与HttpClient的在.NET 4.5和C＃HTTP HEAD请求(HTTP HEAD requ

是否有可能创建新的HTTP一个HEAD请求HttpClient在.NET 4.5？唯一的方法我能看到的是GetAsync ， DeleteAsync ， PutAsync和PostAsync 。我知道HttpWebRequest -class是能够做到这一点，但我想用现代HttpClient 。

Answer 1:

使用SendAsync与实例方法HttpRequestMessage这是利用人工HttpMethod.Head 。

GetAsync ， PostAsync等都是方便的包装围绕SendAsync ; 不太常见的HTTP方法，如HEAD ， OPTIONS等，没有得到的包装。

Answer 2:

我需要做到这一点，让TotalCount ，我是从我的Web API的get方法返回自动取款机。

当我试图@ SMIG的回答，我从我的Web API以下响应。

MethodNotAllowed：杂注：无缓存X-SourceFiles：= UTF-的8B dfdsf的Cache-Control：？？？无缓存时间：星期三，2017年3月22日20点42分五十七秒格林尼治标准时间服务器：Microsoft-IIS / 10.0 X-ASPNET -version：4.0.30319 X供电-者：ASP.NET

只好在@内置SMIG的回答让这个成功的工作。我发现在Web API方法需要明确允许Http HEAD在操作方法为属性指定它的动词。

下面是由代码注释的方式直列解释的完整代码。我已经删除了敏感的代码。

在我的Web客户端：

        HttpClient client = new HttpClient();

        // set the base host address for the Api (comes from Web.Config)
        client.BaseAddress = new Uri(ConfigurationManager.AppSettings.Get("ApiBase"));
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add( 
          new MediaTypeWithQualityHeaderValue("application/json"));

        // Construct the HEAD only needed request. Note that I am requesting
        //  only the 1st page and 1st record from my API's endpoint.
        HttpRequestMessage request = new HttpRequestMessage(
          HttpMethod.Head, 
          "api/atms?page=1&pagesize=1");

        HttpResponseMessage response = await client.SendAsync(request);

        // FindAndParsePagingInfo is a simple helper I wrote that parses the 
        // json in the Header and populates a PagingInfo poco that contains 
        // paging info like CurrentPage, TotalPages, and TotalCount, which 
        // is the total number of records in the ATMs table.
        // The source code is pasted separately in this answer.
        var pagingInfoForAtms = HeaderParser.FindAndParsePagingInfo(response.Headers);

        if (response.IsSuccessStatusCode)
            // This for testing only. pagingInfoForAtms.TotalCount correctly
            //  contained the record count
            return Content($"# of ATMs {pagingInfoForAtms.TotalCount}");

            // if request failed, execution will come through to this line 
            // and display the response status code and message. This is how
            //  I found out that I had to specify the HttpHead attribute.
            return Content($"{response.StatusCode} : {response.Headers.ToString()}");
        }

在Web API。

    // Specify the HttpHead attribute to avoid getting the MethodNotAllowed error.
    [HttpGet, HttpHead]
    [Route("Atms", Name = "AtmsList")]
    public IHttpActionResult Get(string sort="id", int page = 1, int pageSize = 5)
    {
        try
        {
            // get data from repository
            var atms =  _atmRepository.GetAll().AsQueryable().ApplySort(sort);
            // ... do some code to construct pagingInfo etc.
            // .......
            // set paging info in header.
            HttpContext.Current.Response.Headers.Add(
              "X-Pagination", JsonConvert.SerializeObject(paginationHeader));
            // ...
            return Ok(pagedAtms));
        }
        catch (Exception exception)
        {
            //... log and return 500 error
        }
    }

FindAndParsePagingInfo Helper方法，用于解析该寻呼报头数据。

public static class HeaderParser
{
public static PagingInfo FindAndParsePagingInfo(HttpResponseHeaders responseHeaders)
{
    // find the "X-Pagination" info in header
    if (responseHeaders.Contains("X-Pagination"))
    {
        var xPag = responseHeaders.First(ph => ph.Key == "X-Pagination").Value;

        // parse the value - this is a JSON-string.
        return JsonConvert.DeserializeObject<PagingInfo>(xPag.First());
    }

    return null;
}

public static string GetSingleHeaderValue(HttpResponseHeaders responseHeaders, 
    string keyName)
{
    if (responseHeaders.Contains(keyName))
        return responseHeaders.First(ph => ph.Key == keyName).Value.First();

    return null;
}

}

Answer 3:

你也可以做如下去取只是标题：

this.GetAsync($"http://url.com", HttpCompletionOption.ResponseHeadersRead).Result;