爲什麼設置ServicePointManager.ServerCertificateValidationCallback = null不起作用？

Question

我有下面的代碼片段，我是從一組集成測試呼叫：

private void Url_Contains_String_With_Certificate_Warning(string url, string expected) { 
    // This line should restore default cert validation behaviour 
    ServicePointManager.ServerCertificateValidationCallback = null; 
    var wc = new WebClient(); 
    try { 
    wc.DownloadString(url); 
    Assert.Fail("Should have thrown a WebException by now"); 
    } catch (WebException x) { 
    Assert.That(x.InnerException is AuthenticationException, "Expected an AuthenticationException inside a WebException due to invalid certificate"); 
    Assert.AreEqual("The remote certificate is invalid according to the validation procedure.", x.InnerException.Message); 
    } 
    // This line overrides cert validation behaviour to accept invalid certs 
    ServicePointManager.ServerCertificateValidationCallback = delegate { return(true); }; 
    var result = wc.DownloadString(url); 
    Assert.That(result.Contains(expected), String.Format("Didn't find expected text '{0}' in HTML response", expected)); 
} 

然而，只有在任何給定的試運行第一個測試將通過......一旦我碰到這條線：

ServicePointManager.ServerCertificateValidationCallback = delegate { return(true); }; 

我不能讓Web客戶端在同一個試運行再次拋出一個證書錯誤，即使我明確地指定此委託爲null。我也嘗試明確返回false;我嘗試添加一個命名委託引用，然後刪除它而不是隻分配/重新分配，甚至檢查回調中的SslPolicyErrors並返回policyErrors == SslPolicyErrors.None - 沒有任何工作。

（我明確驗證了我們的測試環境中的某些URL返回了證書警告，而且我還需要驗證如果用戶忽略了證書警告，他們將看到一個特定的頁面，因此稍微有點奇怪的證書處理）

任何想法？

Answer 1

集System.Net.ServicePointManager.MaxServicePointIdleTime 0

沒有這個連接通道保持開放，因此沒有委託調用

http://blogs.msdn.com/b/jpsanders/archive/2009/05/20/understanding-maxservicepointidletime-and-defaultconnectionlimit.aspx

Answer 2

你應該叫 -

ServicePointManager.ServerCertificateValidationCallback == delegate { return(true); }; 

在創建請求之前，請在您的情況下致電

var wc = new WebClient();