The Contract Net Protocol (CNP)

A CNP Initiator

public class CNIAgent extends Agent {

int bestOffer = 50; // max price I will pay

public void setup() {
ACLMessage cfp = new ACLMessage(ACLMessage.CFP);
cfp.setProtocol(
FIPANames.InteractionProtocol.FIPA_CONTRACT_NET);
cfp.setContent("we must have whiskey or we'll die");
AID[] providers = DFUtils.searchDF(this, "whiskey");
for(int i = 0; i < providers.length; i++) {
cfp.addReceiver(providers[i]);
}
addBehaviour(new CNIBehavior(this, cfp));
}
}

Behavior

class CNIBehavior extends ContractNetInitiator {
public CNIBehavior(Agent a, ACLMessage cfp) { super(a, cfp); }

protected void handlePropose(ACLMessage msg, Vector acceptances) {
int offer = Integer.parseInt( msg.getContent());
System.out.println("CNI considering an offer for $" + offer);
CNIAgent myCNIAgent = (CNIAgent)myAgent;
ACLMessage response = msg.createReply();
if (offer < myCNIAgent.bestOffer) {
myCNIAgent.bestOffer = offer;
response.setPerformative(ACLMessage.ACCEPT_PROPOSAL);
response.setContent("it's a deal!");
} else {
response.setPerformative(ACLMessage.REJECT_PROPOSAL);
response.setContent("you gotta be kidding!");
}
acceptances.add(response);
}
protected void handleInform(ACLMessage msg) {
System.out.println("Inform received: " + msg.getContent());
}
protected void handleRefuse(ACLMessage msg) {
System.out.println("Refusal received: " + msg.getContent());
}
protected void handleFailure(ACLMessage msg) {
System.out.println("Failure received: " + msg.getContent());
}
}

A CNP Responder

public class CNRAgent extends Agent {

Random generator = new Random();
int price = generator.nextInt(70);

public void setup() {

DFAgentDescription dfd = new DFAgentDescription();
dfd.setName(getAID());

ServiceDescription service = new ServiceDescription();
service.setType( "whiskey" );
service.setName( getLocalName() );

try {
DFAgentDescription list[] = DFService.search( this, dfd );
if ( list.length > 0 ) DFService.deregister(this);
dfd.addServices(service);
DFService.register(this, dfd);
}
catch (FIPAException fe) {
System.err.println(fe.getMessage());
}

MessageTemplate mt =
ContractNetResponder.createMessageTemplate(
FIPANames.InteractionProtocol.FIPA_CONTRACT_NET);
addBehaviour(new CNRBehavior(this, mt));
}
}

Behavior

class CNRBehavior extends ContractNetResponder {
public CNRBehavior(Agent a, MessageTemplate mt) { super(a, mt); }

protected ACLMessage prepareResponse(ACLMessage msg)
throws NotUnderstoodException, RefuseException {
System.out.println("cfp received: " + msg.getContent());

ACLMessage response = msg.createReply();
response.setPerformative(ACLMessage.PROPOSE);
response.setContent("" + ((CNRAgent)myAgent).price);
return response;
}
protected ACLMessage prepareResultNotification(
ACLMessage cfp, ACLMessage propose, ACLMessage accept) {
System.out.println(
"acceptance received: " + accept.getContent());
ACLMessage response = accept.createReply();
response.setPerformative(ACLMessage.INFORM);
response.setContent("your whiskey is on its way!");
return response;
}

protected void handleRejectProposal(
ACLMessage cfp, ACLMessage propose, ACLMessage reject) {
System.out.println(
"rejection received: " + reject.getContent());
}
}

Output

cfp received: we must have whiskey or we'll die
cfp received: we must have whiskey or we'll die
cfp received: we must have whiskey or we'll die
cfp received: we must have whiskey or we'll die
CNI considering an offer for $53
CNI considering an offer for $54
CNI considering an offer for $19
CNI considering an offer for $14
rejection received: you gotta be kidding!
rejection received: you gotta be kidding!
acceptance received: it's a deal!
acceptance received: it's a deal!
Inform received: your whiskey is on its way!
Inform received: your whiskey is on its way!