== '''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''.


{{{
     1	#include <string>
     2	#include "ariba/utility/system/StartupWrapper.h"
     3	#include "PingPong.h"
     4	
     5	using std::string;
     6	using ariba::utility::StartupWrapper;
     7	using ariba::application::pingpong::PingPong;
     8	
     9	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::startSystem();
    17	
    18		// this will do the main functionality and block
    19		PingPong ping;
    20		StartupWrapper::startup(&ping);
    21	
    22		// --> we will run blocking until <enter> is hit
    23	
    24		StartupWrapper::shutdown(&ping);
    25		StartupWrapper::stopSystem();
    26	
    27		return 0;
    28	}
}}}
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:

{{{
     1	#include "PingPong.h"
     2	#include "ariba/utility/configuration/Configuration.h"
     3	#include "ariba/utility/visual/DddVis.h"
     4	
     5	using ariba::utility::Configuration;
     6	using namespace ariba;
     7	
     8	namespace ariba {
     9	namespace application {
    10	namespace pingpong {
    11	
    12	// logging
    13	use_logging_cpp( PingPong );
    14	
    15	// the service that the pingpong wants to use
    16	ServiceID PingPong::PINGPONG_SERVICEID = ServiceID( 111 );
    17	
    18	// construction
    19	PingPong::PingPong() : pingId( 0 ) {
    20		Timer::setInterval( 1000 );
    21	}
    22	
    23	// destruction
    24	PingPong::~PingPong() {
    25	}
    26	
    27	// implementation of the startup interface
    28	void PingPong::startup() {
    29	
    30		logging_info( "starting up PingPong service ... " );
    31	
    32		// create ariba module
    33		logging_debug( "creating ariba underlay module ... " );
    34		ariba = new AribaModule();
    35	
    36		Name spovnetName("pingpong");
    37		Name nodeName = Name::UNSPECIFIED;
    38		this->name = string("<ping>");
    39	
    40		// get settings from configuration object
    41		if( Configuration::haveConfig() ){
    42			Configuration& config = Configuration::instance();
    43	
    44			// get node name
    45			if (config.exists("node.name"))
    46				nodeName = config.read<string> ("node.name");
    47	
    48			// configure ariba module
    49			if (config.exists("ariba.endpoints"))
    50				ariba->setProperty("endpoints", config.read<string>("ariba.endpoints"));
    51			if (config.exists("ariba.bootstrap.hints"))
    52				ariba->setProperty("bootstrap.hints", config.read<string>("ariba.bootstrap.hints"));
    53			if (config.exists("pingpong.name"))
    54				name = config.read<string>("pingpong.name");
    55	
    56			// get visualization
    57			if( config.exists("ariba.visual3d.ip") && config.exists("ariba.visual3d.port")){
    58				string ip = config.read<string>("ariba.visual3d.ip");
    59				unsigned int port = config.read<unsigned int>("ariba.visual3d.port");
    60				unsigned int color = config.exists("node.color") ?
    61						config.read<unsigned int>("node.color") : 0;
    62				ariba::utility::DddVis::instance().configure(ip, port, color);
    63			}
    64	
    65		} // if( Configuration::haveConfig() )
    66	
    67		// start ariba module
    68		ariba->start();
    69	
    70		// create node and join
    71		node = new Node( *ariba, nodeName );
    72	
    73		// bind communication and node listener
    74		node->bind( this );                              /*NodeListener*/
    75		node->bind( this, PingPong::PINGPONG_SERVICEID); /*CommunicationListener*/
    76	
    77		// start node module
    78		node->start();
    79	
    80		// when initiating, you can define the overlay type, default is Chord [CHORD_OVERLAY]
    81		SpoVNetProperties params;
    82		//params.setBaseOverlayType( SpoVNetProperties::ONE_HOP_OVERLAY ); // alternative: OneHop
    83	
    84		// initiate the spovnet
    85		logging_info("initiating spovnet");
    86		node->initiate(spovnetName, params);
    87	
    88		// join the spovnet
    89		logging_info("joining spovnet");
    90		node->join(spovnetName);
    91	
    92		// ping pong started up...
    93		logging_info( "pingpong starting up with"
    94				<< " [spovnetid " << node->getSpoVNetId().toString() << "]"
    95				<< " and [nodeid " << node->getNodeId().toString() << "]" );
    96	}
}}}

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).
 

{{{
    99	void PingPong::shutdown() {
   100	
   101		logging_info( "pingpong service starting shutdown sequence ..." );
   102	
   103		// stop timer
   104		Timer::stop();
   105	
   106		// leave spovnet
   107		node->leave();
   108	
   109		// unbind communication and node listener
   110		node->unbind( this );                               /*NodeListener*/
   111		node->unbind( this, PingPong::PINGPONG_SERVICEID ); /*CommunicationListener*/
   112	
   113		// stop the ariba module
   114		ariba->stop();
   115	
   116		// delete node and ariba module
   117		delete node;
   118		delete ariba;
   119	
   120		// now we are completely shut down
   121		logging_info( "pingpong service shut down" );
   122	}
}}}

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.

So far, the node is up and running, created or joined a SpoVNet instance. As very node starts a timer as soon as it has joined, we now inspect what happens when the timer is triggered.

{{{
   125	void PingPong::eventFunction() {
   126	
   127		// we ping all nodes that are known in the overlay structure
   128		// this can be all nodes (OneHop) overlay or just some neighbors
   129		// in case of a Chord or Kademlia structure
   130	
   131		// in this sample we use auto-links: we just send out our message
   132		// to the node and the link is established automatically. for more
   133		// control we would use the node->establishLink function to create
   134		// a link and start using the link in the CommunicationListener::onLinkUp
   135		// function that is implemented further down in PingPong::onLinkUp
   136	
   137		logging_info( "pinging overlay neighbors with ping id " << ++pingId );
   138		PingPongMessage pingmsg( pingId, name );
   139	
   140		//-----------------------------------------------------------------------
   141		// Option 1: get all neighboring nodes and send the message to each
   142		//-----------------------------------------------------------------------
   143		counter++;
   144		if (counter<0 || counter>4) {
   145			counter = 0;
   146			string s;
   147			for (int i=0; i<names.size();i++) {
   148				if (i!=0) s+= ", ";
   149				s = s+names[i];
   150			}
   151			logging_info("----> I am " << name << " and I know " << s);
   152			names.clear();
   153		}
   154	
   155		vector<NodeID> nodes = node->getNeighborNodes();
   156		BOOST_FOREACH( NodeID nid, nodes ){
   157			logging_info( "sending ping message to " << nid.toString() );
   158			node->sendMessage( pingmsg, nid, PingPong::PINGPONG_SERVICEID );
   159		}
   160	
   161		//-----------------------------------------------------------------------
   162		// Option 2: send a "broadcast message" that actually does the same thing
   163		//           internally, gets all neighboring nodes and sends the message
   164		//-----------------------------------------------------------------------
   165		// node->sendBroadcastMessage( pingmsg, PingPong::PINGPONG_SERVICEID );
   166	}
}}}

Everytime the timer 'fires', ''eventFunction'' is called on a node. In this example, every node sends a message to every node that is part of the network at this point in time. To accomplish this, it builds a message (line 15) and iterates through all neighboring nodes (line 20-23). To each of this nodes, it sends the message. Sending messages is simply done by passing the message object to ''Ariba'', together with the target node ID. . 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. 

{{{
   187	void PingPong::onMessage(const DataMessage& msg, const NodeID& remote, const LinkID& lnk) {
   188		PingPongMessage* pingmsg = msg.getMessage()->convert<PingPongMessage> ();
   189		bool found=false;
   190		for (int i=0;i<names.size(); i++) if (names[i]==pingmsg->getName()) found=true;
   191		if (!found) names.push_back(pingmsg->getName());
   192		logging_info( "received ping message on link " << lnk.toString()
   193				<< " from node " << remote.toString()
   194				<< ": " << pingmsg->info() );
   195	}
}}}

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).