我们有一个用.NET Standard 2.0编译的库，它有一个WCF服务。为了向Web服务的请求添加自定义标头，我们在此处实现了代码：https://blogs.msdn.microsoft.com/mohamedg/2012/12/13/adding-http-headers-to-wcf-calls/
当我们在.NET Framework应用程序中引用此库时，我们可以对我们想要的Web服务进行任何调用，并且返回正确的结果。但是，在.NET Core 2.0应用程序中，库通常（但不总是！）会抛出System.FormatException，具体取决于我们设置的用户代理。
像“Mozilla / 4.0”这样的东西不会抛出错误，但“Mozilla / 4.0（兼容; MSIE 6.0; MS Web服务客户端协议4.0.30319.42000）”将但仅带有错误消息“值的格式”（兼容; MSIE 6.0; MS Web服务客户端协议4.0.30319.42000）的核心应用程序无效。“。
简而言之，这是代码（从接口中省略了没有实现的方法）。当前用户代理仅为了排除故障而硬编码。
internal class ClientUserAgentMessage : IClientMessageInspector
{
public ClientUserAgentMessage(string userAgent) { }
public object BeforeSendRequest(ref Message request, IClientChannel channel)
{
HttpRequestMessageProperty property = new HttpRequestMessageProperty();
//This is an example user agent that fails, and we would not expect it to.
property.Headers["User-Agent"] = "Mozilla/4.0 (compatible; MSIE 6.0; MS Web Services Client Protocol 4.0.30319.42000)";
request.Properties.Add(HttpRequestMessageProperty.Name, property);
return null;
}
}
internal class UserAgentEndpointBehavior : IEndpointBehavior
{
public UserAgentEndpointBehavior() { }
public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
{
clientRuntime.ClientMessageInspectors.Add(new ClientUserAgentMessage());
}
}
上面的代码是在引用标准dll的应用程序中实现的（省略客户端初始化详细信息）：
//SoapClient and related WCF code is generated from the web service via svcutil.exe
SoapClient client = new SoapClient(...);
client.Endpoint.EndpointBehaviors.Add(new UserAgentEndpointBehavior());
//Call some web service functions...
//This succeeds in a .NET 4.7 app,
//but blows up in a .NET Core 2.0 app due to the user agent being an "invalid format".
//client.Login();
当用户代理实际上看起来是有效格式时，为什么这只是.NET Core的问题？它似乎抱怨哪里有更多的1 /，括号，冒号，分号，空格......基本上除了第一个/，下划线和小数之外的任何非字母数字。
根据要求，完整的堆栈跟踪：
at System.Net.Http.Headers.HttpHeaderParser.ParseValue(String value, Object storeValue, Int32& index)
at System.Net.Http.Headers.ProductInfoHeaderValue.Parse(String input)
at System.ServiceModel.Channels.HttpChannelFactory`1.HttpClientRequestChannel.HttpClientChannelAsyncRequest.PrepareMessageHeaders(Message message)
at System.ServiceModel.Channels.HttpChannelFactory`1.HttpClientRequestChannel.HttpClientChannelAsyncRequest.<SendRequestAsync>d__13.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.ServiceModel.Channels.RequestChannel.<RequestAsync>d__33.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.ServiceModel.Channels.RequestChannel.<RequestAsyncInternal>d__32.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.TaskHelpers.WaitForCompletionNoSpin[TResult](Task`1 task)
at System.ServiceModel.Channels.RequestChannel.Request(Message message, TimeSpan timeout)
at System.ServiceModel.Dispatcher.RequestChannelBinder.Request(Message message, TimeSpan timeout)
at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(MethodCall methodCall, ProxyOperationRuntime operation)
at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(MethodInfo targetMethod, Object[] args)
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Reflection.DispatchProxyGenerator.Invoke(Object[] args)
at generatedProxy_1.Login(LoginRequest )
at MyServiceNamespace.SoapClient.ServiceNamespace.Soap.Login(LoginRequest request)
at MyServiceNamespace.SoapClient.Login(String strUser, String strPass, String strKey)
at MyLibraryNamespace.MyClass.Login(String sUser, String sPass, String sKey)
FWIW，你可以设置为“User-Agent”以外的标题，一切都很好（至少，我试过“XTESTX”，也没有例外）。