C# in WebAssembly looks promising, but…

In past few days, we have seen several samples of C# code compiled or interpreted using the WebAssembly: Blazor, for example.

I really like the idea of running C# code in the browser, and I immediately got an idea how to incorporate this mechanism in DotVVM. Running C# code on the client side could really change the way how .NET web applications are developed today, and I am sure that a lot of new front end frameworks will appear sooner or later.


Currently, there are two ways how to pack C# code so it can be executed in the browser. The easier (and slower) way is to interpret the actual MSIL code, which is done by DotNetAnywhere (used by Blazor) for example. The other way, which Mono is going, is to really compile the .NET assembly to WebAssembly. It will take some time until these technologies are mature enough, but the future seems pretty clear.


Imagine for a while, that your new web app has some C# code that runs in the browser. How would you access your data? Through some API, of course. And that’s where it gets uncomfortable.

No, I am not going to cry for ASP.NET Web Services which had the greatest tooling I have ever seen. Yes, it was a question of few clicks and there was really nothing to break, but there was a ton of disadvantages.

WCF was also great when it came to writing the services and call them. The number of features and possibilities was really impressive, but the configuration was a hell on wheels.



Today, REST is the probably the most popular solution. If you go this way, you need to build your Web API which is quite simple.

But then, you need to configure Swagger and generate client-side code that can be used in the browser. This process is not very straight-forward - there is no magic button for that in Visual Studio. You need to install some Nuget packages, configure it, then you try to generate the API client in the Visual Studio which works only sometimes so you might need to use NSwag or other tool to do that. If the Web API is not your own, there might not be Swagger metadata available and you will need to find some hand-crafted library on GitHub (which will be most probably outdated and not maintained), or you will need just write the API client by yourself.

If the API is yours, it makes the things simpler, but still - you may want to regenerate your API clients in the CI process which is possible, but not easy to set up.

And finally, Swagger itself has a bunch of limitations. The generic types and polymorphism are difficult to do, if not impossible at all. The API versioning works somehow, but it feels like they forgot about it at the beginning.

And finally, there is no standard way to do paging or sorting of data - you will need to do everything by yourself.


Graph QL

You can try Graph QL as it is also very popular today. If you haven’t heard about it yet, it works like this: you send a “something-like-JSON without data” with the properties or child objects you will need, and the server will load the data in the object and send it to back to you. You can do filtering, paging and includes in it, and it is strongly typed which is nice. There are several .NET libraries which claim to support this protocol.

However, I have found very difficult to implement this kind of API on the server side. The user can basically ask for any set of the properties and child objects. If you use SQL database with Entity Framework to access the data, which is the most frequent case, you never know how will the query look like.

The user can ask for so many objects and generate so many Includes, that you won’t probably do it on a single SQL query. If the database is large, you should not permit the user to make any kind of Includes as it may kill the performance of the app and it is an easy way for a DOS attack. And there are so many combinations of stuff what the user can do, that you will spend hours and hours by deciding what to allow, what to restrict, whether to make a separate SQL query for some collections etc.


Other ways?

OData tries to solve a similar problem like Graph QL and it looks easier to implement on the server side, because it is more restrictive. But there are some issues too, and many people would tell you that it’s dead. The main issue can be the lack of good clients for non-.NET platforms, and you may run into similar issues like with Graph QL when you try to implement it on the server side.


Lot of ideas…

One of the things I like when I use DotVVM to build web apps is that I don’t have to build and maintain the API myself. The framework handles the server-client communication for me which is extremely helpful when the web app changes its UI and structure of the data frequently. Almost every such change would require changing the API, and if this API is used by anyone else, a mobile application for example, it creates an additional overhead with versioning of this API.

With DotVVM, I can just deploy a new version of the app with a different viewmodel and that’s it. If there is a mobile app, it has its own API, so changes of the web UI don’t require changes of the API. And provided the application is well structured, the API controller is a very tiny class that only calls methods from the business layer. And of course, the viewmodel calls similar or the same methods, so the business logic is shared by the mobile and web app.


If we decide to create a WebAssembly version of DotVVM, we should really focus on making the client-server communication simple. I don’t want to build my better Swagger, because it is a lot of work, but still - there must be an easier way.

I am really looking forward what new possibilities the WebAssembly unleashes. And I hope that new frameworks and tools will make things simpler, not more difficult.