[Components] Prerrendering startup experience

[javiercn]

Runtime changes to support the new components startup experience.

I still need to do a bit of cleanup and add more tests, but the main pieces and functional tests are in to show that it works.

I'll expand the PR tomorrow morning with the changes to the components template.

[rynowak]

I still don't love that this is IEnumerable<string> but it seem OK for now.

[javiercn]

@rynowak For the MVC case we need to buffer the output as we need to write it synchronously. We could buffer it on a byte array, but I believe that would be more painful.
Another option would be to abstract it behind a type and provide overloads to write it to a stream/pipe (essentially an IHtmlContentResult like type).

[rynowak]

hmmm

[rynowak]

This is one of the first things I've seen (based on this approach) which makes me wonder if it's not totally generic.

[javiercn]

IMO, it's totally generic, but IMO in general it's easy for us to get it right, but easy for users to get wrong. It also makes it really hard to reorganize individual callbacks,etc in order to resolve conflicts (what if you have two pieces that add a callback and override each other).

In general, when we have this type of composition, I like it when it's backed by primitives and visible, so that:

1. I get a clear understanding of how the system works.
2. I can reorder/reconfigure the system to suit my needs without having to go bonkers or digging into the details of how each component on the stack works.

[SteveSandersonMS]

If we extend the static files system to have a more native mechanism for plugging in multiple content sources, perhaps it also needs to be able to have things like response header defaults on a per-content-source basis.

[rynowak]

Yeah Steve found a better way of saying what I was thinking. It's a bit of a heavy hand for us configure caching settings for all static files, yet we do care about having this set for our stuff.

[rynowak]

I think it's OK to have their quirk in this release, but we should known issues or release notes this.

[pranavkm]

I think there's a couple of design questions we need to resolve, but this PR looks great for preview3

[javiercn]

@pranavkm filed #7807 to track the layering issue

[rynowak]

Should builder be a strong type instead of the interface? This will offer these suggestions on all of the builders.

[javiercn]

Yeah, but that has its drawbacks too. If we wrap the builder then other conventions can't reliably downcast it to RouteEndpointConventionBuilder and you can't do things based on Order or Pattern.

I think its fine for now to leave it as it is. I have an email thread where I lay out the issues and discuss the pros/cons. I can file an issue to track it for preview4

[rynowak]

It looks like this might be your solution to manually registering signalR. I think it's a fine choice to leave this as-is for now 👍

[javiercn]

Yeah.

[javiercn]

It looks like this might be your solution to manually registering signalR. I think it's a fine choice to leave this as-is for now 👍

That too, but I'm just too tired to pull thoughts out of my head 😄

[rynowak]

from me! I'm really excited about the final shape of this!

[javiercn]

Ubuntu has a failing unrelated test: Microsoft.DotNet.Watcher.Tools.FunctionalTests.DotNetWatcherTests.RunsWithIterationEnvVariable

[davidfowl]

Ubuntu has a failing unrelated test: Microsoft.DotNet.Watcher.Tools.FunctionalTests.DotNetWatcherTests.RunsWithIterationEnvVariable

Time to disable that test, it fails EVERYWHERE

[javiercn]

The only thing failing here is that one test in Ubuntu. @mkArtakMSFT please override.

Squash and merge with the following message

[Components] Prerrendering startup experience
* Introduces an IComponentPrerrenderer to handle Prerrendering
  * MVC registers a basic static prerrrenderer.
  * Components registers a more feature complete prerrender that will
    handle reconnection to the original circuit after prerrendering in
    the future to allow for prerrendered interactive components.
* Removes UseRazorComponents
  * Removes the SPA fallback in favor of a catch all route in
    Index.cshtml
  * Moves the framework files to be served by the default StaticFiles
    middleware in the pipeline by way of plugging specific providers
    through options.
  * Lifts UseSignalR(r => r.MapHub<ComponentHub>()) into startup and
    replaces it with a shorthand for MapHub using endpoint routing.
  * Adds extension methods to map components to selectors for a given
    hub.
* Updates the razor component templates to include prerendering and use a razor page as the entry 
   point.

[plasticalligator]

I just wanted to say, thank you for your hard work!

[SteveSandersonMS]

This looks so good now! Awesome job, @javiercn!

[davidfowl]

It does. It’s also fast to load because of the pre-rendering