Category Archives: .Net 5

Compiling Code Files in C# Using Roslyn

I started investigating this for a unit test. I wanted to compile a separate project, and then copy the output into the test directory. As it happens, by the time I’d figured this out in Roslyn, I’d worked out it probably wasn’t right for the test that I was writing; however, given the amount of effort involved in actually piecing together the tiny amount of documentation available, I definitely thought it was worthy of documenting.

This particular post will focus on reading code files and compiling them into an executable or library. I may play around with this some more in the future: I suspect this might have quite a lot of mileage in the unit test space.


Let’s start with the dependencies:

    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.11.0" />
    <PackageReference Include="Microsoft.CodeDom.Providers.DotNetCompilerPlatform" Version="3.6.0" />

It’s worth bearing in mind that there are a few other libraries knocking about from previous incarnations of Roslyn, and similar tools; however, it’s my understanding that these are not in the Microsoft namespace. I probably spent the first couple of hours trying to get this to work with CSharpCodeProvider. If you found your way here searching for this error:

System.PlatformNotSupportedException: ‘Operation is not supported on this platform.’

Then you’re in good company.


The following code will produce a library called qwerty.dll; it requires a variable giving the sourceFilesLocation and another, destinationLocation:

	// 1
            DirectoryInfo d = new DirectoryInfo(sourceFilesLocation); 
            string[] sourceFiles = d.EnumerateFiles("*.cs", SearchOption.AllDirectories)                
                .Select(a => a.FullName).ToArray();
	// 2
            List<SyntaxTree> trees = new List<SyntaxTree>();
            foreach (string file in sourceFiles)
                string code = File.ReadAllText(file);
                SyntaxTree tree = CSharpSyntaxTree.ParseText(code);
	// 3
            MetadataReference mscorlib =
            MetadataReference codeAnalysis =
            MetadataReference csharpCodeAnalysis =

            MetadataReference[] references = { mscorlib, codeAnalysis, csharpCodeAnalysis };

	// 4
            var compilation = CSharpCompilation.Create("qwerty.dll",
                   new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
            var result = compilation.Emit(Path.Combine(destinationLocation, "qwerty.dll"));

Let’s break the code down (you may notice that there are 4 comments, that to the untrained eye, appear useless).

1. The first part scans the source files directory and returns a list of files.
2. We then build a syntax tree list by reading all the files and calling the ParseText method on each; they are added to a list of parsed files.
3. We now build up a list of references needed to compile the code.
4. Finally, we create the dll, passing in the files that we built up in 2 & 3. .Create creates an in-memory version of the dll, so we then need to call .Emit to write it to disk.

Summary and caveats

This is a very simplistic example – as I’ve said, I need to spend some more time looking at some of the more advanced cases, but if you have a very simple library, this will compile and produce the DLL for you.


Beginner’s Guide to Docker – Part 2 – Debugging a Docker Build

In this post I covered the very basics of getting started with Docker. Once you start to experiment, you’ll need to learn how to debug and investigate some of the unexpected things that happen.


In this post, you’ll see references to WebbApplication4 and WebApplication5. This is simply because, during creating the post, I switched, didn’t realise the screenshots were a mix of both, and now don’t consider it worth my time to change. Just consider the two interchangeable.

Asp.Net 5

For this example, we’ll use the default dockerfile that comes with Asp.Net 5; however, we’ll build it up ourselves. Just build a new Asp.Net project.

When setting this up, do not enable docker support:

If we had enabled docker support, we would get a docker file – so let’s build that (this is taken directly from that file). We’ll put it in the same directory as the sln file.

FROM AS base

FROM AS build
COPY ["WebApplication4/WebApplication4.csproj", "WebApplication4/"]
RUN dotnet restore "WebApplication4/WebApplication4.csproj"
COPY . .
WORKDIR "/src/WebApplication4"
RUN dotnet build "WebApplication4.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "WebApplication4.csproj" -c Release -o /app/publish

FROM base AS final
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "WebApplication4.dll"]

To give a quick rundown of what’s happening in this file:
– Where you can see `AS base`, `AS build`, etc, these are known as stages (we’ll come back to that).
– The `FROM` statements are telling docker to build on an existing image.
– WORKDIR changes the running directory inside the container: if this directory doesn’t exist, then the command will create it.
– COPY does what you would think: copies whatever you tell it from the first parameter (the host machine) into the second (the docker container)
– RUN executes a command in the container.
– Finally, ENTRYPOINT tells docker what to do when it starts the container – it our case, we’re running `dotnet WebApplication4.dll`.

Building and Running

To build the image, go to the application’s solution directory (where your sln file is located):

docker build -t pcm-web-app-4 . 

Once the image builds successfully, you can run it like this:

docker run pcm-web-app-4 -p 1234:80

In this post, we’re going to be more interested in debugging the build itself that running the container. Having said that, we should quickly visit the port mapping (-p); the command above is mapping the port 80 inside the container (in the docker file, we issues an EXPOSE on that port) to post 1234 on the host (so you would navigate to localhost:1234 on the host machine to connect).

Listing Docker Containers, Stopping, Killing, and Attaching

You can list running docker containers by issuing the command:

docker ps

Once you have the container ID (highlighted in the image), you can do various things with it.


To attach to the instance:

docker attach 229

Notice that I only used the first three letters of the container instance ID? That’s because docker will let you abridge the ID to the smallest unique set of numbers. This will attach to the container, and you can browse around.

Stop and Kill

If you want to remove an instance, the command is:

docker stop 229

Which will stop the current instance. However, the instance is still there. You can see it by calling:

docker ps -a

To remove the instance completely, you’ll need to call:

docker rm 229

However, you will only be able to remove the container once it’s stopped.

Now that we’ve covered some basics, let’s get into the debugging.


The first useful tip here is to use the target parameter. To build the dockerfile above, you may do something like this (as shown above):

docker build -t web-app-5 . 

That will build the entire image; but if you get an issue, it may fail at an intermediate stage; in that case, you can break down the build; for example:

docker build --target build -t pcm-web-app-5 .

You can then have a look around at the build files by attaching to the container:

docker run -it pcm-web-app-5

A similar technique can be used if you’re getting issues with the entry point not functioning as expected.


In the dockerfile, you can simply comment out the ENTRYPOINT:

#ENTRYPOINT ["dotnet", "WebApplication5.dll"]

Now, if you run the container; for example:

docker run -d -it pcm-web-app-5

-d launches the container in detached mode; you can then attach:

docker attach eb5

You can then manually run the entry point; for example:

Finally, let’s see how we can see details of a running container.

Inspecting the Container

While the container is running, there’s a set of metadata that is accessible. This contains things like the IP, ports, Mac Address, Name, etc… To view this, call:

docker inspect <container ID>

For example:

docker inspect 41b

There’s a lot of information here, and you can traverse it by using the -f parameter to specify a specific attribute. For example:

docker inspect -f '{{ .State.Status }}' 07a

This will show specific properties without the need to scroll through the full JSON.