将响应标头添加到ASP.NET Core中间件 [英] Add Response Headers to ASP.NET Core Middleware

问题描述

我想像这样向我的ASP.NET Core WebApi添加一个处理时间中间件

I want to add a processing time middleware to my ASP.NET Core WebApi like this

public class ProcessingTimeMiddleware  
{
    private readonly RequestDelegate _next;

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

    public async Task Invoke(HttpContext context)
    {
        var watch = new Stopwatch();
        watch.Start();

        await _next(context);

        context.Response.Headers.Add("X-Processing-Time-Milliseconds", new[] { watch.ElapsedMilliseconds.ToString() });
    }
}

但是这样做会抛出一个异常提示

But doing this throws an exception saying

 System.InvalidOperationException: Headers are readonly, reponse has already started.

如何在响应中添加标题?

How can I add headers to the response?

推荐答案

没关系，代码在这里

    public async Task Invoke(HttpContext context)
    {
        var watch = new Stopwatch();
        watch.Start();

        //To add Headers AFTER everything you need to do this
        context.Response.OnStarting(state => {
            var httpContext = (HttpContext)state;
            httpContext.Response.Headers.Add("X-Response-Time-Milliseconds", new[] { watch.ElapsedMilliseconds.ToString() });

            return Task.CompletedTask;
        }, context);

        await _next(context);
    }

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