Building and installing a CorDapp

CorDapps run on the Corda platform and integrate with it and each other. This article explains how to build CorDapps. To learn what a CorDapp is, please read What is a CorDapp?.

CorDapp format

A CorDapp is a semi-fat JAR that contains all of the CorDapp’s dependencies except the Corda core libraries and any other CorDapps it depends on.

For example, if a Cordapp depends on corda-core, your-other-cordapp and apache-commons, then the Cordapp JAR will contain:

  • All classes and resources from the apache-commons JAR and its dependencies
  • Nothing from the other two JARs

Build tools

In the instructions that follow, we assume you are using Gradle and the cordapp plugin to build your CorDapp. You can find examples of building a CorDapp using these tools in the Kotlin CorDapp Template and the Java CorDapp Template.

To ensure you are using the correct version of Gradle, you should use the provided Gradle Wrapper by copying across the following folder and files from the Kotlin CorDapp Template or the Java CorDapp Template to the root of your project:

  • gradle/
  • gradlew
  • gradlew.bat

Setting your dependencies

Choosing your Corda, Quasar and Kotlin versions

Several ext variables are used in a CorDapp’s build.gradle file to define version numbers that should match the version of Corda you’re developing against:

  • ext.corda_release_version defines the version of Corda itself
  • ext.corda_gradle_plugins_version defines the version of the Corda Gradle Plugins
  • ext.quasar_version defines the version of Quasar, a library that we use to implement the flow framework
  • ext.kotlin_version defines the version of Kotlin (if using Kotlin to write your CorDapp)

The current versions used are as follows:

ext.corda_release_version = '4.0'
ext.corda_gradle_plugins_version = '4.0.42'
ext.quasar_version = '0.7.11_r3'
ext.kotlin_version = '1.2.71'

Please note that Corda Enterprise 4 uses patched releases of Quasar and Caffeine to work around shortcomings identified in these libraries while a proper fix is under way. In order to get hold of the patched versions of these libraries, corda-dependencies needs to be added to your list of gradle repositories. This repository is required for any project referencing Corda Enterprise 4 packages to provide transitive dependencies:

repositories {
    // ... other dependencies
    maven { url "https://software.r3.com/artifactory/corda-dependencies" } // access to the patched Quasar and Caffeine version
}

In certain cases, you may also wish to build against the unstable Master branch. See Building CorDapps against a non-release branch.

Corda dependencies

The cordapp plugin adds three new gradle configurations:

  • cordaCompile, which extends compile
  • cordaRuntime, which extends runtime
  • cordapp, which extends compile

cordaCompile and cordaRuntime indicate dependencies that should not be included in the CorDapp JAR. These configurations should be used for any Corda dependency (e.g. corda-core, corda-node) in order to prevent a dependency from being included twice (once in the CorDapp JAR and once in the Corda JARs). The cordapp dependency is for declaring a compile-time dependency on a “semi-fat” CorDapp JAR in the same way as cordaCompile, except that Cordformation will only deploy CorDapps contained within the cordapp configuration.

Here are some guidelines for Corda dependencies:

  • When building a CorDapp, you should always include net.corda:corda-core:$corda_release_version as a cordaCompile dependency, and net.corda:corda:$corda_release_version as a cordaRuntime dependency
  • When building an RPC client that communicates with a node (e.g. a webserver), you should include net.corda:corda-rpc:$corda_release_version as a cordaCompile dependency.
  • When you need to use the network bootstrapper to bootstrap a local network (e.g. when using Cordformation), you should include net.corda:corda-node-api:$corda_release_version as either a cordaRuntime or a runtimeOnly dependency. You may also wish to include an implementation of SLF4J as a runtimeOnly dependency for the network bootstrapper to use.
  • To use Corda’s test frameworks, add net.corda:corda-test-utils:$corda_release_version as a testCompile dependency. Never include corda-test-utils as a compile or cordaCompile dependency.
  • Any other Corda dependencies you need should be included as cordaCompile dependencies.

Here is an overview of the various Corda dependencies:

  • corda - The Corda fat JAR. Do not use as a compile dependency. Required as a cordaRuntime dependency when using Cordformation
  • corda-confidential-identities - A part of the core Corda libraries. Automatically pulled in by other libraries
  • corda-core - Usually automatically included by another dependency, contains core Corda utilities, model, and functionality. Include manually if the utilities are useful or you are writing a library for Corda
  • corda-core-deterministic - Used by the Corda node for deterministic contracts. Not likely to be used externally
  • corda-djvm - Used by the Corda node for deterministic contracts. Not likely to be used externally
  • corda-finance-contracts, corda-finance-workflows and deprecated corda-finance. Corda finance CorDapp, use contracts and flows parts respectively. Only include as a cordaCompile dependency if using as a dependent Cordapp or if you need access to the Corda finance types. Use as a cordapp dependency if using as a CorDapp dependency (see below)
  • corda-jackson - Corda Jackson support. Use if you plan to serialise Corda objects to and/or from JSON
  • corda-jfx - JavaFX utilities with some Corda-specific models and utilities. Only use with JavaFX apps
  • corda-mock - A small library of useful mocks. Use if the classes are useful to you
  • corda-node - The Corda node. Do not depend on. Used only by the Corda fat JAR and indirectly in testing frameworks. (If your CorDapp _must_ depend on this for some reason then it should use the compileOnly configuration here - but please don’t do this if you can possibly avoid it!)
  • corda-node-api - The node API. Required to bootstrap a local network
  • corda-node-driver - Testing utility for programmatically starting nodes from JVM languages. Use for tests
  • corda-rpc - The Corda RPC client library. Used when writing an RPC client
  • corda-serialization - The Corda core serialization library. Automatically included by other dependencies
  • corda-serialization-deterministic - The Corda core serialization library. Automatically included by other dependencies
  • corda-shell - Used by the Corda node. Never depend on directly
  • corda-test-common - A common test library. Automatically included by other test libraries
  • corda-test-utils - Used when writing tests against Corda/Cordapps
  • corda-tools-explorer - The Node Explorer tool. Do not depend on
  • corda-tools-network-bootstrapper - The Network Builder tool. Useful in build scripts
  • corda-tools-shell-cli - The Shell CLI tool. Useful in build scripts
  • corda-webserver-impl - The Corda webserver fat JAR. Deprecated. Usually only used by build scripts
  • corda-websever - The Corda webserver library. Deprecated. Use a standard webserver library such as Spring instead

Dependencies on other CorDapps

Your CorDapp may also depend on classes defined in another CorDapp, such as states, contracts and flows. There are two ways to add another CorDapp as a dependency in your CorDapp’s build.gradle file:

  • cordapp project(":another-cordapp") (use this if the other CorDapp is defined in a module in the same project)
  • cordapp "net.corda:another-cordapp:1.0" (use this otherwise)

The cordapp gradle configuration serves two purposes:

  • When using the cordformation Gradle plugin, the cordapp configuration indicates that this JAR should be included on your node as a CorDapp
  • When using the cordapp Gradle plugin, the cordapp configuration prevents the dependency from being included in the CorDapp JAR

Note that the cordformation and cordapp Gradle plugins can be used together.

Other dependencies

If your CorDapps have any additional external dependencies, they can be specified like normal Kotlin/Java dependencies in Gradle. See the example below, specifically the apache-commons include.

For further information about managing dependencies, see the Gradle docs.

Signing the CorDapp JAR

The cordapp plugin can sign the generated CorDapp JAR file using JAR signing and verification tool. Signing the CorDapp enables its contract classes to use signature constraints instead of other types of the constraints, for constraints explanation refer to API: Contract Constraints. By default the JAR file is signed by Corda development certificate. The signing process can be disabled or configured to use an external keystore. The signing entry may contain the following parameters:

  • enabled the control flag to enable signing process, by default is set to true, set to false to disable signing
  • options any relevant parameters of SignJar ANT task, by default the JAR file is signed with Corda development key, the external keystore can be specified, the minimal list of required options is shown below, for other options referer to SignJar task:
    • keystore the path to the keystore file, by default cordadevcakeys.jks keystore is shipped with the plugin
    • alias the alias to sign under, the default value is cordaintermediateca
    • storepass the keystore password, the default value is cordacadevpass
    • keypass the private key password if it’s different than the password for the keystore, the default value is cordacadevkeypass
    • storetype the keystore type, the default value is JKS

The parameters can be also set by system properties passed to Gradle build process. The system properties should be named as the relevant option name prefixed with ‘signing.’, e.g. a value for alias can be taken from the signing.alias system property. The following system properties can be used: signing.enabled, signing.keystore, signing.alias, signing.storepass, signing.keypass, signing.storetype. The resolution order of a configuration value is as follows: the signing process takes a value specified in the signing entry first, the empty string “” is also considered as the correct value. If the option is not set, the relevant system property named signing.option is tried. If the system property is not set then the value defaults to the configuration of the Corda development certificate.

The example cordapp plugin with plugin signing configuration:

cordapp {
    signing {
        enabled true
        options {
            keystore "/path/to/jarSignKeystore.p12"
            alias "cordapp-signer"
            storepass "secret1!"
            keypass "secret1!"
            storetype "PKCS12"
        }
    }
    //...

CorDapp auto-signing allows to use signature constraints for contracts from the CorDapp without need to create a keystore and configure the cordapp plugin. For production deployment ensure to sign the CorDapp using your own certificate e.g. by setting system properties to point to an external keystore or by disabling signing in cordapp plugin and signing the CordDapp JAR downstream in your build pipeline. CorDapp signed by Corda development certificate is accepted by Corda node only when running in the development mode. In case CordDapp signed by the (default) development key is run on node in the production mode (e.g. for testing), the node may be set to accept the development key by adding the cordappSignerKeyFingerprintBlacklist = [] property set to empty list (see Configuring a node).

Signing options can be contextually overwritten by the relevant system properties as described above. This allows the single build.gradle file to be used for a development build (defaulting to the Corda development keystore) and for a production build (using an external keystore). The example system properties setup for the build process which overrides signing options:

./gradlew -Dsigning.keystore="/path/to/keystore.jks" -Dsigning.alias="alias" -Dsigning.storepass="password" -Dsigning.keypass="password"

Without providing the system properties, the build will sign the CorDapp with the default Corda development keystore:

./gradlew

CorDapp signing can be disabled for a build:

./gradlew -Dsigning.enabled=false

Other system properties can be explicitly assigned to options by calling System.getProperty in cordapp plugin configuration. For example the below configuration sets the specific signing algorithm when a system property is available otherwise defaults to an empty string:

cordapp {
    signing {
        options {
            sigalg System.getProperty('custom.sigalg','')
        }
    }
    //...

Then the build process can set the value for custom.sigalg system property and other system properties recognized by cordapp plugin:

./gradlew -Dcustom.sigalg="SHA256withECDSA" -Dsigning.keystore="/path/to/keystore.jks" -Dsigning.alias="alias" -Dsigning.storepass="password" -Dsigning.keypass="password"

To check if CorDapp is signed use JAR signing and verification tool:

jarsigner --verify path/to/cordapp.jar

Cordformation plugin can also sign CorDapps JARs, when deploying set of nodes, see Creating nodes locally.

If your build system post-processes the Cordapp JAR, then the modified JAR content may be out-of-date or not complete with regards to a signature file. In this case you can sign the Cordapp as a separate step and disable the automatic signing by the cordapp plugin. The cordapp plugin contains a standalone task signJar which uses the same signing configuration. The task has two parameters: inputJars - to pass JAR files to be signed and an optional postfix which is added to the name of signed JARs (it defaults to “-signed”). The signed JARs are returned as outputJars property.

For example in order to sign a JAR modified by modifyCordapp task, create an instance of the net.corda.plugins.SignJar task (below named as sign). The output of modifyCordapp task is passed to inputJars and the sign task is run after modifyCordapp one:

task sign(type: net.corda.plugins.SignJar) {
    inputJars modifyCordapp
}
modifyCordapp.finalizedBy sign
cordapp {
    signing {
        enabled false
    }
    //..
}

The task creates a new JAR file named *-signed.jar which should be used further in your build/publishing process. Also the best practice is to disable signing by the cordapp plugin as shown in the example.

Example

Below is a sample CorDapp Gradle dependencies block. When building your own CorDapp, use the build.gradle file of the Kotlin CorDapp Template or the Java CorDapp Template as a starting point.

dependencies {
    // Corda integration dependencies
    cordaCompile "$corda_release_distribution:corda-core:$corda_release_version"
    cordaCompile "$corda_release_distribution:corda-finance-contracts:$corda_release_version"
    cordaCompile "net.corda:corda-finance-workflows:$corda_release_version"
    cordaCompile "$corda_release_distribution:corda-jackson:$corda_release_version"
    cordaCompile "$corda_release_distribution:corda-rpc:$corda_release_version"
    cordaCompile "$corda_release_distribution:corda-node-api:$corda_release_version"
    cordaCompile "$corda_release_distribution:corda-webserver-impl:$corda_release_version"
    cordaRuntime "$corda_release_distribution:corda:$corda_release_version"
    cordaRuntime "$corda_release_distribution:corda-webserver:$corda_release_version"
    testCompile "$corda_release_distribution:corda-test-utils:$corda_release_version"

    // Corda Plugins: dependent flows and services
    // Identifying a CorDapp by its module in the same project.
    cordapp project(":cordapp-contracts-states")
    // Identifying a CorDapp by its fully-qualified name.
    cordapp "$corda_release_distribution:bank-of-corda-demo:1.0"

    // Some other dependencies
    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
    testCompile "org.jetbrains.kotlin:kotlin-test:$kotlin_version"
    testCompile "junit:junit:$junit_version"

    compile "org.apache.commons:commons-lang3:3.6"
}

Creating the CorDapp JAR

Once your dependencies are set correctly, you can build your CorDapp JAR(s) using the Gradle jar task

  • Unix/Mac OSX: ./gradlew jar
  • Windows: gradlew.bat jar

Each of the project’s modules will be compiled into its own CorDapp JAR. You can find these CorDapp JARs in the build/libs folders of each of the project’s modules.

Warning

The hash of the generated CorDapp JAR is not deterministic, as it depends on variables such as the timestamp at creation. Nodes running the same CorDapp must therefore ensure they are using the exact same CorDapp JAR, and not different versions of the JAR created from identical sources.

The filename of the JAR must include a unique identifier to deduplicate it from other releases of the same CorDapp. This is typically done by appending the version string to the CorDapp’s name. This unique identifier should not change once the JAR has been deployed on a node. If it does, make sure no one is relying on FlowContext.appName in their flows (see Versioning).

Installing the CorDapp JAR

Note

Before installing a CorDapp, you must create one or more nodes to install it on. For instructions, please see Creating nodes locally.

At start-up, nodes will load any CorDapps present in their cordapps folder. In order to install a CorDapp on a node, the CorDapp JAR must be added to the <node_dir>/cordapps/ folder (where node_dir is the folder in which the node’s JAR and configuration files are stored) and the node restarted.

CorDapp configuration files

CorDapp configuration files should be placed in <node_dir>/cordapps/config. The name of the file should match the name of the JAR of the CorDapp (eg; if your CorDapp is called hello-0.1.jar the config should be config/hello-0.1.conf).

Config files are currently only available in the Typesafe/Lightbend config format. These files are loaded when a CorDapp context is created and so can change during runtime.

CorDapp configuration can be accessed from CordappContext::config whenever a CordappContext is available. For example:

@StartableByRPC
class GetStringConfigFlow(private val configKey: String) : FlowLogic<String>() {
    object READING : ProgressTracker.Step("Reading config")
    override val progressTracker = ProgressTracker(READING)

    @Suspendable
    override fun call(): String {
        progressTracker.currentStep = READING
        val config = serviceHub.getAppContext().config
        return config.getString(configKey)
    }
}

Using CorDapp configuration with the deployNodes task

If you want to generate CorDapp configuration when using the deployNodes Gradle task, then you can use the cordapp or projectCordapp properties on the node. For example:

task deployNodes(type: net.corda.plugins.Cordform, dependsOn: ['jar']) {
    nodeDefaults {
        // this external CorDapp will be included in each project
        cordapp("$corda_release_group:corda-finance-contracts:$corda_release_version")
        // this external CorDapp will be included in each project with the given config
        cordapp("$corda_release_group:corda-finance-workflows:$corda_release_version") {
            config "issuableCurrencies = [ USD ]"
        }
    }
    node {
        name "O=Bank A,L=London,C=GB"c
        ...
        // This adds configuration for another CorDapp project within the build
        cordapp (project(':my-project:workflow-cordapp')) {
            config "someStringValue=test"
        }
        cordapp(project(':my-project:another-cordapp')) {
            // Use a multiline string for complex configuration
            config '''
                someStringValue=test
                anotherStringValue=10
             '''
        }
    }
    node {
        name "O=Bank B,L=New York,C=US"
        ...
        // This adds configuration for the default CorDapp for this project
        projectCordapp {
            config project.file("src/config.conf")
        }
    }
}

There is an example project that demonstrates this in the samples folder of the Corda Git repository, called cordapp-configuration . API documentation can be found at api/kotlin/corda/net.corda.core.cordapp/index.html.

Minimum and target platform version

CorDapps can advertise their minimum and target platform version. The minimum platform version indicates that a node has to run at least this version in order to be able to run this CorDapp. The target platform version indicates that a CorDapp was tested with this version of the Corda Platform and should be run at this API level if possible. It provides a means of maintaining behavioural compatibility for the cases where the platform’s behaviour has changed. These attributes are specified in the JAR manifest of the CorDapp, for example:

'Min-Platform-Version': 4
'Target-Platform-Version': 4
Defaults
  • Target-Platform-Version (mandatory) is a whole number and must comply with the rules mentioned above.
  • Min-Platform-Version (optional) will default to 1 if not specified.

Using the cordapp Gradle plugin, this can be achieved by putting this in your CorDapp’s build.gradle:

cordapp {
    targetPlatformVersion 4
    minimumPlatformVersion 4
}

Separation of CorDapp contracts, flows and services

It is recommended that contract code (states, commands, verification logic) be packaged separately from business flows (and associated services). This decoupling enables contracts to evolve independently from the flows and services that use them. Contracts may even be specified and implemented by different providers (eg. Corda currently ships with a cash financial contract which in turn is used in many other flows and many other CorDapps).

As of Corda 4, CorDapps can explicitly differentiate their type by specifying the following attributes in the JAR manifest:

'Cordapp-Contract-Name'
'Cordapp-Contract-Version'
'Cordapp-Contract-Vendor'
'Cordapp-Contract-Licence'

'Cordapp-Workflow-Name'
'Cordapp-Workflow-Version'
'Cordapp-Workflow-Vendor'
'Cordapp-Workflow-Licence'

Defaults

Cordapp-Contract-Name (optional) if specified, the following Contract related attributes are also used:

  • Cordapp-Contract-Version (mandatory), must be a whole number starting from 1.
  • Cordapp-Contract-Vendor (optional), defaults to UNKNOWN if not specified.
  • Cordapp-Contract-Licence (optional), defaults to UNKNOWN if not specified.

Cordapp-Workflow-Name (optional) if specified, the following Workflow related attributes are also used:

  • Cordapp-Workflow-Version (mandatory), must be a whole number starting from 1.
  • Cordapp-Workflow-Vendor (optional), defaults to UNKNOWN if not specified.
  • Cordapp-Workflow-Licence (optional), defaults to UNKNOWN if not specified.

As with the general CorDapp attributes (minimum and target platform version), these can be specified using the Gradle cordapp plugin as follows:

For a contract only CorDapp we specify the contract tag:

cordapp {
    targetPlatformVersion 4
    minimumPlatformVersion 3
    contract {
        name "my contract name"
        versionId 1
        vendor "my company"
        licence "my licence"
    }
}

For a CorDapp that contains flows and/or services we specify the workflow tag:

cordapp {
    targetPlatformVersion 4
    minimumPlatformVersion 3
    workflow {
        name "my workflow name"
        versionId 1
        vendor "my company"
        licence "my licence"
    }
}

Note

It is possible, but not recommended, to include everything in a single CorDapp jar and use both the contract and workflow Gradle plugin tags.

Warning

Contract states may optionally specify a custom schema mapping (by implementing the Queryable interface) in its contracts JAR. However, any associated database schema definition scripts (eg. Liquibase change set XML files) must currently be packaged in the flows JAR. This is because the node requires access to these schema definitions upon start-up (contract JARs are now loaded in a separate attachments classloader). This split also caters for scenarios where the same contract CorDapp may wish to target different database providers (and thus, the associated schema DDL may vary to use native features of a particular database). The finance CorDapp provides an illustration of this packaging convention. Future versions of Corda will de-couple this custom schema dependency to remove this anomaly.

CorDapp Contract Attachments

As of Corda 4, CorDapp Contract JARs must be installed on a node by a trusted uploader, either by

>>> run uploadAttachment jar: path/to/the/file.jar

Contract attachments that are received from a peer over the p2p network are considered untrusted and will throw a UntrustedAttachmentsException exception when processed by a listening flow that cannot resolve that attachment from its local attachment storage. The flow will be suspended and sent to the nodes Flow Hospital for recovery and retry. The untrusted attachment JAR will be stored in the nodes local attachment store for review by a node operator. It can be downloaded for viewing using the following CRaSH shell command:

>>> run openAttachment id: <hash of untrusted attachment given by `UntrustedAttachmentsException` exception

Should the node operator deem the attachment trustworthy, they may then issue the following CRaSH shell command to reload it as trusted:

>>> run uploadAttachment jar: path/to/the/trusted-file.jar

and subsequently retry the failed flow (currently this requires a node re-start).

Note

this behaviour is to protect the node from executing contract code that was not vetted. It is a temporary precaution until the Deterministic JVM is integrated into Corda whereby execution takes place in a sandboxed environment which protects the node from malicious code.