Silver Light and Blue Sky

C# and Infrastructure. Code is everything.

Update OpenShift ASP.NET Core s2i to .NET Core 1.1 Preview1

OpenShift provides ASP.NET Core s2i image.

GitHub - openshift-s2i/s2i-aspnet: Source-to-Image template for ASP.NET applications GitHub - openshift-s2i/s2i-aspnet-example: Example projects for the ASP.NET builder image

Now .NET Core 1.1 Preview 1 is released.

So I updated s2i image to .NET Core 1.1 Preview1. Here are the steps.

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P/Invoke in .NET Core on Red Hat Enterprise Linux

This post was originally published on Red Hat Developers, the community to learn, code, and share faster. To read the original post, click here.

P/Invoke(Platform Invocation Service) is one of the features of CLI (Common Language Interface) on .NET Framework. P/Invoke enables managed code to call a native function in DLL (Dynamic Link Library). It’s a powerful tool for .NET Framework to execute existing C-style functions easily. .NET Core also has a P/Invoke feature and it means we can call a native function in .so file (Linux) and . file (Max OSX). I will show you the short example P/Invoke in .NET Core on Red Hat Enterprise Linux (RHEL).

Here is the simple P/Invoke sample using read function in libc. It is the same way as .NET Framework on Windows to import native function.

using System;
using System.Runtime.InteropServices;
using System.Text;

namespace ConsoleApplication
    public class Program
        static extern int read(int handle, byte[] buf, int n);

        public static void Main(string[] args)
            Console.Write("Input value:");
            var buffer = new byte[100];
            read(0, buffer, 100);
            Console.WriteLine("Input value is:" + Encoding.UTF8.GetString(buffer));

[dllimport] is the attribute to import a native function. We can declare method name as a native function name, and declare method name as you like with specifying native function name in EntryPoint attribute value as below.

[DllImport("libc", EntryPoint="read")]
static extern int Read(int handle, byte[] buf, int n);

We can read text from console input with native libc method.

Next, I’d like to execute GUI sample written in .NET Core on RHEL. .NET Core doesn’t have GUI Framework at this point. However, we can call GUI library such as gtk+ from managed code in .NET Core. At first, install the package.

$ sudo yum install gtk3-devel

Now we can call functions in gtk+ from C# code. Here is the whole code to open dialog from C#.

using System;
using System.Runtime.InteropServices;

namespace ConsoleApplication
    public class Program
        private static extern void gtk_init (ref int argc, ref IntPtr argv);
        static extern IntPtr gtk_message_dialog_new(IntPtr parent_window, DialogFlags flags, MessageType type, ButtonsType bt, string msg, IntPtr args);
        static extern int gtk_dialog_run(IntPtr raw);
        static extern void gtk_widget_destroy(IntPtr widget);
        public enum DialogFlags 
            Modal = 1 << 0,
            DestroyWithParent = 1 << 1,

        public enum MessageType
        public enum ButtonsType

        public static void Main(string[] args)
            var argc = 0;
            var argv = IntPtr.Zero;
            gtk_init(ref argc, ref argv);
            var diag = gtk_message_dialog_new(IntPtr.Zero, DialogFlags.Modal, MessageType.Error, ButtonsType.Ok, "Hello from .NET Core on Red Hat!", IntPtr.Zero);
            var res = gtk_dialog_run(diag);

Here is a result. The dialog is opened.


P/Invoke was a technology only for Windows platform, but now it enables many platforms to call native function easily from managed code. Of course, we shouldn’t forget Mono, which enabled P/Invoke on Linux.

How to queue and cancel build from C# code with VSTS Nuget library


Visual Studio Team Services has an API, so we can queue and cancel build via API.

Visual Studio Team Services and Team Foundation Server REST API Reference

Here is an API about the build.

Builds | REST API Reference for Visual Studio Team Services and Team Foundation Server

Microsoft provides four NuGet libraries for VSTS API.

.NET Client Libraries for Visual Studio Team Services (and TFS)

Microsoft.TeamFoundationServer.Client is the library to execute build operation. However, it's hard to use. I write sample codes for queuing and cancelling build.

Queue build

Here is a sample.

QueueBuildAsync, which is a method to queue a build, has the Build object as a parameter. Build object has many properties. However, there is no document which property is required. I found Definition.Id (id of build definition) and Project property are necessary after several tries.

Cancel build

Next, I'd like to cancel the queued build from C# code. What do I do? There is no API in the list. "Delete" method is not the API for cancelling but for deleting the completed build itself.

The answer is executing "update" method. We should update the queued build status to "cancel".

We should execute two or more API calls to queue or cancel build. That's the way to execute them from C# code.

Getting session source information at RDP session by C#

I'd like to get the information of remote session source at the destination server with this function*1.

WTSQuerySessionInformation function (Windows)

It can be written by C# with DllImport. The value of WTS_CURRENT_SESSION is uint.MaxValue.

It takes some doing because the structure of ppBuffer is changed depending on the specified value in WTSInfoClass. Here is a struct when WTSInfoClassis WTSClientAddress.

WTS_CLIENT_ADDRESS structure (Windows)

If you get all the sessions except itself, you can use this function.

WTSEnumerateSessions function (Windows)

*1:It seems OK for launching app with UAC elevation