ASP .NET Core：CORS 标头仅适用于某些静态文件类型

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（CORS 标头显示）。但是，对于某些文件类型（例如 JSON），它们的 CORS 标头不会显示，并且客户端站点无法看到内容。如果我将文件重命名为未知类型（例如 JSONX），它将使用 CORS 标头提供服务，没有问题。我怎样才能让这个东西为所有带有 CORS 标头的东西提供服务？

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();
    }

以下是我的配置

    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。 我最近已经让它可以用于 JavaScript 源代码了。 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)
    {
        if (fieldValue == null) {
            return false;
        }

        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);
    }
}