在ASP.NET核心中间件中设置响应状态

public class ExceptionHandlingMiddleware
{
    private readonly RequestDelegate _next;

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

    public async Task Invoke(HttpContext context)
    {
        try
        {
            await _next.Invoke(context);
        }
        catch (Exception exception)
        {
            var message = "Exception during processing request";
            using (var writer = new StreamWriter(context.Response.Body))
            {
                context.Response.StatusCode = 500; //works as it should,response status 500
                await writer.WriteAsync(message);
                context.Response.StatusCode = 500; //response status 200
            }
        }
    }
}

我的问题是,如果我在写主体之前设置响应状态,客户端将看到此状态,但如果我在向主体写入消息后设置状态,则客户端将收到状态为200的响应.

有人可以解释一下为什么会这样吗？

附：我正在使用ASP.NET Core 1.1