Set minimum and maximum file size For file upload in asp.net core

In my opinion, if you want to check the minimum and maximum file size For file upload, I suggest you could try to create a custom middleware to check the httpcontentlength, if the http content length doesn't match the minimum and maximum size, then you could return the custom response.

More details, you could refer to below codes:

Add below middleware into the startup.cs Configure method:

Notice: I use app.usewhen to check the path, this will only work for the url path contains "api". If you want to match all the request, you could directly use app.Use.

            app.UseWhen(context =>
context.Request.Path.StartsWithSegments("/api"),
CheckRequestLengthAsync);

CheckRequestLengthAsync method:

    private void CheckRequestLengthAsync(IApplicationBuilder app)
    {
        app.Use(async (context, next) =>
        {
            if (context.Request.ContentLength <50 && context.Request.ContentLength > 5)
            {
                context.Response.StatusCode = 500;
                context.Response.ContentType = "text/html";
                await context.Response.WriteAsync("Not match the content length");
            }
            else
            {
                // Do work that doesn't write to the Response.
                await next();
                // Do other work that doesn't write to the Response.
            }


        });
    }

Result: