Scott Hanselman

Lynx is dead - Long live Browsh for text-based internet browsing

July 13, '18 Comments [8] Posted in Docker | Open Source
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The standard for browsing the web over a text-=based terminal is Lynx, right? It's the legendary text web browser that you can read about at or, even better, run right now with

docker run --rm -it nbrown/lynx lynx

Awesome, right? But it's text. Lynx runs alt-text rather than images, and doesn't really take advantage of modern browser capabilities OR modern terminal capabilities.

Enter Browsh!

Browsh is a fully-modern text-based browser. It renders anything that a modern browser can; HTML5, CSS3, JS, video and even WebGL. Its main purpose is to be run on a remote server and accessed via SSH/Mosh

Imagine running your browser on a remote machine connected to full power while ssh'ing into your hosted browsh instance. I don't know about you, but my laptop is currently using 2 gigs of RAM for Chrome and it's basically just all fans. I might be able to get 12 hours of battery life if I hung out in tmux and used browsh! Not to mention the bandwidth savings. If I'm tethered or overseas on a 3G network, I can still get a great browsing experience and just barely sip data.

Browsing my blog with Browsh

You can even open new tabs! Check out the keybindings! You gotta try it. Works great on Windows 10 with the new console. Just run this one Docker command:

docker run -it --rm browsh/browsh

If you think this idea is silly, that's OK. I think it's brilliant and creative and exactly the kind of clever idea the internet needs. This solves an interesting browser in an interesting fact it returns us back to the "dumb terminal" days, doesn't it?

There was a time when I my low-power machine waited for text from a refrigerator-sized machine. The fridge did the work and my terminal did the least.

Today my high-powered machine waits for text from another high-powered machine and then struggles to composite it all as 7 megs of JavaScript downloads from But I'm not bitter. ;)

Check out my podcast site on Browsh. Love it.

Tiny pixelated heads made with ASCII

If you agree that Browsh is amazing and special, consider donating! It's currently maintained by just one person and they just want $1000 a month on their Patreon to work on Browsh all the time! Go tell Tom on Twitter that you think is special, then give him some coins. What an exciting and artful project! I hope it continues!

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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Detecting that a .NET Core app is running in a Docker Container and SkippableFacts in XUnit

June 29, '18 Comments [5] Posted in Docker | DotNetCore | Open Source
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Container Ship by NOAA used under CCI have moved my podcast site over to ASP.NET Core 2.1 and I've got it running in a Docker container. Take a moment a check out some of the blog posts, as I've been blogging as I've been learning.

I've added Unit Tests as well as Selenium Tests that are also run with the XUnit Unit Test Runner. However, I don't want those Selenium Tests that automate Google Chrome to run within the context of Docker.

I tried to add an Environment Variable within my Dockerfile like this:


I figured I'd check for that variable and conditionally skip tests. Simple, right? Well, I decided to actually READ the Dockerfiles that my ASP.NET Core 2.1 app uses. Remember, Dockerfiles (and the resulting images) are layered, and with all things .NET, are Open Source. 

Looking at my own layers and exploring the source on Github, I see I'm using:

Nice, so I don't need to set anything to know I'm running .NET in a Container! I wouldn't have known any of this if I hadn't taken 15 minutes and exploring/asserted/confirmed my stack. Just because I'm running Docker containers doesn't mean it's not useful to take the time to KNOW what I'm running! Assert your assumptions and all that, right?

I added a little helper in my Tests:

private bool InDocker { get { return Environment.GetEnvironmentVariable("DOTNET_RUNNING_IN_CONTAINER") == "true";} }

Since I'm using XUnit, I decided to bring in the very useful helper Xunit.SkippableFact!

For example:

public void LoadTheMainPageAndCheckTitle()
    Skip.If(InDocker, "We are in Docker, y'all!");
    Assert.StartsWith("Hanselminutes Technology Podcast - Fresh Air and Fresh Perspectives for Developers", Browser.Title);

SkippableFact lets me skip tests for basically any reason. I could help if I'm in Docker, as I'm doing here. Or, given that Selenium Tests will throw an "OpenQA.Selenium.WebDriverException" when it can't find the Selenium Web Driver, I could also do this, skipping because a specific Exception was through. Note this means it's a SKIP not a FAIL.

public void KevinScottTestThenGoHome()
   Browser.Navigate().GoToUrl(Server.RootUri + "/631/how-do-you-become-a-cto-with-microsofts-cto-kevin-scott");

   var headerSelector = By.TagName("h1");
   var link = Browser.FindElement(headerSelector);

The results look like this:

Total tests: 22. Passed: 18. Failed: 0. Skipped: 4.
Test Run Successful.
Test execution time: 8.7878 Seconds

You could choose to Skip Tests if a backend, 3rd party API, or DB was down, but you still wanted to test as much as possible. I'm pretty happy with the results!

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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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.NET Core and Docker

June 26, '18 Comments [4] Posted in Docker | DotNetCore | Open Source
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If you've got Docker installed you can run a .NET Core sample quickly just like this. Try it:

docker run --rm microsoft/dotnet-samples

If your Docker for Windows is in "Windows Container mode" you can try .NET Framework (the 4.x Windows Framework) like this:

docker run --rm microsoft/dotnet-framework-samples

vs-docker-toolsI did a video last week with a write up showing how easy it is to get a containerized application into Azure AND cheaply with per-second billing.

Container images are easy to share via Docker Hub, the Docker Store, and private Docker registries, such as the Azure Container Registry. Also check out Visual Studio Tools for Docker. It all works very nicely together.

I like this quote from Richard Lander:

Imagine five or so years ago someone telling you in a job interview that they care so much about consistency that they always ship the operating system with their app. You probably wouldn’t have hired them. Yet, that’s exactly the model Docker uses!

And it's a good model! It gives you guaranteed consistency. "Containers include the application and all of its dependencies. The application executes the same code, regardless of computer, environment or cloud." It's also a good way to make sure your underlying .NET is up to date with security fixes:

Docker is a game changer for acquiring and using .NET updates. Think back to just a few years ago. You would download the latest .NET Framework as an MSI installer package on Windows and not need to download it again until we shipped the next version. Fast forward to today. We push updated container images to Docker Hub multiple times a month.

The .NET images get built using the official Docker images which is nice.

.NET images are built using official images. We build on top of Alpine, Debian, and Ubuntu official images for x64 and ARM. By using official images, we leave the cost and complexity of regularly updating operating system base images and packages like OpenSSL, for example, to the developers that are closest to those technologies. Instead, our build system is configured to automatically build, test and push .NET images whenever the official images that we use are updated. Using that approach, we’re able to offer .NET Core on multiple Linux distros at low cost and release updates to you within hours.

Here's where you can find .NET Docker Hub repos:

.NET Core repos:

.NET Framework repos:

  • microsoft/dotnet-framework – includes .NET Framework runtime and sdk images.
  • microsoft/aspnet – includes ASP.NET runtime images, for ASP.NET Web Forms and MVC, configured for IIS.
  • microsoft/wcf – includes WCF runtime images configured for IIS.
  • microsoft/iis – includes IIS on top of the Windows Server Core base image. Works for but not optimized for .NET Framework applications. The microsoft/aspnet and microsoft/wcfrepos are recommended instead for running the respective application types.

There's a few kinds of images in the microsoft/dotnet repo:

  • sdk — .NET Core SDK images, which include the .NET Core CLI, the .NET Core runtime and ASP.NET Core.
  • aspnetcore-runtime — ASP.NET Core images, which include the .NET Core runtime and ASP.NET Core.
  • runtime — .NET Core runtime images, which include the .NET Core runtime.
  • runtime-deps — .NET Core runtime dependency images, which include only the dependencies of .NET Core and not .NET Core itself. This image is intended for self-contained applications and is only offered for Linux. For Windows, you can use the operating system base image directly for self-contained applications, since all .NET Core dependencies are satisfied by it.

For example, I'll use an SDK image to build my app, but I'll use aspnetcore-runtime to ship it. No need to ship the SDK with a running app. I want to keep my image sizes as small as possible!

For me, I even made a little PowerShell script (runs on Windows or Linux) that builds and tests my Podcast site (the image tagged podcast:test) within docker. Note the volume mapping? It stores the Test Results outside the container so I can look at them later if I need to.

docker build --pull --target testrunner -t podcast:test .
docker run --rm -v c:\github\hanselminutes-core\TestResults:/app/hanselminutes.core.tests/TestResults podcast:test

Pretty slick.

Results File: /app/hanselminutes.core.tests/TestResults/_898a406a7ad1_2018-06-28_22_05_04.trx

Total tests: 22. Passed: 22. Failed: 0. Skipped: 0.
Test execution time: 8.9496 Seconds

Go read up on how the .NET Core images are built, managed, and maintained. It made it easy for me to get my podcast site - once dockerized - running on .NET Core on a Raspberry Pi (ARM32).

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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Building, Running, and Testing .NET Core and ASP.NET Core 2.1 in Docker on a Raspberry Pi (ARM32)

May 16, '18 Comments [14] Posted in Docker | DotNetCore
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I love me some Raspberry Pi. They are great little learning machines and are super fun for kids to play with. Even if those kids are adults and they build a 6 node Kubernetes Raspberry Pi Cluster.

Open source .NET Core runs basically everywhere - Windows, Mac, and a dozen Linuxes. However, there is an SDK (that compiles and builds) and a Runtime (that does the actual running of your app). In the past, the .NET Core SDK (to be clear, the ability to "dotnet build") wasn't supported on ARMv7/ARMv8 chips like the Raspberry Pi. Now it is.

.NET Core is now supported on Linux ARM32 distros, like Raspbian and Ubuntu!

Note: .NET Core 2.1 is supported on Raspberry Pi 2+. It isn’t supported on the Pi Zero or other devices that use an ARMv6 chip. .NET Core requires ARMv7 or ARMv8 chips, like the ARM Cortex-A53. Folks on the Azure IoT Edge team use the .NET Core Bionic ARM32 Docker images to support developers writing C# with Edge devices.

There's two ways to run .NET Core on a Raspberry Pi.

One, use Docker. This is literally the fastest and easiest way to get .NET Core up and running on a Pi. It sounds crazy but Raspberry Pis are brilliant little Docker container capable systems. You can do it in minutes, truly. You can install Docker quickly on a Raspberry Pi with just:

curl -sSL | sh
sudo usermod -aG docker pi

After installing Docker you'll want to log in and out. You might want to try a quick sample to make sure .NET Core runs! You can explore the available Docker tags at and you can read about the .NET Core Docker samples here

Now I can just docker run and then pass in "dotnet --info" to find out about dotnet on my Pi.

pi@raspberrypi:~ $ docker run --rm -it microsoft/dotnet:2.1-sdk dotnet --info
.NET Core SDK (reflecting any global.json):
Version: 2.1.300-rc1-008673
Commit: f5e3ddbe73

Runtime Environment:
OS Name: debian
OS Version: 9
OS Platform: Linux
RID: debian.9-x86
Base Path: /usr/share/dotnet/sdk/2.1.300-rc1-008673/

Host (useful for support):
Version: 2.1.0-rc1
Commit: eb9bc92051

.NET Core SDKs installed:
2.1.300-rc1-008673 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
Microsoft.NETCore.App 2.1.0-rc1 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:

This is super cool. There I'm on the Raspberry Pi (RPi) and I just ask for the dotnet:2.1-sdk and because they are using "multiarch" docker files, Docker does the right thing and it just works. If you want to use .NET Core on ARM32 with Docker, you can use any of the following tags.

Note: The first three tags are multi-arch and bionic is Ubuntu 18.04. The codename stretch is Debian 9. So I'm using 2.1-sdk and it's working on my RPi, but I can be specific if I'd prefer.

  • 2.1-sdk
  • 2.1-runtime
  • 2.1-aspnetcore-runtime
  • 2.1-sdk-stretch-arm32v7
  • 2.1-runtime-stretch-slim-arm32v7
  • 2.1-aspnetcore-runtime-stretch-slim-arm32v7
  • 2.1-sdk-bionic-arm32v7
  • 2.1-runtime-bionic-arm32v7
  • 2.1-aspnetcore-runtime-bionic-arm32v7

Try one in minutes like this:

docker run --rm microsoft/dotnet-samples:dotnetapp

Here it is downloading the images...

Docker on a Raspberry Pi

In previous versions of .NET Core's Dockerfiles it would fail if you were running an x64 image on ARM:

standard_init_linux.go:190: exec user process caused "exec format error"

Different processors! But with multiarch per Kendra from Microsoft it just works with 2.1.

Docker has a multi-arch feature that microsoft/dotnet-nightly recently started utilizing. The plan is to port this to the official microsoft/dotnet repo shortly. The multi-arch feature allows a single tag to be used across multiple machine configurations. Without this feature each architecture/OS/platform requires a unique tag. For example, the microsoft/dotnet:1.0-runtime tag is based on Debian and microsoft/dotnet:1.0-runtime-nanoserver if based on Nano Server. With multi-arch there will be one common microsoft/dotnet:1.0-runtime tag. If you pull that tag from a Linux container environment you will get the Debian based image whereas if you pull that tag from a Windows container environment you will get the Nano Server based image. This helps provide tag uniformity across Docker environments thus eliminating confusion.

In these examples above I can:

  • Run a preconfigured app within a Docker image like:
    • docker run --rm microsoft/dotnet-samples:dotnetapp
  • Run dotnet commands within the SDK image like:
    • docker run --rm -it microsoft/dotnet:2.1-sdk dotnet --info
  • Run an interactive terminal within the SDK image like:
    • docker run --rm -it microsoft/dotnet:2.1-sdk

As a quick example, here I'll jump into a container and new up a quick console app and run it, just to prove I can. This work will be thrown away when I exit the container.

pi@raspberrypi:~ $ docker run --rm -it microsoft/dotnet:2.1-sdk
root@063f3c50c88a:/# ls
bin boot dev etc home lib media mnt opt proc root run sbin srv sys tmp usr var
root@063f3c50c88a:/# cd ~
root@063f3c50c88a:~# mkdir mytest
root@063f3c50c88a:~# cd mytest/
root@063f3c50c88a:~/mytest# dotnet new console
The template "Console Application" was created successfully.

Processing post-creation actions...
Running 'dotnet restore' on /root/mytest/mytest.csproj...
Restoring packages for /root/mytest/mytest.csproj...
Installing Microsoft.NETCore.DotNetAppHost 2.1.0-rc1.
Installing Microsoft.NETCore.DotNetHostResolver 2.1.0-rc1.
Installing NETStandard.Library 2.0.3.
Installing Microsoft.NETCore.DotNetHostPolicy 2.1.0-rc1.
Installing Microsoft.NETCore.App 2.1.0-rc1.
Installing Microsoft.NETCore.Platforms 2.1.0-rc1.
Installing Microsoft.NETCore.Targets 2.1.0-rc1.
Generating MSBuild file /root/mytest/obj/mytest.csproj.nuget.g.props.
Generating MSBuild file /root/mytest/obj/mytest.csproj.nuget.g.targets.
Restore completed in 15.8 sec for /root/mytest/mytest.csproj.

Restore succeeded.
root@063f3c50c88a:~/mytest# dotnet run
Hello World!
root@063f3c50c88a:~/mytest# dotnet exec bin/Debug/netcoreapp2.1/mytest.dll
Hello World!

If you try it yourself, you'll note that "dotnet run" isn't very fast. That's because it does a restore, build, and run. Compilation isn't super quick on these tiny devices. You'll want to do as little work as possible. Rather than a "dotnet run" all the time, I'll do a "dotnet build" then a "dotnet exec" which is very fast.

If you're doing to do Docker and .NET Core, I can't stress enough how useful the resources are over at

Building .NET Core Apps with Docker

Develop .NET Core Apps in a Container

  • Develop .NET Core Applications - This sample shows how to develop, build and test .NET Core applications with Docker without the need to install the .NET Core SDK.
  • Develop ASP.NET Core Applications - This sample shows how to develop and test ASP.NET Core applications with Docker without the need to install the .NET Core SDK.

Optimizing Container Size

ARM32 / Raspberry Pi

I found the samples to be super sure to dig into the Dockerfiles themselves as it'll give you a ton of insight into how to structure your own files. Being able to do Multistage Dockerfiles is crucial when building on a small device like a RPi. You want to do as little work as possible and let Docker cache as many layers with its internal "smarts." If you're not thoughtful about this, you'll end up wasting 10x the time building image layers every build.

Dockerizing a real ASP.NET Core Site with tests!

Can I take my podcast site and Dockerize it and build/test/run it on a Raspberry Pi? YES.

FROM microsoft/dotnet:2.1-sdk AS build

# copy csproj and restore as distinct layers
COPY *.sln .
COPY hanselminutes.core/*.csproj ./hanselminutes.core/
COPY hanselminutes.core.tests/*.csproj ./hanselminutes.core.tests/
RUN dotnet restore

# copy everything else and build app
COPY . .
WORKDIR /app/hanselminutes.core
RUN dotnet build

FROM build AS testrunner
WORKDIR /app/hanselminutes.core.tests
ENTRYPOINT ["dotnet", "test", "--logger:trx"]

FROM build AS test
WORKDIR /app/hanselminutes.core.tests
RUN dotnet test

FROM build AS publish
WORKDIR /app/hanselminutes.core
RUN dotnet publish -c Release -o out

FROM microsoft/dotnet:2.1-aspnetcore-runtime AS runtime
COPY --from=publish /app/hanselminutes.core/out ./
ENTRYPOINT ["dotnet", "hanselminutes.core.dll"]

Love it. Now I can "docker build ." on my Raspberry Pi. It will restore, test, and build. If the tests fail, the Docker build will fail.

See how there's an extra section up there called "testrunner" and then after it is "test?" That testrunner section is a no-op. It sets an ENTRYPOINT but it is never used...yet. The ENTRYPOINT is an implicit run if it is the last line in the Dockerfile. That's there so I can "Run up to it" if I want to.

I can just build and run like this:

docker build -t podcast .
docker run --rm -it -p 8000:80 podcast

NOTE/GOTCHA: Note that the "runtime" image is microsoft/dotnet:2.1-aspnetcore-runtime, not microsoft/dotnet:2.1-runtime. That aspnetcore one pre-includes the binaries I need for running an ASP.NET app, that way I can just include a single reference to "<PackageReference Include="Microsoft.AspNetCore.App" Version="2.1.0-rc1-final" />" in my csproj. If didn't use the aspnetcore-runtime base image, I'd need to manually pull in all the ASP.NET Core packages that I want. Using the base image might make the resulting image files larger, but it's a balance between convenience and size. It's up to you. You can manually include just the packages you need, or pull in the "Microsoft.AspNetCore.App" meta-package for convenience. My resulting "podcast" image ended up 205megs, so not to bad, but of course if I wanted I could trim in a number of ways.

Or, if I JUST want test results from Docker, I can do this! That means I can run the tests in the Docker container, mount a volume between the Linux container and (theoretical) Window host, and then open the .trx resulting file in Visual Studio!

docker build --pull --target testrunner -t podcast:test .
docker run --rm -v D:\github\hanselminutes-core\TestResults:/app/hanselminutes.core.tests/TestResults podcast:test

Check it out! These are the test results from the tests that ran within the Linux Container:

XUnit Tests from within a Docker Container on Linux viewed within Visual Studio on Windows

Here's the result. I've now got my Podcast website running in Docker on an ARM32 Raspberry Pi 3 with just an hours' work (writing the Dockerfile)!

It's my podcast site running under Docker on .NET Core 2.1 on a Raspberry Pi

Second - did you make it this far down? - You can just install the .NET Core 2.1 SDK "on the metal." No Docker, just get the tar.gz and set it up. Looking at the RPi ARM32v7 Dockerfile, I can install it on the metal like this. Note I'm getting the .NET Core SDK *and* the ASP.NET Core shared runtime. In the final release build you will just get the SDK and it'll include everything, including ASP.NET.

$ sudo apt-get -y update
$ sudo apt-get -y install libunwind8 gettext
$ wget
$ wget
$ sudo mkdir /opt/dotnet
$ sudo tar -xvf dotnet-sdk-2.1.300-rc1-008673-linux-arm.tar.gz -C /opt/dotnet/
$ sudo tar -xvf aspnetcore-runtime-2.1.0-rc1-final-linux-arm.tar.gz -C /opt/dotnet/
$ sudo ln -s /opt/dotnet/dotnet /usr/local/bin
$ dotnet --info

Cross-platform for the win!

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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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A multi-player server-side GameBoy Emulator written in .NET Core and Angular

March 5, '18 Comments [4] Posted in Docker | DotNetCore | Javascript | Open Source
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Server-side GameBoyOne of the great joys of sharing and discovering code online is when you stumble upon something so truly epic, so amazing, that you have to dig in. Head over to and ask yourself why this GitHub project has only 20 stars?

Alex Haslehurst has created some retro hardware libraries in open source .NET Core with an Angular Front End!


A multiplayer server-side Game Boy emulator. Epic.

You can run it in minutes with

docker run -p 2500:2500 alexhaslehurst/server-side-gameboy

Then just browse to http://localhost:2500 and play Tetris on the original GameBoy!

I love this for a number of reasons.

First, I love his perspective:

Please check out my GameBoy emulator written in .NET Core; Retro.Net. Yes, a GameBoy emulator written in .NET Core. Why? Why not. I plan to do a few write-ups about my experience with this project. Firstly: why it was a bad idea.

  1. Emulation on .NET
  2. Emulating the GameBoy CPU on .NET

The biggest issue one has trying to emulate a CPU with a platform like .NET is the lack of reliable high-precision timing. However, he manages a nice from-scratch emulation of the Z80 processor, modeling low level things like registers in very high level C#. I love that public class GameBoyFlagsRegister is a thing. ;) I did similar things when I ported a 15 year old "Tiny CPU" to .NET Core/C#.

Address space diagram from

Be sure to check out Alex's extremely detailed explanation on how he modeled the Z80 microprocessor.

Luckily the GameBoy CPU, a Sharp LR35902, is derived from the popular and very well documented Zilog Z80 - A microprocessor that is unbelievably still in production today, over 40 years after it’s introduction.

The Z80 is an 8-bit microprocessor, meaning that each operation is natively performed on a single byte. The instruction set does have some 16-bit operations but these are just executed as multiple cycles of 8-bit logic. The Z80 has a 16-bit wide address bus, which logically represents a 64K memory map. Data is transferred to the CPU over an 8-bit wide data bus but this is irrelevant to simulating the system at state machine level. The Z80 and the Intel 8080 that it derives from have 256 I/O ports for accessing external peripherals but the GameBoy CPU has none - favouring memory mapped I/O instead

He didn't just create an emulator - there's lots of those - but uniquely he runs it on the server-side while allowing shared controls in a browser. "In between each unique frame, all connected clients can vote on what the next control input should be. The server will choose the one with the most votes… most of the time." Massively multi-player online GameBoy! Then he streams out the next frame! "GPU rendering is completed on the server once per unique frame, compressed with LZ4 and streamed out to all connected clients over websockets."

This is a great learning repository because:

  • it has complex business logic on the server-side but the front end uses Angular and web-sockets and open web technologies.
  • It's also nice that he has a complete multi-stage Dockerfile that is itself a great example of how to build both .NET Core and Angular apps in Docker.
  • Extensive (thousands) of Unit Tests with the Shouldly Assertion Framework and Moq Mocking Framework.
  • Great example usages of Reactive Programming
  • Unit Testing on both server AND client, using Karma Unit Testing for Angular

Here's a few favorite elegant code snippets in this huge repository.

The Reactive Button Presses:

_joyPadSubscription = _joyPadSubject
    .Where(x => x.Any())
    .Subscribe(presses =>
                    var (button, name) = presses
                        .Where(x => !string.IsNullOrEmpty(
                        .GroupBy(x => x.button)
                        .OrderByDescending(grp => grp.Count())
                        .Select(grp => (button: grp.Key, name: grp.Select(x =>
                    Publish(name, $"Pressed {button}");


The GPU Renderer:

private void Paint()
    var renderSettings = new RenderSettings(_gpuRegisters);

    var backgroundTileMap = _tileRam.ReadBytes(renderSettings.BackgroundTileMapAddress, 0x400);
    var tileSet = _tileRam.ReadBytes(renderSettings.TileSetAddress, 0x1000);
    var windowTileMap = renderSettings.WindowEnabled ? _tileRam.ReadBytes(renderSettings.WindowTileMapAddress, 0x400) : new byte[0];

    byte[] spriteOam, spriteTileSet;
    if (renderSettings.SpritesEnabled) {
        // If the background tiles are read from the sprite pattern table then we can reuse the bytes.
        spriteTileSet = renderSettings.SpriteAndBackgroundTileSetShared ? tileSet : _tileRam.ReadBytes(0x0, 0x1000);
        spriteOam = _spriteRam.ReadBytes(0x0, 0xa0);
    else {
        spriteOam = spriteTileSet = new byte[0];

    var renderState = new RenderState(renderSettings, tileSet, backgroundTileMap, windowTileMap, spriteOam, spriteTileSet);

    var renderStateChange = renderState.GetRenderStateChange(_lastRenderState);
    if (renderStateChange == RenderStateChange.None) {
        // No need to render the same frame twice.
        _frameSkip = 0;

    _lastRenderState = renderState;
    _tileMapPointer = _tileMapPointer == null ? new TileMapPointer(renderState) : _tileMapPointer.Reset(renderState, renderStateChange);
    var bitmapPalette = _gpuRegisters.LcdMonochromePaletteRegister.Pallette;
    for (var y = 0; y < LcdHeight; y++) {
        for (var x = 0; x < LcdWidth; x++) {
            _lcdBuffer.SetPixel(x, y, (byte) bitmapPalette[_tileMapPointer.Pixel]);

            if (x + 1 < LcdWidth) {

        if (y + 1 < LcdHeight){
    _frameSkip = 0;

The GameBoy Frames are composed on the server side then compressed and sent to the client over WebSockets. He's got backgrounds and sprites working, and there's still work to be done.

The Raw LCD is an HTML5 canvas:

<canvas #rawLcd [width]="lcdWidth" [height]="lcdHeight" class="d-none"></canvas>
<canvas #lcd
        [style.max-width]="maxWidth + 'px'"
        [style.max-height]="maxHeight + 'px'"
        [style.min-width]="minWidth + 'px'"
        [style.min-height]="minHeight + 'px'"

I love this whole project because it has everything. TypeScript, 2D JavaScript Canvas, retro-gaming, and so much more!

const raw: HTMLCanvasElement = this.rawLcdCanvas.nativeElement;
const rawContext: CanvasRenderingContext2D = raw.getContext("2d");
const img = rawContext.createImageData(this.lcdWidth, this.lcdHeight);

for (let y = 0; y < this.lcdHeight; y++) {
  for (let x = 0; x < this.lcdWidth; x++) {
    const index = y * this.lcdWidth + x;
    const imgIndex = index * 4;
    const colourIndex = this.service.frame[index];
    if (colourIndex < 0 || colourIndex >= colours.length) {
      throw new Error("Unknown colour: " + colourIndex);

    const colour = colours[colourIndex];[imgIndex] =;[imgIndex + 1] =;[imgIndex + 2] =;[imgIndex + 3] = 255;
rawContext.putImageData(img, 0, 0);

context.drawImage(raw, lcdX, lcdY, lcdW, lcdH);

I would encourage you to go STAR and CLONE and give it a run with Docker! You can then use Visual Studio Code and .NET Core to compile and run it locally. He's looking for help with GameBoy sound and a Debugger.

Sponsor: Get the latest JetBrains Rider for debugging third-party .NET code, Smart Step Into, more debugger improvements, C# Interactive, new project wizard, and formatting code in columns.

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.