OWIN中间件来关联和记录请求和响应？

Question

我正在编写一个自定义OWIN中间件来记录所有http请求及其响应。 我想用trackingId“关联”这些。 这是代码：

public class PacketTrackingMiddleware
{
    private readonly AppFunc _next;

    public PacketTrackingMiddleware(AppFunc next)
    {
        _next = next;
    }

    public async Task Invoke(IDictionary<string, object> environment)
    {
        IOwinContext context = new OwinContext(environment);            
        var request = context.Request;
        var response = context.Response;

        //capture details about the caller identity

        var identity = (request.User != null && request.User.Identity.IsAuthenticated)
            ? request.User.Identity.Name
            : "(anonymous)";

        var apiPacket = new ApiPacket
        {
            CallerIdentity = identity
        };

        //buffer the request stream in order to intercept downstream reads
        var requestBuffer = new MemoryStream();
        request.Body = requestBuffer;

        //buffer the response stream in order to intercept downstream writes
        var responseStream = response.Body;
        var responseBuffer = new MemoryStream();
        response.Body = responseBuffer;

        //add the "Http-Tracking-Id" response header
        context.Response.OnSendingHeaders(state =>
        {
            var ctx = state as IOwinContext;
            if (ctx == null) return;
            var resp = ctx.Response;

            //adding the tracking id response header so that the user
            //of the API can correlate the call back to this entry
            resp.Headers.Add("http-tracking-id", new[] { apiPacket.TrackingId.ToString("d") });
        }, context);

        //invoke the next middleware in the pipeline
        await _next.Invoke(environment);

        //rewind the request and response buffers to record their content
        WriteRequestHeaders(request, apiPacket);
        requestBuffer.Seek(0, SeekOrigin.Begin);
        var requestReader = new StreamReader(requestBuffer);
        apiPacket.Request = await requestReader.ReadToEndAsync();

        WriteResponseHeaders(response, apiPacket);
        responseBuffer.Seek(0, SeekOrigin.Begin);
        var reader = new StreamReader(responseBuffer);
        apiPacket.Response = await reader.ReadToEndAsync();

        //write the apiPacket to the database
        //await database.InsterRecordAsync(apiPacket);
        System.Diagnostics.Debug.WriteLine("TrackingId: " + apiPacket.TrackingId);

        //make sure the response we buffered is flushed to the client
        responseBuffer.Seek(0, SeekOrigin.Begin);
        await responseBuffer.CopyToAsync(responseStream);
    }
    private static void WriteRequestHeaders(IOwinRequest request, ApiPacket packet)
    {
        packet.Verb = request.Method;
        packet.RequestUri = request.Uri;
        packet.RequestHeaders = request.Headers;
    }
    private static void WriteResponseHeaders(IOwinResponse response, ApiPacket packet)
    {
        packet.StatusCode = response.StatusCode;
        packet.ReasonPhrase = response.ReasonPhrase;
        packet.ResponseHeaders = response.Headers;
    }
}

我在将http-tracking-id添加到响应头（这里是这些行）时遇到了麻烦。

context.Response.OnSendingHeaders(state =>
{
    var ctx = state as IOwinContext;
    if (ctx == null) return;
    var resp = ctx.Response;

    resp.Headers.Add("http-tracking-id", new[] { apiPacket.TrackingId.ToString("d") });
}, context);

添加标题时，我有时会收到此错误：

HttpException未被用户代码处理。

附加信息：在发送HTTP标头后，服务器无法附加标头。

---

编辑1：我正在测试这个，只需运行api，打开chrome到我的http：// localhost：64051 / address。 例如，如果我浏览到任何实际的API（ http：// localhost：64051 / api / Accounts / 21067 ），我就不会收到错误。 浏览到网站的根目录时，我应该以某种方式发回404吗？

Answer 1

我认为这可能是一个简单的修复。 请试试：

var responseHeaders = (IDictionary<string, string[]>)environment["owin.ResponseHeaders"];
responseHeaders["http-tracking-id"] = new[] {apiPacket.TrackingId.ToString("d")};

但不是在context.Response.OnSendingHeaders 。 与其他人一致。