背景：

之前博文对照过多次C-MOVE与C-GET服务的差别，两者最大的差别在于C-GET是基于单个TCP连接的点对点的双方服务。而C-MOVE是基于两个TCP连接的三方服务（详情參见：《DICOM：C-GET与C-MOVE对照剖析》。以及DICOM：C-GET与C-MOVE对照剖析（续））。

加之前一篇专栏博文DICOM：DICOM3.0网络通信协议之“开源库实现剖析”也已具体对照了dcm4che和fo-dicom开源库的底层实现，因此本篇博文直接给出基于fo-dicom开源库的C-GET服务实现的主要代码，着重介绍C-GET服务端与C-MOVE服务端发起C-STORE 子操作的差别。

C-GET-SCU：

在fo-dicom开源库中DICOM的各种Client端已经抽象出了DicomClientBase类，针对各种DIMSE-C服务（诸如C-STORE、C-GET、C-MOVE、C-ECHO、C-FIND）唯一不同的就是绑定各自相应的托付就可以。

C-GET-SCUclient的核心代码例如以下：

        #region Protected Overrides

        protected override void OnConnected()

        {

            DcmAssociate associate = new DcmAssociate();

            byte pcid = associate.AddPresentationContext(_getSopClass);

            associate.AddTransferSyntax(pcid, DicomTransferSyntax.ExplicitVRLittleEndian);

            associate.AddTransferSyntax(pcid, DicomTransferSyntax.ImplicitVRLittleEndian);

            byte pcid2 = associate.AddPresentationContext(DicomUID.CTImageStorage);

            associate.AddTransferSyntax(pcid2, DicomTransferSyntax.ExplicitVRLittleEndian);

            associate.AddTransferSyntax(pcid2, DicomTransferSyntax.ImplicitVRLittleEndian);

            associate.CalledAE = CalledAE;

            associate.CallingAE = CallingAE;

            associate.MaximumPduLength = MaxPduSize;

            //zssure:2015/07/06

            //Add UserIdentity Information

            //http://medical.nema.org/medical/dicom/current/output/html/part07.html#sect_D.3.3.7

            if (userIdentity == null)

                SendAssociateRequest(associate);

            else

                SendAssociateRequest(associate, userIdentity);

            //zssure:end,2015/07/06

        }

        private void PerformQueryOrRelease()

        {

            if (_getQueries.Count > 0)

            {

                byte pcid = Associate.FindAbstractSyntax(GetSopClassUID);

                if (Associate.GetPresentationContextResult(pcid) == DcmPresContextResult.Accept)

                {

                    current = _getQueries.Dequeue();

                    SendCGetRequest(pcid,1,Priority,current.ToDataset());

                }

                else

                {

                    SendReleaseRequest();

                }

            }

            else

            {

                SendReleaseRequest();

            }

        }

        protected override void OnReceiveCStoreRequest(byte presentationID, ushort messageID, DicomUID affectedInstance,

            DcmPriority priority, string moveAE, ushort moveMessageID, DcmDataset dataset, string fileName)

        {

            try

            {

                if (OnCStoreRequest != null)

                    OnCStoreRequest(presentationID, messageID, affectedInstance, priority, moveAE, moveMessageID, dataset, fileName);

                SendCStoreResponse(presentationID, messageID, affectedInstance, DcmStatus.Success);

            }

            catch (System.Exception ex)

            {

                SendCStoreResponse(presentationID, messageID, affectedInstance, DcmStatus.ProcessingFailure);

            }

            Console.WriteLine("c-get c-store RQ!");

        }

        protected override void OnReceiveAssociateAccept(DcmAssociate association)

        {

            PerformQueryOrRelease();

        }

        protected override void OnReceiveCGetResponse(byte presentationID, ushort messageID, DcmDataset dataset,

            DcmStatus status, ushort remain, ushort complete, ushort warning, ushort failure)

        {

            if (OnCGetResponse != null)

            {

                OnCGetResponse(current, dataset, status, remain, complete, warning, failure);

            }

            if (remain == 0 && status != DcmStatus.Pending)

            {

                PerformQueryOrRelease();

            }

        }

【注意】：这里须要注意的有几点：
1）CGETClient端须要响应服务端发起的C-STORE-RQ。因此须要重写OnReceiveCStoreRequest函数；
2）之前在博文DICOM：參考dcm4che2扩展fo-dicom(mDCM)中的UserIdentity字段已经介绍过扩展Association加入UserIdentity字段

C-GET-SCP：

C-GET服务端差别于C-MOVE服务端在于，DicomService服务类自身须要实现OnReceiveCStoreResponse函数，而之前C-MOVE服务端是在发送C-STORE-RQ时直接绑定OnReceiveCStoreResponse事件到CStoreClient。核心代码例如以下：

        private ConcurrentDictionary<ushort, CGetParameters> cgetProcessDic = new ConcurrentDictionary<ushort, CGetParameters>();

        protected override void OnReceiveCStoreResponse(byte presentationID, ushort messageIdRespondedTo, DicomUID affectedInstance, DcmStatus status)

        {

            CGetParameters cgetPara = null;

            if (status == DcmStatus.Success)

            {

                try

                {

                    cgetProcessDic.TryGetValue(messageIdRespondedTo, out cgetPara);

                    cgetPara.CGetStatus.Complete++;

                    cgetPara.CGetStatus.Remain--;

                    SendCGetResponse(presentationID, messageIdRespondedTo, DcmStatus.Pending, cgetPara.CGetStatus.Remain, cgetPara.CGetStatus.Complete, cgetPara.CGetStatus.Warning, cgetPara.CGetStatus.Fail);

                    if (cgetPara.CGetStatus.Remain > 0)

                    {

                    ///self do something

                    }

                        else

                        {

                            cgetPara.CGetStatus.Fail++;

                            cgetPara.CGetStatus.Remain--;

                            SendCGetResponse(presentationID, messageIdRespondedTo, DcmStatus.Pending, cgetPara.CGetStatus.Remain, cgetPara.CGetStatus.Complete, cgetPara.CGetStatus.Warning, cgetPara.CGetStatus.Fail);

                        }

                    }

                    else if (cgetPara.CGetStatus.Remain == 0)

                    {

                        if (cgetProcessDic.TryRemove(messageIdRespondedTo, out cgetPara))

                            SendCGetResponse(presentationID, messageIdRespondedTo, DcmStatus.Success, cgetPara.CGetStatus.Remain, cgetPara.CGetStatus.Complete, cgetPara.CGetStatus.Warning, cgetPara.CGetStatus.Fail);

                        else

                        {

                            Log.Info("ReceiveCStoreResponse for CGet failed when remove from ConcurrentDictionary<ushort, CGetParameters>");

                            try

                            {

                                cgetProcessDic.TryRemove(messageIdRespondedTo, out cgetPara);

                            }

                            catch (System.Exception ex2)

                            {

                                Log.Info("ReceiveCStoreResponse for CGet failed when remove from ConcurrentDictionary<ushort, CGetParameters> again,{0},{1}", ex2.Message, ex2.StackTrace);

                            }

                        }

                    }

                }

                catch (System.Exception ex)

                {

                    Log.Info("ReceiveCStoreResponse for CGet failed! {0},{1}", ex.Message, ex.StackTrace);

                    SendCGetResponse(presentationID, messageIdRespondedTo, DcmStatus.InvalidArgumentValue, cgetPara.CGetStatus.Complete, cgetPara.CGetStatus.Remain, cgetPara.CGetStatus.Warning, cgetPara.CGetStatus.Fail);

                }

            }

            else

            {

                cgetPara.CGetStatus.Fail++;

                cgetPara.CGetStatus.Remain--;

                SendCGetResponse(presentationID, messageIdRespondedTo, DcmStatus.Pending, cgetPara.CGetStatus.Remain, cgetPara.CGetStatus.Complete, cgetPara.CGetStatus.Warning, cgetPara.CGetStatus.Fail);

            }

        }

【注意】：上述代码须要注意是：

通过线程安全集合类ConcurrentDictionary在C-GET与C-STORE两种服务间同步状态，由于在OnReceiveCGetRequest函数中服务端是能够明白定位client请求的数据的，可是在接收到clientC-STORE-RSP时，通过简单的DICOM Message是无法得知之前在OnReceiveCGetRequest中定位的数据的，因此须要在服务类中加入一个线程安全集合类来共享状态。如是可见，上述代码中大量的操作是在维护ConcurrentDictionary的状态，用于协调C-STORE与C-MOVE在同一个TCP连接中消息的传递。

备注：

这里纠正之前博文DICOM：C-GET与C-MOVE对照剖析中对于C-GET服务的C-STORE和C-MOVE消息流的流程错误。例如以下图所看到的：

作者：zssure@163.com

时间：2015-12-16