Remoting 如何穿越防火墙

 
http://www.glacialcomponents.com/ArticleDetail.aspx?articleID=CAOMN

（翻译中...）

Introduction
"When I create a CAO from inside my network/router, everything works fine.? However, when I have a client outside my network that creates a CAO inside the network, it fails the first time I call a function.? What am I doing wrong!?!?!"

“在内部网中，我产生一个客户端激活对象(CAO),所有的都很正常。当我的客户端位于外部网，我调用远程对象的方法时，我得到了一个失败的结果，我错在什么地方？”

I hear this question on newsgroups and bulletin boards almost every day. The answer is actually pretty straightforward although it can get deeper if you wish to spice up the functionality.

我几乎每天经常听到这样的问题,如果你只想解决问题的话，答案非常简单；当然，你可以试着探索别后的机制，你将发现那很有趣。

Why this happens

When a CAO is created the server returns a URI that points to the unique instance of the CAO on the server.?This is how the server knows the unique instance you are using. (This is also why its very difficult to load balance CAO objects).The URI that the server sends back contains either the IP that it thinks it is or the IP you tell it that it really is.

当服务器产生CAO时同时也产生了一个URI，服务器根据这个URI标示远程客户端使用的对象实例。URI中包含了服务器实际IP的信息。（如果服务器位于内部网，实际上这个IP是一个内部IP,这是问题的根源）

How to fix it (the quick fix)

The simple fix for this that will work on most setups is to set the 'machineName' property of the channel on the server to the EXTERNAL ip that the client sees. This allows the server to return the external ip instead of its local internal IP. Typically you want to set the machineName equal to the EXTERNAL ip. This is the IP that your firewall or router has. This is also the IP that machines will see from outside your LAN when they go to connect to your remote object.

快速修正

最简单的修正办法就是设置通道的'machineName'属性为外部IP地址;这样，服务器返回给客户端的地址将是外部IP地址；

你可以用代码完成设置工作。(注:可以修改配置文件)

For example, for a TcpChannel you would do the following on the SERVER side of your code.

 IDictionary prop = new Hashtable(); prop["port"] = 4000; prop["machineName"] = "myexternalip.com"; tcpChannel = new TcpChannel(prop, null, null); ChannelServices.RegisterChannel(tcpChannel);

 

That's all you need.?Your server should now work perfectly from outside your LAN/Firewall/Router.

There is a second method of fixing this problem which is much more complete, yet more complicated

A complete solution

What do I do if I need to access the server from both inside the LAN and outside without having to set machine name. Or what if I don't know what the machineName will be and I don't want to bother my users with having to know something mildly technical like that The machineName fix is ok, but it leaves a lot to be desired in many situations. This can be a real problem if its for a home or small business application where you may or may not have someone with a clue. Wouldn't it be easier if we just had a solution that worked everywhere Well your in luck！Because thats exactly what this is. This solution uses the IP that the CLIENT sees the server as (which you of course know or the client wouldn't be able to even connect to the server in the first place.

如果我不想设置“ machine name”属性，我该如何做？有很多原因使得我有这样的要求，例如，我可能不知道路由器的IP。既然客户端知道服务器的IP,我们是否可以利用这个IP，替换前面那种属性设置方案呢？

This solution also works very well where you have a multi-homed server (common in corporate intranets). A server with multiple NIC cards may be seen by many IPs each requiring a different route in and out of the server.This will work perfectly for that situation as well.

So how do I create a CAO on a server and have it work regardless if I'm inside or outside the local network。The answer lies in a rarely used class called the TrackingHandler. The basic process is as follows. We create our SAO Class Factory first, then when we go to create our CAO, we send the IP the client sees the server as in the creation call. This then puts the information in the CallContext where the tracking handler picks it up when it is fired during CAO creation and return.The tracking handler takes the URI that is being returned and replaces the server address with the address you have told the server you see it as. From then on, your CAO will work flawlessly against the server, you never have to do another thing.

解决办法是使用TrackingHandler，这是个很少使用的类。基本过程是这样，在产生CAO对象之前，我们将IP的信息传到CallContext中(调用环境)，然后通过 tracking handler 来获取IP信息，并且用它来处理URI。

 

 

Now that I've given you the overview, lets get into the details.

First, this approach assumes that you are using a simple factory pattern to create your CAO.? You can see an explanation of factory pattern CAO creation in my article here.? This will also work if you use interfaces instead of abstract classes but for the purposes of this article we will focus on abstract class share type.

The factory create method for your CAO should accept a string.? This string will hold the address the client sees the server as.? Define it first in the abstract class then implement it in your SAO factory implementation.? I included a regular factory implementation along with the address based one so you can see both approaches.

// share.dll abstract SAO factory namespace ShareDLL { public abstract class SAOCAOClassFactoryDef : MarshalByRefObject { public abstract CAOClassDef CreateCAOClass(); public abstract CAOClassDef CreateCAOClass( string strIP ); } } // implementation SAOCAOClassFactory.cs public class SAOCAOClassFactory : ShareDLL.SAOCAOClassFactoryDef { public override CAOClassDef CreateCAOClass() { // this is important to clear out or it will get the address you left in on a previous factory c CallContext.FreeNamedDataSlot( "ObservedIP" ); return new CAOClass(); // class factory create } public override CAOClassDef CreateCAOClass( string strAddress ) { CallContext.SetData("ObservedIP", strAddress); return new CAOClass(); // class factory create } }
Now that we have the address in the call context we can implement our tracking handler.?

Our tracking handler will grab the address out of the call context and insert it into the URI.

// trackinghandler.cs in server.exe public class ExampleTrackingHandler : ITrackingHandler { // Notify a handler that an object has been marshaled. public void MarshaledObject(Object obj, ObjRef or) { // Assumption: We have a server channel sink that sets a call context flag // called "ObservedIP" whenever we are processing a remote request object ObservedIP = CallContext.GetData("ObservedIP"); // for local clients we don't do anything here // if they don't specify the remote IP then we just use the servers IP if (ObservedIP == null) return; if (or.ChannelInfo == null) return; string strAddress = (string)ObservedIP; for ( int i = or.ChannelInfo.ChannelData.GetLowerBound(0); i <= or.ChannelInfo.ChannelData.GetUpperBound(0); i++ ) { // Check for the ChannelDataStore object that we don't want to copy if(or.ChannelInfo.ChannelData[i] is ChannelDataStore) { // Personally I don't know why ChannelURIs is an array... I am only // familiar with there being one URI in each ChannelDataStore object foreach(string uri in ((ChannelDataStore)or.ChannelInfo.ChannelData[i]).ChannelUris) { // this will get the first part of the uri int nOffset = uri.IndexOf( "//" ) + 2; string strNewUri = uri.Substring( 0, nOffset ); strNewUri += strAddress; nOffset = uri.IndexOf( ":", nOffset ); strNewUri += uri.Substring( nOffset, uri.Length - nOffset ); string[] strarray = new string[1] { strNewUri }; ChannelDataStore cds = new ChannelDataStore( strarray ); or.ChannelInfo.ChannelData[i] = cds; } } } } } We have our class factory and our tracking handler, the last thing we need to do is make sure we register our tracking handler during the registration in our server. We do that with the simple RegisterTrackingHandler.

ChannelServices.RegisterChannel( new TcpChannel( 4000 ) ); // this will handle converting the returned CAO uri to the correct server IP TrackingServices.RegisterTrackingHandler(new ExampleTrackingHandler()); Type thisType = Type.GetType("Server.SAOCAOClassFactory,Server"); RemotingConfiguration.RegisterWellKnownServiceType(thisType,       "SAOCAOClassFactoryURI", WellKnownObjectMode.SingleCall ); Thats all you need!? At this point you can instantiate your CAO from the client with your SAO factory.?If you have any comments, recommendations, questions, feel free to contact me. I try to answer? all of my email.

I've tested all the code several times to make sure I didn't include any errors, however if you do find any mistakes or have any questions, feel free to email me [email protected].?

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