MapFallbackToFile is returning 404

[HarelM]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

MapFallbackToFile doesn't return the required file

Expected Behavior

The required file should be returned when no middleware is hit.

Steps To Reproduce

The following is the project program file:

app.UseResponseCompression();
    app.UseCors(b => b.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader());
    app.MapControllers();
    app.MapHealthChecks("/api/health");
    // wwwroot
    app.UseDefaultFiles();
    app.UseStaticFiles(new StaticFileOptions
    {
        ContentTypeProvider = new FileExtensionContentTypeProvider
        {
            Mappings = { {".pbf", "application/x-protobuf"} } // for the fonts files
        }
    });
    app.UseSwagger();
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "Israel Hiking Map API V1");
    });
    // This should be the last middleware
    app.UseMiddleware<CrawlersMiddleware>();
    app.MapFallbackToFile("/index.html");

It can be found here:
https://github.com/IsraelHikingMap/Site/blob/58dbe698bff288d9d24466ffa5a604535b2a2f93/IsraelHiking.Web/Program.cs#L41

Exceptions (if any)

No exception, just 404 when surfing to unknown route such as:
localhost:5000/map/1/2/3

.NET Version

7.0.202

Anything else?

This is not the first issue I'm having with trying to properly define the middlewares for my SPA project.
See the following issue: #45903
The fact that I'm getting it wrong so easily means that the code here is now well documented and doesn't do what is expected of it, especially in this case the MapFallbackToFile.

Every time I try to change this initialization code something else breaks, and my project is not that complicated, honestly.
The documentation is writing about the parameters instead of giving good examples of how one should be using the calls.

[HarelM]

I wrote the following code to overcome this issue if anyone finds this issue in the future:

/// <summary>
/// This middleware is responsible in returning the index.html file
/// </summary>
public class SpaDefaultHtmlMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IWebHostEnvironment _environment;

    /// <summary>
    /// Constructor
    /// </summary>
    /// <param name="next"></param>
    /// <param name="environment"></param>
    public SpaDefaultHtmlMiddleware(RequestDelegate next, 
        IWebHostEnvironment environment)
    {
        _next = next;
        _environment = environment;
    }
    /// <summary>
    /// Main middleware method required for asp.net
    /// </summary>
    /// <param name="context"></param>
    public async Task InvokeAsync(HttpContext context)
    {
        if (context.Request.Path.StartsWithSegments("/api"))
        {
            await _next.Invoke(context);
            return;
        }
        var indexFileInfo = _environment.WebRootFileProvider.GetFileInfo("/index.html");
        context.Response.ContentType = "text/html";
        context.Response.ContentLength = indexFileInfo.Length;
        await context.Response.SendFileAsync(indexFileInfo);
    }
}

[vsosinga]

Had a similar problem, my mistake was that the index.html wasn't served out of the wwwroot folder. When I changed that everything worked fine.

[HarelM]

My index.html file is inside wwwroot folder, but this issue still exists...

[HarelM]

This isn't a PR...

[haroldrandom]

how to fix or workaround? dotnet 6 produced still.

[danielelkington]

I found that the following worked:

app.MapFallbackToFile("index.html", new StaticFileOptions
{
    FileProvider = new PhysicalFileProvider(app.Environment.WebRootPath ?? app.Environment.ContentRootPath)
});

By default, MapFallbackToFile seems to use the WebRootPath, which depending on how you are hosting may be null.