.NET 4.5 和 C# 中带有 HttpClient 的 HTTP HEAD 请求
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HTTP HEAD request with HttpClient in .NET 4.5 and C#
提问by The Wavelength
Is it possible to create a HTTP HEAD request with the new HttpClientin .NET 4.5? The only methods I can find are GetAsync, DeleteAsync, PutAsyncand PostAsync. I know that the HttpWebRequest-class is able to do that, but I want to use the modern HttpClient.
是否可以使用HttpClient.NET 4.5 中的新内容创建 HTTP HEAD 请求？唯一的方法我能看到的是GetAsync，DeleteAsync，PutAsync和PostAsync。我知道HttpWebRequest-class 能够做到这一点，但我想使用现代HttpClient.
采纳答案by Smigs
Use the SendAsyncmethod with an instance of HttpRequestMessagethat was constructed using HttpMethod.Head.
将该SendAsync方法与HttpRequestMessage使用 构造的实例一起使用HttpMethod.Head。
GetAsync, PostAsync, etc are convenient wrappersaround SendAsync; the less common HTTP methods such as HEAD, OPTIONS, etc, don't get a wrapper.
GetAsync，PostAsync等是方便的包装周围SendAsync; 不太常见的HTTP方法，如HEAD，OPTIONS等，没有得到的包装。
回答by Shiva
I needed to do this, to get TotalCountof ATMs that I was returning from my Web API's GETMethod.
我需要这样做，以获取TotalCount我从 Web API 的GET方法返回的 ATM 。
When I tried @Smig's answer I got the following Response from my Web API.
当我尝试@Smig 的回答时，我从我的 Web API 得到了以下响应。
MethodNotAllowed : Pragma: no-cache X-SourceFiles: =?UTF-8?B?dfdsf Cache-Control: no-cache Date: Wed, 22 Mar 2017 20:42:57 GMT Server: Microsoft-IIS/10.0 X-AspNet-Version: 4.0.30319 X-Powered-By: ASP.NET
MethodNotAllowed : Pragma: no-cache X-SourceFiles: =?UTF-8?B?dfdsf Cache-Control: no-cache Date: Wed, 22 Mar 2017 20:42:57 GMT Server: Microsoft-IIS/10.0 X-AspNet -版本：4.0.30319 X-Powered-By：ASP.NET
Had to built upon @Smig's answer to get this working successfully. I found out that the Web API methods needs to explicitly allow the Http HEADverb by specifying it in the Actionmethod as an Attribute.
必须建立在@Smig 的回答上才能成功完成这项工作。我发现 Web API 方法需要Http HEAD通过在Action方法中将动词指定为属性来明确允许该动词。
Here's the complete code with inline explanation by way of code comments. I've removed the sensitive code.
这是通过代码注释的方式内联解释的完整代码。我已经删除了敏感代码。
In my Web Client:
在我的 Web 客户端中：
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()}");
}
In the Web API.
在 Web API 中。
// 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 method for parsing the paging header data.
FindAndParsePagingInfo 解析分页头数据的辅助方法。
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;
}
}
}
回答by rothschild86
You may also do as follows to fetch just the headers:
您还可以执行以下操作来仅获取标题：
this.GetAsync($"http://url.com", HttpCompletionOption.ResponseHeadersRead).Result;
