README.md

Ping-Pong CorDapp

This CorDapp allows a node to ping any other node on the network that also has this CorDapp installed.

It demonstrates how to use Corda for messaging and passing data using a flow that initiates a communication session without saving any states or using any contracts.

Concepts

The ping utility is normally used to send an Send ICMP ECHO_REQUEST packets to network hosts. The idea being that the receiving host will echo the message back.

We can use corda abstractions to accomplish the same thing.

We define a state (the "ping" to be shared), define a contract (the way to make sure our ping is received correctly), and define the flow (the control flow of our cordapp).

Flows

You'll notice in our code we call these two classes ping and pong, the flow that sends the "ping", and the flow that returns with a "pong".

Take a look at initiating flow PingFlow.kt.

You'll notice that this flow does what we expect, which is to send an outbound ping, and expect to receive a pong. If we receive a pong, then our flow is sucessful.

    @Suspendable
    override fun call() {
        val counterpartySession = initiateFlow(counterparty)
        val counterpartyData = counterpartySession.sendAndReceive<String>("ping")
        counterpartyData.unwrap { msg ->
            assert(msg == "pong")
        }
    }

And of course we see a similar behavior in responder flow Pong.

We expect to receive data from a counterparty that contains a ping, when we receive it, we respond with a pong.

    @Suspendable
    override fun call() {
        val counterpartyData = counterpartySession.receive<String>()
        counterpartyData.unwrap { msg ->
            assert(msg == "ping")
        }
        counterpartySession.send("pong")
    }

Pre-Requisites

For development environment setup, please refer to: Setup Guide.

Running the nodes

Open a terminal and go to the project root directory and type: (to deploy the nodes using bootstrapper)

./gradlew clean deployNodes

Then type: (to run the nodes)

./build/nodes/runnodes

Pinging a node:

Pinging from the shell

Run the following command from PartyA's shell:

start ping counterparty: PartyB

Since we are not using any start or transaction, if we want to see the trace of the action. We can look it up from /build/nodes/PartyA/logs/XXXXX.log it will be something like:

[pool-8-thread-1] shell.FlowShellCommand. - Executing command "flow start ping counterparty: PartyB",

RPC via Gradle:

Run the following command from the root of the project:

• Unix/Mac OSX: ./gradlew pingPartyBKotlin -Paddress="[your RPC address]" -PnodeName="[name of node to ping]"
• Windows: gradlew pingPartyBKotlin -Paddress="[your RPC address]" -PnodeName="[name of node to ping]"

For example, if your node has the RPC address localhost:10006, you'd ping party B from a Unix/Mac OSX machine by running:

./gradlew pingPartyBKotlin -Paddress=localhost:10006 -PnodeName="O=PartyB,L=New York,C=US"

You should see the following message, indicating that PartyB responded to your ping:

Successfully pinged O=PartyB,L=New York,C=US.