Running your CorDapp

Now that you’ve written a CorDapp, it’s time to test it by running it on some real Corda nodes.

Deploying your CorDapp

Let’s take a look at the nodes you’re going to deploy. Open the project’s build.gradle file and scroll down to the task deployNodes section. This section defines three nodes. There are two standard nodes (PartyA and PartyB), plus a special network map/notary node that is running the network map service and advertises a validating notary service.

task deployNodes(type: net.corda.plugins.Cordform, dependsOn: ['jar']) {

    nodeDefaults {
        projectCordapp {
            deploy = false
        }
        cordapp project(':contracts')
        cordapp project(':workflows')
        runSchemaMigration = true
    }
    node {
        name "O=Notary,L=London,C=GB"
        notary = [validating : false]
        p2pPort 10002
        rpcSettings {
            address("localhost:10003")
            adminAddress("localhost:10043")
        }
    }
    node {
        name "O=PartyA,L=London,C=GB"
        p2pPort 10005
        rpcSettings {
            address("localhost:10006")
            adminAddress("localhost:10046")
        }
        rpcUsers = [[ user: "user1", "password": "test", "permissions": ["ALL"]]]
    }
    node {
        name "O=PartyB,L=New York,C=US"
        p2pPort 10008
        rpcSettings {
            address("localhost:10009")
            adminAddress("localhost:10049")
        }
        rpcUsers = [[ user: "user1", "password": "test", "permissions": ["ALL"]]]
    }
}

You 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 your CorDapp already installed.

To do this, run the command that corresponds to your operating system from the root of your project:

  • Mac OSX: ./gradlew clean deployNodes
  • Windows: gradlew clean deployNodes

Running the nodes

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

.
|____additional-node-infos
|____certificates
|____corda.jar                  // The runnable node.
|____cordapps
|____djvm
|____drivers
|____logs
|____network-parameters
|____node.conf                // The node's configuration file.
|____nodeInfo
|____persistence.mv.db
|____persistence.trace.db

Start the nodes by running the following command from the root of the project:

  • Mac OSX: build/nodes/runnodes
  • Windows: build/nodes/runnodes.bat

This will start a terminal window for each node. 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.”.

running node

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, you’d generally provide a web API sitting on top of our node. Here, for simplicity, you’ll be interacting with the node via its built-in CRaSH shell.

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

You want to create an IOU of 99 with PartyB. To start the IOUFlow, type the following syntax:

start IOUFlow iouMessage: 99, otherParty: "O=PartyB,L=New York,C=US"

This single command will cause PartyA and PartyB to automatically agree an IOU. This is one of the great advantages of the flow framework - it allows you to reduce complex negotiation and update processes into a single function call.

Starting this flow will return the following:

✅   Starting
         Requesting signature by Notary Service
             Requesting signature by Notary Service
             Validating response from Notary Service
    ✅   Broadcasting transaction to participants
➡️   Done
Flow completed with result: null

If the flow worked, it should have recorded a new IOU in the vaults of both PartyA and PartyB. Let’s check.

You can check the contents of each node’s vault by running:

run vaultQuery contractStateType: com.template.states.IOUState

The vaults of PartyA and PartyB should both display the following output:

states:
- state:
    data: !<com.template.states.IOUState>
      value: "99"
      lender: "O=PartyA, L=London, C=GB"
      borrower: "O=PartyB, L=New York, C=US"
    contract: "com.template.contracts.TemplateContract"
    notary: "O=Notary, L=London, C=GB"
    encumbrance: null
    constraint: !<net.corda.core.contracts.SignatureAttachmentConstraint>
      key: "aSq9DsNNvGhYxYyqA9wd2eduEAZ5AXWgJTbTEw3G5d2maAq8vtLE4kZHgCs5jcB1N31cx1hpsLeqG2ngSysVHqcXhbNts6SkRWDaV7xNcr6MtcbufGUchxredBb6"
  ref:
    txhash: "D189448F05D39C32AAAAE7A40A35F4C96529680A41542576D136AEE0D6A80926"
    index: 0
statesMetadata:
- ref:
    txhash: "D189448F05D39C32AAAAE7A40A35F4C96529680A41542576D136AEE0D6A80926"
    index: 0
  contractStateClassName: "com.template.states.IOUState"
  recordedTime: "2020-10-19T11:09:58.183Z"
  consumedTime: null
  status: "UNCONSUMED"
  notary: "O=Notary, L=London, C=GB"
  lockId: null
  lockUpdateTime: null
  relevancyStatus: "RELEVANT"
  constraintInfo:
    constraint:
      key: "aSq9DsNNvGhYxYyqA9wd2eduEAZ5AXWgJTbTEw3G5d2maAq8vtLE4kZHgCs5jcB1N31cx1hpsLeqG2ngSysVHqcXhbNts6SkRWDaV7xNcr6MtcbufGUchxredBb6"
totalStatesAvailable: -1
stateTypes: "UNCONSUMED"
otherResults: []

This is the transaction issuing our IOUState onto a ledger.

However, if you run the same command on the other node (the notary), you will see the following:

{
  "states" : [ ],
  "statesMetadata" : [ ],
  "totalStatesAvailable" : -1,
  "stateTypes" : "UNCONSUMED",
  "otherResults" : [ ]
}

This is the result of Corda’s privacy model. Because the notary was not involved in the transaction and had no need to see the data, the transaction was not distributed to them.

Conclusion

You have written a simple CorDapp that allows IOUs to be issued onto the ledger. This CorDapp is made up of two key parts:

  • The IOUState, which represents IOUs on the blockchain.
  • The IOUFlow, which orchestrates the process of agreeing the creation of an IOU on-ledger.

After completing this tutorial, your CorDapp should look like this:

Next steps

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

  • You could add unit tests, using the contract-test and flow-test frameworks.
  • You could change IOUState.value from an integer to a proper amount of a given currency.
  • You could add an API, to make it easier to interact with the CorDapp.

But for now, the biggest priority is to add an IOUContract imposing constraints on the evolution of each IOUState over time - see Applying contract constraints.

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