CorDapp basics

A CorDapp is an application that runs on the Corda platform using the platform APIs and plugin system. They are self contained in separate JARs from the node server JAR that are created and distributed.

App plugins

Note

Currently apps are only supported for JVM languages.

To create an app plugin you must extend from CordaPluginRegistry. The JavaDoc contains specific details of the implementation, but you can extend the server in the following ways:

  1. Required flows: Specify which flows will be whitelisted for use in your RPC calls.
  2. Service plugins: Register your services (see below).
  3. Web APIs: You may register your own endpoints under /api/ of the bundled web server.
  4. Static web endpoints: You may register your own static serving directories for serving web content from the web server.
  5. Whitelisting your additional contract, state and other classes for object serialization. Any class that forms part of a persisted state, that is used in messaging between flows or in RPC needs to be whitelisted.

Services

Services are classes which are constructed after the node has started. It is provided a PluginServiceHub which allows a richer API than the ServiceHub exposed to contracts. It enables adding flows, registering message handlers and more. The service does not run in a separate thread, so the only entry point to the service is during construction, where message handlers should be registered and threads started.

Starting nodes

To use an app you must also have a node server. To create a node server run the gradle deployNodes task.

This will output the node JAR to build/libs/corda.jar and several sample/standard node setups to build/nodes. For now you can use the build/nodes/nodea configuration as a template.

Each node server by default must have a node.conf file in the current working directory. After first execution of the node server there will be many other configuration and persistence files created in this workspace directory. The directory can be overridden by the --base-directory=<workspace> command line argument.

Note

Outside of development environments do not store your node directories in the build folder.

Warning

Also note that the bootstrapping process of the corda.jar unpacks the Corda dependencies into a temporary folder. It is therefore suggested that the CAPSULE_CACHE_DIR environment variable be set before starting the process to control this location.

Installing apps

Once you have created your app JAR you can install it to a node by adding it to <node_dir>/plugins/. In this case the node_dir is the location where your node server’s JAR and configuration file is.

Note

If the directory does not exist you can create it manually.

Starting your node

Now you have a node server with your app installed, you can run it by navigating to <node_dir> and running:

Windows:   java -jar corda.jar
UNIX:      ./corda.jar

The plugin should automatically be registered and the configuration file used.

Warning

If your working directory is not <node_dir> your plugins and configuration will not be used.

The configuration file and workspace paths can be overidden on the command line e.g.

./corda.jar --config-file=test.conf --base-directory=/opt/r3corda/nodes/test.

Otherwise the workspace folder for the node is the current working path.

Debugging your node

To enable remote debugging of the corda process use a command line such as:

java -Dcapsule.jvm.args="-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=5005" -jar corda.jar

This command line will start the debugger on port 5005 and pause the process awaiting debugger attachment.

Viewing persisted state of your node

To make examining the persisted contract states of your node or the internal node database tables easier, and providing you are using the default database configuration used for demos, you should be able to connect to the internal node database over a JDBC connection at the URL that is output to the logs at node start up. That URL will be of the form jdbc:h2:tcp://<host>:<port>/node.

The user name and password for the login are as per the node data source configuration.

The name and column layout of the internal node tables is in a state of flux and should not be relied upon to remain static at the present time, and should certainly be treated as read-only.

Building against Corda

To publish to your local Maven repository (in ~/.m2 on Unix and %HOMEPATH%\.m2 on Windows) run the following in the root directory of the Corda code:

./gradlew install

This will publish corda-$version.jar, finance-$version.jar, core-$version.jar and node-$version.jar to the group net.corda. You can now depend on these as you normally would a Maven dependency, using the group id net.corda.

There are several Gradle plugins that reduce your build.gradle boilerplate and make development of CorDapps easier. The available plugins are in the gradle-plugins directory of the Corda repository.

To install to your local Maven repository the plugins that CorDapp gradle files require, enter the gradle-plugins directory and then run ../gradle install. The plugins will now be installed to your local Maven repository.

Using Gradle plugins

To use the plugins, if you are not already using the CorDapp template project, you must modify your build.gradle. Add the following segments to the relevant part of your build.gradle.

buildscript {
    ext.corda_release_version = '<enter the corda version you build against here>'
    ext.corda_gradle_plugins_version = '<enter the gradle plugins version here>' // This is usually the same as corda_release_version.
    ... your buildscript ...

    repositories {
        ... other repositories ...
        mavenLocal()
    }

    dependencies {
        ... your dependencies ...
        classpath "net.corda.plugins:cordformation:$corda_gradle_plugins_version"
        classpath "net.corda.plugins:quasar-utils:$corda_gradle_plugins_version"
        classpath "net.corda.plugins:publish-utils:$corda_gradle_plugins_version"
    }
}

apply plugin: 'net.corda.plugins.cordformation'
apply plugin: 'net.corda.plugins.quasar-utils'
apply plugin: 'net.corda.plugins.publish-utils'

repositories {
    mavenLocal()
    ... other repositories here ...
}

dependencies {
    compile "net.corda.core:$corda_release_version"
    compile "net.corda.finance:$corda_release_version"
    compile "net.corda.node:$corda_release_version"
    compile "net.corda.corda:$corda_release_version"
    ... other dependencies here ...
}

... your tasks ...

// Standard way to publish CorDapps to maven local with the maven-publish and publish-utils plugin.
publishing {
    publications {
        jarAndSources(MavenPublication) {
            from components.java
            // The two lines below are the tasks added by this plugin.
            artifact sourceJar
            artifact javadocJar
        }
    }
}

Cordformation

Cordformation is the local node deployment system for CorDapps, the nodes generated are intended to be used for experimenting, debugging, and testing node configurations and setups but not intended for production or testnet deployment.

To use this gradle plugin you must add a new task that is of the type net.corda.plugins.Cordform to your build.gradle and then configure the nodes you wish to deploy with the Node and nodes configuration DSL. This DSL is specified in the JavaDoc. An example of this is in the CorDapp template and below is a three node example;

task deployNodes(type: net.corda.plugins.Cordform, dependsOn: ['jar']) {
    directory "./build/nodes" // The output directory
    networkMap "CN=Controller,O=R3,OU=corda,L=London,C=UK" // The distinguished name of the node named here will be used as the networkMapService.address on all other nodes.
    node {
        name "CN=Controller,O=R3,OU=corda,L=London,C=UK"
        nearestCity "London"
        advertisedServices = [ "corda.notary.validating" ]
        p2pPort 10002
        rpcPort 10003
        webPort 10004
        h2Port 11002
        cordapps []
    }
    node {
        name "CN=NodeA,O=R3,OU=corda,L=London,C=UK"
        nearestCity "London"
        advertisedServices = []
        p2pPort 10005
        rpcPort 10006
        webPort 10007
        h2Port 11005
        cordapps []
    }
    node {
        name "CN=NodeB,O=R3,OU=corda,L=New York,C=USA"
        nearestCity "New York"
        advertisedServices = []
        p2pPort 10008
        rpcPort 10009
        webPort 10010
        h2Port 11008
        cordapps []
    }
}

You can create more configurations with new tasks that extend Cordform.

New nodes can be added by simply adding another node block and giving it a different name, directory and ports. When you run this task it will install the nodes to the directory specified and a script will be generated to run the nodes with one command (runnodes). On MacOS X this script will run each node in a new terminal tab, and on Linux it will open up a new XTerm for each node. On Windows the (runnodes.bat) script will run one node per window.

Other CorDapps can also be specified if they are already specified as classpath or compile dependencies in your build.gradle.