All posts by jonskeet

Mad props to @arcaderage for the "Princess Rescue" image - see for the full original

Posting to in code


I started blogging back in 2005, shortly before attending the only MVP summit I’ve managed to go to. I hosted the blog on, back when that was a thing.

In 2014 I migrated to, in the hope that this would make everything nice and simple: it’s a managed service, dedicated to blogging, so I shouldn’t have to worry about anything but the writing. It’s not been quite that simple.

I don’t know when I started writing blog posts in Markdown instead of using Windows Live Writer to create the HTML for me, but it’s definitely my preferred way of writing. It’s the format I use all over the place, it makes posting code easy… it’s just “the right format” (for me).

Almost all my problems with have fallen into one of two categories:

  • Markdown on WordPress (via JetPack, I believe) not quite working as I expect it to.
  • The editor on being actively hostile to Markdown users

In the first category, there are two problems. First, there’s my general annoyance at line breaks being relevant outside code. I like writing paragraphs including line breaks, so that the text is nicely in roughly 80-100 character lines. Unfortunately both WordPress and GitHub decide to format such paragraphs as multiple short lines, instead of flowing a single paragraph. I don’t know why the decision was made to format things this way, and I can see some situations in which it’s beneficial (e.g. a diff of “adding a single word” showing as just that diff rather than all the lines in the paragraph changing) but I mostly dislike it.

The second annoyance is that angle brackets in code (either code fences or just in backticks) behave unpredictably in WordPress, in a way that I don’t remember seeing anywhere else. The most common cause of having to update a post is to fix some generics in C# code, mangling to Markdown to escape the angle brackets. One of these days I may try to document this so that I can get it right in future posts, but it’s certainly a frustration.

I don’t expect to be able to do anything about either of these aspects. I could potentially run posts through some sort of preprocessor, but I suspect tha unwrapping paragraphs but not code blocks could get fiddly pretty fast. I can live with it.

The second category of annoyance – editing on – is what this post is mostly about.

I strongly suspect that most bloggers want a reasonably-WYSIWYG experience, and they definitely don’t want to see their post in its raw, unformatted version (usually HTML, but Markdown for me). For as long as I can remember, there have been two modes in the editor: visual and text. In some cases just going into the visual editor would cause the Markdown to be converted into HTML which would then show up in the text editor… it’s been fiddly to keep it as text. My habit is to keep a copy of the post as text (originally just in StackEdit but now in GitHub) and copy the whole thing into WordPress any time I wanted to edit anything. That way I don’t really care what WordPress does with it.

However, have now made even that workflow even harder – they’ve moved to a “blocks” editor in the easy-to-get-to UI, and you can only get to the text editor via the admin UI.

I figured enough was enough. If I’ve got the posts as text locally (then stored on GitHub), there’s no need to go to the UI for anything other than comments. Time to crack open the API.

What no .NET package?

WordPress is a pretty common blogging platform, let’s face it. I was entirely unsurprised to find out that there’s a REST API for it, allowing you to post to it. (The fact that I’d been using StackEdit to post for ages was further evidence of that.) It also wasn’t surprising that it used OAuth2 for authentication, given OAuth’s prevalance.

What was surprising was my inability to find any .NET packages to let me write a C# console application to call the API with really minimal code. I couldn’t even find any simple “do the OAuth dance for me” libraries that would work in a console application rather than in a web app. RestSharp looked promising, as the home page says “Basic, OAuth 1, OAuth 2, JWT, NTLM are supported” – but the authentication docs could do with some love, and looking at the source code suggested there was nothing that would start a local web server just to receive the OAuth code that could then be exchanged for a full auth token. (I know very little about OAuth2, but just enough to be aware of what’s missing when I browse through some library code.) WordPressPCL also looked promising – but requires JWT authentication, which is available via a plugin. I don’t want to upgrade from a personal account to a business account just for the sake of installing a single plugin. (I’m aware it could have other benefits, but…)

So, I have a few options:

  • Upgrade to a business account, install the JWT plugin, and try to use WordPressPCL
  • Move off entirely, run WordPress myself (or find another site like, I suppose) and make the JWT plugin available, and again use WordPressPCL
  • Implement the OAuth2 dance myself

Self-hosting WordPress

I did toy with the idea of running WordPress myself. I have a Google Kubernetes Engine cluster already, that I use to host and some other sites. I figured that by now, installing WordPress on a Kubernetes cluster would be pretty simple. It turns out there’s a Bitnami Helm chart for it, so I decided to give that a go.

First I had to install Helm – I’ve heard of it, but never used it before. My first attempt to use it, via a shell script, failed… but with Chocolatey, it installed okay.

Installing WordPress was a breeze – until it didn’t actually work, because my Kubernetes cluster doesn’t have enough spare resources. It is a small cluster, certainly – it’s not doing anything commercial, and I’m paying for it out of my own pocket, so I try to keep the budget relatively low. Apparently too low.

I investigated how much it might cost to increase the capacity of my cluster so I could run WordPress myself, and when it ended up being more expensive than the business account on (even before the time cost of maintaining the site), I figured I’d stop going down that particular rabbit hole.

Implementing OAuth2

In the end, I really shouldn’t have been so scared of implementing the OAuth2 dance myself. It’s not too bad, particularly when I’m happy to do a few manual steps each time I need a new token, rather than automating everything.

First I had to create an “application” on That’s really just a registration for a client_secret and client_id, along with approved redirect URIs for the OAuth dance. I knew I’d be running a server locally for the browser to redirect to, so I allowed as a redirect URI, and created the app appropriately.

The basic flow is:

  • Start a local web server to receive a redirect response from the WordPress server
  • Visit a carefully-constructed URL on WordPress in the browser
  • Authorize the request in the browser
  • The WordPress response indicates a redirect to the local server, that includes a code
  • The local server then exchanges that code for a token by making another HTTP request to the WordPress server
  • The local server displays the access token so I can copy and paste it for use elsewhere

In a normal application the user never needs to see the access token of course – all of this happens behind the scenes. However, doing that within my eventual “console application which calls the WordPress API to create or update posts” would be rather more hassle than copy/paste and hard-coding the access token. Is this code secure, if it ever gets stolen? Absolutely not. Am I okay with the level of risk here? Yup.

So, what’s the simplest way of starting an HTTP server in a standalone app? (I don’t need this to integrate with anything else.) You could obviously create a new empty ASP.NET Core application and find the right place to handle the request… but personally I reached for the .NET Functions Framework. I’m clearly biased as the author of the framework, but I was thrilled to see how easy it was to use for a real task. The solution is literally a single C# file and a project file, created with dotnet new gcf-http. The C# file contains a single class (Function) with a single method (HandleAsync). The C# file is 50 lines of code in total.

Mind you, it still took over an hour to get a working token that was able to create a WordPress post. Was this due to intricacies of URL encoding in forms? No, despite my investigations taking me in that direction. Was it due to needing to base64 encode the token when making a request? No, despite many attempts along those lines too.

I made two mistakes:

  • In my exchange-code-for-token server, I populated the redirect_uri field in the exchange request with "" instead of ""
  • In the test-the-token application, I specified a scheme of "Basic" instead of "Bearer" in AuthenticationHeaderValue

So just typos, basically. Incredibly frustrating, but I got there.

As an intriguing thought, now I’ve got a function that can do the OAuth dance, there’s nothing to stop me deploying that as a real Google Cloud Function so I could get an OAuth access token at any time just by visiting a URL without running anything locally. I’d just need a bit of configuration – which ASP.NET Core makes easy, of course. No need to do that just yet.

Posting to WordPress

At this point, I have a test application that can create a WordPress post (as Markdown, importantly). It can update the post as well.

The next step is to work out what I want my blogging flow to be in the future. Given that I’m storing the blog content in GitHub, I could potentially trigger the code from a GitHub action – but I’m not sure that’s a particularly useful flow. For now, I’m going to go with “explicitly running an app when I want to create/update a post”.

Now updating a post requires knowing the post ID – which I can get within the WordPress UI, but I also get when creating the post in the first place. But I’d need somewhere to store it. I could create a separate file with metadata for posts, but this is all starting to sound pretty complex.

Instead, my current solution is to have a little metadata “header” before the main post. The application can read that, and process it appropriately. It can also update it with the post ID when it first creates the post on That also avoids me having to specify things like a title on the command line. At the time of writing this, this post has a header like this:

title: Posting to in code
categories: C#, General

After running my application for the first time, I expect it to be something like this:

postId: 12345
title: Posting to in code
categories: C#, General

The presence of the postId field will trigger the app to use “update” instead of “create” next time I ask it to process this file.

Will it work? I’ll find out in just a few minutes. This code hasn’t been run at all yet. Yes, I could write some tests for it. No, I’m not actually going to write the tests. I think it’ll be just as quick to iterate on it by trial and error. (It’s not terribly complicated code.)


If you can see this post, I have a new process for posting to my blog. I will absolutely not create this post manually – if the code never works, you’ll never see this text.

Is this a process that other people would want to use? Maybe, maybe not. I’m not expecting to open source it. But it’s a useful example of how it really doesn’t take that much effort to automate away some annoyance… and I was able to enjoy using my own Functions Framework for realsies, which is a bonus :)

Time to post!

Travis logs and .NET Core console output

This is a blog post rather than a bug report, partly because I really don’t know what’s at fault. Others with more knowledge of how the console works in .NET Core, or exactly what the Travis log does, might be able to dig deeper.

TL;DR: If you’re running jobs using .NET Core 3.1 on Travis and you care about the console output, you might want to set the TERM environment variable to avoid information being swallowed.

Much of my time is spent in the Google Cloud Libraries for .NET repository. That single repository hosts a lot of libraries, and many of the pull requests are from autogenerated code where the impact on the public API surface may not be immediately obvious. (It would be easy to miss one breaking change within dozens of comment changes, for example.) Our Travis build includes a job to work out the public API changes, which is fantastically useful. (Example)

When we updated our .NET Core SDK to 3.1 – or at least around that time; it may have been coincidence – we noticed that some of the log lines in our Travis jobs seemed to be missing. They were actually missing from all the jobs, but it was particularly noticeable for that “change detection” job because the output can often be small, but should always contain a “Diff level” line. It’s really obvious when that line is missing.

I spent rather longer trying to diagnose what was going wrong than I should have done. A colleague noted that clicking on “Raw log” showed that we were getting all the output – it’s just that Travis was swallowing some of it, due to control characters being emitted. This blog post is a distillation of what I learned when trying to work out what was going on.

A simple set of Travis jobs

In my DemoCode repository I’ve created a Travis setup for the sake of this post.

Here are the various files involved:


dist: xenial  

language: csharp  
mono: none  
dotnet: 3.1.301  

    - name: "Default terminal, no-op program"  
      script: TravisConsole/ 0  

    - name: "Default terminal, write two lines"  
      script: TravisConsole/ 2  

    - name: "Mystery terminal, no-op program"  
      env: TERM=mystery  
      script: TravisConsole/ 0  

    - name: "Mystery terminal, write two lines"  
      env: TERM=mystery  
      script: TravisConsole/ 2  

    - name: "Mystery terminal, write two lines, no logo"  
      env: TERM=mystery DOTNET_NOLOGO=true  
      script: TravisConsole/ 2



set -e  

cd $(readlink -f $(dirname ${BASH_SOURCE}))  

echo "Before dotnet run (first)"  
dotnet run -- $1  
echo "After dotnet run (first)"  

echo "Before dotnet run (second)"  
dotnet run -- $1  
echo "After dotnet run (second)"


using System;  

class Program  
    static void Main(string[] args)  
        int count = int.Parse(args[0]);  
        for (int i = 1; i <= count; i++)  
             Console.WriteLine($"Line {i}");  

So each job runs the same .NET Core console application twice with the same command line argument – either 0 (in which case nothing is printed out) or 2 (in which case two it prints out “Line 1” then “Line 2”). The shell script also logs before and after executing the console application. The only other differences are in terms of the environment variables:

  • Some jobs use TERM=mystery instead of the default
  • The final job uses DOTNET_NOLOGO=true

I’ll come back to the final job right at the end – we’ll concentrate on the impact of the TERM environment variable first, as that’s the main point of the post. Next we’ll look at the output of the jobs – in each case showing it in the “pretty” log first, then in the “raw” log. The pretty log has colour, and I haven’t tried to reproduce that. I’ve also only shown the relevant bit – the call to

You can see all of the output shown here in the Travis UI, of course.

Job 1: Default terminal, no-op program

Pretty log

$ TravisConsole/ 0
Before dotnet run (first)
Welcome to .NET Core 3.1!
SDK Version: 3.1.301
Explore documentation:
Report issues and find source on GitHub:
Find out what's new:
Learn about the installed HTTPS developer cert:
Use 'dotnet --help' to see available commands or visit:
Write your first app:
Before dotnet run (second)
The command "TravisConsole/ 0" exited with 0.

Note the lack of After dotnet run in each case.

Raw log

[0K$ TravisConsole/ 0
Before dotnet run (first)

Welcome to .NET Core 3.1!


SDK Version: 3.1.301


Explore documentation:

Report issues and find source on GitHub:

Find out what's new:

Learn about the installed HTTPS developer cert:

Use 'dotnet --help' to see available commands or visit:

Write your first app:

[?1h=[?1h=[?1h=[?1h=[?1h=[?1h=[?1h=After dotnet run (first)
Before dotnet run (second)
[?1h=[?1h=[?1h=[?1h=[?1h=[?1h=[?1h=After dotnet run (second)
[0K[32;1mThe command "TravisConsole/ 0" exited with 0.[0m

In the raw log, we can see that After dotnet run is present each time, but with [?1h=[?1h=[?1h=[?1h=[?1h=[?1h=[?1h= before it. Let’s see what happens when our console application actually writes to the console.

Job 2: Default terminal, write two lines

Pretty log

$ TravisConsole/ 2
Before dotnet run (first)
Welcome to .NET Core 3.1!
SDK Version: 3.1.301
Explore documentation:
Report issues and find source on GitHub:
Find out what's new:
Learn about the installed HTTPS developer cert:
Use 'dotnet --help' to see available commands or visit:
Write your first app:
Line 2
Before dotnet run (second)
Line 2
The command "TravisConsole/ 2" exited with 0.

This time we don’t have After dotnet run – and we don’t have Line 1 either. As expected, they are present in the raw log, but with control characters before them:

[0K$ TravisConsole/ 2
Before dotnet run (first)

Welcome to .NET Core 3.1!


SDK Version: 3.1.301


Explore documentation:

Report issues and find source on GitHub:

Find out what's new:

Learn about the installed HTTPS developer cert:

Use 'dotnet --help' to see available commands or visit:

Write your first app:

[?1h=[?1h=[?1h=[?1h=[?1h=[?1h=Line 1
Line 2
[?1h=After dotnet run (first)
Before dotnet run (second)
[?1h=[?1h=[?1h=[?1h=[?1h=[?1h=Line 1
Line 2
[?1h=After dotnet run (second)
[0K[32;1mThe command "TravisConsole/ 2" exited with 0.[0m

Now let’s try with the TERM environment variable set.

Job 3: Mystery terminal, no-op program

$ TravisConsole/ 0
Before dotnet run (first)
Welcome to .NET Core 3.1!
SDK Version: 3.1.301
Explore documentation:
Report issues and find source on GitHub:
Find out what's new:
Learn about the installed HTTPS developer cert:
Use 'dotnet --help' to see available commands or visit:
Write your first app:
After dotnet run (first)
Before dotnet run (second)
After dotnet run (second)
The command "TravisConsole/ 0" exited with 0.

That’s more like it! This time the raw log doesn’t contain any characters within the script execution itself. (There are still blank lines in the “logo” part, admittedly. Not sure why, but we’ll get rid of that later anyway.)

[0K$ TravisConsole/ 0
Before dotnet run (first)

Welcome to .NET Core 3.1!


SDK Version: 3.1.301


Explore documentation:

Report issues and find source on GitHub:

Find out what's new:

Learn about the installed HTTPS developer cert:

Use 'dotnet --help' to see available commands or visit:

Write your first app:

After dotnet run (first)
Before dotnet run (second)
After dotnet run (second)
[0K[32;1mThe command "TravisConsole/ 0" exited with 0.[0m

Let’s just check that it still works with actual output:

Job 4: Mystery terminal, write two lines

Pretty log

4.45s$ TravisConsole/ 2
Before dotnet run (first)
Welcome to .NET Core 3.1!
SDK Version: 3.1.301
Explore documentation:
Report issues and find source on GitHub:
Find out what's new:
Learn about the installed HTTPS developer cert:
Use 'dotnet --help' to see available commands or visit:
Write your first app:
Line 1
Line 2
After dotnet run (first)
Before dotnet run (second)
Line 1
Line 2
After dotnet run (second)
The command "TravisConsole/ 2" exited with 0.

Exactly what we’d expect from inspection. The raw log doesn’t hold any surprises either.

Raw log

[0K$ TravisConsole/ 2
Before dotnet run (first)

Welcome to .NET Core 3.1!


SDK Version: 3.1.301


Explore documentation:

Report issues and find source on GitHub:

Find out what's new:

Learn about the installed HTTPS developer cert:

Use 'dotnet --help' to see available commands or visit:

Write your first app:

Line 1
Line 2
After dotnet run (first)
Before dotnet run (second)
Line 1
Line 2
After dotnet run (second)
[0K[32;1mThe command "TravisConsole/ 2" exited with 0.[0m

Job 5: Mystery terminal, write two lines, no logo

While job 4 is almost exactly what we want, it’s still got the annoying “Welcome to .NET Core 3.1!” section. That’s a friendly welcome for users in an interactive context, but pointless for continuous integration. Fortunately it’s now easy to turn off by setting DOTNET_NOLOGO=true. We now have exactly the log we’d want:

Pretty log

$ TravisConsole/ 2
Before dotnet run (first)
Line 1
Line 2
After dotnet run (first)
Before dotnet run (second)
Line 1
Line 2
After dotnet run (second)
The command "TravisConsole/ 2" exited with 0.

Raw log

[0K$ TravisConsole/ 2
Before dotnet run (first)
Line 1
Line 2
After dotnet run (first)
Before dotnet run (second)
Line 1
Line 2
After dotnet run (second)
[0K[32;1mThe command "TravisConsole/ 2" exited with 0.[0m


The use of mystery as the value of the TERM environment variable isn’t special, other than “not being a terminal that either Travis or .NET Core will have any fixed expectations about”. I expect that .NET Core is trying to be clever with its output based on the TERM environment variable, and that Travis isn’t handling the control characters in quite the way that .NET Core expects it to. Which one is right, and which one is wrong? It doesn’t really matter to me, so long as I can fix it.

This does potentially have a cost, of course. Anything which would actually produce prettier output based on the TERM environment variable is being hampered by this change. But so far we haven’t seen any problems. (It certainly isn’t stopping our Travis logs from using colour, for example.)

I discovered the DOTNET_NOLOGO environment variable – introduced in .NET Core 3.1.301, I think – incidentally while researching this problem. It’s not strictly related to the core problem, but it is related to the matter of “making CI logs readable” so I thought I’d include it here.

I was rather surprised not to see complaints about this all over the place. As you can see from the code above, it’s not like I’m doing anything particularly “special” – just writing lines out to the console. Are other developers not having the same problem, or just not noticing the problem? Either way, I hope this post helps either the .NET Core team to dive deeper, find out what’s going on and fix it (talking to the Travis team if appropriate), or at least raise awareness of the issue so that others can apply the same workaround.

V-Drum Explorer: Blazor and the Web MIDI API

Blazor and the Web MIDI API

Friday, 9pm

Yesterday, speaking to the NE:Tech user group about V-Drum Explorer, someone mentioned the Web MIDI API– a way of accessing local MIDI devices from a browser.

Now my grasp of JavaScript is tenuous at best… but that’s okay, because I can write C# using Blazor. So in theory, I could build an equivalent to V-Drum Explorer, but running entirely in the browser using WebAssembly. That means I’d never have to worry about the installer again…

Now, I don’t want to get ahead of myself here. I suspect that WPF and later MAUI are still the way forward, but this should at least prove a fun investigation. I’ve never used the Web MIDI API, and I haven’t used Blazor for a few years. This weekend I’m sure I can find a few spare hours, so let’s see how far I can get.

Just for kicks, I’m going to write up my progress in this blog post as I go, adding a timestamp periodically so we can see how long it takes to do things (admittedly whilst writing it up at the same time). I promise not to edit this post other than for clarity, typos etc – if my ideas turn out to be complete failures, such is life.

I have a goal in mind for the end of the weekend: a Blazor web app, running locally to start with (deploying it to k8s shouldn’t be too hard, but isn’t interesting at this point), which can detect my drum module and list the names of the kits on the module.

Here’s the list of steps I expect to take. We’ll see how it goes.

  1. Use JSFiddle to try to access the Web MIDI API. If I can list the ports, open an input and output port, listen for MIDI messages (dumped to the console), and send a SysEx message hard-coded to request the name for kit 1.
  2. Start a new Blazor project, and check I can get it to work.
  3. Try to access the MIDI ports in Blazor – just listing the ports to start with.
  4. Expand the MIDI access test to do everything from step 1.
  5. Loop over all the kits instead of just the first one – this will involve doing checksum computation in the app, copying code from the V-Drum Explorer project. If I get this far, I’ll be very happy.
  6. As a bonus step, if I get this far, it would be really interesting to try to depend on V-Drum Explorer projects (VDrumExplorer.Model and VDrumExplorer.Midi) after modifying the MIDI project to use Web MIDI. At that point, the code for the Blazor app could be really quite simple… and displaying a read-only tree view probably wouldn’t be too hard. Maybe.

Sounds like I have a fun weekend ahead of me.

Saturday morning

Step 1: JSFiddle + MIDI

Time: 07:08

Turn on the TD-27, bring up the MIDI API docs and JSFiddle, and let’s give it a whirl…

It strikes me that it might be useful to be able to save some efforts here. A JSFiddle account may not be necessary for that, but it may make things easier… let’s create an account.

First problem: I can’t see how to make the console (which is where I expect all the results to end up) into more than a single line in the bottom right hand corner. I could open up Chrome’s console, of course, but as JSFiddle has one, it would be nice to use that. Let’s see what happens if I just write to it anyway… ah, it expands as it has data. Okay, that’ll do.

Test 1: initialize MIDI at all

The MIDI API docs have a really handy set of examples which I can just copy/paste. (I’m finding it hard to resist the temptation to change the whitespace to something I’m more comfortable with, but hey…)

So, copy the example in 9.1:

“Failed to get MIDI access – SecurityError: Failed to execute ‘requestMIDIAccess’ on ‘Navigator’: Midi has been disabled in this document by Feature Policy.”

Darn. Look up Feature-Policy on MDN, then a search for “JSFiddle Feature-Policy” finds – which is specifically about MIDI access! And it has a workaround… apparently things work slightly differently with a saved Fiddle. Let’s try saving and reloading…

"MIDI ready!"


Test 2: list the MIDI ports

Copy/paste example 9.3 into the Fiddle (with a couple of extra lines to differentiate between input and output), and call listInputsAndOuptuts from onMIDISuccess

"MIDI ready!"
"Input ports"
"Input port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Input port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Input port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Input port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Input port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Input port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Output ports"
"Output port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Output port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Output port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Output port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Output port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"
"Output port [type:'undefined'] id:'undefined' manufacturer:'undefined' name:'undefined' version:'undefined'"

Hmm. That’s not ideal. It’s clearly found some ports (six inputs and outputs? I’d only expect one or two), but it can’t use any properties in them.

If I add console.log(output) in the loop, it shows “entries”, “keys”, “values”, “forEach”, “has” and “get”, suggesting that the example is iterating over the properties of a collection rather than the entries.

Using for (var input in midiAccess.inputs.values()) still doesn’t give me anything obviously useful. (Keep in mind I know very little JavaScript – I’m sure the answer is obvious to many of you.)

Let’s try using forEach instead like this:

function listInputsAndOutputs( midiAccess ) {
  console.log("Input ports");
  midiAccess.inputs.forEach(input => {
    console.log( "Input port [type:'" + input.type + "'] id:'" + +
      "' manufacturer:'" + input.manufacturer + "' name:'" + +
      "' version:'" + input.version + "'" );

  console.log("Output ports");
  midiAccess.outputs.forEach(output => {
    console.log( "Output port [type:'" + output.type + "'] id:'" + +
      "' manufacturer:'" + output.manufacturer + "' name:'" + +
      "' version:'" + output.version + "'" );

Now the output is much more promising:

"MIDI ready!"
"Input ports"
"Input port [type:'input'] id:'input-0' manufacturer:'Microsoft Corporation' name:'5- TD-27' version:'10.0'"
"Output ports"
"Output port [type:'output'] id:'output-1' manufacturer:'Microsoft Corporation' name:'5- TD-27' version:'10.0'"

Test 3: dump MIDI messages to the console

I can just hard-code the input and output port IDs for now – when I get into C#, I can do something more reasonable.

Adapting example 9.4 from the Web MIDI docs very slightly, we get:

function logMidiMessage(message) {
var line = "MIDI message: "
for (var i = 0; i <; i++) {
line += "0x" +[i].toString(16) + " ";

function onMIDISuccess(midiAccess) {
var input = midiAccess.inputs.get('input-0');
input.onmidimessage = logMidiMessage;

Now when I hit a drum, I see MIDI messages – and likewise when I make a change on the module (e.g. switching kit) that gets reported as well – so I know that SysEx messages are working.

Test 4: request the name of kit 1

Timestamp: 07:44

At this point, I need to go back to the V-Drum Explorer code and the TD-27 docs. The kit name is in the first 12 bytes of the KitCommon container, which is at the start of each Kit container. The Kit container for kit 1 starts at 0x04_00_00_00, so I just need to create a Data Request message for the 12 bytes starting at that address. I can do that just by hijacking a command in my console app, and getting it to print out the MIDI message. I need to send these bytes:

F0 41 10 00 00 00 63 11 04 00 00 00 00 00 00 0C 70 F7

That should be easy enough, adapting example 9.5 of the Web MIDI docs…

(Note of annoyance at this point: forking in JSFiddle doesn’t seem to be working properly for me. I get a new ID, but I can’t change the title in a way that shows up in “Your fiddles” properly. Ah – it looks like I need to do “fork, change title, set as base”. Not ideal, but it works.)

So I’d expect this code to work:

var output = midiAccess.outputs.get('output-1');
var requestMessage = [0xf0, 0x41, 0x10, 0x00, 0x00, 0x00, 0x63, 0x11, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0c, 0x70, 0xf7];

But I don’t see any sign that the kit has sent back a response – and worse, if I add console.log("After send"); to the script, that doesn’t get logged either. Maybe it’s throwing an exception?

Aha – yes, there’s an exception:

Failed to execute ‘send’ on ‘MIDIOutput’: System exclusive message is not allowed at index 0 (240).

Ah, my requestMIDIAccess call wasn’t specifically requesting SysEx access. It’s interesting that it was able to receive SysEx messages even though it couldn’t send them.

After changing the call to pass { sysex: true }, I get back a MIDI message which looks like it probably contains the kit name. Hooray! Step 1 done :)

Timestamp: 08:08 (So all of this took an hour. That’s not too bad.)

Step 2: Vanilla Blazor project

Okay, within the existing VDrumExplorer solution, add a new project.

Find the Blazor project template, choose WebAssembly… and get interested by the “ASP.NET Core Hosted” option. I may want that eventually, but let’s not bother for now. (Side-thought: for the not-hosted version, I may be able to try it just by hosting the files in Google Cloud Storage. Hmmm.)

Let’s try to build and run… oh, it failed:

The "ResolveBlazorRuntimeDependencies" task failed unexpectedly.
error MSB4018: System.IO.FileNotFoundException: Could not load file or assembly 'VDrumExplorer.Blazor.dll' or one of its dependencies. The system cannot find the file specified.

That’s surprising. It’s also surprising that it looks like it’s got ASP.NET Core, given that I didn’t tick the box.

There’s a Visual Studio update available… maybe that will help? Upgrading from 16.6.1 to 16.6.3…

For good measure, let’s blow away the new project in case the project template has changed in 16.6.3.

Time to make a coffee…

Try again with the new version… nope, still failing in the same way.

I wonder whether I’ve pinned the .NET Core SDK to an older version and that’s causing a problem?

Ah, yes – there’s a global.json file in Drums, and that specifies 3.1.100.

Aha! Just updating that to use 3.1.301 works. A bit of time wasted, but not too bad.

Running the app now works, including hitting a breakpoint. Time to move onto MIDI stuff.

Timestamp: 08:33

Step 3: Listing MIDI ports in Blazor

Substep 1: create a new page

Let’s create a new Razor page. I’d have thought that would be “Add -> New Item -> Razor Page” but that comes up with a .cshtml file instead of the .razor file that everything else is.

Maybe despite being in a “Pages” directory with a .razor extension, these aren’t Razor Pages but Razor Component? Looks like it.

I’m feeling I could get out of my depth really rapidly here. If I were doing this “properly” I’d now read a bunch of docs on Razor. (I’ve been to various talks on it, and used it before, but I haven’t done either for quite a while.)

The “read up on the fundamentals first” and “hack, copy, paste, experiment” approaches to learning a new technology both have their place… I just generally feel a little less comfortable with the latter. It definitely gets to some results quicker, but doesn’t provide a good foundation for doing real work.

Still, I’m firmly in experimentation territory here, so hack on.

The new page has an “initialize MIDI” button, and two labels for input ports and output ports.

Add this to the nav menu, run it, and all seems well. (Eventually I may want to make this the default landing page, but that can come later.)

Time to dive into JS interop…

Substep 2: initialize MIDI

Let’s not rush to listing the ports – just initializing MIDI at all would be good. So add a status field and label, and start looking up JS interop.

I’ve heard of Blazor University before, so that’s probably a good starting point. And yes, there’s a section about JavaScript interop. It’s worryingly far down the TOC (i.e. I’m skipping an awful lot of other information to get that far) but we’ll plough on.

Calling the requestMIDIAccess function from InitializeMidi is relatively straightforward, with one caveat: I don’t know how to express the result type. I know it’s a JavaScript promise, but how do refer to that within the C# code? Let’s just use object to start with:

private async Task InitializeMidi()
    var promise = await JSRuntime.InvokeAsync<object>("navigator.requestMIDIAccess", TimeSpan.FromSeconds(3));

Looking more carefully at some docuemntation, it doesn’t look like I can effectively keep a reference to a JavaScript object within the C# code – everything is basically JSON serialized/deserialized across the boundary.

That’s fairly reasonable – but it means we’ll need to write more JavaScript code, I suspect.


  • Write a bunch of JavaScript code in the Razor page. (Yes, I’d want to move it if I were doing this properly…)
  • Keep a global midi variable to keep “the initialized MIDI access”
  • Declare JavaScript functions for everything I need to do with MIDI, that basically proxy through the midi variable

I’d really hoped to avoid writing any JavaScript while running Blazor, but never mind.

Plan fails on first step: we’re not meant to write scripts within Razor pages. Okay, let’s create a midi.js script and include that in index.html.

Unfortunately, the asynchrony turns out to be tricky. We really want to be able to pass a callback to the JavaScript code, but that involves creating a DotNetObjectReference and managing lifetimes. That’s slightly annoying and fiddly.

I’ll come back to that eventually, but for now I can just keep all the state in JavaScript, and ask for the status after waiting for a few seconds:

private async Task InitializeMidi()
    await JSRuntime.InvokeAsync<object>("initializeMidi", TimeSpan.FromSeconds(3));
    await Task.Delay(3000);
    status = await JSRuntime.InvokeAsync<string>("getMidiStatus");

Result: yes, I can see that MIDI has been initialized. The C# code can fetch the status from the JavaScript.

That’s all the time I have for now – I have a meeting at 9:30. When I come back, I’ll look at making the JavaScript a bit cleaner, and writing a callback.

Timestamp: 09:25

Substep 3: use callbacks and a better library pattern

Timestamp: 10:55

Back again.

Currently my midi.js file just introduces functions into the global namespace. Let’s follow the W3C JavaScript best practices page guidance instead:

var midi = function() {
    var access = null;
    var status = "Uninitialized";

    function initialize() {
        success = function (midiAccess) {
            access = midiAccess;
            status = "Initialized";
        failure = (message) => status = "Failed: " + message;
        navigator.requestMIDIAccess({ sysex: true })
            .then(success, failure);

    function getStatus() {
        return status;

    return {
        initialize: initialize,
        getStatus: getStatus

Is that actually any good? I really don’t know – but it’s at least good enough for now.

Next, let’s work out how to do a callback. Ideally, we’d be able to return something from the JavaScript initialize() method and await that. There’s an interesting blog post about doing just that, but it’s really long. (That’s not a criticism – it’s a great post that explains everything really well. It’s just it’s very involved.)

I suspect that a bit of hackery will allow a “simpler but less elegant” solution, which is fine by me. Let’s create a PromiseHandler class with a proxy object for JavaScript:

using Microsoft.JSInterop;
using System;
using System.Threading.Tasks;

namespace VDrumExplorer.Blazor
    public class PromiseHandler : IDisposable
        public DotNetObjectReference<PromiseHandler> Proxy { get; }
        private readonly TaskCompletionSource<int> tcs;

        public PromiseHandler()
            Proxy = DotNetObjectReference.Create(this);
            tcs = new TaskCompletionSource<int>();

        public void Success() =>

        public void Failure(string message) =>
            tcs.TrySetException(new Exception(message));

        public Task Task => tcs.Task;

        public void Dispose() => Proxy.Dispose();

We can then create an instance of that in InitializeMidi, and pass the proxy to the JavaScript:

private async Task InitializeMidi()
    var handler = new PromiseHandler();
    await JSRuntime.InvokeAsync<object>("midi.initialize", TimeSpan.FromSeconds(3), handler.Proxy);
        await handler.Task;
        status = "Initialized";
    catch (Exception e)
        status = $"Initialization failed: {e.Message}";

The JavaScript then uses the proxy object for its promise handling:

function initialize(handler) {
    success = function (midiAccess) {
        access = midiAccess;
    failure = message => handler.invokeMethodAsync("Failure", message);
    navigator.requestMIDIAccess({ sysex: true })
        .then(success, failure);

It’s all quite explicit, but it seems to do the job, at least for now, and didn’t take too long to get working.

Timestamp: 11:26

Substep 4: listing MIDI ports

Listing ports doesn’t involve promises, but it does involve an iterator, and I’m dubious that I’ll be able to return that directly. Let’s create an array in JavaScript and copy ports into it:

function getInputPorts() {
    var ret = [];
    access.inputs.forEach(input => ret.push({ id:, name: }));
    return ret;

(I initially tried just pushing input into the array, but that way I didn’t end up with any data – it’s not clear to me what JSON was returned across the JS/.NET boundary, but it didn’t match what I expected.)

In .NET I then just need to declare a class to receive the data:

public class MidiPort
    public string Id { get; set; }

    public string Name { get; set; }

And I can get the input ports, and display them via a field that’s hooked up in the Razor page:

var inputs = await JSRuntime.InvokeAsync<List<MidiPort>>("midi.getInputPorts", Timeout);
inputDevices = string.Join(", ", inputs.Select(input => $"{input.Id} ({input.Name})"));


Listing ports in Blazor

Timestamp: 11:46 (That was surprisingly quick.)

Step 4: Retrieve the “kit 1” name in Blazor

We need two extra bits of MIDI functionality: sending and receiving data. I’m hoping that exchanging byte arrays via Blazor will be straightforward, so this should just be a matter of creating a callback and adding functions to the JavaScript to send messages and add a callback when a message is received.

Timestamp: 12:16

Okay, well it turned out that exchanging byte arrays wasn’t quite as simple as I’d hoped: I needed to base64-encode on the JS side, otherwise it was transmitted as a JSON object. Discovering that went via creating a MidiMessage class, which I might as well keep around now that I’ve got it. I can now receive messages.

Timestamp: 12:21

Blazor’s state change detection doesn’t include calls to List.Add, which is reasonable. It’s a shame it doesn’t spot ObservableCollection.Add either, though. We can fix this just by calling StateHasChanged though.

I now have a UI that can display messages. The three bits involved (as well as the simple MidiMessage class) are a callback class that delegates to an action:

public class MidiMessageHandler : IDisposable
    public DotNetObjectReference<MidiMessageHandler> Proxy { get; }
    private readonly Action<MidiMessage> handler;

    public MidiMessageHandler(Action<MidiMessage> handler)
        Proxy = DotNetObjectReference.Create(this);
        this.handler = handler;

    public void OnMessageReceived(MidiMessage message) => handler(message);

    public void Dispose() => Proxy.Dispose();

The JavaScript to use that:

function addMessageHandler(portId, handler) {
    access.inputs.get(portId).onmidimessage = function (message) {
        // We need to base64-encode the data explicitly, so let's create a new object.
        var jsonMessage = { data: window.btoa(, timestamp: message.timestamp };
        handler.invokeMethodAsync("OnMessageReceived", jsonMessage);

And then the C# code to receive the callback, and subscribe to it:

// In InitializeMidi()
var messageHandler = new MidiMessageHandler(MessageReceived);
await JSRuntime.InvokeVoidAsync("midi.addMessageHandler", Timeout, inputs[0].Id, messageHandler.Proxy);

// Separate method for the callback - we could have used a local
// method or lambda though.
private void MessageReceived(MidiMessage message)
    // Blazor doesn't "know" that the collection has changed - even if we make it an ObservableCollection

Timestamp: 12:26

Now let’s try sending the SysEx message to request kit 1’s name… this should be the easy bit!

… except it doesn’t work. The log shows the following error:

Unhandled exception rendering component: Failed to execute ‘send’ on ‘MIDIOutput’: No function was found that matched the signature provided.

Maybe this is another base64-encoding issue. Let’s try explicitly base64-decoding the data in JavaScript…

Nope, same error. Let’s try hard-coding the data we want to send, using JavaScript that has worked before…

That does work, which suggests my window.atob() call isn’t behaving as expected.

Now I could use some logging here, but let’s try putting a breakpoint in JavaScript. I haven’t done that before. Hopefully it’ll open in the Chrome console.

Whoa! The breakpoint worked, but in Visual Studio instead. That’s amazing! I can see that atob(data) has returned a string, not an array.

This Stack Overflow question has a potential option. This is really horrible, but if it works, it works…

And it works. Well, sort of. The MIDI message I get back is much longer than I’d expected, and it’s longer than I get in JSFiddle. Maybe my callback wasn’t working properly before.

Timestamp 12:42

Okay, so btoa() isn’t what I want either. This Stack Overflow question goes into details, but the accepted answer uses a ton of code.

Hmmm… right-clicking on “wwwroot” gives me an option of “Add… Client-Side Library”. Let’s give that a go and see if it make both sides of the base64 problem simpler.

Timestamp: 12:59

Well it didn’t “just work”. The library was added to my wwwroot directory, and trying to use it from midi.js added an import statement at the start of midi.js… which then caused an error of:

Cannot use import statement outside a module

I guess I really need to know what a JavaScript module is, and whether midi.js should be one. Hmm. Time for lunch.

Saturday afternoon

Timestamp: 14:41

Back from lunch and a chat with my parents. Let’s have another look at this base64 library…

(Side note: Visual Studio, while I’m not doing anything at all and I don’t have any documents open, is taking up 80% of my CPU. That doesn’t seem right. Oh well.)

If I just try to import the byte-base64 script directly with a script tag then I end up with an error of:

Uncaught ReferenceError: exports is not defined

Bizarrely enough, the error message often refers to lib.ts, even if I’ve made sure there’s no Typescript library in wwwroot.

Okay, I’ve now got it to work, by the horrible hack of copying the file to base64.js in wwwroot, removing and removing everything about exports. I may investigate other libraries at some point, but fundamentally this inabilty to correctly base64 encode/decode has been the single most time-consuming and frustrating part so far. Sigh.

(Also, the result is something I’m not happy to put on GitHub, as it involves just a copy of the library file rather than using it as intended.)

Timestamp: 15:01

Step 5: Retrieve all kit names in Blazor

Okay, so I’ve got the not-at-all decoded kit name successfully.

Let’s try looping to get all of them, decoding as we go.

This will involve copying some of the “real” V-Drum Explorer code so I can create Data Request messages programmatically, and decode Data Set messages. While I’d love to just add a reference to VDrumExplorer.Midi, I’m definitely not there yet. (I’d need to remove the commons-midi references and replace everything I use. That’s going to be step 6, maybe…)

Timestamp: 15:41

Success! After copying quite a bit of code, everything just worked… nothing was particularly unexpected at this stage, which is deeply encouraging.

Listing TD-27 kits in Blazor

I’m going to leave it there for the day, but tomorrow I can try to change the abstraction used by V-Drum Explorer so that it can all integrate nicely…

Saturday evening

Timestamp: 17:55

Interlude: refactoring MIDI access

Okay, so it turns out I really don’t want to wiat until tomorrow. However, the next step is going to be code I genuinely want to keep, so let’s commit everything I’ve done so far to a new branch, but then go back to the branch I was on.

The aim of this step is to make the MIDI access replaceable. It doesn’t need to be “hot-replaceable” – at least not yet – so I don’t mind using a static property for “the current MIDI implementation”. I make make it more DI-friendly later on.

The two projects I’m going to change are VDrumExplorer.Model, and VDrumExplorer.Midi. Model refers to Midi at the moment, and Midi refers to the managed-midi library. The plan is to move most of the code from Midi to Model, but without any reference to managed-midi types. I’ll define a few interfaces (e.g. IMidiInput, IMidiOutput, IMidiManager) and write all the rest of the MIDI-related code to refer to those interfaces. I can then ditch VDrumExplorer.Midi, but add VDrumExplorer.Midi.ManagedMidi which will implement my Model interfaces in terms of the managed-midi library – with the hope that tomorrow I can have a Blazor implementation of the same libraries.

I have confidence that this will work reasonably well, as I’ve done the same thing for audio recording/playback devices (with an NAudio implementation project).

Let’s go for it.

Timestamp: 18:03

Okay, that went pretty much as planned. I was actually able to simplify the code a bit, which is nice. There’s potentially more refactoring to do, now that ModuleAddress, DataSegment and RolandMidiClient are in the same project – I can make RolandMidiClient.RequestDataAsync accept a ModuleAddress and return a DataSegment. That can come later though.

(Admittedly testing this found that kit 1 has an invalid value for one instrument. I’ll need to look into that later, but I don’t think it’s a new issue.)

Timestamp: 18:55

The Blazor MIDI interface implementation can wait until tomorrow – but I don’t anticipate it being tricky at all.

Sunday morning

Timestamp: 06:54

Okay, let’s do this :) My plan is:

  • Remove all the code that I copied from the rest of V-Drum Explorer into the Blazor project; we shouldn’t need that now.
  • Add a reference from the Blazor project to VDrumExplorer.Model
  • Implement the MIDI interfaces
  • Rework the code just enough to get the previous functionality working again
  • Rewrite the code to not have any hard-coded module addresses, instead detecting the right schema and listing the kits for any attached (and supported) module, not just the TD-27
  • Maybe publish it

Removing the code and adding the project reference are both trivial, of course. At that point, the code doesn’t compile, but I have a choice: I could get the code compiling again using the MIDI interfaces, but without implementing the interfaces, or I could implement the interface first.

Rewriting existing application code

Despite the order listed above, I’m going to rewrite the application part first, because that will clear the error list, making it easier to spot any mistakes while I am implementing the interface. The downside is that there’ll be bits of code I need to stash somewhere, because they’ll be part of the MIDI implementation eventually, but without wanting to get them right just yet.

I create a WebMidi folder for the implementation, and a scratchpad.txt file in to copy any “not required right now” code.

At this point I’m getting really annoyed with the syntax highlighting of the .razor file. I know it’s petty, but the grey background just for code is really ugly to me:

Ugly colours in Blazor

As I’m going to have to go through all the code anyway, let’s actually use “Add New Razor Page” this time, and move the code into there as I fix it up.

Two minutes later, it looks like what VS provides (at least with that option) isn’t quite what I want. What I really want is a partial class, not a code-behind for the model. It’s entirely possible that they’d be equivalent in this case, but the partial class is closer to what I have right now. This blog post tells me exactly what I need.

Timestamp: 07:10

Starting to actually perform the migration, I realise I need an ILogger. For the minute, I’ll use a NullLogger, but later I’ll want to implement a logger that adds to the page. (I already have a Log method, so this should be simple.)

Timestamp: 07:19

That was quicker than I’d expected. Of course, I don’t know whether or not it works.

Implementing the MIDI interfaces

Creating the WebMidiManager, WebMidiInput and WebMidiOutput classes shows me just how little I really need to do – and it’s all code I’ve written before, of course.

For the moment, I’m not going to worry about closing the MIDI connection on IMidiInput.Dispose() etc – we’ll just leave everything open once it’s opened. What I will do is use a single .NET-side event handler for each input port, and do event subscribe/remove handling on the .NET side. If I don’t manage that, the underlying V-Drum Explorer interface will end up getting callbacks on client instances after disposal, and other oddities. The outputs can just be reused though – they’re stateless, effectively.

Timestamp: 07:56

Okay, so that wasn’t too bad. No significant surprises, although there’s one bit of slight ugliness: my IMidiOutput.Send(MidiMessage) method is synchronous, but we’re calling into JavaScript interop which is always asynchronous. As it happens, that’s mostly okay: the Send message is meant to be effectively fire-and-forget anyway, but it does mean that if the call fails, we won’t spot it.

Let’s see if it actually works

Nope, not yet – initialization fails:

Cannot read property ‘inputs’ of null

Oddly, a second click of the button does initialize MIDI (although it doesn’t list the kits yet). So maybe there’s a timing thing going on here. Ah yes – I’d forgotten that for initialization, I’ve got to await the initial “start the promise” call, then await the promise handler. That’s easy enough.

Okay, so that’s fixed, but we’re still not listing the kits. While I can step through in the debugger (into the Model code), it would really help if I’d got a log implementation at this point. Let’s do that quickly.

Timestamp: 08:07

Great – I now get a nice log of how device detection is going:

  • Input device: ‘5- TD-27’
  • Output device: ‘5- TD-27’
  • Detecting devices for MIDI ports with name ‘5- TD-27’
  • No devices detected for MIDI port ‘5- TD-27’. Skipping.
  • No known modules detected. Aborting

So it looks like we’re not receiving a response to our “what devices are on this port” request.

Nothing’s obviously wrong with the code via a quick inspection – let’s add some console logging in the JavaScript side to get a clearer picture.

Hmm: “Sending message to port [object Object]” doesn’t sound promising. That should be a port ID. Ah yes, simple mistake in WebMidiOutput. This line:

runtime.InvokeVoidAsync("midi.sendMessage", runtime, message.Data);

should be

runtime.InvokeVoidAsync("midi.sendMessage", port, message.Data);

It’s amazing how often my code goes wrong as soon as I can’t lean on static typing…

Fix that, and boom, it works!

Generalizing the application code

Timestamp: 08:16

So now I can list the TD-27 kits, but it won’t list anything if I’ve got my TD-17 connected instead… and I’ve got fairly nasty code computing the module addresses to fetch. Let’s see how much easier I can make this now that I’ve got the full power of the Model project to play with…

Timestamp: 08:21

It turns out it’s really easy – but very inefficient. I don’t have any public information in the schema about which field container stores the kit name. I can load all the data for one kit at a time, and retrieve the formatted kit name for that loaded data, but that involves loading way more information than I really need.

So that’s not ideal – but it worked first time. First I listed the kits on my TD-27, and that worked as before. Turn that off and turn on the TD-17, rerun, and boom:

Listing TD-17 kits in Blazor

It even worked with my Aerophone, which I only received last week. (They’re mostly “InitTone” as the Aerophone splits user kits from preset kits, and the user kits aren’t populated to start with. The name is repeated as there’s no “kit subname” on the Aerophone, and I haven’t yet changed the code to handle that. But hey, it works…)

Listing Aerophone tones in Blazor

That’s enough for this morning, certainly. I hadn’t honestly expected the integration to go this quickly.

This afternoon I’ll investigate hosting options, and try to put the code up for others to test…

Timestamp: 08:54

After just tidying up this blog post a bit, I’ve decided I definitely want to include the code on GitHub, and publish the result online. That will mean working out what to do with the base64 library (which is at least MIT-licensed, so that shouldn’t be too bad) but this will be a fabulous thing to show in the talks I give about V-Drum Explorer. And everyone can laugh at my JavaScript, of course.

Sunday afternoon

Publishing as a web site

Timestamp: 13:12

Running dotnet publish -c Release in the Blazor directory creates output that looks like I should be able to serve it statically, which is what I’d hoped having unchecked the “ASP.NET Core Hosting” box on project creation.

One simple way of serving static content is to use Google Cloud Storage, uploading all the files to a bucket and then configuring the bucket appropriately. Let’s give it a go.

The plan is to basically follow the tutorial, but once I’ve got a simple index.html file working, upload the Blazor application. I already have HTTPS load balancing with Google Cloud, and the domain is hosted in Google Domains, so it should all be straightforward.

I won’t take you through all the steps I went through, because the tutorial does a good job of that – but the sample page is up and working, served over HTTPS with a new Google-managed SSL certificate.

Timestamp: 13:37

Time to upload the Blazor app. It’s not in a brilliant state at the moment – once this step is done I’ll want to get rid of the “counter” sample etc, but that can come later. I’m somewhat-expecting to have to edit MIME types as well, but we’ll see.

In the Google Cloud Storage browser, let’s just upload all the files – yup, it works. Admittedly it’s slightly irritating that I had to upload each of the directories separately – just uploading wwwroot would create a new wwwroot directory. I expect that using gsutil from the command line will make this easier in the future.

But then… it just worked!

Timestamp: 13:51 (the previous step only took a few minutes at the computer, but I was also chasing our cats away from the frogs they were hunting in the garden)

Tidying up the Blazor app

The point of the site is really just a single page. We don’t need the navbar etc.

Timestamp: 14:12

Okay, that looks a lot better :)

Speeding up kit name access

If folks are going to be using this though, I really want to speed up the kit loading. Let’s see how hard it is to do that – it should all be in Model code.

Timestamp: 14:20

Done! 8 minutes to implement the new functionality. (A bit less, actually, due to typing up what I was going to do.)

The point of noting that isn’t to brag – it’s to emphasize that having performed the integration with the main Model code (which I’m much more comfortable in) I can develop really quickly. Doing the same thing in either JavaScript or in the Blazor code would have been much less pleasant.


Let’s try that gsutil command I was mentioning earlier:

  • Delete everything in the Storage bucket
  • Delete the previous release build
  • Publish again with dotnet publish -c Release
  • cd bin/Release/netstandard2.1/publish
  • gsutil -m cp -r . gs://vdrumexplorer-web

The last command explained a bit more:
gustil: invoke the gsutil tool
-m: perform operations in parallel
cp: copy
-r: recursively
.: source directory
gs://vdrumexplorer-web: target bucket

Hooray – that’s much simpler than doing it through the web interface (useful as that is, in general).

Load balancer updating

My load balancer keeps on losing the configuration for the backend bucket and certificate. I strongly suspect that’s because it was created in Kubernetes engine. What I should actually do is update the k8s configuraiton and then let that flow.

Ah, it turns out that the k8s ingress doesn’t currently support a Storage Bucket backend, so I had to create a new load balancer. (While I could have served over HTTP without a load balancer, in 2020 anything without HTTPS support feels pretty ropy.)

Of course, load balancers cost money – I may not keep this up forever, just for the sake of a single demo app. But I’m sure I can afford it for a while, and it could be useful for other static sites too.

The other option is to serve the application from my k8s cluster – easy enough to do, just a matter of adding a service.


Okay, I’m done. This has been an amazing weekend – I’m thrilled with where I ended up. If you’ve got a suitable Roland instrument, you can try it for yourself at

The code isn’t on GitHub just yet, but I expect it to be within a week (in the normal place).

(Edited) I was initially slightly disappointed that it didn’t seem to work on my phone. I’m sure what happened when I tried innitially (and I don’t know why it’s still claiming the connection is insecure), but I’ve now managed to get the site working on my phone, connecting over Bluetooth to my TD-27. Running .NET code talking to Javascript talking MIDI over Bluetooth to list the contents of my drum module… it really just feels like it shouldn’t work. But it does.

The most annoying aspect of all of this was definitely the base64 issue… firstly that JavaScript doesn’t come with a reliable base64 implementation (for the situation I’m in, anyway) and secondly that adding a client library was rather more fraught than I’d have expected. I’m sure it’s all doable, but beyond my level of expertise.

Overall, I’ve been very impressed with Blazor, and I’ll definitely resurrect the Noda Time Blazor app for time zone conversions that I was working on a while ago.

V-Drum Explorer: Planning notes for MVVM

My current clunky “put all the code in the view” approach to V-Drum Explorer is creaking at the seams. I’m really not a WPF developer, and my understanding of MVVM is more theoretical than practical. I’ve read a reasonable amount, but quite a lot of aspects of V-Drum Explorer don’t really fit with the patterns described.

Eventually I’d like to present blog posts with a nice clean solution, and details of how it avoids all the current problems – but I’m not there yet, and pretending that good designs just drop fully formed onto the keyboard doesn’t feel healthy. So this blog post is a pretty raw copy/paste of the notes I’ve made around what I think I’ll do.

There’s no conclusion here, because life isn’t that neatly defined. I do hope I find time to tackle this reasonably soon – it’s going to be fun, but I’m not sure it’s going to be feasible to refactor in small steps.


The current design has the following issues:

  • A lot of the UI controls are created within the code-behind for the view, so styling is hard
  • The logic handling “how the UI reacts to changes” is really tricky, due to chain reactions:
  • Changing a tempo sync value changes which field is displayed next to it
  • Selecting a MultiFX option changes all the fields in the overlay
  • Selecting an instrument group changes which instruments are selected, and the vedit parameters available
  • Selecting an instrument can change the vedit parameters (e.g. cymbal size)
  • The UI currently “knows” about data segments, addresses etc – it shouldn’t need to care
  • The way that the schema is constructed makes the address logic bleed out; we can populate all the “fixed” containers and only generate fields for overlay containers when necessary
  • Using inheritance for the commonality between ModuleExplorer and KitExplorer is a bit weird

Ideas and questions that might end up being part of the answer

  • My schema has a “physical layout” and a “logical layout” – for example (in the TD-27), each kit has 24x KitPadCommon, 24x KitPadMain, 24x KitPadSub, 24x KitPadMainVEdit, 24xKitPadSubVEdit. It makes more sense to show “24x instrument info”. Is that information part of the model or the view-model?
    • I suspect it’s part of the model, effectively.
    • Perhaps the ViewModel shouldn’t even see the physical layout at all?
    • The logical layout is worryingly “tree view + details pane”-centric though
  • We have “snapshotting” in two ways when editing:
    • Overall commit/cancel
    • Remembering values for each multi-fx / vedit overlay while editing, so you can tweak, change to a different overlay accidentally, then change back to the original one and still have the tweaked values.
    • Should this logic be in the ViewModel or the Model?
  • Should the model implement INotifyPropertyChanged (et al)?
    • Looks like there’s genuine disagreement between practitioners on this
    • Feels like a pretty stark choice: either ViewModel controls everything, including how overlays work (i.e. when changing instrument, change the overlay too) or the model needs to tell the ViewModel when things are changing.
  • Where do we keep the actual data? Still in a ModuleData?
    • We could generate a model (e.g. with Kit, KitPadInst etc being full types)
    • We’d then either need to generate all the corresponding ViewModels, or access everything via reflection, which defeats half the point
    • Would definitely be easier to debug using a model
    • Generators are a lot of work…
  • Possibly reify “schema + data” in the model, to avoid having to pass the data in all over the place (hard to do binding on properties without this…)
    • Reify overlays in just-in-time fashion, to avoid creating vast numbers of fields.


  • Broadly the same UI we have now. At least the same features.
  • No code in the View – eventually. Not clear what creates a new window when we load a file etc, but we can try to remove as much as possible to start with and chip away at the rest.
  • ViewModel shouldn’t need to touch ModuleAddress. Access is view ModuleSchema, containers, ModuleData.
  • 7-bit addressing should be isolated even within the model, ideally to just ModuleAddress.
  • ViewModel interaction with fields should be simple.
  • The command line app should be able to work with the model easily – and may require lower-level access than the UI.

V-Drum Explorer: Memory and 7-bit addressing

So, just to recap, I’m writing an explorer for my Roland V-Drums set (currently a TD-17, but with a TD-27 upgrade on the way, excitingly). This involves copying configuration data from the module (the main bit of electronics involved) into the application, displaying with it, editing it, then copying it back again so that I can use the changes I’ve made. I use MIDI System Exclusive (SysEx) messages to request data from the module.

(Since I last wrote about all of this, MIDI 2.0 has been ratified, which has more sensible 2-way communication. However, I don’t think the V-Drums line supports MIDI 2.0 yet, and even if it does I expect we’ll need to wait a while for drivers, then managed APIs exposing them.)

In fact, most of the time that I’m working on the V-Drum Explorer I don’t have it connected to the drum kit: it’s much easier (and quicker) to load the data from a file. Once it’s in memory, it really doesn’t matter where the data came from. I’ll go into the file formats I’m using in another post.

This post is about how that configuration data is organized, and particularly about the 7-bit addressing it uses.

Download the docs!

If you’d like to know about all of this in more detail, it’s well worth downloading some of the reference documentation Roland very helpfully provides. The TD-17 is the simplest of the modules we’re talking about, so I’d suggest downloading the TD-17 MIDI implementation so you can go at least one level deeper than this blog post, if you’re interested. If you think you’re likely to want to do that, I’d suggest doing so before reading any further. The important bit starts on page 5 – the “Parameter Address Map” which is the bulk of the document.

Configuration as memory

The configuration data in the module isn’t stored in any kind of file system, or with separate SysEx messages for different kinds of data. Instead, it’s modeled as if the module contains a big chunk of memory, and different areas of that memory have different effects on the module. I don’t know what the implementation is like within the module itself, of course; this is just the interface presented over MIDI.

As the simplest possible example, address 0 in the memory (on all three of the modules I have documentation for) represents “the currently selected kit”. It accepts values between 0 and 99 inclusive, to represent kits 1 to 100 inclusive. (As a reminder, a kit is a configuration of all the pads, allowing you to switch the whole module between (say) a rock feel or something more electro-funky.) So as an example, if my module is currently on kit 11 (“Studio / Live room”), and I asked the module to give me the content of address 0, it would return 10. If instead I set the value of address 0 to 30, the module would display kit 31 (“More cowbell / pop”) and all the sounds would change accordingly.

The documentation describes a number of containers – that’s my own term for it, but it seems reasonable. Each container is named, and has its own description in terms of its content at different offsets. For example, address 0 belongs in the [Current] container, which is documented very simply:

| Offset Address | Description                        |
|          00 00 | 0aaa aaaa | Drum Kit Number (0-99) |
|                |                             1-100  |
| 00 00 00 01    | Total Size                         |

The 0aaa aaaa shows that 7 bits of the value are used. Due to MIDI’s inherent 7-bit nature, each address can only store 7 bits. Whenever a larger number is required, it’s stored across multiple addresses, typically using only the bottom four bits of each 7 bit value.

The content of each container is broadly broken into three types of data – again, all the terminology is mine:

  • Primitive fields: strings, numbers etc
  • Fields which are other containers (often repeated, e.g. Kit 1 to Kit 100)
  • Overlaid containers (fields directly in this container, interpreted according to a different container)

I’ll talk about overlaid containers at length another time, as they’re tricky.

So basically you end up with a natural tree structure. So far, so good… except for 7-bit addressing.

7-bit addressing

I entirely understand why the values in memory are 7-bit values. That’s inherent in MIDI. But Roland also chose to use a 7-bit address space, which makes the code much more complex than it needs to be.

All addresses and offsets are documented using hex as if it were entirely normal – but the top bit of every byte of an address is always clear. So address 00 7F is followed directly by address 01 00 – even if they’re within the same container. Now this does mean that the values in the MIDI request messages are exactly the documented addresses: the top bit of each byte in the request message has to be clear, and that drops out naturally from this. But it makes everything else hard to reason about. I’ve been bitten multiple times by code which looks like it should be okay, but it’s either skipping some data when it shouldn’t, or it’s not skipping addresses when it should. By contrast, it would have been really simple (IMO) to document everything with a contiguous address space, and just specify that when requesting data, the address is specified in seven-bit chunks (so bits 27-21 in the first request byte, then 20-14, then 13-7, then 6-0).

I’ve tried to isolate this into a ModuleAddress struct, but the details have still leaked out into a few more places. Over the past few days I’ve tried to be more rigorous about this with a DisplayValue (7-bit) and a separate LogicalValue (contiguous), but it’s still leaking more than I want it to. I don’t think I can fix it without a more serious rewrite – which I probably want to attempt reasonably soon anyway.

You might wonder why I don’t just model everything using the logical contiguous address space, removing all the gaps entirely. The problem is that all the schema information is basically copied from the documentation – and that refers to the 7-bit addressing scheme. I really want the schema to match the documentation, so I can’t move away from that entirely. Another thing that makes it tricky is that a lot of the time I deal in offsets rather than addresses. For example, the “Kit Unit Common 1” part of a “Kit” container is always at offset 00 20 00 relative to the start of the container. That’s not too bad on its own, but I also need to express the “gap between offsets” which is a sort of offset in its own right (maybe). For example, “Kit Unit Common 2” is at offset 00 21 00 within a kit, so in the schema when I describe the “Kit Unit Common” repeated field, I describe it as having an initial offset of 00 20 00, with a gap of 00 01 00. That sounds fine – until you’ve got a repeated field which is large enough to have a gap in the middle, so you need to model that by making the offset have a gap as well. (I’m reminded of calendar arithmetic, which has similar weirdnesses.)

The lesson I’ve learned from this is that when there’s hairiness like this, it’s worth abstracting it away really thoroughly. I wish I’d stopped at the first abstraction leak and thought, “maybe I need to redesign rather than live with this”.


Even without 7-bit addressing, there would have been plenty of challenging choices in the design of the V-Drum Explorer, particularly in field and container representation. More details of those choices will come in future posts – but at least they feel inherently tricky… the kind of thing software engineers are expected to have to think about.

7-bit addressing feels like it was a choice made to make one small use case (MIDI request/response messages) simple, but made everything else trickier. I’d be fascinated to know the module code is a lot more complicated because of this as well, or whether so much is effectively hard-coded (because it needs to actually do stuff rather than just display data on a screen) that it doesn’t make much difference.

Next time: using data vs code to represent differences between modules.

New and improved JonSkeet.DemoUtil

It’s amazing how sometimes small changes can make you very happy.

This week I was looking at how DragonFruit does its entry point magic, and realized I had a great use case for the same kind of thing.

Some of my oldest code that’s still in regular use is ApplicationChooser – a simple tool for demos at conferences and user groups. Basically it allows you to write multiple classes with Main methods in a single project, and when you run it, it allows you to choose which one you actually want to run.

Until today, as well as installing the NuGet package, you had to create a Program.cs that calling ApplicationChooser.Run directly, and then explicitly set that as the entry point. But no more! That can all be done via build-time targets, so now it’s very simple, and there’s no extraneous code to explain away. Here’s a quick walkthrough for anyone who would like to adopt it for their own demos.

Create a console project

It’s just a vanilla console app…

$ mkdir FunkyDemo
$ cd FunkyDemo
$ dotnet new console

Add the package, and remove the previous Program.cs

You don’t have to remove Program.cs, but you probably should. Or you could use that as an entry point if you really want.

$ dotnet add package JonSkeet.DemoUtil
$ rm Program.cs

Add demo code

For example, add two files, Demo1.cs and Demo2.cs

// Demo1.cs
using System;

namespace FunkyDemo
    class Demo1
        static void Main() =>
            Console.WriteLine("Simple example without description");

// Demo2.cs
using System;
using System.ComponentModel;
using System.Threading.Tasks;

namespace FunkyDemo
    // Optional description to display in the menu
    [Description("Second demo")]
    class Demo2
        // Async entry points are supported,
        // as well as the original command line args
        static async Task Main(string[] args)
            foreach (var arg in args)
                await Task.Delay(500);


$ dotnet run -- abc def ghi
0: Demo1
1: [Second demo] Demo2

Entry point to run (or hit return to quit)?


That’s all there is to it – it’s simple in scope, implementation and usage. Nothing earth-shattering, for sure – but if you give lots of demos with console applications, as I do, it makes life a lot simpler than having huge numbers of separate projects.

Reducing my international speaking

I’ve been immensely privileged to be invited to speak at various international developer conferences, and until now I’ve usually tried to accept the majority of those invitations. I’ve had a wonderful time, and made many dear friends – who I’ve often then caught up with at other events.

However, I’ve recently found that travelling has become increasingly disruptive for me as a human – mostly in terms of missing my family. Additionally, I’m finding it hard to justify taking so many flights when it comes to the environmental cost of flying.

I still intend to do some international speaking (assuming I’m still invited, of course) and probably more UK-based talks. Additionally, I’m very happy to work with any conferences who’d be interested in me speaking remotely via a live stream. I’m hoping that the future of developer conferences is a mixture of in-person talks (which absolutely still have their place) and remote talks which retain the element of interactivity with attendees. I’m more than happy to get up in the middle of the night to fit in with a schedule, etc.

I’ll be linking to this post if/when I decline invitations on these grounds, partly as a way of demonstrating “It’s not you, it’s me.” If you’re reading this post in that context, please understand that I wish you all the best for your conference, and I’m pretty confident that you’ll be able to find a much more interesting speaker than me anyway :)

V-Drum Explorer: MIDI interface

If this is the first blog post about V-Drum Explorer you’ve read, see the first post in this series for the background. In this post we’ll look at the MIDI interface I use in V-Drum Explorer to send and receive configuration information.

MIDI basics

(Apologies to anyone who really knows their stuff about MIDI – this section is the result of bits of reading and experience working with my drum kit. Please leave corrections in comments!)

MIDI is a protocol for communications between musical instruments, computers, synthesizers and the like. There are many different ways of connecting devices together, including dedicated MIDI cables, USB, TCP/IP and Bluetooth, but applications shouldn’t need to care much about this. They should only need to worry about the messages defined by the protocol.

MIDI is one-directional, in that APIs expose both input ports and output ports which are effectively independent even if they’re connected between the same pair of devices. Messages are sent on output ports and received on input ports.

Most electronic instruments (of all kinds, not just drums) support at least basic MIDI functionality. There are several simple messages with standard representations, including:

  • Channel Voice messages (such as “note on” and “note off”)
  • Channel Mode messages (such as “all sounds off”)
  • System Exclusive messages which are manufacturer-specific

The channel voice and channel mode messages apply to a specific MIDI channel. It’s possible for multiple devices to be daisy-chained together so that they can be controlled over a single port, but using different channels. Each of these messages has a fixed size.

Note: one irritating problem with the protocol is that I haven’t found a way of detecting which channel a particular device is on. This is why channel-specific operations in V-Drum Explorer (such as recording instrument sounds) need a user interface element. If there’s something I’ve missed here, I’d love to hear about it.

Only a few operations in V-Drum Explorer need to simulate or react to the channel messages. Most of the time we’re interested in the system exclusive messages which allow the configuration data to be fetched and set.

System Exclusive Messages

System Exclusive Messages – often abbreviated to SysEx – are manufacturer-specific messages for additional functionality. The size of the data isn’t fixed, but is indicated by a byte of 0xF0 indicating the start of the data, and another byte of 0xF7 indicating the end of the data. Each byte within the data has to have the top bit cleared.

The first byte of data is conventionally the manufacturer ID as assigned by the MIDI Manufacturers Association, which allows a device to ignore messages it wouldn’t properly understand. For example, all Roland SysEx messages have a first byte of 0x41.

Protocol design note: MIDI is a relatively old protocol, dating back to 1983. I’d hope that these days we’d allow more than one byte for a manufacturer ID, and use a length-prefix instead of restricting every data byte to 7 useful bits. Oh well.

SysEx messages are divided into realtime and non-realtime messages. There are also universal SysEx messages which are non-manufacturer-specific, using “fake” manufacturer IDs of 0x7E (for non-realtime) and 0x7F (for realtime).

For the V-Drum Explorer, we’re interested in four SysEx messages:

  • We send Identity Request (universal, non-realtime)
  • We receive Identity Reply (universal, non-realtime)
  • We send Data Request (Roland, non-realtime)
  • We send and receive Data Set (Roland, non-realtime)

The identity request and identity reply messages are used to discover information about the connected devices. V-Drum Explorer uses them to check whether you have any supported devices connected (currently just the TD-17 and TD-50) and present the appropriate schema for the device.

The Data Request and Data Set messages are more interesting from the perspective of V-Drum Explorer: they’re the messages used to communicate the configuration data.

You can think of the configuration data as a bank of memory in the module. (We’ll look at the layout next time.) The Data Request message indicates “Give me X bytes starting at address Y.” The Data Set message indicates “Here are some bytes starting at address X.” Interestingly, Data Set is used both to respond to Data Request and to set new data in the module. When loading data from the device, I send a Data Request and wait for a corresponding Data Set. When copying data to the device, I just send a Data Set message. The device also sends Data Set messages when the configuration data is modified on the module itself (if a particular setting is turned on).

There are a few tricky aspects to this though, all effectively related to the protocol being two independent streams rather than being request/response in the way that HTTP is, for example:

  • Can the code rely on all the data from a single Data Request being returned in a single Data Set? (Answer: no in theory, but in practice if you ask for small enough chunks, it’s fine.)
  • How long should the code wait for after sending an Identity Request until it can assume it’s seen all the Identity Reply messages it’s going to?
  • How long should the code wait for after sending a Data Request until it can assume there’s something wrong if it doesn’t get a reply?
  • How long should the code wait between sending Data Set messages when copying data to the device?
  • What should we do with messages we didn’t initiate?

V-Drum Explorer MIDI code

In the V-Drum Explorer MIDI code, I’ve modeled Identity Request / Identity Reply using an event for “I’ve seen this device”, and I just leave half a second for all devices to respond. For Data Request / Data Set things are a little trickier. For better or worse, I expose an asynchronous API along the lines of

async Task<byte[]> RequestDataAsync(int address, int size)

I keep a collection of “address/size pairs I’m waiting to see data about”, and when I receive a Data Set message I see whether I’m expecting it, I complete the corresponding task, with a buffer of unexpected messages for diagnostic purposes.

The current implementation uses the Sanford.Multimedia.Midi library, which at least assembles multiple packets into SysEx messages for me. I’m trying to move to managed-midi though, as that’s more cross-platform. (In particular, it should make a Xamarin client possible, as well as running a CLI on a Raspberry Pi.) The managed-midi library is quite low-level, so I’ll need to perform the reassembly myself – but that shouldn’t be too hard.

One thing I’m really hoping is that I can reimplement the VDrumExplorer.Midi project with almost no changes to VDrumExplorer.Wpf.

Next time…

In the next post, I’ll go into more detail about the layout of the configuration data, and the annoyance of 7-bit addressing.

V-Drum Explorer: Introduction

This is the first in what I expect to be quite a long series of blog posts, meandering over a fairly wide range of topics as they crop up. There’s nothing particularly technical in this introductory post. It’s really just a starting point.


In July 2019, inspired/encouraged by a friend name Alice, I bought an electronic drum kit. It was a Roland TD-17KV; I now have the Roland TD-17KVX because I’m a sucker for upgrades.

Both of these are kits using the TD-17 as the module. That’s the part of an electronic drum kit that turns electrical signals from the triggers on the pads into sound and/or MIDI messages. The module is sometimes known as the “brain” of the kit. There’s quite a lot of terminology involved in electronic drum kits, and I suspect I’ve barely scratched the surface in the few months since I’ve started.

The TD-17 series is just one option within a suite of products called Roland V-Drums. The TD-17 is currently the most recent part of this suite. It’s a mid-tier product; currently the high-end kit is the TD-50 and the entry level is the TD-1. When I was choosing between the TD-1 and thd TD-17 (with the TD-50 never being an option) I was basically drawn to the greater flexibility of the TD-17 module over the TD-1. I didn’t know how feasible it would be to configure it programmatically, but it at least felt like something I’d have fun investigating.

Configuring a TD-17

In order to understand why I was even considering coding for this, it’s worth having a look at what you can configure on the TD-17 module.

There are a few top-level things you rarely need to configure, such as which triggers you have attached to the module. Most of the configuration happens within a kit – and there are lots of kits. Now this is already slightly confusing because right at the start I talk about buying an “electronic drum kit”. The term is effectively overloaded, unfortunately, but most of the time in this blog series I’ll be using the term “kit” in the sense it’s used within the module.

The TD-17 supports 100 kits. There are 50 presets, and 50 user-defined kits. There’s no real difference between the presets and user-defined kits in terms of what you can do with them – you can think of it as “There are 100 kits available, but Roland got bored after creating 50 of them and left the other 50 in a default configuration.” A single kit is selected at a time, and this controls everything about how the drums sound.

At the top level of a kit, you can configure:

  • Its name and volume
  • The instruments (this is going to be another overloaded term)
  • Its MIDI configuration (which MIDI instruments are triggered)
  • Its ambience (simulations for being in a concert hall, or arena etc)
  • Its MultiFX (sound effects such as reverb)

There are 20 “instruments” to configure – one for the kick pedal, two for most other triggers (snare, toms, crash cymbals, hi-hat, and a general purpose aux), and three for the ride cymbal. There are two instruments for most triggers because you can configure the head and the edge/rim separately – as an extreme example, you could set the crash cymbal to sound like a gong when you hit the rim, and a snare drum when you hit the head. You probably wouldn’t want to, but you could.

For each of these instruments, you can set:

  • The left/right pan (primarily for playing with headphones, so everything sounds like it’s in the right place)
  • Equalizer settings (low/medium/high frequency response)
  • The instrument (this is the overloading…) – for example “13 inch maple tom”
  • The “sub-instrument” which is a second instrument layered under the first (e.g. the first preset kit has a beech kick with a sub-instrument of a deep shell kick) and how the two instruments are layered together
  • How much the ambience and sound effects affect this particular instrument

Each main/sub instrument then has its own extra tweaks in terms of tuning/size, muffling, and snare buzz – depending on the instrument.

Of course, you can just play the TD-17 with the preset kits, never going into any of this. But I saw possibilities… the user interface is designed very well considering the physical constraints, but I tend to think that complex configuration like this is more easily managed on a computer.

V-Drum Explorer

And so the idea of the V-Drum Explorer was born. Of course, it’s open source – it’s part of my demo code GitHub repository. There’s even documentation with screenshots so you can get the general idea, and a Windows installer downloadable from the GitHub releases page.

From the very start, I imagined a user interface with a tree view on the left and details on the right. It’s possible that by thinking of that from that early on, I’ve missed out on much better UI options.

This blog series is partially a diary of what I’ve done and the challenges I’ve faced, and partly a set of thoughts about how this affects professional development.

I expect to blog about:

  • The MIDI protocol used to communicate with the TD-17
  • The configuration data model
  • The challenges of 7-bit addressing
  • Enabling Hi-DPI for .NET Core 3 WinForms apps
  • Initial code vs schema considerations
  • The transition to a full schema
  • Displaying data more usefully: the logical tree
  • Working with real users: remote diagnostics
  • Immutabilty and cyclic references
  • Performance: WPF vs WinForms
  • Performance: field instances
  • Code signing
  • Windows installers
  • (Maybe) Xamarin and BLE MIDI
  • Moving back from schema JSON to code for ViewModels

That’s likely to take a very long time, of course. I hope it proves as interesting to read about as it has been to implement.

Options for .NET’s versioning issues

This post revisits the problem described in Versioning Limitations in .NET, based on reactions to that post and a Twitter discussion which occurred later.

Before getting onto the main topic of the post, I wanted to comment a little on that Twitter discussion. I personally found it frustrating at times, and let that frustration leak out into some of my responses. As Twitter debates go, this was relatively mild, but it was still not as constructive as it might have been, and I take my share of responsibility for that. Sorry, folks. I’m sure that everyone involved – both in that Twitter discussion and more generally in the .NET community – genuinely wants the best outcome here. I’ve attempted to frame this post with that thought at the top of mind, assuming that all opinions on the topic are held and expressed in good faith. As you’ll see, that doesn’t mean I have to agree with everyone, but it hopefully helps me respect arguments I disagree with. I’m happy to make corrections (probably with some sort of history) if I misrepresent things or miss out some crucial pros/cons. The goal of this post is to help the community weigh up options as pragmatically as possible.

Scope, terminology and running example

There are many aspects to versioning, of course. In the future I plan to blog about some interesting impacts of multi-targeting libraries, and the choices involved in writing one library to effectively augment another. But those are topics for another day.

The primary situation I want to explore in this post is the problem of breaking changes, particularly with respect to the diamond dependency problem. I’ve found it helpful to make things very, very concrete when it comes to versioning. So we’ll consider the following situation.

  • A team is building an application called Time Zone Magic. They’re using .NET Core 3.0, and everything they need to use targets .NET Standard 2.0 – so they have no problems there.
  • The team is completely in control of the application, and doesn’t need to worry about any versioning for the application itself. (Just to simplify things…)
  • The application depends on Noda Time, naturally, for all the marvellous ways in which Noda Time can help you with time zones.
  • The application also depends on DarkSkyCore1.

Now DarkSkyCore depends on NodaTime 2.4.7. But the Time Zone Magic application needs to depend on NodaTime 3.0.0 to take advantage of some of the newest functionality. (To clarify, NodaTime 3.0.0 hasn’t actually been released at the time of writing this blog post. This part is concrete but fictional, just like the application itself.) So, we have a diamond dependency problem. It’s entirely possible that DarkSkyCore depends on functionality that’s in NodaTime 2.4.7 but has been removed from 3.0.0. If that’s the case, with the current way .NET works (whether desktop or Core), an exception will occur at some point – exactly how that’s surfaced will probably vary based on a number of factors that I don’t explore in this post.

Currently, as far as I can tell, DarkSkyCore doesn’t refer to any NodaTime types in its public API. We’ll consider what difference this makes in the various options under consideration. I’ll mention a term that I learned during the Twitter conversation: type exchange. I haven’t seen a formal definition of this, but I’m assuming it means one library referring to a type from another library within its public API, e.g. as a parameter or return type, or even as a base class or implemented interface.

The rest of this post consists of some options for what could happen, instead of the current situation. These are just the options I’ve considered; I certainly don’t want to give the impression it’s exhaustive or that we (as a community) should stop trying to think of other options too.

1 I’ve never used this package, and have no opinion on it. It’s just a plausible package to use that depends on NodaTime.

Option 1: Decide to do nothing

It’s always including the status quo as a possible option. We can acknowledge that the current situation has problems (the errors thrown at hard-to-predict places) but we may consider that every alternative is worse, either in terms of end result or cost to implement.

It’s worth bearing in mind that .NET has been around for nearly 20 years, and while this is certainly a known annoyance, I seem to care about it more than most developers I encounter – suggesting that this problem doesn’t make all development on .NET completely infeasible.

I do believe it will hinder the community’s growth in the future though, particularly if (as I hope) the Open Source ecosystem flourishes more and more. I believe one of the reasons this hasn’t bitten the platform very hard so far is that the framework provides so much, and ASP .NET (including Core) dominate on the web framework side of things. In the future, if there are more small, “do one thing well” packages that are popular, the chances of incompatibilities will increase.

Option 2: Never make breaking changes

If we never make breaking changes, there can’t be any incompatibilities. We keep the major version at 1, and it doesn’t matter which minor version anyone depends on.

This has been the approach of the BCL team, very largely (aside from “keeping the major version at 1”) – and is probably appropriate for absolutely “system level” packages. Quite what counts as “system level” is an open question: Noda Time is relatively low level, and attempts to act as a replacement for system types, so does that mean I should never make any breaking changes either?

I could potentially commit to not making any future breaking changes – but deciding to do that right from day 1 would seriously stifle innovation. Releasing version 1.0 is scary enough as it is, without the added pressure of “you own every API mistake in here, forever.” There’s a huge cost involved in the kind of painstaking review of every API element that the BCL team goes through. That’s a cost most open source authors probably can’t bear, and it’s not going to be a good investment of time for 99.9% of libraries… but for the 0.1% that make it and become Json.NET-like in terms of ubiquity, it would be great.

Maybe open source projects should really aim for 2.infinity: version 1.x is to build momentum, and 2.x is forever. Even that leaves me pretty uncomfortable, to be honest.

There’s another wrinkle in this in terms of versioning that may be relevant: platform targeting. One of the reasons I’ve taken a major version bump for NodaTime 3.0 is that I’m dropping support for older versions of .NET. As of NodaTime 3.0, I’m just targeting .NET Standard 2.0. Now that’s a breaking change in that it stops anyone using a platform that doesn’t support .NET Standard 2.0 from taking a dependency on NodaTime 3.0, but it doesn’t have the same compatibility issues as other breaking changes. If the only thing I did for NodaTime 3.0 was to change the target framework, the diamond dependency problem would be a non-issue, I believe: any code that could run 3.0 would be compatible with code expecting 2.x.

Now in Noda Time 3.0 I also removed binary serialization, and I’d be very reluctant not to do that. Should the legacy of binary serialization haunt a library forever? Is there actually some acceptable deprecation period for things like this? I’m not sure.

Without breaking changes, type exchange should always be fine, barring code that relies on bugs in older versions.

Option 3: Put the major version in the package name

The current versioning guidance from Microsoft suggests following SemVer 2.0, but in the breaking changes guidance it states:

CONSIDER publishing a major rewrite of a library as a new NuGet package.

Now, it’s not clear to me what’s considered a “major rewrite”. I implemented a major rewrite of a lot of Noda Time functionality between 1.2 and 1.3, without breaking the API. For 2.0 there was a more significant rewrite, with some breaking changes when we moved to nanosecond precision. It’s worth at least considering the implications of interpreting that as “consider publishing a breaking change as a new NuGet package”. This is effectively putting the version in the package name, e.g. NodaTime1, NodaTime2 etc.

At this point, on a per-package basis, we have no breaking changes, and we’d keep the major version at 1 forever, aside from potentially dropping support for older target platforms, as described in option 2. The differences are:

  • The package names become pretty ugly, in my opinion – something that I’d argue is inherently part of the version number has leaked elsewhere. It’s effectively an admission that .NET and SemVer don’t play nicely together.
  • We don’t see breaking changes in the app example above, because DarkSkyCore would depend on NodaTime2 and the Time Zone Magic application would depend directly on NodaTime3.
  • Global state becomes potentially more problematic: any singleton in both NodaTime2 and NodaTime3 (such as DateTimeZoneProviders.Tzdb for NodaTime) would be a “singleton per package” but not a “global singleton”. With the example of DateTimeZoneProviders.Tzdb, that means different parts of Time Zone Magic could give different results for the same time zone ID, based on whether the data was retrieved via NodaTime2 or NodaTime3. Ouch.
  • Type exchange doesn’t work out of the box: if DarkSkyCore exposed a NodaTime2 type in its API, the Time Zone Magic code wouldn’t be able to take that result and pass it into NodaTime3 code. On the other hand, it would be feasible to create another package, NodaTime2To3 which depended on both NodaTime2 and NodaTime3 and provided conversions where feasible.
  • Having largely-the-same code twice in memory could have performance implications – twice as much JITting etc. This probably isn’t a huge deal in most scenarios, but could be painful in some cases.

No CLR changes are required for this – it’s an option that anyone can adopt right now.

One point that’s interesting to note (well, I think so, anyway!) is that in the Google Cloud Client Libraries we already have a version number in the package name: it’s the version number of the network API that the client library targets. For example, Google.Cloud.Speech.V1 targets the “Speech V1” API. This means there can be a “Speech V2” API with a different NuGet package, and the two packages can be versioned entirely independently. (And you can use both together.) That feels appropriate to me, because it’s part of “the purpose of the package” – whereas the version number of the package itself doesn’t feel right being in the package name.

Option 4: Major version isolation in the CLR

This option is most simply described as “implicit option 3, handled by tooling and the CLR”. (If you haven’t read option 3 yet, please do so now.) Imagine we kept the package name as just NodaTime, but all the tooling involved (MSBuild, NuGet etc) treated “NodaTime v2.x” and “NodaTime v3.x” as independent packages. All the benefits and drawbacks of option 3 would still apply, except the drawback of the version number leaking into the package name.

It’s possible that no CLR changes would be required for this – I don’t know. One of the interesting aspects on the Twitter thread was that AssemblyLoadContext could be used in .NET Core 3 for some of what I’d been describing, but that there were performance implications. Microsoft engineers also reported that what I’d been proposing before would be a huge amount of work and complexity. I have no reason to doubt their estimation here.

My hunch is that if 90% of this could be done in tooling, we should be able to achieve a lot without execution-time penalties. Maybe we’d need to do something like using the major version number as a suffix on the assembly filename, so that NodaTime2.dll and NodaTime3.dll could live side-by-side in the same directory. I could live with that – although I readily acknowledge that it’s a hugely disruptive change. Whatever the implementation, the lack of type exchange would be very disruptive, to the extent that maybe this should be an opt-in (on the part of the package owner) mechanism. “I want more freedom for major version coexistence, at the expense of type exchange.”

Another aspect of feedback in the Twitter thread was that the CLR has supported side-by-side assembly loading for a very long time (forever?) but that customers didn’t use it in practice. Again, I have no reason to dispute the data – but I would say that it’s not evidence that it’s a bad feature. Even great features need to be exposed well before they’ll be used… look at generic variance in the CLR, which was already present in .NET 2.0, but was effectively unused until languages (e.g. C# 4) and the framework (e.g. interfaces such as a IEnumerable) supported it too.

It took a long time to get from “download a zip file, copy the DLLs to a lib directory, and add a reference to that DLL” to “add a reference to a versioned NuGet package which might require its own NuGet dependencies”. I believe many aspects of the versioning story aren’t really exposed in that early xcopy-dependency approach, and so maybe we didn’t take advantage of the CLR facilities nearly as early as we should have don.

If you hadn’t already guessed, this option is the one I’d like to pursue with the most energy. I want to acknowledge that it’s easy for me to write that in a blog post, with none of the cost of fully designing, implementing and supporting such a scheme. Even the exploratory work to determine the full pros and cons, estimate implementation cost etc would be very significant. I’d love the community to help out with this work, while realizing that Microsoft has the most experience and data in this arena.

Option 5: Better error detection

When laying out the example, I noted that for the purposes of DarkSkyCore, NodaTime 2.4.7 and NodaTime 3.0 may be entirely compatible. DarkSkyCore may not need any of the members that have been removed in 3.0. More subtly, even if there are areas of incompatibility, the parts of DarkSkyCore that are accessed by the Time Zone Magic application may not trigger those incompatibilities.

One relatively simple (I believe) first step would be to have a way of determining the first kind of “compatibility despite a major version bump”. I expect that with Mono.Cecil or similar packages, it should be feasible to:

  • List every public member (class, struct, interface, method, property etc) present in NodaTime 3.0, by analyzing NodaTime.dll
  • List every public member from NodaTime 2.4.7 used within DarkSkyCore, by analyzing DarkSkyCore.dll
  • Check whether there’s anything in the second list that’s not in the first. If there isn’t, DarkSkyCore is probably compatible with NodaTime 3.0.0, and Time Zone Magic will be okay.

This ignores reflection of course, along with breaking behavioral changes, but it would at least give a good first indicator. Note that if we’re primarily interested in binary compatibility rather than source compatibility, there are lots of things we can ignore, such as parameter names.

It’s very possible that this tooling already exists, and needs more publicity. Please let me know in comments if so, and I’ll edit a link in here. If it doesn’t already exist, I’ll prototype it some time soon.

If we had such a tool, and it could be made to work reliably (if conservatively), do we want to put that into our normal build procedure? What would configuration look like?

I’m a firm believer that we need a lot more tooling around versioning in general. I recently added a version compatibility detector written by a colleague into our CI scripts, and it’s been wonderful. That’s a relatively “home-grown” project (it lives in the Google Cloud client libraries repository) but something similar could certainly become a first class citizen in the .NET ecosystem.

In my previous blog post, I mentioned the idea of “private dependencies”, and I’d still like to see tooling around this, too. It doesn’t need any CLR or even NuGet support to be useful. If the DarkSkyCore authors could say “I want to depend on NodaTime, but I want to be warned if I ever expose any NodaTime types in my public API” I think that would be tremendously useful as a starting point. Again, it shouldn’t be hard to at least prototype.


As I mentioned at the start, corrections and alternative viewpoints are very welcome in comments, and I’ll assume (unless you say otherwise) that you’re happy for me to edit them into the main post in some form or other (depending on the feedback).

I want to encourage a vigorous but positive discussion about versioning in .NET. Currently I feel slightly impotent in terms of not knowing how to proceed beyond blogging and engaging on Twitter, although I’m hopeful that the .NET Foundation can have a significant role in helping with this. Suggestions for next steps are very welcome as well as technical suggestions.