DICOM：C-GET服务

背景：

之前博文对比过多次C-MOVE与C-GET服务的区别，两者最大的区别在于C-GET是基于单个TCP连接的点对点的两方服务，而C-MOVE是基于两个TCP连接的三方服务（详情参见：《DICOM：C-GET与C-MOVE对比剖析》，以及DICOM：C-GET与C-MOVE对比剖析（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”也已详细对比了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 子操作的区别。

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对应的委托即可。C-GET-SCU客户端的核心代码如下：

        #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】：这里需要注意的有几点：
1）CGETClient端需要响应服务端发起的C-STORE-RQ，因此需要重写OnReceiveCStoreRequest函数；
2）之前在博文 DICOM：参考dcm4che2扩展fo-dicom(mDCM)中的UserIdentity字段已经介绍过扩展Association添加UserIdentity字段

C-GET-SCP：

C-GET服务端区别于C-MOVE服务端在于，DicomService服务类自身需要实现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。核心代码如下：

        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】：上述代码需要注意是：
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，因为在OnReceiveCGetRequest函数中服务端是可以明确定位客户端请求的数据的，但是在接收到客户端C-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，因此需要在服务类中添加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对比剖析中对于C-GET服务的C-STORE和C-MOVE消息流的流程错误，如下图所示：

作者：[email protected]
时间：2015-12-16