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Corda

After testing the Weaver interoperation mechanisms on basic sample networks, you may be interested in finding out how you can equip an existing real network, whether in development or in production, to exercise these mechanisms. In this document, we will demonstrate how to equip a Corda network and application with Weaver components and capabilities.

Model

The figure below illustrates a typical Corda network. The infrastructure consists of a set of nodes (each maintaining its share of the global state in a local vault), notaries, and CAs. On the nodes are installed one or more CorDapps, representing shared business logic across subsets of those nodes. The core of a CorDapp consists of a collection of workflows (or flows) and contracts acting on states; we layer the flows above the contracts in thebelow image just to illustrate that flows represent transaction (state update) triggers, and contract validations occur during the executions of flows. Further up in the stack lie client applications associated with CorDapps that can are used to trigger flows (and by implication, contracts).

alt text

Such a network equipped with Weaver components and capabilities will look like the figure below. Legacy components are marked in grey and Weaver and bridging components in green.

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The relay and driver are the only additional infrastructure that need to be installed. One or more relays can be installed, as can one or more drivers. The drivers are illustrated in the client layer rather than in the bottom layer because, though they are coupled with relays, they trigger flows just like any client application does.

Existing CorDapp flows and contracts deployed on the network's nodes remain undisturbed. All that is required is the deployment of an Interoperation CorDapp (flows and contracts) on every node that needs to offer or consume state from foreign networks.

Client applications will need some additional code and configuration because the decisions to exercise interoperation mechanisms (relay queries for data sharing or atomic asset exchanges) are strictly part of business logic. But Weaver's Corda Interoperation Node SDK offers various helper functions to ease this process and keep the adaptation to a minimum, as we wil see later in this document. Finally, an identity service must be offered by the network to expose its CAs' certificate chains to foreign networks, thereby laying the basis for interoperation. This service simply needs to offer a REST endpoint, and can be implemented as a standalone application or (more conveniently) as an augmentation of one or more of the existing client layer applications.

Procedure

Let us walk through the changes that are required in different phases of your network's creation.

Development

A Corda distributed application's business logic code spans three layers as illustrated in the network model:

  • Flows CorDapp: no code changes are required for Weaver enablement, as mentioned above

  • Contracts CorDapp: no code changes are required for Weaver enablement, as mentioned above

  • Client Layer applications: let us examine the adaptations required in detail:

    • Identity Service: A Corda network needs to share its security domain (or membership) configuration, i.e., its nodes' CA certificate chains, with a foreign network with which it seeks to interoperate. Though such sharing can be implemented using several different mechanisms, ranging from manual to automated, the simplest and most modular way is to expose a REST endpoint that agents in foreign networks can reach. Further, this REST endpoint can be implemented as a standalone web application or it can be an extension of one or more of the existing client layer applications. (Multiple apps can expose the same endpoint serving the same information for redundancy.) We will demonstrate an example of this while leaving other implementation modes to the user. Let's say a Corda network consists of two nodes called PartyA and PartyB, each running a client layer application with a web server whose URL prefixes are http://partya.mynetwork.com:9000 and http://partyb.mynetwork.com:9000 respectively. Each app then can expose a REST endpoint (again, as an example) http://partya.mynetwork.com:9000/node_sec_grp and http://partyb.mynetwork.com:9000/node_sec_grp respectively. At each web server's backend, you need to implement logic to retrieve the node's ID and it's associated certificated chains. Sample code is given below for a Kotlin implementation built on weaver-corda-sdk. You can use this code verbatim, except for some minor changes like <path-to-root-corda-net-folder>, other parameters like security domain, and list of names of nodes as appropriate for your environment:

      import com.weaver.corda.sdk.CredentialsCreator
      import com.google.protobuf.util.JsonFormat


      @RestController
      @CrossOrigin
      @RequestMapping("/") // The paths for HTTP requests are relative to this base path.
      class Controller {
      // Expose "node_sec_grp" endpoint using Rest Controller
      @RequestMapping(value = ["/node_sec_grp"], method = arrayOf(RequestMethod.GET), produces = arrayOf("application/json"))
      private fun GetNetworkConfig(): String {
      val jsonPrinter = JsonFormat.printer().includingDefaultValueFields()

      val credentialsCreator = CredentialsCreator(
      "<path-to-root-corda-net-folder>/build/nodes",
      "mynetwork", // security domain name
      ["PartyA", "PartyB"], // list of nodes
      "",
      ""
      )

      // Generate Membership
      val membership = credentialsCreator.createMembership()
      return jsonPrinter.print(membership)
      }
      }

      An agent from a foreign network can query either http://partya.mynetwork.com:9000/sec_group or http://partyb.mynetwork.com:9000/sec_group and obtain the security domain (or membership) configuration of the entire network.

    • Interoperation Helpers: Your Corda network's client layer applications have business logic embedded in them that, broadly speaking, accept data from users and other external agents and invoke workflows. With the option of interoperability with other networks available through Weaver, other options can be added, namely requesting and accepting data from foreign networks, and triggering locks and claims for atomic exchanges spanning two networks. Weaver's Corda SDK (currently implemented both in Java and Kotlin) offers a library to exercise these options. But this will involve modification to the application's logic. The following examples will illustrate how you can adapt your applications.

      • Data sharing: Consider a scenario inspired by the global trade use case where a letter of credit (L/C) management business logic is installed in the trade-finance-network network, supports a flow named UploadBillOfLading, which validates and records a bill of lading (B/L) supplied by a user via a UI. Weaver will enable such a B/L to be fetched from a different network trade-logistics-network by querying the function GetBillOfLading exposed by the chaincode shipmentcc installed in the tradelogisticschannel channel (The trade logistics network can be built on Corda as well. The steps for Weaver-enablement will mostly be the same, with the exception of view address creation logic. Here, for demonstration purposes, we assume that that counter-party network is built on Fabric).

        (In preparation, a suitable access control policy must be recorded on tradelogisticschannel in trade-logistics-network, and a suitable verification policy must be recorded in the vault of trade-finance-network. We will see how to do this in the Startup and Bootstrap Weaver Components section later.)

        You will need to insert some code in the client layer application that accepts a B/L and submits a UploadBillOfLading request in trade-finance-network. (No code changes need to be made in any application in the other network.) The logic to accept a B/L should be replaced (or you can simply add an alternative) by a call to the InteroperableHelper.interopFlow function offered by the weaver-corda-sdk library. The following code sample illustrates this:

        import com.weaver.corda.sdk.InteroperableHelper
        import com.mynetwork.flow.UploadBillOfLading

        val viewAddress = InteroperableHelper.createFabricViewAddress(
        'trade-logistics-network', // Security Domain/Group
        <trade-logistics-relay-url[:<port>], // Replace with remote network's relay
        'tradelogisticschannel', // Remote network's channel
        'shipmentcc', // Remote network's cc
        'GetBillOfLading', // Remote network's cc Fun
        [ <shipment-reference> ] // Replace <shipment-reference> with a value that can be used to look up the right B/L
        )
        try {
        val response = InteroperableHelper.interopFlow(
        proxy, // CordaRPCOps instance to start flows
        viewAddress,
        <trade-finance-relay-url>[:<port>] // Replace with local network's relay address and port
        ).fold({
        println("Error in Interop Flow: ${it.message}")
        }, {
        val linearId = it.toString()
        val BoLString = InteroperableHelper.getExternalStatePayloadString(
        proxy,
        linearId
        )
        val result = proxy.startFlow(::UploadBillOfLading, BoLString)
        println("$result")
        }
        } catch (e: Exception) {
        println("Error: ${e.toString()}")
        }

        Let us understand this code snippet better. The function UploadBillOfLading expects one argument, the bill of lading contents. The InteroperableHelper.createFabricViewAddress is used to create view address that is to passed to InteroperableHelper.interopFlow function. The equivalent function to create a view address for a remote Corda network is InteroperableHelper.createCordaViewAddress.

        The rest of the code ought to be self-explanatory. Values are hardcoded for explanation purposes.

        You need to create a personal access token with read:packages access in Github, to access weaver packages. You also need to add the following to your application's build.gradle file:

        repositories {
        maven {
        url https://maven.pkg.github.com/hyperledger-labs/weaver-dlt-interoperability
        credentials {
        username <github-email>
        password <github-personal-access-token>
        }
        }
        }
        dependencies {
        implementation(group: 'com.weaver.corda.sdk', name: 'weaver-corda-sdk', version: "1.2.3")
        implementation(group: 'com.weaver.corda.app.interop', name: 'interop-contracts', version: "1.2.3")
        implementation(group: 'com.weaver.corda.app.interop', name: 'interop-workflows', version: "1.2.3")
        implementation(group: 'com.weaver', name: 'protos-java-kt', version: "1.2.3")
        }

        (Or check out the package website and select a different version.)

      • Asset exchange: TBD

Pre-Configuration

No changes are required in your network's pre-configuration process for Weaver enablement.

Typically, pre-configuration involves:

  • Bootstraping Network: Generating node folders for each participating node in the network, which contains CorDapps, certificates, persistence db, etc sub directories. Using Gradle task net.corda.plugins.Cordform or net.corda.plugins.Dockerform, the folders get created under the directory build/nodes (this path is used in above sample code for Identity Service).

    The RPC address, username and password specified in above task will be used to create an instance of CordaRPCOps, which is the first argument for most weaver-corda-sdk static functions as we saw in previous section. For example, one of them is InteroperableHelper.interopFlow:

    val response = InteroperableHelper.interopFlow(
    proxy, // CordaRPCOps instance to start flows
    viewAddress,
    <trade-finance-relay-url>[:<port>], // Replace with local network's relay address and port
    )

    Also, the Corda Driver (which we will setup in the following sections) needs a specific RPC user to be created, so make sure to add that in the Gradle task above, and note the credentials.

    Sample net.corda.plugins.Dockerform task:

    task prepareDockerNodes(type: net.corda.plugins.Dockerform, dependsOn: ['jar']) {
    def HOST_ADDRESS = "0.0.0.0"
    nodeDefaults {
    projectCordapp {
    deploy = false
    }
    }
    node {
    name "O=Notary,L=London,C=GB"
    notary = [validating : true]
    p2pPort 10004
    rpcSettings {
    address("$HOST_ADDRESS:10003")
    adminAddress("$HOST_ADDRESS:10005")
    }
    cordapps.clear()
    }
    node {
    name "O=PartyA,L=London,C=GB"
    p2pPort 10007
    rpcSettings {
    address("$HOST_ADDRESS:10003")
    adminAddress("$HOST_ADDRESS:10005")
    }
    rpcUsers = [
    [ user: "user1", "password": "test", "permissions": ["ALL"]],
    [ user: "driverUser1", "password": "test", "permissions": ["ALL"]]] // <-- Driver RPC User
    }
    node {
    name "O=PartyB,L=London,C=GB"
    p2pPort 10009
    rpcSettings {
    address("$HOST_ADDRESS:10003")
    adminAddress("$HOST_ADDRESS:10005")
    }
    rpcUsers = [
    [ user: "user1", "password": "test", "permissions": ["ALL"]],
    [ user: "driverUser1", "password": "test", "permissions": ["ALL"]]] // <-- Driver RPC User
    }
    }
  • Install Interoperation CorDapp on Nodes: After bootstrapping the nodes folder, copy the following two CorDapps in build/nodes/PartyA/cordapps and build/nodes/PartyB/cordapps folders (PartyA and PartyB node names are for example only):

    Notes
    You can follow any installation process for this CorDapp, but make sure it is installed on all the nodes that maintain the states involved in cross-network operations in their vaults.

Startup and Bootstrap Weaver components

To launch a network using containerized components, you will typically use a Docker Compose or Kubernetes configuration file. No modifications are needed to the node's configurations. Sample instructions are given below for networks launched using Docker Compose; we leave it to the reader to adapt these to their custom launch processes.

Launch Relay

You can start a relay within a Docker container using a pre-built image. You just need to customize the container configuration for your Corda network, which you can do by simply creating a folder (let's call it relay_config) and configuring the following files in it:

  • .env: This sets suitable environment variables within the relay container. Copy the .env.template file from the repository and customize it for your purposes, as indicated in the below sample:

    PATH_TO_CONFIG=./config.toml
    RELAY_NAME=<"name" in config.toml>
    RELAY_PORT=<relay-server-port/"port" in config.toml>
    EXTERNAL_NETWORK=<docker-bridge-network>
    DOCKER_REGISTRY=ghcr.io/hyperledger-labs
    DOCKER_IMAGE_NAME=weaver-relay
    DOCKER_TAG=1.2.4

    The PATH_TO_CONFIG variable should point to the config.toml (you can name this whatever you wish) specified below.

    The RELAY_NAME variable specifies a unique name for this relay. It should match what's specified in the config.toml (more on that below).

    The RELAY_PORT variable specifies the port this relay server will listen on. It should match what's specified in the config.toml (more on that below).

    The EXTERNAL_NETWORK variable should be set to the name of your Corda network.

    The DOCKER_* variables are used to specify the image on which the container will be built. Make sure you set DOCKER_TAG to the latest version you see on Github.

    For more details, see the Relay Docker README ("Relay Server Image" and "Running With Docker Compose" sections).

  • config.toml: This specifies properties of the relay and the driver(s) is associates with. A sample is given below:

    name=<relay-name>
    port=<relay-port>
    host="0.0.0.0"
    db_path="db/<relay-name>/requests"
    remote_db_path="db/<relay-name>/remote_request"

    # FOR TLS
    cert_path="credentials/cert.pem"
    key_path="credentials/key"
    tls=<true/false>

    [networks]
    [networks.<network-name>]
    network="<driver-name>"

    [relays]
    [relays.<foreign-relay-name>]
    hostname="<foreign-relay-hostname-or-ip-address>"
    port="<foreign-relay-port>"

    [drivers]
    [drivers.<driver-name>]
    hostname="<driver-hostname-or-ip-address>"
    port="<driver-port>"

    <relay-name> should be a unique ID representing this relay; e.g., my_network_relay. It should match the RELAY_NAME value in .env.

    <relay-port> is the port number the relay server will listen on. It should match the RELAY_PORT value in .env.

    db_path and remote_db_path are used internally by the relay to store data. Replace <relay-name> with the same value set for the name parameter. (These can point to any filesystem paths in the relay's container.)

    If you set tls to true, the relay will enforce TLS communication. The cert_path and key_path should point to a Corda TLS certificate and key respectively.

    <network-name> is a unique identifier for your local network. You can set it to whatever value you wish.

    <driver-name> refers to the driver used by this relay to respond to requests. This also refers to one of the drivers's specifications in the drivers section further below. In this code snippet, we have defined one driver. Under [drivers.<driver-name>], you should also specify the hostname and port for the driver (whose configuration we will handle later).

    The relays section specifies all foreign relays this relay can connect to. The <foreign-relay-name> value should be a unique ID for a given foreign relay, and this value will be used by your client layer applications when constructing view addresses for data sharing requests. Under [relays.<foreign-relay-name>], you should specify the hostname and port for the foreign relay.

    Notes
    You can specify more than one driver instance in the drivers section.
    You can specify more than one foreign relay instance in the relays section.
  • docker-compose.yaml: This specifies the properties of the relay container. You can use the file in the repository verbatim.

To start the relay server, navigate to the folder containing the above files and run the following:

docker-compose up -d relay-server

Launch Driver

You can start a driver within a Docker container using a pre-built image. You just need to customize the container configuration for your Corda network, which you can do by simply configuring the following:

  • .env: This sets suitable environment variables within the driver container. Copy the .env.template file from the repository and customize it for your purposes, as indicated in the below sample:

    NETWORK_NAME=<container-name-suffix>
    DRIVER_PORT=<driver-server-port>
    DRIVER_RPC_USERNAME=<driver-rpc-username>
    DRIVER_RPC_PASSWORD=<driver-rpc-username>
    EXTERNAL_NETWORK=<docker-bridge-network>
    DOCKER_IMAGE_NAME=ghcr.io/hyperledger-labs/weaver-corda-driver
    DOCKER_TAG=1.2.4-alpha.7

    The NETWORK_NAME is only used as suffix for container and has no other significance.

    The DRIVER_PORT variable should be set to the port this driver will listen on.

    The DRIVER_RPC_USERNAME variable should be set to rpc user created above for the driver.

    The DRIVER_RPC_PASSWORD variable should be set to password of above rpc user.

    The EXTERNAL_NETWORK variable should be set to the name of your Corda network.

  • docker-compose.yaml: This specifies the properties of the driver container. You can use the file in the repository verbatim.

To start the driver, navigate to the folder containing the above files and run the following:

docker-compose up -d

Vault Initialization

To prepare your network for interoperation with a foreign network, you need to record the following to your vault using the Corda SDK (com.weaver.corda.sdk):

  • Access control policies: Let's take the example of the request made from trade-finance-network to trade-logistics-network for a B/L earlier in this document. trade-logistics-network can have a policy of the following form permitting access to the GetBillOfLading function from a client representing the PartyA node in trade-finance-network as follows:

    {
    "securityDomain":"trade-finance-network",
    "rules":
    [
    {
    "principal":"<PartyA-certificate-pem>",
    "principalType":"certificate",
    "resource":"exporternode:10003;carriernode:10003#com.mynetwork.flow.GetBillOfLading:*",
    "read":true
    }
    ]
    }

    In this sample, a single rule is specified for requests coming from trade-finance-network: it states that a workflow call to com.mynetwork.flow.GetBillOfLading made to exporter and carrier nodes of remote Corda network is permitted for a requestor whose certificate is specified in the principal attribute. The * at the end indicates that any arguments passed to the function will pass the access control check. The exporternode:10003 and carriernode:10003 are of form <hostname/IP>:<RPC_Port>, for exporter and carrier nodes respectively in the remote Corda network.

    You need to record this policy rule on your Corda network's vault by invoking either the AccessControlPolicyManager.createAccessControlPolicyState function or the AccessControlPolicyManager.updateAccessControlPolicyState function on the weaver-corda-sdk; use the former if you are recording a set of rules for the given securityDomain for the first time and the latter to overwrite a set of rules recorded earlier. The above JSON needs to be converted to protobuf object of com.weaver.protos.common.access_control.AccessControl.AccessControlPolicy, using google's protobuf library, and the object is the second argument of above functions (first being the instance of CordaRPCOps).

  • Verification policies: Taking the same example as above, an example of a verification policy for a B/L requested by the trade-finance-network from the trade-logistics-network is as follows:

    {
    "securityDomain":"trade-logistics-network",
    "identifiers":
    [
    {
    "pattern":"tradelogisticschannel:shipmentcc:GetBillOfLading:*",
    "policy":
    {
    "type":"Signature",
    "criteria":
    [
    "ExporterMSP",
    "CarrierMSP"
    ]
    }
    }
    ]
    }

    In this sample, a single verification policy rule is specified for data views coming from trade-logistics-network: it states that the data returned by the GetBillOfLading query made to the shipmentcc chaincode on the tradelogisticschannel channel requires as proof two signatures, one from a peer in the organization whose MSP ID is ExporterMSP and another from a peer in the organization whose MSP ID is CarrierMSP.

    Notes
    If the remote network is built on Corda, the resource specified in the access control policy can be used here as the pattern, with different node names specified in the criteria.

    You need to record this policy rule on your Corda network's vault by invoking Corda sdk's function VerificationPolicyManager.createVerificationPolicyState(proxy, verificationPolicyProto), where proxy is an instance of CordaRPCOps as described in previous sections, and verificationPolicyProto is an object of protobuf com.weaver.protos.common.verification_policy.VerificationPolicyOuterClass.VerificationPolicy. You can examine the full proto structure here. (Google's protobuf library can be used to convert above JSON to protobuf object.)

    Notes
    For any cross-network data request, make sure an access control policy is recorded in the source network (trade-logistics-network in the above example) and a corresponding verification policy is recorded in the destination network (trade-finance-network in the above example) before any relay request is triggered.
  • Foreign network security domain (membership) configuration: Run the following procedure (pseudocode) to record security domain configuration for every foreign network you wish your Corda network to interoperate with (you will need to collect the identity service URLs for all the foreign networks first):

    for each foreign network:
    send an HTTP GET request to the network's identity service (using 'curl' or 'wget' from a shell script or equivalent programming language APIs).
    convert the response string to protobuf object of 'com.weaver.protos.common.membership.MembershipOuterClass.Membership'.
    invoke 'MembershipManager.createMembershipState(proxy, membershipProto)' or 'MembershipManager.updateMembershipState(proxy, membershipProto)' on Corda sdk.

    As in the above two cases, use createMembershipState to record a confiuration for the first time for a given securityDomain and updateMembershipState to overwrite a configuration.

    Notes
    Security domain configurations (organization lists and their certificate chains) for any Fabric/Corda network are subject to change, so you should run the above procedure periodically in a loop.

Your Corda network is now up and running with the necessary Weaver components, and your network's vault is bootstrapped with the initial configuration necessary for cross-network interactions!