如何在使用IHttpActionResult時設置自定義標題？

Question

在的ASP.NET Web API 2，IHttpActionResult提供了很多有價值的簡化控制器代碼，我不願意停止使用它，但我已經打了一個問題。

我需要設置一個ETag上的輸出響應，我找不到這使我獲得了響應的頭部任何財產。此刻，我使用ApiController中的Ok<T>(T content)幫助器方法，該方法返回OkNegotiatedContentResult<T>對象。這似乎沒有任何暴露，讓我修改標題。

我缺少的東西，或者是真的沒有辦法同時使用存量IHttpActionResult類型做到這一點？我考慮過一個消息處理程序，但是接下來我必須弄清楚如何將ETag傳遞出動作（對於不同的動作，ETag的生成方式不同），所以這不是爲所有動作製作通用處理程序的問題。

我想避免使用原始HttpResponseMessage，但此刻是在尋找困難。

Answer 1

對於您的情況，您需要創建一個自定義IHttpActionResult。以下是我從OkNegotiatedContentResult<T>派生的示例，因爲它運行的是Content-Negotiation並設置了Ok狀態碼。

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>得出，在這種情況下，您需要提供的StatusCode自己。希望這可以幫助。

你可以找到OkNegotiatedContentResult<T>和NegotiatedContentResult<T>，正如你可以想像是簡單的實際的源代碼。

Answer 2

您可以創建一個HttpResponseMessage，根據需要添加標題，然後創建ResponseMessageResult從中：

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

Answer 3

這可以用一個ActionFilterAttribute，將審查控制器功能後的反應，但前實現它熄滅，那麼你可以設置在控制器方法屬性添加此信息，這裏是我下面的實現：

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 4

這裏是一個解決方案，我在我的常見的Web API 2庫代碼中使用，可以輕鬆支持設置任何頭 - 或者在ExecuteAsync提供--without被捆綁到任何具體的HttpResponseMessage任何其他屬性衍生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; 
    } 
} 

和用法的例子：

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

Answer 5

這是我沒有ActionFilterAttributes簡單的實現，類似於AlexACD的響應。我的解決方案使用實現IHttpActionResult接口的ResponseMessageResult。

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

Answer 6

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; 
     } 
    } 
}