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