Running our CorDapp¶

Clean up¶

Before running our node, delete the client/TemplateClient.java (for Java) or client/TemplateClient.kt (for Kotlin) file. We won’t be using it, and it will cause build errors unless we remove it.

Deploying our CorDapp¶

Let’s take a look at the nodes we’re going to deploy. Open the project’s build.gradle file and scroll down to the task deployNodes section. This section defines three nodes - the Controller, NodeA, and NodeB:

task deployNodes(type: net.corda.plugins.Cordform, dependsOn: ['jar']) {
    directory "./build/nodes"
    networkMap "CN=Controller,O=R3,OU=corda,L=London,C=UK"
    node {
        name "CN=Controller,O=R3,OU=corda,L=London,C=UK"
        advertisedServices = ["corda.notary.validating"]
        p2pPort 10002
        rpcPort 10003
        cordapps = []
    }
    node {
        name "CN=NodeA,O=NodeA,L=London,C=UK"
        advertisedServices = []
        p2pPort 10005
        rpcPort 10006
        webPort 10007
        cordapps = []
        rpcUsers = [[ user: "user1", "password": "test", "permissions": []]]
    }
    node {
        name "CN=NodeB,O=NodeB,L=New York,C=US"
        advertisedServices = []
        p2pPort 10008
        rpcPort 10009
        webPort 10010
        cordapps = []
        rpcUsers = [[ user: "user1", "password": "test", "permissions": []]]
    }
}

We have three standard nodes, plus a special Controller node that is running the network map service, and is also advertising a validating notary service. Feel free to add additional node definitions here to expand the size of the test network.

We can run this deployNodes task using Gradle. For each node definition, Gradle will:

• Package the project’s source files into a CorDapp jar
• Create a new node in build/nodes with our CorDapp already installed

We can do that now by running the following commands from the root of the project:

// On Windows
gradlew clean deployNodes

// On Mac
./gradlew clean deployNodes

Running the nodes¶

Running deployNodes will build the nodes under build/nodes. If we navigate to one of these folders, we’ll see the three node folders. Each node folder has the following structure:

.
|____corda.jar                     // The runnable node
|____corda-webserver.jar           // The node's webserver
|____dependencies
|____node.conf                     // The node's configuration file
|____plugins
  |____java/kotlin-source-0.1.jar  // Our IOU CorDapp

Let’s start the nodes by running the following commands from the root of the project:

// On Windows
build/nodes/runnodes.bat

// On Mac
build/nodes/runnodes

This will start a terminal window for each node, and an additional terminal window for each node’s webserver - eight terminal windows in all. Give each node a moment to start - you’ll know it’s ready when its terminal windows displays the message, “Welcome to the Corda interactive shell.”.

Interacting with the nodes¶

Now that our nodes are running, let’s order one of them to create an IOU by kicking off our IOUFlow. In a larger app, we’d generally provide a web API sitting on top of our node. Here, for simplicity, we’ll be interacting with the node via its built-in CRaSH shell.

Go to the terminal window displaying the CRaSH shell of Node A. Typing help will display a list of the available commands.

We want to create an IOU of 100 with Node B. We start the IOUFlow by typing:

start IOUFlow arg0: 99, arg1: "NodeB"

start IOUFlow iouValue: 99, otherParty: "NodeB"

Node A and Node B will automatically agree an IOU. If the flow worked, it should have led to the recording of a new IOU in the vaults of both Node A and Node B.

We can check the flow has worked by using an RPC operation to check the contents of each node’s vault. Typing run will display a list of the available commands. We can examine the contents of a node’s vault by running:

run vaultAndUpdates

And we can also examine a node’s transaction storage, by running:

run verifiedTransactions

The vaults of Node A and Node B should both display the following output:

first:
- state:
    data:
      value: 99
      lender: "CN=NodeA,O=NodeA,L=London,C=GB"
      borrower: "CN=NodeB,O=NodeB,L=New York,C=US"
      contract:
        legalContractReference: "559322B95BCF7913E3113962DC3F3CBD71C818C66977721580C045DC41C813A5"
      participants:
      - "CN=NodeA,O=NodeA,L=London,C=GB"
      - "CN=NodeB,O=NodeB,L=New York,C=US"
    notary: "CN=Controller,O=R3,OU=corda,L=London,C=GB,OU=corda.notary.validating"
    encumbrance: null
  ref:
    txhash: "656A1BF64D5AEEC6F6C944E287F34EF133336F5FC2C5BFB9A0BFAE25E826125F"
    index: 0
second: "(observable)"

Conclusion¶

We have written a simple CorDapp that allows IOUs to be issued onto the ledger. Like all CorDapps, our CorDapp is made up of three key parts:

• The IOUState, representing IOUs on the ledger
• The IOUContract, controlling the evolution of IOUs over time
• The IOUFlow, orchestrating the process of agreeing the creation of an IOU on-ledger

Together, these three parts completely determine how IOUs are created and evolved on the ledger.

Next steps¶

There are a number of improvements we could make to this CorDapp:

• We could require signatures from the lender as well the borrower, to give both parties a say in the creation of a new IOUState
• We should add unit tests, using the contract-test and flow-test frameworks
• We should change IOUState.value from an integer to a proper amount of a given currency
• We could add an API, to make it easier to interact with the CorDapp

We will explore some of these improvements in future tutorials. But you should now be ready to develop your own CorDapps. There’s a more fleshed-out version of the IOU CorDapp with an API and web front-end, and a set of example CorDapps in the main Corda repo, under samples. An explanation of how to run these samples here.

As you write CorDapps, you can learn more about the API available here.

If you get stuck at any point, please reach out on Slack, Discourse, or Stack Overflow.