Calling UseEndpoints multiple times from multiple IStartupFilters

[kimbell]

We are building up a collection of .NET Core services. We also have internal libraries that may add middleware. As this collection grows, one of the things we want to maintain is a consistent setup on how middleware is configured; this might change over time.

IStartupFilter is one way we automatically add middleware. I've been looking around on the Internet, and explored the code from Steeltoe. In their codebase they are using IStartupFilter to call UseEndpoints(). Depending on what has been added to the IServiceCollection, the UseEndpoints() will be called multiple times.

https://github.com/SteeltoeOSS/Steeltoe/blob/b3928ed4ec527be9fc07e917a615bbebad22c254/src/Management/src/EndpointCore/Loggers/LoggersStartupFilter.cs

https://github.com/SteeltoeOSS/Steeltoe/blob/b3928ed4ec527be9fc07e917a615bbebad22c254/src/Management/src/EndpointCore/Mappings/MappingsStartupFilter.cs

I haven't seen this approach anywhere else, so is this a supported option?

Are there other options I can explore, or do I need to create my own framework specific for our needs?

[Tratcher]

IStartupFilter isn't a great middleware composition model because it gives very little control over ordering, and in this case duplication. Calling UseEndpoints multiple times isn't ideal because it will add multiple EndpointMiddleware to the pipeline.

aspnetcore/src/Http/Routing/src/Builder/EndpointRoutingApplicationBuilderExtensions.cs

Line 105 in 8c8cb4d

return builder.UseMiddleware<EndpointMiddleware>();

I'm not aware of a good built-in solution for this scenario. Do you control the primary Startup class and Configure method? If so you should be able to provide your own interface like IEndpointSetup.ConfigureEndpoints(IEndpointRouteBuilder builder), inject IEnumerable<IEndpointSetup> into Startup.Configure, and then call them inside the UseEndpoints configuration lambda. You could do something similar for inserting other middleware at designated points in your pipeline.

[kimbell]

I control the startup class and have similar ideas on how to solve this. Since I saw this pattern in a library, I just wanted to check if there was something I had missed.