The Ping-Pong Example

To help getting into using Ariba, we provide a short example of how to use the architecture. For this, assume a simple service whose only intention is to exchange data packets between two participating nodes, just like playing ping pong. You will find the whole code within the package under sample/pingpong.

The source files divide into the main code (PingPong.h/.cpp) and the used message format (declared in PingPongMessage.h/.cpp). In addition, main.cpp acts as the entry point to the ping-pong example. We will first give a high-level introduction about what the example does and later dig deeper into the code.

What it does

As already mentioned, the example service simply exchanges packets between participating network nodes. This is accomplished by using the Ariba abstraction to create a communication context and hide underlay details. The participants form a SpoVNet instance in which the first one (as the initiator) creates the instance, while the second joins. As soon as some nodes have successfully joined the instance, they starts sending packets to each other periodically. This happens until a button is pressed.

How it does it

Let's take a look at the code now. Writing a service is pretty simple when using Ariba because most difficulties and annoyances that could come up when struggling with writing network code are taken from the developer. We start with the main.cpp.

01 #include <string>
02 #include "ariba/utility/system/StartupWrapper.h"
03 #include "PingPong.h"
04 
05 using std::string;
06 using ariba::utility::StartupWrapper;
07 using ariba::application::pingpong::PingPong;
08
09 int main( int argc, char** argv ) {
10
11	// get config file
12	string config = "../etc/settings.cnf";
13	if (argc >= 2) config = argv[1];
14
15	StartupWrapper::initConfig( config );
16	StartupWrapper::initSystem();
17
18	// this will do the main functionality and block
19	PingPong ping;
20	StartupWrapper::startup(&ping, true);
21
22	// --> we will run blocking until <enter> is hit
23
24	StartupWrapper::shutdown(&ping);
25	return 0;
26}

The main.cpp serves us as an entry point to the application. In the first lines we include class definitions we need here (e.g. strings because we want to handle some). Also, we include the StartupWrapper class that comes with Ariba. It provides some handy helpers for initialization. Finally, we need to include the PingPong.h, because this is the actual thing we want to execute. Then, we declare the used namespaces (lines 05-07) to be able to use the functionalities. Now we get to the main method, being our starting point. After determining the location of our config file, we initialize the system by passing the config file's location to the StartupWrapper and telling the same to start the architecture up (lines 15-16). Now we are ready to start the ping-pong service, which we first have to create (line 19). Finally, we start the service up by calling the specific method in the StartupWrapper. Now the service will run until we press the enter button.

Now we look into the PingPong.cpp, containing the actual ping pong code. We leave out .h files here because they only do definitions. Everyone intending to use Ariba should be familiar with the subject matter. The first parts look like this:

01 #include "PingPong.h"
02 #include "ariba/utility/configuration/Configuration.h"
03
04 using ariba::utility::Configuration;
05 using namespace ariba;
06
07 namespace ariba {
08 namespace application {
09 namespace pingpong {
10
11 // logging
12 use_logging_cpp( PingPong );
13
14 // the service that the pingpong wants to use
15 ServiceID PingPong::PINGPONG_SERVICEID = ServiceID( 111 );
16
17 // construction
18 PingPong::PingPong() : pingId( 0 ) {
19	Timer::setInterval( 5000 );
20 }
21
22 // destruction
23 PingPong::~PingPong() {
24 }
25
26 // implementation of the startup interface
27 void PingPong::startup() {
28
29	logging_info( "starting up PingPong service ... " );
30
31	// create ariba module
32	logging_debug( "creating ariba underlay module ... " );
33	ariba = new AribaModule();
34
35	// get the configuration object
36	Configuration& config = Configuration::instance();
37
38	// generate spovnet name
39	Name spovnetName("pingpong");
40
41	// get initiator flag
42	this->isInitiator = Configuration::instance().read<bool>("node.initiator");
43
44	// get node name
45	Name nodeName = Name::UNSPECIFIED;
46	if (config.exists("node.name")) nodeName = config.read<string> ("node.name");
47
48	// configure ariba module
49	if (config.exists("ariba.ip.addr")) ariba->setProperty("ip.addr",
50			config.read<string>("ariba.ip.addr"));
51	if (config.exists("ariba.tcp.port")) ariba->setProperty("tcp.port",
52			config.read<string>("ariba.tcp.port"));
53	if (config.exists("ariba.udp.port")) ariba->setProperty("udp.port",
54			config.read<string>("ariba.udp.port"));
55	if (config.exists("ariba.bootstrap.hints")) ariba->setProperty("bootstrap.hints",
56			config.read<string>("ariba.bootstrap.hints"));
57
58	// start ariba module
59	ariba->start();
60
61	// create node and join
62	node = new Node( *ariba, nodeName );
63
64	// bind communication and node listener
65	node->bind( this );                              /*NodeListener*/
66	node->bind( this, PingPong::PINGPONG_SERVICEID); /*CommunicationListener*/
67
68	// start node module
69	node->start();
70
71	// initiate or join the spovnet
72	if (!isInitiator) node->join(spovnetName);
73	else node->initiate(spovnetName);
74
75	// ping pong started up...
76	logging_info( "pingpong starting up with"
77			<< " [spovnetid " << node->getSpoVNetId().toString() << "]"
78			<< " and [nodeid " << node->getNodeId().toString() << "]" );
79 }

First we include the .h file, define the namespace, turn logging functionality on (line 12) and set the ID of the Service. Every service using Ariba is connected to a specific ID that may be chosen initially and arbitrarily. This ID serves Ariba to distinguish between several services that may use it concurrently.

After definitions for construction und destruction (the first also setting a timer to 5 seconds), we come to the startup method. The startup method (lines 20 ff.) is called from the StartupWrapper, jolting the operation of the ping pong service. Here, we first create an AribaModule object, serving as our port to Ariba (line 33). Then, we give our network instance a specific name (being spovnet in the example), before we collect some configurational parameters (lines 46-56). Those parameters are defined in the config file, they serve e.g. in giving IP adresses and port numbers to ariba instances. In line 56, we start Ariba. Also, we need a Node object, reflecting our application running over Ariba (more than one could possibly be using one Ariba). This is created in line 62 and the bound to the ariba object with its specific ServiceID. After this bnind operation, the Node is able to receive signals and messages from Ariba. After this, we start the node object and either initiate or join the network instance (depending on the role of the actual node, wich could be initiator or joiner). Finally, we may give out all kinds of logging infos by calling the method logging_info (line 76).

01 void PingPong::shutdown() {
02
03	logging_info( "pingpong service starting shutdown sequence ..." );
04
05	// stop timer
06	Timer::stop();
07
08	// leave spovnet
09	node->leave();
10
11	// unbind communication and node listener
12	node->unbind( this );                               /*NodeListener*/
13	node->unbind( this, PingPong::PINGPONG_SERVICEID ); /*CommunicationListener*/
14
15	// stop the ariba module
16	ariba->stop();
17
18	// delete node and ariba module
19	delete node;
20	delete ariba;
21
22	// now we are completely shut down
23	logging_info( "pingpong service shut down" );
24}

To shut a service down after its usage, every service provides a method shutdown which is automatically called upon finishing. In here, we stop the timer, leave the instance, unbind all bindings and finally stop the node and Ariba. Don't forget to delete yopur objects to prevent from memory leaks.

80 void PingPong::onNodeJoin( const NodeID& nodeid, const SpoVNetID& spovnetid ){
81
82	if( !startping ){
83		
84		logging_info( "establishing link to node " << nodeid.toString() );
85		const LinkID link = overlay->establishLink( nodeid, PingPong::PINGPONG_ID );
86
87		logging_info( "adding node to registered nodes in pingpong: " << nodeid.toString() );
88		remoteNodes.insert( make_pair(nodeid,link) );
89		
90		Timer::setInterval( 2000 );
91		Timer::start();
92	}
93 }

Ariba provides several callback functions that may used by services to catch all kinds of events that could be of interest. In this exampe we limit ourselves to the event cases of node joins and node leaves. When a node successfull joines to the SpoVNet instance, onNodeJoin is triggered nn the initiator's service side. He may then react to this event, exemplary shown in line 80-93, implementing onNodeJoin. In this case, the initiator starts establishing a link to the joined node (line 85), essentially for all kinds of communications via Ariba. We then store the link for further usage (line 88) and prepare a timer which intention is to trigger periodic events. In our case we initialize the timer to be triggered every 2 seconds (line 90), before starting it (line 91).

100 void PingPong::onNodeLeave( const NodeID& id, const SpoVNetID& spovnetid ){
101	RemoteNodes::iterator i = remoteNodes.find( id );
102	if( i != remoteNodes.end() ) remoteNodes.erase( i );
103 }

Node leaves in our case only lead to deletion of links we had stored before, for we don't need them anymore (line 102).

So far, the node is up and running, created or joined a SpoVNet instance. The initiaor started a timer as soon as another node had joined. Now we see what happens when the timer is triggered.

110 void PingPong::eventFunction(){
111
112	logging_info( "pinging our remote nodes" );
113
114	RemoteNodes::iterator i = remoteNodes.begin();
115	RemoteNodes::iterator iend = remoteNodes.end();
116
117	pingid++;
118
119	for( ; i != iend; i++ ){
120		logging_info( "     -> pinging " << i->first );
121
122		PingPongMessage pingmsg( pingid );
123		overlay->sendMessage( &pingmsg, i->second );
124	}
125 }

Everytime the timer 'fires', eventFunction is called on a node (lines 110-125). In this example, the initiator sends a message to every node that has joined up to this point in time. To accomplish this, it iterates through all established links (line 119), builts a message for every link and finally sends the message using the Base Overlay in Ariba (line 123). Sending messages is done by passing the message object to Ariba, together with the target link to use. . We will now take a short look at how such a message is composed in the ping pong example.

01 #include "PingPongMessage.h"
02
03 namespace ariba {
04 namespace application {
05 namespace pingpong {
06
07 vsznDefault(PingPongMessage);
08
09 PingPongMessage::PingPongMessage() : id(0) {
10 }
11
12 PingPongMessage::PingPongMessage(uint8_t _id) : id(_id) {
13 }
14
15 PingPongMessage::~PingPongMessage(){
16 }
17
18 string PingPongMessage::info(){
19	return "ping pong message id " + ariba::utility::Helper::ultos(id);
20 }
21
22 uint8_t PingPongMessage::getid(){
23	return id;
24 }
25
26 }}} // namespace ariba, appplication, pingpong

Lines 01-26 show the whole PingPongMessage.cpp. One can see here that defining message types in Ariba is pretty simple. As the message in our case is empty and not of higher importance, we refer the reader to the documentation for details.

130 bool PingPong::receiveMessage(const Message* message, const LinkID& link, const NodeID& node){
131	
132	PingPongMessage* incoming = ((Message*)message)->decapsulate<PingPongMessage>();
133	
134	logging_info( "received ping message on link " << link.toString() <<
135				 " from node with id " << (int)incoming->getid());
136
137 }

Getting back to PingPong.cpp: After the initiator has send a message to a joiner, it will arrive and has to be handled. This is accomplished in receiveMessage (the name says it). Every received message has to be decapsulated by a service, casting the data back to the service's message format (line 132).