我遇到了一个问题：
System.Net.WebException：底层连接已关闭：An 接收时发生意外错误。 System.NullReferenceException： 对象引用未设置为对象的实例。
我在某些Windows 10环境中遇到此问题。相同的代码适用于其他环境。
我从下面的行收到此错误 response =（HttpWebResponse）request.GetResponse（）;
下面是详细的堆栈跟踪：
{System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a receive. ---> System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.SharePoint.Administration.SPServer.get_RegistryEncodedServerId()
at Microsoft.SharePoint.Utilities.SPMonitoredScope.PushParent()
at Microsoft.SharePoint.Utilities.SPMonitoredScope..ctor(Boolean clearCorrelationId, String name, TraceSeverity traceLevel, ISPScopedPerformanceMonitor[] monitors)
at Microsoft.SharePoint.SPCertificateValidator.SPImmutableCertificateValidator.Validate(X509Certificate2 certificate)
at Microsoft.SharePoint.SPCertificateValidator.Validate(X509Certificate2 certificate)
at Microsoft.SharePoint.SPCertificateValidator.IsValid(X509Certificate2 certificate)
at System.Net.Security.RemoteCertificateValidationCallback.Invoke(Object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
at System.Net.ServerCertValidationCallback.Callback(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Net.ServerCertValidationCallback.Invoke(Object request, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
at System.Net.Security.SecureChannel.VerifyRemoteCertificate(RemoteCertValidationCallback remoteCertValidationCallback)
at System.Net.Security.SslState.CompleteHandshake()
at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.ConnectStream.WriteHeaders(Boolean async)
--- End of inner exception stack trace ---
代码是：
public static string SendMessage(SharePointAdapter adr, string uri, Stream postStream, string contentType)
{
string responseText = null;
Stream requestStream = null;
System.Net.WebRequest request = null;
byte[] buffer = null;
HttpWebResponse response = null;
Stream receiveStream = null;
StreamReader readStream = null;
try
{
//Create a request
request = WebRequest.Create(uri);
request.Timeout = 180000;
request.Method = "POST";
request.ContentType = contentType;
request.Headers.Add("X-Vermeer-Content-Type", "application/x-www-form-urlencoded");
request.Credentials = adr.Credentials.NetworkCredentials;
HttpWebRequest httprequest = request as HttpWebRequest;
httprequest.KeepAlive = false;
adr.certificates.CopyCertificatesToCollection(httprequest.ClientCertificates);
if (adr.AdapterProxy != null)
{
request.Proxy = adr.AdapterProxy;
}
httprequest.CookieContainer = new CookieContainer();
adr.CookieManager.AddCookiesTo(httprequest.CookieContainer);
ServicePointManager.SecurityProtocol = (SecurityProtocolType)192 | (SecurityProtocolType)768 | (SecurityProtocolType)3072 | (SecurityProtocolType)48;
requestStream = request.GetRequestStream();
int iRead = 1;
int iBufferSize = 4096;
buffer = new byte[iBufferSize];
//Go to the beginning of the stream
postStream.Seek(0, SeekOrigin.Begin);
//Read from the post stream to the request stream
while (iRead > 0)
{
iRead = postStream.Read(buffer, 0, iBufferSize);
requestStream.Write(buffer, 0, iRead);
}
requestStream.Close();
response = (HttpWebResponse)request.GetResponse();
receiveStream = response.GetResponseStream();
readStream = new StreamReader(receiveStream, Encoding.UTF8);
responseText = readStream.ReadToEnd();
response.Close();
readStream.Close();
}
finally
{
requestStream = null;
request = null;
buffer = null;
response = null;
receiveStream = null;
readStream = null;
System.GC.Collect();
}
return responseText;
}
答案 0 :(得分：0)
System.NullReferenceException不是很具体。很难找到问题，特别是因为你的方法中的所有内容都在一个大的try / catch块中。
仅在需要的块上使用try/catch块，避免使用只有一个通用try / catch的大方法。有关详细信息，请参阅https://docs.microsoft.com/en-us/dotnet/standard/exceptions/best-practices-for-exceptions。
我强烈建议您使用HttpClient代替WebRequest。 HttpClient类可以在.Net Framework 4.5.2+上使用，以下是一些详细的说明以及使用它的原因：Deciding between HttpClient and WebClient。
此外，不是手动操作流，而是使用StreamContent：
client.PostAsync (url, new StreamContent(stream));
在您的代码上，您应该使用IDisposable功能（使用using）来确保关闭和处理流和其他非托管资源。例如：
using (var client = new HttpClient())
{
}
最后，避免直接操作GC，因为它会引起副作用，特别是对性能的影响。 GC只应在非常具体的情况下进行操作。有关https://msdn.microsoft.com/en-us/library/ms973837.aspx
的更多信息，请参阅这些提示可能有助于减少未来的问题，提高代码的可维护性和可读性（甚至可能会发现System.NullReferenceException问题）。