[dcmnet] Extend DcmSCU::negotiateAssociation to take a cancel token a…

…s argument

We'll use this cancel token to cancel ongoing TCP connect attempts. A cancel token
allows the client to decide how a request should be cancelled, for example using
std::stop_token in the implementation of the ICancelToken.

dcmnet/include/dcmtk/dcmnet/scu.h

@@ -185,6 +185,13 @@ class DCMTK_DCMNET_EXPORT RetrieveResponse : public QRResponse
     RetrieveResponse& operator=(const RetrieveResponse& other);
 };
 
+class IDcmCancelToken
+{
+public:
+    virtual ~IDcmCancelToken() {}
+    virtual bool IsCanceled() const = 0;
+};
+
 /** Base class for implementing DICOM Service Class User functionality. The class offers
  *  support for negotiating associations and sending and receiving arbitrary DIMSE messages
  *  on that connection. DcmSCU has built-in C-ECHO support so derived classes do not have to
@@ -226,7 +233,7 @@ class DCMTK_DCMNET_EXPORT DcmSCU
      *  @return EC_Normal if negotiation was successful, otherwise error code.
      *          NET_EC_AlreadyConnected if SCU is already connected.
      */
-    virtual OFCondition negotiateAssociation();
+    virtual OFCondition negotiateAssociation(IDcmCancelToken* tcpCancelToken = NULL);
 
     /** After negotiation association, this call returns the first usable presentation context
      *  given the desired abstract syntax and transfer syntax

dcmnet/libsrc/scu.cc

@@ -259,7 +259,7 @@ OFCondition DcmSCU::initNetwork()
     return cond;
 }
 
-OFCondition DcmSCU::negotiateAssociation()
+OFCondition DcmSCU::negotiateAssociation(IDcmCancelToken* tcpCancelToken)
 {
     /* Return error if SCU is already connected */
     if (isConnected())