PowerShell For Fun

Research on MshHost & MshHostUserInterface abstract class.

The msh.exe is actully a console program hosting monad engine. In another word: monad engine does not worry about user interface, it is host environment's job.  My Remote MSH server is not INTERACTIVE (For example: remote user will not be prompted to input credentials when invoking "get-credential" at server) because I use DefaultHost which does not Implement MshHostUserInterface. 

OK, OK, it is to fast, let's start from Create a Runspace:
System.Management.Automation.Runspaces.RunspaceFactory.CreateRunspace()

public static Runspace CreateRunspace()
{
      Runspace runspace1;
      using (IDisposable disposable1 = RunspaceFactory._tracer.TraceMethod())
      {
            runspace1 = RunspaceFactory.CreateRunspace(new DefaultHost(Thread.CurrentThread.CurrentCulture, Thread.CurrentThread.CurrentUICulture));
      }
      return runspace1;
}

So it acually create a Runspace using DefaultHost
Microsoft.Management.Automation.Internal.DefaultHost is a implement of MshHost abstract class.

internal class DefaultHost : MshHost
{
      // Methods
      static DefaultHost();
      internal DefaultHost(CultureInfo currentCulture, CultureInfo currentUICulture);
      public override void EnterNestedPrompt();
      public override void ExitNestedPrompt();
      public override void NotifyBeginApplication();
      public override void NotifyEndApplication();
      public override void SetShouldExit(int exitCode);

      // Properties
      public override CultureInfo CurrentCulture { get; }
      public override CultureInfo CurrentUICulture { get; }
      public override Guid InstanceId { get; }
      public override string Name { get; }
      public override MshHostUserInterface UI { get; }
      public override Version Version { get; }

      // Fields
      private CultureInfo currentCulture;
      private CultureInfo currentUICulture;
      private Guid id;
      [TraceSource("DefaultHost", "DefaultHost subclass of S.M.A.MshHost Tracer")]
      private static MshTraceSource tracer;
      private Version ver;
}

Let's take a look at System.Management.Automation.Host.MshHost

public abstract class MshHost
{
      // Methods
      protected MshHost();
      public abstract void EnterNestedPrompt();
      public abstract void ExitNestedPrompt();
      public abstract void NotifyBeginApplication();
      public abstract void NotifyEndApplication();
      public abstract void SetShouldExit(int exitCode);

      // Properties
      public abstract CultureInfo CurrentCulture { get; }
      public abstract CultureInfo CurrentUICulture { get; }
      public abstract Guid InstanceId { get; }
      public abstract string Name { get; }
      public virtual MshObject PrivateData { get; }
      public abstract MshHostUserInterface UI { get; }
      public abstract Version Version { get; }
}

MshHostUserInterface is the object which actully deals with user interface:

public abstract class MshHostUserInterface
{
      // Methods
      protected MshHostUserInterface();
      public abstract Dictionary<string, MshObject> Prompt(string caption, string message, Collection<FieldDescription> descriptions);
      public abstract int PromptForChoice(string caption, string message, Collection<ChoiceDescription> choices, int defaultChoice);
      public abstract MshCredential PromptForCredential(string caption, string message, string userName, string targetName);
      public abstract MshCredential PromptForCredential(string caption, string message, string userName, string targetName, MshCredentialTypes allowedCredentialTypes, MshCredentialUIOptions options);
      public abstract string ReadLine();
      public abstract SecureString ReadLineAsSecureString();
      public abstract void Write(string value);
      public abstract void Write(ConsoleColor foregroundColor, ConsoleColor backgroundColor, string value);
      public abstract void WriteDebugLine(string message);
      public abstract void WriteErrorLine(string value);
      public virtual void WriteLine();
      public abstract void WriteLine(string value);
      public virtual void WriteLine(ConsoleColor foregroundColor, ConsoleColor backgroundColor, string value);
      public abstract void WriteProgress(long sourceId, ProgressRecord record);
      public abstract void WriteVerboseLine(string message);
      public abstract void WriteWarningLine(string message);

      // Properties
      public abstract MshHostRawUserInterface RawUI { get; }
}

But when we check the public property UI in DefaultHost:

public override MshHostUserInterface UI
{
      get
      {
            MshHostUserInterface interface1;
            using (IDisposable disposable1 = DefaultHost.tracer.TraceProperty())
            {
                  interface1 = null;
            }
            return interface1;
      }
}

So, it is a null object.

If we want a REAL interactive remote shell, we have to implement our own MshHost and MshHostUserInterface (and maybe MshHostRawUserInterface). MshHostUserInterface will be responsible to write results to and get input from remote client. I bet this is the way Microsoft monad team will be using to provide remote access (maybe in version 2 of msh).

For me, it is too much work (and I would not compete with monad team). I really wish someone can show a example of implementation of MshHost and MshHostUserInterface. Maybe monad team would like to share their  source code of msh.exe

Hehe, You know I am joking, right?

Added on Mar 15th 10:50am
I just find out that Microsoft Command Shell (MSH) Programmer's Guide are online now! It has exact information I needed.

Have Fun!

Tags: msh    monad