c# - ASP.NET 核心 : CORS headers only for certain static file types

Question

我有一个 ASP .NET Core 自托管项目。我正在提供静态文件夹中的内容(没问题)。它可以毫无问题地跨站点提供图像(显示 CORS header )。但是，对于某些文件类型，例如 JSON，它们的 CORS header 不会显示，客户端站点也看不到内容。如果我将文件重命名为未知类型(例如 JSONX)，它会使用 CORS header 提供服务，没问题。我怎样才能让这个东西为所有带有 CORS header 的东西提供服务？

我在 Startup.cs 中设置了以下 CORS 策略:

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddCors(options =>
        {
            options.AddPolicy("CorsPolicy",
                builder => builder.AllowAnyOrigin()
                .AllowAnyMethod()
                .AllowAnyHeader()
                .AllowCredentials() );
        });

        // Add framework services.
        services.AddMvc();
    }

下面是我的配置

    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        app.UseCors("CorsPolicy");
        loggerFactory.AddConsole(Configuration.GetSection("Logging"));
        loggerFactory.AddDebug();

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
            app.UseBrowserLink();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
        }

        // Static File options, normally would be in-line, but the SFO's file provider is not available at instantiation time
        var sfo = new StaticFileOptions() { ServeUnknownFileTypes = true, DefaultContentType = "application/octet-stream", RequestPath = "/assets"};
        sfo.FileProvider = new PhysicalFileProvider(Program.minervaConfig["ContentPath"]);
        app.UseStaticFiles(sfo);

        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });
    }

Answer 1

中间件可以帮助处理这种复杂的逻辑。我最近已经将它用于 JavaScript 源代码。看起来 JSON 的媒体类型是“application/json”。

/*
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;

Made available under the Apache 2.0 license.
https://www.apache.org/licenses/LICENSE-2.0
*/

/// <summary>
/// Sets response headers for static files having certain media types.
/// In Startup.Configure, enable before UseStaticFiles with 
/// app.UseMiddleware<CorsResponseHeaderMiddleware>();
/// </summary>
public class CorsResponseHeaderMiddleware
{
    private readonly RequestDelegate _next;

    // Must NOT have trailing slash
    private readonly string AllowedOrigin = "http://server:port";


    private bool IsCorsOkContentType(string fieldValue)
    {
        var fieldValueLower = fieldValue.ToLower();

        // Add other media types here.
        return (fieldValueLower.StartsWith("application/javascript"));
    }


    public CorsResponseHeaderMiddleware(RequestDelegate next) {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        context.Response.OnStarting(ignored =>
        {
            if (context.Response.StatusCode < 400 &&
                IsCorsOkContentType(context.Response.ContentType))
            {
                context.Response.Headers.Add("Access-Control-Allow-Origin", AllowedOrigin);
            }

            return Task.FromResult(0);
        }, null);

        await _next(context);
    }
}