B-PingPongApp

Step B - PingPing Application

In this step we extend the PingPong protocol to implement a simple interactive application that sends a ping message and waits for a pong reply. To do this, the developer needs to use InterProcess Communication (IPC) abstractions, to enable the application to coordinate with the PingPong protocol.

InterProcess Communication Abstractions

Babel offers simple and generic IPC abstractions that allow the developer to easily implement complex applications that use multiple protocols.

Babel offers two types of IPC abstractions:

• Request-Reply: used to send a direct request to a protocol. The requested protocol can produce an asynchronous reply to the requester protocol.
• Notification: used to notify a protocol/application of an event that occurred in another protocol/application. A single notification can go to multiple protocols/applications.

Request-Reply Abstractions

To use the Request-Reply abstractions, the developer needs to extend the ProtoRequest and ProtoReply classes. These classes are used to define the request and reply message between protocols that are in the same Babel processes.

import pt.unl.fct.di.novasys.babel.generic.ProtoRequest;

public class MyProtocolRequest extends ProtoRequest {
    
    public static final short REQUEST_ID = 1;
    
    public MyProtocolRequest() {
        super(MyProtocol.REQUEST_ID);
    }
}

import pt.unl.fct.di.novasys.babel.generic.ProtoReply;

public class MyProtocolReply extends ProtoReply {

    public static final short REPLY_ID = 1;

    public MyProtocolReply() {
        super(MyProtocol.REPLY_ID);
    }
}

Babel offers API calls that are defined in the GenericProtocol class to send requests and replies to the protocol with the corresponding numerical unique identifier.

sendRequest(new MyProtocolRequest(), SomeOtherProtocol.PROTO_ID);

private void uponMyProtocolRequest(MyProtocolRequest request, short requesterProto) {
    // handle the request
    sendReply(new MyProtocolReply(), requesterProto);
}

Notification Abstractions

To use the Notification abstractions, the developer needs to extend the ProtoNotification class. This class is used to define notification messages between protocols that are in the same Babel processes.

public class MyProtocolNotification extends ProtoNotification {
    
    public static final short NOTIFICATION_ID = 1;
    
    public MyProtocolNotification() {
        super(MyProtocol.NOTIFICATION_ID);
    }
}

Babel offers API calls that are defined in the GenericProtocol class to register interest in receiving notifications (subscribe) and to trigger notifications.

subscribeNotification(MyProtocolNotification.NOTIFICATION_ID, notificationHandler);

triggerNotification(new MyProtocolNotification());

Exercise

Modify the PingPong protocol in Step A to implement the PingPing application. Create a new App protocol that reads from the console the ping command and performs a request to the PingPongProtocol.

The App protocol send a PingRequest request to the PingPongProtocol and waits for a PongReply reply. When the reply is received, the App protocol prints the reply to the console.

The App protocol should be able to handle a single command in the format:

ping <target_addr:target_port> <message> [n_pings]

where <target_addr:target_port> is the address and port of the target node, <message> is the message to be sent in the PingRequest and [n_pings] is the number of pings to send (default is 1).

The App protocol should look like this:

import pt.unl.fct.di.novasys.babel.core.GenericProtocol;

public class App extends GenericProtocol {
    
    public App() {
        super("App", (short) 2);
    }
    
    public void init(Properties props) {
        // implement the initialization of the protocol
        // need to register handlers for events, timers and messages
    }
    
    private void uponPongReply(PongReply reply, short sourceProto) {
        // what to do when a "PongReply" is received
    }
    
    private void readSystemIn() {
        // read from the console
    }
}

How to compile

To compile your code, run the following commands:

• mvn clean package
• docker build -t babel-tutorial/b-pingpongapp .

How to run

Setup

You need to create a docker network for the tutorial:

docker network create babel-tutorial-net

To remove the network:

docker network rm babel-tutorial-net

Args

The applications need to be run with the following arguments:

• interface=eth0

Run

To run the protocol, you need to run the following commands:

This will run the application in server mode:

docker run --network babel-tutorial-net --rm -h ping-server --name ping-server -it babel-tutorial/b-pingpongapp interface=eth0

This will run the protocol in client mode:

docker run --network babel-tutorial-net --rm -h ping-client --name ping-client -it babel-tutorial/b-pingpongapp interface=eth0