Re: [Static web assets] Support watch in static web assets

[aomader]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Watching files on the new IFileProvider introduced in .NET6 is not working and thus breaking development workflows.

This was tracked in #40372 by @javiercn, but that issues was closed as completed without any further insights. Given that this issue is not solved, I am opening this ticket to further track it and request a status update.

PS: There is also #40369, but both are closed and locked without any further information on the status in ASP.NET Core.

Expected Behavior

I expect watching files to work correctly.

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

9.0.200

Anything else?

No response

[javiercn]

@aomader thanks for contacting us.

What are you looking for that its missing? The watch functionality should work with static assets in current versions (that's why the issues were closed).

The other one might be referring/asking about some of the implementation details related to static web assets, which we don't normally document.

Is there anything you are trying to accomplish that is not working?

[aomader]

@javiercn Yeah correct, something is not working.

During development, sources in the web root are changed, while the application is already running and not restarted. Hence, files change while the application runs.

These files are used in the application and are served with hash values. These hash values obviously must match the files that are served.

To achieve this, we use something like the following:

string GetHash(IWebHostEnvironment env, IMemoryCache cache, string path)
{
    if (cache.TryGetValue(path, out var hash))
    {
        var fileProvider = env.WebRootFileProvider;

        var cacheEntryOptions = new MemoryCacheEntryOptions();

        // this is apparently not working, since the cache entry never expires
        cacheEntryOptions.AddExpirationToken(fileProvider.Watch(path));

        hash = ...

        cache.Set(path, hash, cacheEntryOptions);
    }
    return hash;
}

Sadly, that is not working, since the cache entry never expires.

[danroth27]

@aomader Thanks for these additional details. The earlier static files middleware doesn't currently support watch. We can consider adding this. However, the newer MapStaticAssets support does support watch. Can you consider moving to the newer model?

[aomader]

@danroth27 Quoting from the release notes of .NET9 (emphasis by me): "MapStaticAssets can replace UseStaticFiles in most situations, however, it's optimized for serving the assets that the app has knowledge of at build and publish time."

That recommendation sort of states that it is not suitable/designed for this use case, i.e., having resources change at runtime. Am I misunderstanding something here?

Edit:

I did a short test with

app.UseEndpoints(e => e.MapStaticAssets());

instead of just app.UseStaticFiles(), but the outcome is the same. The cache entry is not evicted.