通过C#实现OPC-UA服务端（⼆）
前⾔
通过我前⾯的⼀篇⽂件，我们已经能够搭建⼀个OPC-UA服务端了，并且也拥有了⼀些基础功能。这⼀次咱们就来了解⼀下OPC-UA的服务注册与发现，如果对服务注册与发现
这个概念不理解的朋友，可以先百度⼀下，由于近年来微服务架构的兴起，服务注册与发现已经成为⼀个很时髦的概念，它的主要功能可分为三点：
1、服务注册；
2、服务发现；
3、⼼跳检测。
如果运⾏过OPC-UA源码的朋友们应该已经发现了，OPC-UA服务端启动之后，每隔⼀会就会输出⼀⾏错误提⽰信息，⼤致内容是"服务端注册失败,xxx毫秒之后重试"，通过查看
源码我们可以知道，这是因为OPC-UA服务端启动之后，会⾃动调⽤"p://localhost:4840/"的RegisterServer2⽅法注册⾃⼰，如果注册失败，则会⽴即调⽤RegisterServer⽅
法再次进⾏服务注册，⽽由于我们没有"p://localhost:4840/"这个服务，所以每隔⼀会⼉就会提⽰服务注册失败。
现在我们就动⼿来搭建⼀个"p://localhost:4840/"服务，在OPC-UA标准中，它叫Discovery Server。
⼀、服务配置
Discovery Server的服务配置与普通的OPC-UA服务配置差不多，只需要注意⼏点：
1、服务的类型ApplicationType是DiscoveryServer⽽不是Server；
2、服务启动时application.Start()传⼊的实例化对象需要实现IDiscoveryServer接⼝。
配置代码如下:
var config = new ApplicationConfiguration()
{
ApplicationName = "Axiu UA Discovery",
ApplicationUri = Utils.Format(@"urn:{0}:AxiuUADiscovery", System.Net.Dns.GetHostName()),
ApplicationType = ApplicationType.DiscoveryServer,
ServerConfiguration = new ServerConfiguration()
{
BaseAddresses = { "p://localhost:4840/" },
MinRequestThreadCount = 5,
MaxRequestThreadCount = 100,
MaxQueuedRequestCount = 200
},
DiscoveryServerConfiguration = new DiscoveryServerConfiguration()
{
BaseAddresses = { "p://localhost:4840/" },
ServerNames = { "OpcuaDiscovery" }
},
SecurityConfiguration = new SecurityConfiguration
{
ApplicationCertificate = new CertificateIdentifier { StoreType = @"Directory", StorePath = @"%CommonApplicationData%\OPC Foundation\CertificateStores\MachineDefault", SubjectName = Utils.Format(@"CN={0}, DC={1}", "AxiuOpcua",        TrustedIssuerCertificates = new CertificateTrustList { StoreType = @"Directory", StorePath = @"%CommonApplicationData%\OPC Foundation\CertificateStores\UA Certificate Authorities" },
TrustedPeerCertificates = new CertificateTrustList { StoreType = @"Directory", StorePath = @"%CommonApplicationData%\OPC Foundation\CertificateStores\UA Applications" },
RejectedCertificateStore = new CertificateTrustList { StoreType = @"Directory", StorePath = @"%CommonApplicationData%\OPC Foundation\CertificateStores\RejectedCertificates" },
AutoAcceptUntrustedCertificates = true,
AddAppCertToTrustedStore = true
},
TransportConfigurations = new TransportConfigurationCollection(),
TransportQuotas = new TransportQuotas { OperationTimeout = 15000 },
ClientConfiguration = new ClientConfiguration { DefaultSessionTimeout = 60000 },
TraceConfiguration = new TraceConfiguration()
};
config.Validate(ApplicationType.DiscoveryServer).GetAwaiter().GetResult();
if (config.SecurityConfiguration.AutoAcceptUntrustedCertificates)
{
config.CertificateValidator.CertificateValidation += (s, e) => { e.Accept = (e.Error.StatusCode == StatusCodes.BadCertificateUntrusted); };
}
var application = new ApplicationInstance
{
ApplicationName = "Axiu UA Discovery",
ApplicationType = ApplicationType.DiscoveryServer,
ApplicationConfiguration = config
};
//application.CheckApplicationInstanceCertificate(false, 2048).GetAwaiter().GetResult();
bool certOk = application.CheckApplicationInstanceCertificate(false, 0).Result;
if (!certOk)
{
Console.WriteLine("证书验证失败!");
}
var server = new DiscoveryServer();
// start the server.
application.Start(server).Wait();
⼆、实现IDiscoveryServer接⼝
下⾯我们就来看看前⾯Discovery服务启动时传⼊的实例化对象与普通服务启动时传⼊的对象有什么不⼀样，在我们启动⼀个普通OPC-UA服务时，我们可以直接使⽤
StandardServer的对象，程序不会报错，只不过是没有任何节点和内容⽽已，⽽现在，如果我们直接使⽤DiscoveryServerBase类的对象，启动Discovery服务时会报错。哪怕是
我们实现了IDiscoveryServer接⼝仍然会报错。为了能启动Discovery服务我们还必须重写ServerBase中
的两个⽅法：
1、EndpointBase GetEndpointInstance(ServerBase server)，默认的GetEndpointInstance⽅法返回的类型是SessionEndpoint对象，⽽Discovery服务应该返回的是
DiscoveryEndpoint；
protected override EndpointBase GetEndpointInstance(ServerBase server)
{
  return new DiscoveryEndpoint(server);//SessionEndpoint
}
2、void StartApplication(ApplicationConfiguration configuration)，默认的StartApplication⽅法没有执⾏任何操作，⽽我们需要去启动⼀系列与Discovery服务相关的操作。
protected override void StartApplication(ApplicationConfiguration configuration)
{
lock (m_lock)
{
try
{
// create the datastore for the instance.
m_serverInternal = new ServerInternalData(
ServerProperties,
configuration,
MessageContext,
new CertificateValidator(),
InstanceCertificate);
/
/ create the manager responsible for providing localized string resources.
ResourceManager resourceManager = CreateResourceManager(m_serverInternal, configuration);
// create the manager responsible for incoming requests.
RequestManager requestManager = new RequestManager(m_serverInternal);
// create the master node manager.
MasterNodeManager masterNodeManager = new MasterNodeManager(m_serverInternal, configuration, null);
// add the node manager to the datastore.
m_serverInternal.SetNodeManager(masterNodeManager);
// put the node manager into a state that allows it to be used by other objects.
masterNodeManager.Startup();
// create the manager responsible for handling events.
EventManager eventManager = new EventManager(m_serverInternal, (uint)configuration.ServerConfiguration.MaxEventQueueSize);
// creates the server object.
m_serverInternal.CreateServerObject(
eventManager,
resourceManager,
requestManager);
// create the manager responsible for aggregates.
m_serverInternal.AggregateManager = CreateAggregateManager(m_serverInternal, configuration);
// start the session manager.
SessionManager sessionManager = new SessionManager(m_serverInternal, configuration);
sessionManager.Startup();
// start the subscription manager.
SubscriptionManager subscriptionManager = new SubscriptionManager(m_serverInternal, configuration);
subscriptionManager.Startup();
// add the session manager to the datastore.
m_serverInternal.SetSessionManager(sessionManager, subscriptionManager);
ServerError = null;
// set the server status as running.
SetServerState(ServerState.Running);
// monitor the configuration file.
if (!String.IsNullOrEmpty(configuration.SourceFilePath))
{
var m_configurationWatcher = new ConfigurationWatcher(configuration);
m_configurationWatcher.Changed += new EventHandler<ConfigurationWatcherEventArgs>(this.OnConfigurationChanged);
}
CertificateValidator.CertificateUpdate += OnCertificateUpdate;
//60s后开始清理过期服务列表，此后每60s检查⼀次
m_timer = new Timer(ClearNoliveServer, null, 60000, 60000);
Console.WriteLine("Discovery服务已启动完成，请勿退出程序");
}
catch (Exception e)
{
Utils.Trace(e, "Unexpected error starting application");
m_serverInternal = null;
ServiceResult error = ServiceResult.Create(e, StatusCodes.BadInternalError, "Unexpected error starting application");
ServerError = error;
throw new ServiceResultException(error);
}
}
}
三、注册与发现服务
服务注册之后，就涉及到服务信息如何保存，OPC-UA标准⾥⾯好像是没有固定要的要求，应该是没有，⾄少我没有发现...傲娇.jpg。
1.注册服务
这⾥我就直接使⽤⼀个集合来保存服务信息，这种⽅式存在⼀个问题：如果Discovery服务重启了，那么在服务重新注册之前这段时间内，所有已注册的服务信息都丢失了(因为OPC-UA服务的⼼跳间隔是30s，也就是最⼤可能会有30s的时间服务信息丢失)。所以如果对服务状态信息敏感的情况，请⾃⾏使⽤其他⽅式，可以存储到数据库，也可以⽤其他分布式缓存来保存。这些就不在我们的讨论范围内了，我们先看看服务注册的代码。
public virtual ResponseHeader RegisterServer2(
RequestHeader requestHeader,
RegisteredServer server,
ExtensionObjectCollection discoveryConfiguration,
out StatusCodeCollection configurationResults,
out DiagnosticInfoCollection diagnosticInfos)
{
configurationResults = null;
diagnosticInfos = null;
ValidateRequest(requestHeader);
// Insert implementation.
try
{
Console.WriteLine(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") + "：服务注册:" + server.DiscoveryUrls.FirstOrDefault());
RegisteredServerTable model = _serverTable.Where(d => d.ServerUri == server.ServerUri).FirstOrDefault();
if (model != null)
{
model.LastRegistered = DateTime.Now;
}
else
{
model = new RegisteredServerTable()
{
DiscoveryUrls = server.DiscoveryUrls,
GatewayServerUri = server.GatewayServerUri,
IsOnline = server.IsOnline,
LastRegistered = DateTime.Now,
ProductUri = server.ProductUri,
SemaphoreFilePath = server.SemaphoreFilePath,
ServerNames = server.ServerNames,
ServerType = server.ServerType,
ServerUri = server.ServerUri
};
_serverTable.Add(model);
}
configurationResults = new StatusCodeCollection() { StatusCodes.Good };
return CreateResponse(requestHeader, StatusCodes.Good);
}
catch (Exception ex)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("客户端调⽤RegisterServer2()注册服务时触发异常:" + ex.Message);
Console.ResetColor();
}
return CreateResponse(requestHeader, StatusCodes.BadUnexpectedError);
}
前⾯有说到，OPC-UA普通服务启动后会先调⽤RegisterServer2⽅法注册⾃⼰，如果注册失败，则会⽴即调⽤RegisterServer⽅法再次进⾏服务注册。所以，为防万⼀。RegisterServer2和RegisterServer我们都需要实现，但是他们的内容其实是⼀样的，毕竟都是⼲⼀样的活--接收服务信息，然后把服务信息保存起来。
public virtual ResponseHeader RegisterServer(
RequestHeader requestHeader,
RegisteredServer server)
{
ValidateRequest(requestHeader);
// Insert implementation.
try
{
Console.WriteLine(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") + "：服务注册:" + server.DiscoveryUrls.FirstOrDefault());
RegisteredServerTable model = _serverTable.Where(d => d.ServerUri == server.ServerUri).FirstOrDefault();
if (model != null)
{
model.LastRegistered = DateTime.Now;
}
else
{
model = new RegisteredServerTable()
{
DiscoveryUrls = server.DiscoveryUrls,
GatewayServerUri = server.GatewayServerUri,
IsOnline = server.IsOnline,
LastRegistered = DateTime.Now,
ProductUri = server.ProductUri,
SemaphoreFilePath = server.SemaphoreFilePath,
ServerNames = server.ServerNames,
ServerType = server.ServerType,
ServerUri = server.ServerUri
};
_serverTable.Add(model);
}
return CreateResponse(requestHeader, StatusCodes.Good);
}
catch (Exception ex)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("客户端调⽤RegisterServer()注册服务时触发异常:" + ex.Message);
Console.ResetColor();
}
return CreateResponse(requestHeader, StatusCodes.BadUnexpectedError);
}
2.发现服务
服务注册之后，我们的Discovery服务就知道有哪些OPC-UA服务已经启动了，所以我们还需要⼀个⽅法来告诉客户端这些已启动的服务信息。FindServers()⽅法就是来⼲这件事的。
public override ResponseHeader FindServers(
RequestHeader requestHeader,
string endpointUrl,
StringCollection localeIds,
StringCollection serverUris,
out ApplicationDescriptionCollection servers)
{
servers = new ApplicationDescriptionCollection();
ValidateRequest(requestHeader);
Console.WriteLine(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") + "：请求查服务...");
string hostName = Dns.GetHostName();
lock (_serverTable)
{
foreach (var item in _serverTable)
tcp ip协议 opc ua
{
StringCollection urls = new StringCollection();
foreach (var url in item.DiscoveryUrls)
{
if (url.Contains("localhost"))
{
string str = url.Replace("localhost", hostName);
urls.Add(str);
}
else
{
urls.Add(url);
}
}
servers.Add(new ApplicationDescription()
{
ApplicationName = item.ServerNames.FirstOrDefault(),
ApplicationType = item.ServerType,
ApplicationUri = item.ServerUri,
DiscoveryProfileUri = item.SemaphoreFilePath,
DiscoveryUrls = urls,
ProductUri = item.ProductUri,
GatewayServerUri = item.GatewayServerUri
});
}
}
return CreateResponse(requestHeader, StatusCodes.Good);
}
3.⼼跳检测
需要注意⼀点，在OPC-UA标准中并没有提供单独的⼼跳⽅法，它采⽤的⼼跳⽅式就是再次向Discovery服务注册⾃⼰，这也就是为什么服务注册失败之后会重试；服务注册成功了，它也还是会重试。所以在服务注册时，我们需要判断⼀下服务信息是否已经存在了，如果已经存在了，那么就执⾏⼼跳的操作。
⾄此，我们已经实现的服务的注册与发现，IDiscoveryServer接⼝要求的内容我们也都实现了，但是有没有发现我们还少了⼀样东西，就是如果我们的某个普通服务关闭了或是掉线了，我们的Discovery服务
还是保存着它的信息，这个时候理论上来讲，已离线的服务信息就应该删掉，不应该给客户端返回了。所以这就需要⼀个⽅法来清理那些已经离线的服务。
private void ClearNoliveServer(object obj)
{
try
{
var tmpList = _serverTable.Where(d => d.LastRegistered < DateTime.Now.AddMinutes(-1) || !d.IsOnline).ToList();
if (tmpList.Count > 0)
{
lock (_serverTable)
{
foreach (var item in tmpList)
{
Console.WriteLine(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") + "：清理服务:" + item.DiscoveryUrls.FirstOrDefault());
_serverTable.Remove(item);
}
}
}
}
catch (Exception ex)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("清理掉线服务ClearNoliveServer()时触发异常:" + ex.Message);
Console.ResetColor();
}
}
我这⾥以⼀分钟为限，如果⼀分钟内都没有⼼跳的服务，我就当它是离线了。关于这个⼀分钟需要根据⾃⾝情况来调整。
补充说明
OPC-UA服务默认是向localhost注册⾃⼰，当然，也可以调整配置信息，把服务注册到其他地⽅去，只需在ApplicationConfiguration对象中修改ServerConfiguration属性如下: ServerConfiguration = new ServerConfiguration() {
BaseAddresses = { "p://localhost:8020/", "localhost:8021/" },
MinRequestThreadCount = 5,
MaxRequestThreadCount = 100,
MaxQueuedRequestCount = 200,
RegistrationEndpoint = new EndpointDescription() {
EndpointUrl = "p://172.17.4.68:4840",
SecurityLevel = ServerSecurityPolicy.CalculateSecurityLevel(MessageSecurityMode.SignAndEncrypt, SecurityPolicies.Basic256Sha256),
SecurityMode = MessageSecurityMode.SignAndEncrypt,
SecurityPolicyUri = SecurityPolicies.Basic256Sha256,
Server = new ApplicationDescription() { ApplicationType = ApplicationType.DiscoveryServer },
}
},
最新的Discovery Server代码在我的GitHub上已经上传，地址：
代码⽂件为：
Axiu.Opcua.Demo.Service.DiscoveryManagement；
Axiu.Opcua.Demo.Service.DiscoveryServer。

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