Elegant way of producing HTTP responses in ASP.NET Core outside of MVC controllers

ASP.NET Core 2.1 introduced support for a little (or, should I say, not at all) documented feature called IActionResultExecutor<T>. It allows us to use some of the action results -those that we are used to from MVC controllers – outside of the controller context, so for example from a middleware component.

Kristian has a great blog post about result executors, that I recommend you check out. From my side, I wanted to show you today a set of extension methods that were recently introduced into WebApiContrib.Core that make working with IActionResultExecutor<T> and in general authoring HTTP endpoints outside of controllers even easier.

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Be careful when manually handling JSON requests in ASP.NET Core

The other day I was reviewing some code in an ASP.NET Core app. It was an HTTP endpoint, written as a simple, lightweight middleware component (so no MVC), that was handling incoming JSON requests.

The endpoint was intended to act as an ingestion point for larger amounts of data, so by definition it was supposed to perform well. I immediately noticed a few things that raised my eyebrow, that I wanted to share with you today.

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Collectible assemblies in .NET Core 3.0

Since the beginning of .NET Core, the one feature that I have been most anxiously waiting for, has been support for collectible assemblies. It took a while (a while!), but finally, in .NET Core 3.0 (at the time of writing 3.0.0-preview-27122-01 from 2018-12-04), it’s here.

It’s going to be a killer functionality, that will support some excellent use cases in .NET Core – especially around application plugins, extensibility and dynamic assembly generation.

Let’s have a quick look at how we can load and unload assemblies in .NET Core.

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Using Roslyn C# Completion Service programmatically

I am involved in a few open source projects built around the Roslyn compiler. One of those projects is OmniSharp, which brings intellisense and C# language services to a number of editors out there, allowing them to provide for their users a rich C# code authoring experience.

Which actually brings me to the point of today’s post. Roslyn is a compiler-as-a-service that you can embed in your own app, and when you do that, you could reach into its C# language services (more specifically, CompletionService) and easily build your own C# intellisense engine.

However, this is not really documented, so I wanted to use this post to show you how you can get started with that.

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dotnet-script 0.27.0 is out – with a ton of features!

It's that time again, the new dotnet-script release, version 0.27.0 is out. It's been 2+ months since the last release so this one is fully packed with great features.

You can get it by running dotnet tool install dotnet-script -g (if you don't have it installed yet) or dotnet tool update dotnet-script -g (if you just need an update).

Let me quickly walk you through some of them.

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No InternalsVisibleTo, no problem – bypassing C# visibility rules with Roslyn

Both the C# compiler and the CLR/CoreCLR runtimes contain a bunch of rules that are in place to save us from ourselves (and to allow us to write code without needing to fully understand ECMA-334 C# Language Specification). That said, there are times where we want to do some things that are normally not allowed, and a good example of that is reaching into reflection to execute some private or internal code.

Today I wanted to show you how to do something quite cool – how to bypass the type/member visibility rules using the Roslyn compiler. In other words, how to get access to internal and private members without needing to use reflection or something like InternalsVisibleToAttribute.

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Convert null-valued results to 404 in ASP.NET Core MVC

ASP.NET Core MVC is pretty flexible in terms of how it expects you to return results from the API actions. You could return an IActionResult, which gives you certain control over the status code and the nature of the response (i.e. object or a file or a status code only and so on). You could return a concrete object instance, and the framework will serialize it to the relevant response format. Finally, you could also return the new ActionResult<T> which allows you to mix both of the previous approaches in a single method, giving you the best of both worlds.

Let’s have a look at what happens in the framework when you return a null object instance and how you can change that behavior.

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Running ASP.NET Core content negotiation by hand

When you are building flexible HTTP APIs, supporting a wide array of different clients, it is common to rely on the process of content negotiation, to allow each client to interact with the API in the most convenient way – be it JSON, XML, Protobuf, Messagepack or any other media type on which both the client and the server can agree.

I have blogged about content negotiation (or in short: conneg) a few times in the past (for example here or here, in ASP.NET Core context). Today I’d like to show you how – in ASP.NET Core – to easily run conneg by hand, instead of relying on the built-in MVC conneg mechanisms.

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