True)]
    [ValidateNotNullOrEmpty()]
    [ScriptBlock] $Callback
  )
  # is this type already defined?
  if (-not ("CallbackEventBridge" -as [type])) {
    Add-Type @"
      using System;
      public sealed class CallbackEventBridge
      {
        public event AsyncCallback CallbackComplete = delegate { };
        private CallbackEventBridge() {}
        private void CallbackInternal(IAsyncResult result)
        {
          CallbackComplete(result);
        }
        public AsyncCallback Callback
        {
          get { return new AsyncCallback(CallbackInternal); }
        }
        public static CallbackEventBridge Create()
        {
          return new CallbackEventBridge();
        }
      }
"@
  }
  $bridge = [callbackeventbridge]::create()
  Register-ObjectEvent -InputObject $bridge -EventName callbackcomplete -Action $Callback -MessageData $args > $null
  $bridge.callback
}

This function can easily be used in asynchronous calls. For instance

$this.AcceptBlock = {
  param( System.IAsyncResult] $AsyncResult )
  [object] $listener = $AsyncResult.AsyncState
  [System.Net.Sockets.TcpClient] $tcpClient = $listener.tcpListener.EndAcceptTcpClient($AsyncResult)

    …. perform custom operations

}

$this.AcceptContextHandler = New-ScriptblockCallback -Callback $this.AcceptBlock
$this.tcpListener = New-Object System.Net.Sockets.TcpListener( $this.IP, $this.port)
$this.tcpListener.Start()
$this.AcceptIAsyncResult = $this.tcpListener.BeginAcceptTcpClient( $this.AcceptContextHandler, $this )

Then the event ‘callbackcomplete’ is raised when the operation completes and the ($this.)AcceptBlock scriptblock is called with the ‘IAsyncResult’ as parameter.

But, from what I've read/understood, the Begin/End methods are going to be abandoned, and what's more, some network calls no longer support/not supported these methods (e.g. Net.WebSockets.ClientWebSocket). Microsoft recommends using the ‘somethingAsync’ methods, which use a 'Task' object to reference the operation.

So my questions are: How can I get these calls to generate an event that can be used simply by Powershell when they are completed ? Is there a function similar to New-ScriptblockCallback that could help me?

I tried to use the Task object in place of IAsyncResult object without any success. To be honest, I wasn't very confident about the results of my tests, even having read that it was possible to cast the Task object as an IAsyncResult object.

How to make Async calls generate event for Powershell script?

0 Answers0