Net Remoting

1Nordjyllands Erhvervakademi - 2009

.Net Remoting

• Configuration files– The .config file– Server side– Client side

• Encapsulate Activator.GetObject– A method

• Remote callback– Callback in general– How to do it


The .config file

• Configuration files are widely used in .Net• A configuration file provides an easy way of changing

different kind of setting.• For example:

– Database connection strings– Authorization settings– Remoting settings– Application specific properties

• In Visual Studio: Add a new item using the “Application Configuration File” template

• Leave the name as app.config. It will be renamed to <assemply filename>.config.

• E.g.: MyProgram.exe.config


Server Configuration file

• It is possible to do the most by configuration files.• Below is the configuration file for the server from the wko

example:

<configuration> <system.runtime.remoting> <application> <channels> <channel ref="http" port="1234" /> </channels> <service> <wellknown mode="Singleton"

type="Server.CustomerManager, Server" objectUri="CustomerManager.soap" />

</service> </application> </system.runtime.remoting></configuration>

<namespace>.<class>

Assembly


Server.cs• Read the configuration file

static void Main(string[] args){

Console.WriteLine("Start service");String filename = @"..\..\server.exe.config";

RemotingConfiguration.Configure(filename,false);

Console.WriteLine("Service startet");Console.ReadLine();

}


Config file with security setting<configuration> <system.runtime.remoting> <application> <channels> <channel ref="http" port="1234" > <serverProviders> <provider ref="wsdl" /> <formatter ref="soap" typeFilterLevel="Full" /> <formatter ref="binary" typeFilterLevel="Full" /> </serverProviders> </channel> </channels> <service> <wellknown mode="Singleton"

type="Server.CustomerManager, Server" objectUri="CustomerManager.soap" />

</service> </application> </system.runtime.remoting></configuration>


client.exe.config

• Same information as in the Activator.GetObject

<configuration> <system.runtime.remoting> <application>

<client> <wellknown type="Server.ICustomerManager, Client" url="http://localhost:1234/CustomerManager.soap" /> </client>

</application> </system.runtime.remoting></configuration>


client.cs

String filename = @"..\..\client.exe.config";RemotingConfiguration.Configure(filename);

ICustomerManager mgr = (ICustomerManager)Activator.GetObject(typeof(ICustomerManager), "http://localhost:1234/CustomerManager.soap");

Console.WriteLine("Reference to CustomerManager created"+mgr);Customer cust = mgr.GetCustomer(4711);

Here is a problem, which?

Information repeated in the

Activator.GetObject


.Net Remoting





Better ways to use the configuration file on client side • Problems:

– Activator.GetObject needs a url and a port– using new demands knowledge of the concrete class

• Goal:– The client shall be able to instantiate remote objects from the

interface without knowing the concrete class.– Use configuration files

• Solution:– Encapsulate Activator

Source: Ingo Rammer


Encapsulate Activator.GetObject

Steps:

1. Construct a RemoteHelper class with a method GetObject.

2. Is initialized by looking up in the RemotingConfiguration and store available remote types in a table.

3. GetObject takes a Type as parameter (can be a interface or a class)

4. GetObject returns a remote object by calling Activator.GetObject

The good news:

The construction can be used for general purpose.

It does not depend on a specific application

Source: Ingo Rammer


RemotingHelper

using System;

using System.Collections;

using System.Runtime.Remoting;

class RemotingHelper

{

private static bool _isInit;

private static IDictionary _wellKnownTypes;

public static Object GetObject(Type type)

{

if (!_isInit) InitTypeCache();

WellKnownClientTypeEntry entr = (WellKnownClientTypeEntry)_wellKnownTypes[type];

if (entr == null)

{

throw new RemotingException("Type not found!");

}

return Activator.GetObject(entr.ObjectType, entr.ObjectUrl);

}

Continued……

Make table with remote types

Lookup on the type

Return the reference


RemotingHelperGenerate table

public static void InitTypeCache()

{

_isInit = true;

_wellKnownTypes = new Hashtable();

foreach (WellKnownClientTypeEntry entr in

RemotingConfiguration.GetRegisteredWellKnownClientTypes())

{

if (entr.ObjectType == null)

{

throw new RemotingException("A configured type could not " +

"be found. Please check spelling");

}

_wellKnownTypes.Add(entr.ObjectType, entr);

}

}

}


In the client:

static void Main(string[] args)

{

string path = @"../../Client.exe.config";

RemotingConfiguration.Configure(path);

IRemoteBank mgr = (IRemoteBank)RemotingHelper.GetObject(typeof(IRemoteBank));

…..

}

Here is both goals achieved.


More on design...

• Classes in the data and business components should not inherit from MarshalByRefObject

• Use proxy pattern instead.• In other words: Construct a class (the proxy) with the same

interface as the real class. Redelegate calls to the real class


.Net Remoting





Callback as in delegate or in observer pattern

• Callback means that the called method or service calls a method on the requesting object instead of returning a value.

• The advantage is that the program executing is not blocked, while waiting for a return.

• Event models are in general built on callback principles

• Here: The server is able to call a method on the client.

• The following example shows an remote implementation of observer pattern, where the connected clients are informed every time a new client connects


Observer pattern Also called Observable in some litteratureMight also be a

interface


In the example

• Observable is on the server.• Clients gets a reference to it by calling a get-method on a

factory class (Factory pattern)• Observers are placed on the clients and attached to the

Observable object.• The server calls back by calling the Notify method on the

Observers


• The shared assembly


The remote interface and the observer interfaces

public interface IObserver { void Notify(string msg); }

public interface IObservable { void Attach(IObserver obj); void Update(string msg); }

public interface IObserverableFactory { IObservable GetFactory(); }


• The server


The factory class

public class Factory : MarshalByRefObject, IObserverableFactory { IObservable _obsevable = null; public IObservable GetFactory() { if (_obsevable == null) _obsevable = new Observable(); return _obsevable; }}


The observable class

public class Observable : MarshalByRefObject, IObservable { List<IObserver> _observers = new List<IObserver>();

public void Attach(IObserver obj) { _observers.Add(obj); }

public void Update(string msg) { foreach (IObserver o in _observers) o.Notify(msg); }}


The config file

<?xml version="1.0" encoding="utf-8" ?><configuration> <system.runtime.remoting> <application> <channels> <channel ref="http" port="1234"> <serverProviders> <provider ref="wsdl" /> <formatter ref="soap" typeFilterLevel="Full" /> </serverProviders> </channel> </channels> <service> <wellknown mode="Singleton” type="Server.Factory, Server"

objectUri="observer.soap" /> </service> </application> </system.runtime.remoting></configuration>


• The client


The observer class

[Serializable] public class Observer : MarshalByRefObject, Shared.IObserver { public void Notify(string msg) { Console.WriteLine(msg); } }


The client class

[Serializable] public class Observer : MarshalByRefObject, Shared.IObserver { public void Notify(string msg) { Console.WriteLine(msg); } }


The observer class

class Program { static void Main(string[] args) { RemotingConfiguration.Configure("Client.exe.config",false); IObserverableFactory serverObj = (IObserverableFactory) RemotingHelper.GetObject (typeof(IObserverableFactory));

IObservable observable = serverObj.GetFactory(); observable.Attach(new Observer()); observable.Update(String.Format("{0}: {1}", DateTime.Now, ”Client startet")); Console.ReadLine(); } }


The config file

<?xml version="1.0" encoding="utf-8" ?><configuration> <system.runtime.remoting> <application> <channels> <channel ref="http" port="0"> <serverProviders> <provider ref="wsdl" /> <formatter ref="soap" typeFilterLevel="Full" /> <formatter ref="binary" typeFilterLevel="Full" /> </serverProviders> </channel> </channels> <client> <wellknown type="Shared.IObserverableFactory, Shared" url="http://localhost:1234/observer.soap" /> </client> </application> </system.runtime.remoting></configuration>


Run the example

• Start the server• The client cannot be started from Visual Studio for security

reasons• Therefore it has to be started from the bin directory.• Start the client twice. Look at the out on the first instance.


Exercises:

• Exercise 1:– Change the server and the client in the remoting bank to use

configuration files• Exercise 2:

– Encapsulate the Activator.GetObject in the client• Exercise 3:

– Make a simple chat application by changing the callback example

Documents

Net Remoting