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 * OPC Foundation MIT License 1.00
 * 
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 * obtaining a copy of this software and associated documentation
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using System;
using System.Threading;
using System.Collections.Generic;
using System.Reflection;
using System.Security.Cryptography.X509Certificates;
using Opc.Ua;
using Opc.Ua.Server;

namespace Quickstarts.ReferenceServer
{
    /// <summary>
    /// Implements a basic Quickstart Server.
    /// </summary>
    /// <remarks>
    /// Each server instance must have one instance of a StandardServer object which is
    /// responsible for reading the configuration file, creating the endpoints and dispatching
    /// incoming requests to the appropriate handler.
    /// 
    /// This sub-class specifies non-configurable metadata such as Product Name and initializes
    /// the EmptyNodeManager which provides access to the data exposed by the Server.
    /// </remarks>
    public partial class ReferenceServer : StandardServer
    {
        #region Overridden Methods
        /// <summary>
        /// Creates the node managers for the server.
        /// </summary>
        /// <remarks>
        /// This method allows the sub-class create any additional node managers which it uses. The SDK
        /// always creates a CoreNodeManager which handles the built-in nodes defined by the specification.
        /// Any additional NodeManagers are expected to handle application specific nodes.
        /// </remarks>
        protected override MasterNodeManager CreateMasterNodeManager(IServerInternal server, ApplicationConfiguration configuration)
        {
            Utils.Trace("Creating the Node Managers.");

            List<INodeManager> nodeManagers = new List<INodeManager>();

            // create the custom node managers.
            nodeManagers.Add(new EmptyNodeManager(server, configuration));

            // get the ShutdownDelay configuration parameter.
            ReferenceServerConfiguration referenceServerConfiguration = configuration.ParseExtension<ReferenceServerConfiguration>();

            if (referenceServerConfiguration != null)
            {
                m_shutdownDelay = referenceServerConfiguration.ShutdownDelay;
            }
            else
            {
                // default value of 5 seconds.
                m_shutdownDelay = 5;
            }

            // create master node manager.
            return new MasterNodeManager(server, configuration, null, nodeManagers.ToArray());
        }

        /// <summary>
        /// Loads the non-configurable properties for the application.
        /// </summary>
        /// <remarks>
        /// These properties are exposed by the server but cannot be changed by administrators.
        /// </remarks>
        protected override ServerProperties LoadServerProperties()
        {
            ServerProperties properties = new ServerProperties();

            properties.ManufacturerName = "OPC Foundation";
            properties.ProductName = "Quickstart Reference Server";
            properties.ProductUri = "http://opcfoundation.org/Quickstart/ReferenceServer/v1.0";
            properties.SoftwareVersion = Utils.GetAssemblySoftwareVersion();
            properties.BuildNumber = Utils.GetAssemblyBuildNumber();
            properties.BuildDate = Utils.GetAssemblyTimestamp();

            // TBD - All applications have software certificates that need to added to the properties.

            return properties;
        }

        /// <summary>
        /// Creates the resource manager for the server.
        /// </summary>
        protected override ResourceManager CreateResourceManager(IServerInternal server, ApplicationConfiguration configuration)
        {
            ResourceManager resourceManager = new ResourceManager(server, configuration);

            System.Reflection.FieldInfo[] fields = typeof(StatusCodes).GetFields(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Static);

            foreach (System.Reflection.FieldInfo field in fields)
            {
                uint? id = field.GetValue(typeof(StatusCodes)) as uint?;

                if (id != null)
                {
                    resourceManager.Add(id.Value, "en-US", field.Name);
                }
            }

            return resourceManager;
        }

        /// <summary>
        /// Called after the server has been started.
        /// </summary>
        protected override void OnServerStarted(IServerInternal server)
        {
            base.OnServerStarted(server);

            // request notifications when the user identity is changed. all valid users are accepted by default.
            server.SessionManager.ImpersonateUser += new ImpersonateEventHandler(SessionManager_ImpersonateUser);
        }

        /// <summary>
        /// Cleans up before the server shuts down.
        /// </summary>
        /// <remarks>
        /// This method is called before any shutdown processing occurs.
        /// </remarks>
        protected override void OnServerStopping()
        {
            try
            {
                // check for connected clients
                IList<Session> currentessions = this.ServerInternal.SessionManager.GetSessions();

                if (currentessions.Count > 0)
                {
                    // provide some time for the connected clients to detect the shutdown state.
                    ServerInternal.Status.Value.ShutdownReason = new LocalizedText("en-US", "Application closed.");
                    ServerInternal.Status.Variable.ShutdownReason.Value = new LocalizedText("en-US", "Application closed.");
                    ServerInternal.Status.Value.State = ServerState.Shutdown;
                    ServerInternal.Status.Variable.State.Value = ServerState.Shutdown;
                    ServerInternal.Status.Variable.ClearChangeMasks(ServerInternal.DefaultSystemContext, true);

                    for (uint timeTillShutdown = m_shutdownDelay; timeTillShutdown > 0; timeTillShutdown--)
                    {
                        ServerInternal.Status.Value.SecondsTillShutdown = timeTillShutdown;
                        ServerInternal.Status.Variable.SecondsTillShutdown.Value = timeTillShutdown;
                        ServerInternal.Status.Variable.ClearChangeMasks(ServerInternal.DefaultSystemContext, true);

                        Thread.Sleep(1000);
                    }
                }
            }
            catch
            {
                // ignore error during shutdown procedure.
            }

            base.OnServerStopping();
        }
        #endregion
        #region User Validation Functions
        /// <summary>
        /// Called when a client tries to change its user identity.
        /// </summary>
        private void SessionManager_ImpersonateUser(Session session, ImpersonateEventArgs args)
        {
            // check for a user name token.
            UserNameIdentityToken userNameToken = args.NewIdentity as UserNameIdentityToken;

            if (userNameToken != null)
            {
                VerifyPassword(userNameToken.UserName, userNameToken.DecryptedPassword);
                args.Identity = new UserIdentity(userNameToken);
                return;
            }

            // check for x509 user token.
            X509IdentityToken x509Token = args.NewIdentity as X509IdentityToken;

            if (x509Token != null)
            {
                VerifyCertificate(x509Token.Certificate);
                args.Identity = new UserIdentity(x509Token);
                Utils.Trace("X509 Token Accepted: {0}", args.Identity.DisplayName);
                return;
            }
        }

        /// <summary>
        /// Validates the password for a username token.
        /// </summary>
        private void VerifyPassword(string userName, string password)
        {
            if (String.IsNullOrEmpty(userName))
            {
                // an empty username is not accepted.
                throw ServiceResultException.Create(StatusCodes.BadIdentityTokenInvalid,
                    "Security token is not a valid username token. An empty username is not accepted.");
            }

            if (String.IsNullOrEmpty(password))
            {
                // an empty password is not accepted.
                throw ServiceResultException.Create(StatusCodes.BadIdentityTokenRejected,
                    "Security token is not a valid username token. An empty password is not accepted.");
            }

            if (!((userName == "user1" && password == "password") ||
                 (userName == "user2" && password == "password1")))
            {
                // construct translation object with default text.
                TranslationInfo info = new TranslationInfo(
                    "InvalidPassword",
                    "en-US",
                    "Invalid username or password.",
                    userName);

                // create an exception with a vendor defined sub-code.
                throw new ServiceResultException(new ServiceResult(
                    StatusCodes.BadUserAccessDenied,
                    "InvalidPassword",
                    "http://opcfoundation.org/UA/Sample/",
                    new LocalizedText(info)));
            }
        }

        /// <summary>
        /// Verifies that a certificate user token is trusted.
        /// </summary>
        private void VerifyCertificate(X509Certificate2 certificate)
        {
            try
            {
                CertificateValidator.Validate(certificate);

                // determine if self-signed.
                bool isSelfSigned = Utils.CompareDistinguishedName(certificate.Subject, certificate.Issuer);

                // do not allow self signed application certs as user token
                if (isSelfSigned && Utils.HasApplicationURN(certificate))
                {
                    throw new ServiceResultException(StatusCodes.BadCertificateUseNotAllowed);
                }
            }
            catch (Exception e)
            {
                TranslationInfo info;
                StatusCode result = StatusCodes.BadIdentityTokenRejected;
                ServiceResultException se = e as ServiceResultException;
                if (se != null && se.StatusCode == StatusCodes.BadCertificateUseNotAllowed)
                {
                    info = new TranslationInfo(
                        "InvalidCertificate",
                        "en-US",
                        "'{0}' is an invalid user certificate.",
                        certificate.Subject);

                    result = StatusCodes.BadIdentityTokenInvalid;
                }
                else
                {
                    // construct translation object with default text.
                    info = new TranslationInfo(
                        "UntrustedCertificate",
                        "en-US",
                        "'{0}' is not a trusted user certificate.",
                        certificate.Subject);
                }

                // create an exception with a vendor defined sub-code.
                throw new ServiceResultException(new ServiceResult(
                    result,
                    info.Key,
                    "http://opcfoundation.org/UA/Sample/",
                    new LocalizedText(info)));
            }
        }

        #region Private Fields
        private uint m_shutdownDelay = 0;
        #endregion 
        #endregion
    }
}