JXTA e Relay

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JXTA e Relay

• Realizzazione di una Jxta Chat

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Peer

• Definizione
• Secondo la filosofia JXTA tutto ciò che è
  collegabile in rete, può diventare un Peer
• Es
• Host, Cellulari, Router,

3
Virtual Network
4
Introduzione
JXTA Virtual Network
Protocolli
Peer
Super Peer
Edge Peer
Randevouz
Relay
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Relay
Firewall
Peer
Peer

• Problem
• How should a host beyond Firewall become a Peer
  ?
• Solution
• Using a Relay

Relay
Peer
Peer
Peer
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Case 1 Outgoing Connection

• Protected Peer connects first to external Peer
• Nice Firewall allows outgoing TCP connections
• Strict Firewall allows only HTTP connections for
  using WWW service

Peer
TCP stable
Peer
HTTP request
Peer
HTTP answer
For each request only one answer is allowed
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Case 2 Incoming Connection
Peer

• External Peer tries to connect to protected Peer
• Firewall blocks the packets

Blocked
Peer
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Using Realy
PeerB

• Using a Relay
• 1) PeerA connects to Relay (TCP or HTTP it
  dipends on what firewall allows)
• 2) PeerB connects to Relay and leave its message
  for PeerA
• 3) Relay routes the connection request to PeerA
  that connects to PeerB (TCP or HTTP it dipends on
  what firewall allows)

2
3
Relay
1
PeerA
Relay keeps the msg until PeerA isnt ready to
retrive it
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Dimostration

• TCP 160.78.28.2362057 160.78.28.2339701
  ESTABLISHED
• This line has been taken from a netstat na
  logfile

Its a stable TCP connection
- Protected Peer IP - Random port means this
peer has started the connection

• - Free Peer IP
• Fixed port means
• this peer has recived
• the connection request

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Services
Randevouz
It keeps PipeAdv in cache

• Discovery Service
• Pipe Service

Pipe
DiscoveryService. Publish(PipeAdv)
PipeService.Create
DHT Chosen Randevouz
Server Peer
Randevouz
Pipe Advertisement
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Services
Randevouz

• Discovery Service
• Pipe Service

Relay should use a Randevouz
DHT Chosen Randevouz
Relay
DiscoveryService. query
Relay should act as Randevouz Himself and calc
DHT
Client Peer
Randevouz
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Query responses
Randevouz

• Asynchronous mechanism for query results

Relay
Client Peer
Query response
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Opening Pipe
Pipe

• Opening Pipe

Relay
Access to remote pipe
Client Peer
Server Peer
Pipe Adv
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Implementation
Relay

• Usually its Server Peer to start the connection
  toward client, but in this case its viceversa,
  only this way the firewall allows it

Blocked
Server Peer
Client Peer
TCP Connection Implements the JXTA Pipe
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Problem Privileges of JVM

• Standard JVM
• java MyClass
• No Restrictions
• JXTA requires privileges to open files,
• It works ok with this JVM

Standard JVM
OK
JXTA
File
File
File
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Problem Privileges of JVM

• JVM Browser Plugin
• Many Restrictions for Security Reasons
• JXTA requires privileges to open files,
• It doesnt work

Plugin JVM
Noooo
JXTA
File
File
File
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Solution Engine, Applet, RMI
ENGINE
APPLET
Plugin JVM
Standard JVM
RMI
Applet
JXTA
Browser
File
File
File
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Engine

• Module running JXTA
• Runs in the Standard JVM with no restrictions
• It does the Real Work
• It passes results up to the Applet
• It acts as Console

Engine Code
DiscoveryService PipeService
JXTA
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Applet
Browser
Applet

• Runs in the restricted JVM Browser Plugin
• Its only task is to recive data from the engine
  and show them on the browser

RMI
Restrictions
No Restriction
Engine Code
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RMI

• RMI Remote Method Invocation
• It allows data exchange between 2 different
  contexts
• Automatic Data Marshaling

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Interface Definition

• To invoke Remote Methods its needed an Interface
  that defines Remote Methods Name, Parameters,
• public interface MyPipeServer extends Remote
• public void addTempMsgListener() throws
  RemoteException

One of my Remote Methods It must be declared that
throws RemoteException
My remote Interface must extend Remote (defined
by RMI)
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Interface Implementation

• Remote Interface must be implemented by a class
  extending UnicastRemoteObject
• public class MyPipeServerImpl extends
  UnicastRemoteObject implements MyPipeServer

• UnicastRemoteObject has this characteristics
• Gives the illusion that the RemoteObject is local
  
• Provides comunication between 2 sides with TCP
• Provides a protocol for invocation, params and
  results

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Registration

• Once created an instance of the
  RemoteUnicastObject it has to be registered in
  the RMI Registry
• Once Registered in RMI Registry it can be
  accessed from any other context
• Naming.rebind(myapp.RMIHost myapp.RMIPort
  myapp.RMIServerName, myapp)

Name my object is registered with in the registry
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Accessing a Remote Object

• A Remote Object is used by its Remote Interface
• It can taken querying the RMI Registry
• tMsgListener (TempMsgListener)
  Naming.lookup(RMIHost RMIPort RMIClientName)

Remote Interface for the Remote Object
Name the object is registered with in the
registry
Interface to use locally to invoke The Remote
Object
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Whats RMI Registry ?

• Its an executable
• Opens a TCP Port and waits for registrations or
  lookups query
• Its the bridge between the 2 contexts
• Server Where the Remote Object Implementation
  stays
• Client Where the Remote Interface is used