The example CorDapp

The example CorDapp allows nodes to agree IOUs with each other. Nodes will always agree to the creation of a new IOU if:

  • Its value is strictly positive
  • The node is not trying to issue the IOU to itself

We will deploy the CorDapp on 4 test nodes:

  • Controller, which hosts the network map service and a validating notary service
  • PartyA
  • PartyB
  • PartyC

Because data is only propagated on a need-to-know basis, any IOUs agreed between PartyA and PartyB become “shared facts” between PartyA and PartyB only. PartyC won’t be aware of these IOUs.

Downloading the example CorDapp

We need to download the example CorDapp from GitHub.

  • Set up your machine by following the quickstart guide
  • Clone the example CorDapp from the cordapp-example repository using the following command: git clone https://github.com/corda/cordapp-example
  • Change directories to the freshly cloned repo: cd cordapp-example

Opening the example CorDapp in IntelliJ

Let’s open the example CorDapp in IntelliJ IDEA.

If opening a fresh IntelliJ instance

  • Open IntelliJ

  • A dialogue box will appear:intellij welcome

  • Click open, navigate to the folder where you cloned the cordapp-example, and click OK

  • IntelliJ will show several pop-up windows, one of which requires our attention:unlinked gradle project

  • Click the ‘import gradle project’ link. Press OK on the dialogue that pops up

  • Gradle will now download all the project dependencies and perform some indexing. This usually takes a minute or so.

    • If the ‘import gradle project’ pop-up does not appear, click the small green speech bubble at the bottom-right of the IDE, or simply close and re-open IntelliJ again to make it reappear.

If you already have IntelliJ open

  • Open the File menu
  • Navigate to Open ...
  • Navigate to the directory where you cloned the cordapp-example
  • Click OK

Project structure

The example CorDapp has the following directory structure:

.
├── config
│   ├── dev
│   │   └── log4j2.xml
│   └── test
│       └── log4j2.xml
├── doc
│   └── example_flow.plantuml
├── gradle
│   └── wrapper
│       ├── gradle-wrapper.jar
│       └── gradle-wrapper.properties
├── lib
│   ├── README.txt
│   └── quasar.jar
├── java-source
│   └── ...
├── kotlin-source
│   ├── build.gradle
│   └── src
│       ├── main
│       │   ├── kotlin
│       │   │   └── com
│       │   │       └── example
│       │   │           ├── api
│       │   │           │   └── ExampleApi.kt
│       │   │           ├── client
│       │   │           │   └── ExampleClientRPC.kt
│       │   │           ├── contract
│       │   │           │   └── IOUContract.kt
│       │   │           ├── flow
│       │   │           │   └── ExampleFlow.kt
│       │   │           ├── model
│       │   │           │   └── IOU.kt
│       │   │           ├── plugin
│       │   │           │   └── ExamplePlugin.kt
│       │   │           ├── schema
│       │   │           │   └── IOUSchema.kt
│       │   │           └── state
│       │   │               └── IOUState.kt
│       │   └── resources
│       │       ├── META-INF
│       │       │   └── services
│       │       │       └── net.corda.webserver.services.WebServerPluginRegistry
│       │       ├── certificates
│       │       │   ├── readme.txt
│       │       │   ├── sslkeystore.jks
│       │       │   └── truststore.jks
│       │       └── exampleWeb
│       │           ├── index.html
│       │           └── js
│       │               └── angular-module.js
│       └── test
│           └── kotlin
│               └── com
│                   └── example
│                       ├── Main.kt
│                       ├── contract
│                       │   └── IOUContractTests.kt
│                       └── flow
│                           └── IOUFlowTests.kt
├── .gitignore
├── LICENCE
├── README.md
├── TRADEMARK
├── build.gradle
├── gradle.properties
├── gradlew
├── gradlew.bat
└── settings.gradle

The key files and directories are as follows:

  • The root directory contains some gradle files, a README and a LICENSE

  • config contains log4j configs

  • gradle contains the gradle wrapper, which allows the use of Gradle without installing it yourself and worrying about which version is required

  • lib contains the Quasar jar which rewrites our CorDapp’s flows to be checkpointable

  • kotlin-source contains the source code for the example CorDapp written in Kotlin

  • kotlin-source/src/main/kotlin contains the source code for the example CorDapp

  • kotlin-source/src/main/resources contains the certificate store, some static web content to be served by the nodes and the WebServerPluginRegistry file

  • kotlin-source/src/test/kotlin contains unit tests for the contracts and flows, and the driver to run the nodes via IntelliJ

  • java-source contains the same source code, but written in Java. CorDapps can be developed in any language targeting the JVM

Running the example CorDapp

There are two ways to run the example CorDapp:

  • Via the terminal
  • Via IntelliJ

In both cases, we will deploy a set of test nodes with our CorDapp installed, then run the nodes. You can read more about how we define the nodes to be deployed here.

Terminal

Building the example CorDapp

  • Open a terminal window in the cordapp-example directory
  • Build the test nodes with our CorDapp using the following command:
    • Unix/Mac OSX: ./gradlew deployNodes
    • Windows: gradlew.bat deployNodes

This will automatically build four pre-configured nodes with our CorDapp installed. These nodes are meant for local testing only

  • After the build process has finished, you will see the newly-build nodes in the kotlin-source/build/nodes folder
    • There will be one folder generated for each node you built, plus a runnodes shell script (or batch file on Windows) to run all the nodes simultaneously
    • Each node in the nodes folder has the following structure:
. nodeName
├── corda.jar
├── node.conf
└── plugins

corda.jar is the Corda runtime, plugins contains our node’s CorDapps, and the node’s configuration is given by node.conf

Running the example CorDapp

Start the nodes by running the following command from the root of the cordapp-example folder:

  • Unix/Mac OSX: kotlin-source/build/nodes/runnodes
  • Windows: call kotlin-source\build\nodes\runnodes.bat

For each node, the runnodes script creates a node tab/window:

   ______               __
  / ____/     _________/ /___ _
 / /     __  / ___/ __  / __ `/         It's kind of like a block chain but
/ /___  /_/ / /  / /_/ / /_/ /          cords sounded healthier than chains.
\____/     /_/   \__,_/\__,_/

--- Corda Open Source 0.12.1 (da47f1c) -----------------------------------------------

📚  New! Training now available worldwide, see https://corda.net/corda-training/

Logs can be found in                    : /Users/joeldudley/Desktop/cordapp-example/kotlin-source/build/nodes/PartyA/logs
Database connection url is              : jdbc:h2:tcp://10.163.199.132:54763/node
Listening on address                    : 127.0.0.1:10005
RPC service listening on address        : localhost:10006
Loaded plugins                          : com.example.plugin.ExamplePlugin
Node for "PartyA" started up and registered in 35.0 sec


Welcome to the Corda interactive shell.
Useful commands include 'help' to see what is available, and 'bye' to shut down the node.

Fri Jul 07 10:33:47 BST 2017>>>

For every node except the controller, the script also creates a webserver terminal tab/window:

Logs can be found in /Users/joeldudley/Desktop/cordapp-example/kotlin-source/build/nodes/PartyA/logs/web
Starting as webserver: localhost:10007
Webserver started up in 42.02 sec

It usually takes around 60 seconds for the nodes to finish starting up. To ensure that all the nodes are running OK, you can query the ‘status’ end-point located at http://localhost:[port]/api/status (e.g. http://localhost:10007/api/status for PartyA).

IntelliJ

  • Select the Run Example CorDapp - Kotlin run configuration from the drop-down menu at the top right-hand side of the IDE
  • Click the green arrow to start the nodes:run config drop down The node driver defined in /src/test/kotlin/com/example/Main.kt allows you to specify how many nodes you would like to run and the configuration settings for each node. For the example CorDapp, the driver starts up four nodes and adds an RPC user for all but the “Controller” node (which serves as the notary and network map service):
fun main(args: Array<String>) {
    // No permissions required as we are not invoking flows.
    val user = User("user1", "test", permissions = setOf())
    driver(isDebug = true) {
        startNode(getX500Name(O="Controller",L="London",C='GB"), setOf(ServiceInfo(ValidatingNotaryService.type)))
        val (nodeA, nodeB, nodeC) = Futures.allAsList(
                startNode(getX500Name(O="PartyA",L="London",C="GB"), rpcUsers = listOf(user)),
                startNode(getX500Name(O="PartyB",L="New York",C="US"), rpcUsers = listOf(user)),
                startNode(getX500Name(O="PartyC",L="Paris",C="FR"), rpcUsers = listOf(user))).getOrThrow()

        startWebserver(nodeA)
        startWebserver(nodeB)
        startWebserver(nodeC)

        waitForAllNodesToFinish()
    }
}
  • To stop the nodes, press the red square button at the top right-hand side of the IDE, next to the run configurations

Later, we’ll look at how the node driver can be useful for debugging your CorDapp.

Interacting with the example CorDapp

Via HTTP

The CorDapp defines several HTTP API end-points and a web front-end. The end-points allow you to list the IOUs a node is involved in, agree new IOUs, and see who is on the network.

The nodes are running locally on the following ports:

  • PartyA: localhost:10007
  • PartyB: localhost:10010
  • PartyC: localhost:10013

These ports are defined in build.gradle and in each node’s node.conf file under kotlin-source/build/nodes/NodeX.

As the nodes start up, they should tell you which port their embedded web server is running on. The available API endpoints are:

  • /api/example/me
  • /api/example/peers
  • /api/example/ious
  • /api/example/create-iou with parameters iouValue and partyName which is CN name of a node

The web front-end is served from /web/example.

An IOU can be created by sending a PUT request to the api/example/create-iou end-point directly, or by using the the web form hosted at /web/example.

Creating an IOU via the endpoint

To create an IOU between PartyA and PartyB, run the following command from the command line:

curl -X PUT 'http://localhost:10007/api/example/create-iou?iouValue=1&partyName=O=PartyB,L=New%20York,C=US'

Note that both PartyA’s port number (10007) and PartyB are referenced in the PUT request path. This command instructs PartyA to agree an IOU with PartyB. Once the process is complete, both nodes will have a signed, notarised copy of the IOU. PartyC will not.

Submitting an IOU via the web front-end

To create an IOU between PartyA and PartyB, navigate to /web/example, click the “create IOU” button at the top-left of the page, and enter the IOU details into the web-form. The IOU must have a positive value. For example:

Counter-party: Select from list
Value (Int):   5

And click submit. Upon clicking submit, the modal dialogue will close, and the nodes will agree the IOU.

Once an IOU has been submitted

Assuming all went well, you should see some activity in PartyA’s web-server terminal window:

>> Signing transaction with our private key.
>> Gathering the counterparty's signature.
>> Structural step change in child of Gathering the counterparty's signature.
>> Collecting signatures from counter-parties.
>> Verifying collected signatures.
>> Done
>> Obtaining notary signature and recording transaction.
>> Structural step change in child of Obtaining notary signature and recording transaction.
>> Requesting signature by notary service
>> Broadcasting transaction to participants
>> Done
>> Done

You can view the newly-created IOU by accessing the vault of PartyA or PartyB:

Via the HTTP API:

Via web/example:

The vault and web front-end of PartyC (on localhost:10013) will not display any IOUs. This is because PartyC was not involved in this transaction.

Via the interactive shell (terminal only)

Nodes started via the terminal will display an interactive shell:

Welcome to the Corda interactive shell.
Useful commands include 'help' to see what is available, and 'bye' to shut down the node.

Fri Jul 07 16:36:29 BST 2017>>>

Type flow list in the shell to see a list of the flows that your node can run. In our case, this will return the following list:

com.example.flow.ExampleFlow$Initiator
net.corda.core.flows.ContractUpgradeFlow$Initiator
net.corda.core.flows.ContractUpgradeFlow$Initiator
net.corda.finance.flows.CashExitFlow
net.corda.finance.flows.CashIssueAndPaymentFlow
net.corda.finance.flows.CashIssueFlow
net.corda.finance.flows.CashPaymentFlow

We can create a new IOU using the ExampleFlow$Initiator flow. For example, from the interactive shell of PartyA, you can agree an IOU of 50 with PartyB by running flow start ExampleFlow$Initiator iouValue: 50, otherParty: "O=PartyB,L=New York,C=US".

This will print out the following progress steps:

✅   Generating transaction based on new IOU.
✅   Verifying contract constraints.
✅   Signing transaction with our private key.
✅   Gathering the counterparty's signature.
    ✅   Collecting signatures from counter-parties.
    ✅   Verifying collected signatures.
✅   Obtaining notary signature and recording transaction.
    ✅   Requesting signature by notary service
            Requesting signature by Notary service
            Validating response from Notary service
    ✅   Broadcasting transaction to participants
✅   Done

We can also issue RPC operations to the node via the interactive shell. Type run to see the full list of available operations.

Via the h2 web console

You can connect directly to your node’s database to see its stored states, transactions and attachments. To do so, please follow the instructions in Node database.

Using the example RPC client

The /src/main/kotlin-source/com/example/client/ExampleClientRPC.kt file is a simple utility that uses the client RPC library to connect to a node. It will log any existing IOUs and listen for any future IOUs. If you haven’t created any IOUs when you first connect to one of the nodes, the client will simply log any future IOUs that are agreed.

Running the client via IntelliJ:

Select the ‘Run Example RPC Client’ run configuration which, by default, connects to PartyA. Click the green arrow to run the client. You can edit the run configuration to connect on a different port.

Running the client via the command line:

Run the following gradle task:

./gradlew runExampleClientRPCKotlin

This will connect the RPC client to PartyA and log their past and future IOU activity.

You can close the application using ctrl+C.

For more information on the client RPC interface and how to build an RPC client application, see:

Running Nodes Across Machines

The nodes can be split across machines and configured to communicate across the network.

After deploying the nodes, navigate to the build folder (kotlin-source/build/nodes) and move some of the individual node folders to a different machine (e.g. using a USB key). It is important that none of the nodes - including the controller node - end up on more than one machine. Each computer should also have a copy of runnodes and runnodes.bat.

For example, you may end up with the following layout:

  • Machine 1: controller, nodea, runnodes, runnodes.bat
  • Machine 2: nodeb, nodec, runnodes, runnodes.bat

You must now edit the configuration file for each node, including the controller. Open each node’s config file, and make the following changes:

  • Change the Artemis messaging address to the machine’s IP address (e.g. p2pAddress="10.18.0.166:10006")
  • Change the network map service’s address to the IP address of the machine where the controller node is running (e.g. networkMapService { address="10.18.0.166:10002" legalName="O=Controller,L=London,C=GB"). The controller will not have the networkMapService configuration entry

After starting each node, the nodes will be able to see one another and agree IOUs among themselves.

Debugging your CorDapp

Debugging is done via IntelliJ as follows:

  • Edit the node driver code in Main.kt based on the number of nodes you wish to start, along with any other configuration options. For example, the code below starts 4 nodes, with one being the network map service and notary. It also sets up RPC credentials for the three non-notary nodes
fun main(args: Array<String>) {
    // No permissions required as we are not invoking flows.
    val user = User("user1", "test", permissions = setOf())
    driver(isDebug = true) {
        startNode(getX500Name(O="Controller",L="London",C="GB"), setOf(ServiceInfo(ValidatingNotaryService.type)))
        val (nodeA, nodeB, nodeC) = Futures.allAsList(
                startNode(getX500Name(O="PartyA",L=London,C=GB"), rpcUsers = listOf(user)),
                startNode(getX500Name(O="PartyB",L=New York,C=US"), rpcUsers = listOf(user)),
                startNode(getX500Name(O="PartyC",L=Paris,C=FR"), rpcUsers = listOf(user))).getOrThrow()

        startWebserver(nodeA)
        startWebserver(nodeB)
        startWebserver(nodeC)

        waitForAllNodesToFinish()
    }
}
  • Select and run the “Run Example CorDapp” run configuration in IntelliJ
  • IntelliJ will build and run the CorDapp. The remote debug ports for each node will be automatically generated and printed to the terminal. For example:
[INFO ] 15:27:59.533 [main] Node.logStartupInfo - Working Directory: /Users/joeldudley/cordapp-example/build/20170707142746/PartyA
[INFO ] 15:27:59.533 [main] Node.logStartupInfo - Debug port: dt_socket:5007
  • Edit the “Debug CorDapp” run configuration with the port of the node you wish to connect to
  • Run the “Debug CorDapp” run configuration
  • Set your breakpoints and start interacting with the node you wish to connect to. When the node hits a breakpoint, execution will pause