為HttpClient添加默認(rèn)請(qǐng)求報(bào)頭的四種解決方案

來(lái)源：本站原創(chuàng)|時(shí)間：2020-01-11|欄目：ASP.NET|點(diǎn)擊：次

前言

HttpClient在Web調(diào)用中具有廣泛的應(yīng)用，而為它添加默認(rèn)請(qǐng)求頭是我們經(jīng)常遇到的需求，本文介紹4種為HttpClient添加默認(rèn)請(qǐng)求頭的方式。下面話不多說(shuō)了，來(lái)一起看看詳細(xì)的介紹吧

第一種方式

直接在創(chuàng)建的HttpClient對(duì)象的DefaultRequestHeaders集合中添加報(bào)頭。

class Program
{
  static Task Main()=> SendAsync1();

  private static async Task SendAsync1()
  {
    var httpClient = new HttpClient();
    AddDefaultHeaders(httpClient);
    await httpClient.GetStringAsync("http://localhost:5000/");
  }

  private static void AddDefaultHeaders(HttpClient httpClient)
  {
    httpClient.DefaultRequestHeaders.Add("x-www-foo", "123");
    httpClient.DefaultRequestHeaders.Add("x-www-bar", "456");
    httpClient.DefaultRequestHeaders.Add("x-www-baz", "789");
  }
}

第二種方式

對(duì)于.NET Core應(yīng)用來(lái)說(shuō)，我們更推薦的做法是采用依賴注入的方式，利用IHttpClientFactory來(lái)創(chuàng)建HttpClient對(duì)象，那么我們?cè)谶M(jìn)行相關(guān)服務(wù)注冊(cè)的時(shí)候就可以設(shè)置默認(rèn)請(qǐng)求報(bào)頭。

class Program
{
  static Task Main()=> SendAsync2();

  private static async Task SendAsync2()
  {
    var services = new ServiceCollection();
    services.AddHttpClient("", AddDefaultHeaders);
    var httpClient = services
      .BuildServiceProvider()
      .GetRequiredService<IHttpClientFactory>()
      .CreateClient();
    await httpClient.GetStringAsync("http://localhost:5000/");
  }

  private static void AddDefaultHeaders(HttpClient httpClient)
  {
    httpClient.DefaultRequestHeaders.Add("x-www-foo", "123");
    httpClient.DefaultRequestHeaders.Add("x-www-bar", "456");
    httpClient.DefaultRequestHeaders.Add("x-www-baz", "789");
  }
}

第三種方式

由于HttpClient在發(fā)送請(qǐng)求的時(shí)候會(huì)利用DiagnosticSource對(duì)象發(fā)送相應(yīng)的診斷事件，并且將作為請(qǐng)求的HttpRequestMessage對(duì)象作為請(qǐng)求事件內(nèi)容負(fù)載。我們可以訂閱該事件，在請(qǐng)求被發(fā)送之前將其攔截下來(lái)，并添加相應(yīng)的請(qǐng)求頭即可。

class Program
{
  static Task Main()=> SendAsync3();

  private static async Task SendAsync3()
  {
    Func<object, HttpRequestMessage> requestAccessor = null;
    DiagnosticListener.AllListeners.Subscribe(listener =>
    {
      if (listener.Name == "HttpHandlerDiagnosticListener")
      {
        listener.Subscribe(kv =>
        {
          if (kv.Key == "System.Net.Http.HttpRequestOut.Start")
          {
            requestAccessor ??= BuildRequestAccessor(kv.Value.GetType());
            var request = requestAccessor(kv.Value);
            AddDefaultHeaders(request);
          }
        });
      }
    });

    var httpClient = new HttpClient();
    await httpClient.GetStringAsync("http://localhost:5000/");
    static Func<object, HttpRequestMessage> BuildRequestAccessor(Type payloadType)
    {
      var property = payloadType.GetProperty("Request", BindingFlags.Instance | BindingFlags.Public);
      var payload = Expression.Parameter(typeof(object));
      var convertedPayload = Expression.Convert(payload, payloadType);
      var getRequest = Expression.Call(convertedPayload, property.GetMethod);
      var convert = Expression.Convert(getRequest, typeof(HttpRequestMessage));
      return Expression.Lambda<Func<object, HttpRequestMessage>>(convert, payload).Compile();
    }
  }

  private static void AddDefaultHeaders(HttpRequestMessage request)
  {
    request.Headers.Add("x-www-foo", "123");
    request.Headers.Add("x-www-bar", "456");
    request.Headers.Add("x-www-baz", "789");
  }
}

第四種方式

上面這種方式可以采用強(qiáng)類型編程方式，具體的代碼如下。

class Program
{
  static Task Main()=> SendAsync4();

  private static async Task SendAsync4()
  {
    DiagnosticListener.AllListeners.Subscribe(listener =>
    {
      if (listener.Name == "HttpHandlerDiagnosticListener")
      {
        listener.SubscribeWithAdapter(new HttpClientListener());
      }
    });
      
    var httpClient = new HttpClient();
    await httpClient.GetStringAsync("http://localhost:5000/");
  }

  private sealed class HttpClientListener
  {
    [DiagnosticName("System.Net.Http.HttpRequestOut.Start")]
    public void OnSend(HttpRequestMessage request) => AddDefaultHeaders(request);

    //Must subscribute the System.Net.Http.HttpRequestOut event.
    [DiagnosticName("System.Net.Http.HttpRequestOut")]
    public void OnSend() { }
  }

  private static void AddDefaultHeaders(HttpRequestMessage request)
  {
    request.Headers.Add("x-www-foo", "123");
    request.Headers.Add("x-www-bar", "456");
    request.Headers.Add("x-www-baz", "789");
  }
}

總結(jié)

以上就是這篇文章的全部?jī)?nèi)容了，希望本文的內(nèi)容對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，謝謝大家對(duì)我們的支持。

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