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Listen(string,int,int) Method

Summary
Establishes a connection to listen for incoming connection requests.
Syntax
C#
C++/CLI
public void Listen( 
   string hostAddress, 
   int hostPort, 
   int maxNumberOfPeers 
) 
public: 
void Listen(  
   String^ hostAddress, 
   int hostPort, 
   int maxNumberOfPeers 
)  

Parameters

hostAddress
The IP address of the host computer (the SCP's address).

hostPort
The port number of the host computer (the SCP's port).

maxNumberOfPeers
Backlog parameter.

Remarks

If hostAddress is an empty string or a null reference (Nothing in VB), the IP address will be the local computer's address.

If hostAddress is "*", the IP address will be all of the local computer's addresses. This is useful if the local computer has more than one network interface and address.

If hostPort is 0, the port number will be the number of the first available port.

The maxNumberOfPeers parameter is the value passed to the WinSock listen() function for the backlog parameter that limits the size of the queue for waiting connections. As an example, suppose that the value is set to 3 and that 4 people try to connect at exactly the same time. In such a case, all 4 will be rejected because the connection backlog queue is full. But if one of the connections has been accepted by the time the 4th is made, then all will work.

To determine how many clients are connected and impose a limit on the number of connections, perform the following steps:

  1. Use the DicomNet.GetClientCount function in the "OnReceiveAssociateRequest" handler.
  2. Compare that value with the maximum number of connections allowed.
  3. If the number of clients connected is greater than the maximum number of connections allowed, send a "SendAssociateReject" command to the client trying to connect.

To connect to a server as a client, you must first create and initialize a DicomNet object. Then call Connect to establish the connection.

To use your computer as an SCP, you must first create a DicomNet object. Then call Listen to listen for incoming connection requests.

Example
C#
using Leadtools; 
using Leadtools.Dicom; 
 
 
[StructLayout(LayoutKind.Sequential)] 
public struct MSG 
{ 
   public IntPtr hwnd; 
   public uint message; 
   public IntPtr wParam; 
   public IntPtr lParam; 
   public uint time; 
   public System.Drawing.Point p; 
} 
 
public enum WaitReturn 
{ 
   Complete, 
   Timeout, 
} 
 
class Utils 
{ 
   [DllImport("user32.dll")] 
   [return: MarshalAs(UnmanagedType.Bool)] 
   static extern bool PeekMessage(out MSG lpMsg, IntPtr hWnd, 
                                  uint wMsgFilterMin, uint wMsgFilterMax, 
                                  uint wRemoveMsg); 
 
   [DllImport("user32.dll")] 
   static extern bool TranslateMessage([In] ref MSG lpMsg); 
   [DllImport("user32.dll")] 
   static extern IntPtr DispatchMessage([In] ref MSG lpmsg); 
 
   const uint PM_REMOVE = 1; 
 
   public static WaitReturn WaitForComplete(double mill, WaitHandle wh) 
   { 
      TimeSpan goal = new TimeSpan(DateTime.Now.AddMilliseconds(mill).Ticks); 
 
      do 
      { 
         MSG msg = new MSG(); 
 
         if (PeekMessage(out msg, IntPtr.Zero, 0, 0, PM_REMOVE)) 
         { 
            TranslateMessage(ref msg); 
            DispatchMessage(ref msg); 
         } 
 
         if (wh.WaitOne(new TimeSpan(0, 0, 0), false)) 
         { 
            return WaitReturn.Complete; 
         } 
 
         if (goal.CompareTo(new TimeSpan(DateTime.Now.Ticks)) < 0) 
         { 
            return WaitReturn.Timeout; 
         } 
 
      } while (true); 
   } 
} 
 
class Client : DicomNet 
{ 
   DicomExceptionCode _LastError = DicomExceptionCode.Success; 
   AutoResetEvent waitEvent = new AutoResetEvent(false); 
 
   public Client() 
       : base(null, DicomNetSecurityMode.None) 
   { 
   } 
 
   public DicomExceptionCode LastError 
   { 
      get 
      { 
         return _LastError; 
      } 
   } 
 
   public bool Wait() 
   { 
      WaitReturn ret; 
 
      _LastError = DicomExceptionCode.Success; 
      ret = Utils.WaitForComplete((5 * 60) * 1000, waitEvent); 
 
      return (ret == WaitReturn.Complete); 
   } 
 
   protected override void OnConnect(DicomExceptionCode error) 
   { 
      _LastError = error; 
      waitEvent.Set(); 
   } 
 
   protected override void OnReceiveAssociateAccept(DicomAssociate association) 
   { 
      waitEvent.Set(); 
   } 
 
   protected override void OnReceiveAssociateReject(DicomAssociateRejectResultType result, 
                                                    DicomAssociateRejectSourceType source, 
                                                    DicomAssociateRejectReasonType reason) 
   { 
      Debug.Assert(result == DicomAssociateRejectResultType.Permanent, "Result should be: " + DicomAssociateRejectResultType.Permanent.ToString()); 
      Debug.Assert(source == DicomAssociateRejectSourceType.User, "Source should be: " + DicomAssociateRejectSourceType.User.ToString()); 
      Debug.Assert(reason == DicomAssociateRejectReasonType.Limit, " Reason should be: " + DicomAssociateRejectReasonType.Limit.ToString()); 
      waitEvent.Set(); 
   } 
 
   protected override void OnReceiveReleaseResponse() 
   { 
      waitEvent.Set(); 
   } 
} 
 
class ServerConnection : DicomNet 
{ 
   public bool Fail = false; 
 
   public ServerConnection() 
       : base(null, DicomNetSecurityMode.None) 
   { 
   } 
 
   protected override void OnReceiveAssociateRequest(DicomAssociate association) 
   { 
      DicomAssociate retAssociation = new DicomAssociate(false); 
 
      if (Fail) 
      { 
         SendAssociateReject(DicomAssociateRejectResultType.Permanent, 
                             DicomAssociateRejectSourceType.User, 
                             DicomAssociateRejectReasonType.Limit); 
         return; 
      } 
 
      Debug.Assert(association.Called == "ServerTest", "Called AETitle should be ServerTest"); 
      Debug.Assert(association.Calling == "ClientTest", "Calling AETitle should be ClientTest"); 
      Debug.Assert(association.ImplementClass == "1.2.840.114257.1", "Implementation class should be 1.2.840.114257.1"); 
      Debug.Assert(association.ImplementationVersionName == "1", "Implementation version should be 1"); 
      Debug.Assert(association.MaxLength == 0x100000, "Max length should be 0x100000"); 
      Debug.Assert(association.GetAbstract(1) == DicomUidType.VerificationClass, "Presentation index 1 should be " + DicomUidType.VerificationClass); 
      Debug.Assert(association.GetTransfer(1, 0) == DicomUidType.ImplicitVRLittleEndian, "Abstract Syntax (1,0) should be " + DicomUidType.ImplicitVRLittleEndian); 
 
      // 
      // Build our Association Accept 
      // 
      retAssociation.Called = association.Called; 
      retAssociation.Calling = association.Calling; 
      retAssociation.ImplementClass = association.ImplementClass; 
      retAssociation.ImplementationVersionName = association.ImplementationVersionName; 
      for (int x = 0; x < association.PresentationContextCount; x++) 
      { 
         byte id = association.GetPresentationContextID(x); 
         string abSyntax = association.GetAbstract(id); 
         string trSyntax = DicomUidType.ImplicitVRLittleEndian; 
 
         retAssociation.AddPresentationContext(id, 0, abSyntax); 
         if (association.GetTransferCount(id) > 0) 
         { 
            trSyntax = association.GetTransfer(id, 0); 
         } 
         //Over here we can call retAssociation.SetAbstract to update the abstract 
         //syntax for any of the sresentation contexts 
         retAssociation.AddTransfer(id, trSyntax); 
         if (retAssociation.GetTransferCount(id) == 0) 
         { 
            // 
            // Presentation id doesn't have any abstract 
            //  syntaxes therefore we will reject it. 
            // 
            retAssociation.SetResult(id, DicomAssociateAcceptResultType.AbstractSyntax); 
            Debug.Assert(retAssociation.GetResult(id) == DicomAssociateAcceptResultType.AbstractSyntax, "Result should be: " + DicomAssociateAcceptResultType.AbstractSyntax.ToString()); 
         } 
 
 
         //  We can also call in here SetPresentationContextID if we would like  
         //  to change some of the presentation IDs 
         //  And SetTransfer to update the Transfer Syntax for a certian 
         //  presentation context. 
 
      } 
      SendAssociateAccept(retAssociation); 
   } 
 
   protected override void OnReceiveReleaseRequest() 
   { 
      SendReleaseResponse(); 
   } 
}; 
 
class Server : DicomNet 
{ 
   ServerConnection client; 
 
   public Server() 
       : base(null, DicomNetSecurityMode.None) 
   { 
   } 
 
   public bool Fail 
   { 
      get 
      { 
         if (client == null) 
            return false; 
 
         return client.Fail; 
      } 
 
      set 
      { 
         if (client != null) 
         { 
            client.Fail = value; 
         } 
      } 
   } 
 
   protected override void OnAccept(DicomExceptionCode error) 
   { 
      client = new ServerConnection(); 
 
      Accept(client); 
   } 
} 
 
public void SendAssociateRequestSample() 
{ 
   DicomEngine.Startup(); 
   DicomNet.Startup(); 
 
   using (Server server = new Server()) 
   { 
      using (Client client = new Client()) 
      { 
         // 
         // Connect to server 
         // 
         server.Listen("127.0.0.1", 104, 1); // start server 
         client.Connect(null, 1000, "127.0.0.1", 104); // connect to server 
         if (!client.Wait()) // wait for connection to finish 
         { 
            Debug.Fail("Connection timed out"); 
         } 
         Debug.Assert(client.LastError == DicomExceptionCode.Success, "Connection failed"); 
         Debug.Assert(client.IsConnected(), "Client not connected"); 
 
         // 
         // Send associate request 
         // 
         DicomAssociate associate = new DicomAssociate(true); 
 
         associate.Called = "ServerTest"; 
         associate.Calling = "ClientTest"; 
         associate.ImplementClass = "1.2.840.114257.1"; 
         associate.ImplementationVersionName = "1"; 
         associate.MaxLength = 0x100000; 
         //We can also call in here associate.Default() to initialize  
         //the association with default values. 
         associate.AddPresentationContext(1, 0, DicomUidType.VerificationClass); 
         associate.AddTransfer(1, DicomUidType.ImplicitVRLittleEndian); 
         client.SendAssociateRequest(associate); 
         if (!client.Wait()) // wait for connection to finish 
         { 
            Debug.Fail("SendAssociateRequest timed out"); 
         } 
 
         // 
         // SendReleaseRequest 
         // 
         client.SendReleaseRequest(); 
         if (!client.Wait()) // wait for connection to finish 
         { 
            Debug.Fail("SendAssociateRequest timed out"); 
         } 
 
         // 
         // Force association to send SendAssociateReject. This is for 
         // testing purposes only.  Only one association should be sent 
         // per connection. 
         // 
         server.Fail = true; 
         client.SendAssociateRequest(associate); 
         if (!client.Wait()) // wait for connection to finish 
         { 
            Debug.Fail("SendAssociateRequest timed out"); 
         } 
         server.Fail = false; 
 
         // 
         // SendReleaseRequest 
         // 
         client.SendReleaseRequest(); 
         if (!client.Wait()) // wait for connection to finish 
         { 
            Debug.Fail("SendAssociateRequest timed out"); 
         } 
 
         client.CloseForced(true); 
      } 
      server.CloseForced(true); 
   } 
 
   DicomEngine.Shutdown(); 
   DicomNet.Shutdown(); 
} 
Requirements

Target Platforms

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