使用IHttpActionResult時如何設置自定義標題？

Question

在ASP.NET Web API 2中， IHttpActionResult在簡化控制器代碼IHttpActionResult提供了很多價值，我不願意停止使用它，但我遇到了問題。

我需要在傳出響應上設置一個ETag，我找不到任何可以訪問響應頭的屬性。 目前我正在使用ApiController的Ok<T>(T content)輔助方法，它返回一個OkNegotiatedContentResult<T>對象。 這似乎沒有暴露任何可以讓我修改標題的東西。

我錯過了什么，或者在使用股票IHttpActionResult類型時是否真的沒辦法做到這一點？ 我考慮過一個消息處理程序，但后來我必須弄清楚如何將ETag從動作中傳出（對於不同的動作，ETag的生成方式不同，所以這不是為所有動作制作通用處理程序的問題）。

我想避免使用原始的HttpResponseMessage，但此刻看起來很難。

Answer 1

對於您的場景，您需要創建自定義IHttpActionResult 。 以下是我從OkNegotiatedContentResult<T>派生的示例，因為它運行Content-Negotiation並設置Ok狀態代碼。

public class CustomOkResult<T> : OkNegotiatedContentResult<T>
{
    public CustomOkResult(T content, ApiController controller)
        : base(content, controller) { }

    public CustomOkResult(T content, IContentNegotiator contentNegotiator, HttpRequestMessage request, IEnumerable<MediaTypeFormatter> formatters) 
        : base(content, contentNegotiator, request, formatters) { }

    public string ETagValue { get; set; }

    public override async Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        HttpResponseMessage response = await base.ExecuteAsync(cancellationToken);

        response.Headers.ETag = new EntityTagHeaderValue(this.ETagValue);

        return response;
    }        
}

控制器 ：

public class ValuesController : ApiController
{
    public IHttpActionResult Get()
    {
        return new CustomOkResult<string>(content: "Hello World!", controller: this)
            {
                    ETagValue = "You ETag value"
            };
    }
}

請注意，您也可以從NegotiatedContentResult<T>派生，在這種情況下，您需要自己提供StatusCode。 希望這可以幫助。

你可以找到OkNegotiatedContentResult<T>和NegotiatedContentResult<T>的源代碼，你可以想象它實際上很簡單。

Answer 2

您可以創建HttpResponseMessage ，根據需要添加標頭，然后從中創建ResponseMessageResult ：

HttpResponseMessage response =new HttpResponseMessage(HttpStatusCode.OK);
response.Headers.Add("MyHeader", "MyHeaderValue");
return ResponseMessage(response);

Answer 3

這是我沒有ActionFilterAttributes的簡單實現，類似於AlexACD的響應。 我的解決方案使用ResponseMessageResult來實現IHttpActionResult接口。

HttpResponseMessage responseMessage = new HttpResponseMessage(HttpStatusCode.OK);
responseMessage.Headers.Add("Headername", "Value");
ResponseMessageResult response = new ResponseMessageResult(responseMessage);
return response;

Answer 4

public static class HttpExtentions
{
    public static IHttpActionResult AddHeader(this IHttpActionResult action,
        string headerName, IEnumerable<string> headerValues)
    {
        return new HeaderActionResult(action, headerName, headerValues);
    }

    public static IHttpActionResult AddHeader(this IHttpActionResult action,
        string headerName, string header)
    {
        return AddHeader(action, headerName, new[] {header});
    }

    private class HeaderActionResult : IHttpActionResult
    {
        private readonly IHttpActionResult action;

        private readonly Tuple<string, IEnumerable<string>> header;

        public HeaderActionResult(IHttpActionResult action, string headerName,
            IEnumerable<string> headerValues)
        {
            this.action = action;

            header = Tuple.Create(headerName, headerValues);
        }

        public async Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
        {
            var response = await action.ExecuteAsync(cancellationToken);

            response.Headers.Add(header.Item1, header.Item2);

            return response;
        }
    }
}

Answer 5

這可以通過ActionFilterAttribute來實現，它將在控制器函數之后但在它出去之前檢查響應，然后你可以在控制器方法上設置屬性來添加這些信息，這是我的實現如下：

public class EnableETag : ActionFilterAttribute
{

    /// <summary>
    /// NOTE: a real production situation, especially when it involves a web garden
    ///       or a web farm deployment, the tags must be retrieved from the database or some other place common to all servers.
    /// </summary>
    private static ConcurrentDictionary<string, EntityTagHeaderValue> etags = new ConcurrentDictionary<string, EntityTagHeaderValue>();

    public override void OnActionExecuting(HttpActionContext context)
    {
        var request = context.Request;
        if (request.Method == HttpMethod.Get)
        {
            var key = GetKey(request);
            ICollection<EntityTagHeaderValue> etagsFromClient = request.Headers.IfNoneMatch;
            if (etagsFromClient.Count > 0)
            {
                EntityTagHeaderValue etag = null;
                if (etags.TryGetValue(key, out etag) && etagsFromClient.Any(t => t.Tag == etag.Tag))
                {
                    context.Response = new HttpResponseMessage(HttpStatusCode.NotModified);
                    SetCacheControl(context.Response);
                }
            }
        }
    }
    public override void OnActionExecuted(HttpActionExecutedContext context)
    {
        var request = context.Request;
        var key = GetKey(request);
        EntityTagHeaderValue etag;
        if (!etags.TryGetValue(key, out etag) || request.Method == HttpMethod.Put ||
        request.Method == HttpMethod.Post)
        {
            etag = new EntityTagHeaderValue("\"" + Guid.NewGuid().ToString() + "\"");
            etags.AddOrUpdate(key, etag, (k, val) => etag);
        }
        context.Response.Headers.ETag = etag;
        SetCacheControl(context.Response);
    }
    private string GetKey(HttpRequestMessage request)
    {
        return request.RequestUri.ToString();
    }

    /// <summary>
    /// Defines the time period to hold item in cache (currently 10 seconds)
    /// </summary>
    /// <param name="response"></param>
    private void SetCacheControl(HttpResponseMessage response)
    {
        response.Headers.CacheControl = new CacheControlHeaderValue()
        {
            MaxAge = TimeSpan.FromSeconds(10),
            MustRevalidate = true,
            Private = true
        };
    }
}

}

Answer 6

這是我在常用的Web API 2庫代碼中使用的解決方案，它可以輕松地支持設置任何標頭 - 或ExecuteAsync提供的HttpResponseMessage上的任何其他屬性 - 而不是綁定到任何特定的派生NegotiatedContentResult實現：

public class FlexibleNegotiatedContentResult<T> : NegotiatedContentResult<T>
{
    private readonly Action<HttpResponseMessage> _responseMessageDelegate;

    public FlexibleNegotiatedContentResult(HttpStatusCode statusCode, T content, IContentNegotiator contentNegotiator, HttpRequestMessage request, IEnumerable<MediaTypeFormatter> formatters)
        : base(statusCode, content, contentNegotiator, request, formatters)
    {
    }

    public FlexibleNegotiatedContentResult(HttpStatusCode statusCode, T content, ApiController controller, Action<HttpResponseMessage> responseMessageDelegate = null)
        : base(statusCode, content, controller)
    {
        _responseMessageDelegate = responseMessageDelegate;
    }

    public override async Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        HttpResponseMessage responseMessage = await base.ExecuteAsync(cancellationToken);

        if (_responseMessageDelegate != null)
        {
            _responseMessageDelegate(responseMessage);
        }

        return responseMessage;
    }
}

和一個示例用法：

new FlexibleNegotiatedContentResult<string>(HttpStatusCode.Created, "Entity created!", controller, response => response.Headers.Location = new Uri("https://myapp.com/api/entity/1"));

Answer 7

很老的問題。 可能其他答案在時間上是有意義的，但今天你可以簡單地添加這一行而不改變或擴展IHttpActionResult 。 它在您的回復中完美地添加了標題。 確保格式化為RFC 1123標准，如下所示。 否則，雖然Last-Modified出現在標題中，但客戶端無法使用HttpClient讀取它。

    System.Web.HttpContext.Current.Response.Headers.
Add(Microsoft.Net.Http.Headers.HeaderNames.LastModified, DBdateModified.Value.ToString("r"));