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Implement a simple event consumer

In this sample, we build upon the Consumer Pull chapter to add functionality to react to transfer completion on the consumer connector side.

Also, in order to keep things organized, the code in this example has been separated into several Java modules:

  • consumer-with-listener: the consumer connector which will be extended by the event consumer
  • listener: contains the TransferProcessListener implementation which will consume an event

Inspect the listener

A TransferProcessListener may define methods that are invoked after a transfer changes state, for example, to notify an external application on the consumer side after data has been produced (i.e. the transfer moves to the completed state).

// in TransferListenerExtension.java
    @Override
    public void initialize(ServiceExtensionContext context) {
        // ...
        var transferProcessObservable = context.getService(TransferProcessObservable.class);
        transferProcessObservable.registerListener(new MarkerFileCreator(monitor));
    }

The TransferProcessStartedListener implements the TransferProcessListener interface. It will consume the transfer STARTED event and write a log message.

public class TransferProcessStartedListener implements TransferProcessListener {

    private final Monitor monitor;

    public TransferProcessStartedListener(Monitor monitor) {
        this.monitor = monitor;
    }

    /**
     * Callback invoked by the EDC framework when a transfer is about to be completed.
     *
     * @param process the transfer process that is about to be completed.
     */
    @Override
    public void preStarted(final TransferProcess process) {
        monitor.debug("TransferProcessStartedListener received STARTED event");
        // do something meaningful before transfer start
    }
}

Run the sample

Assuming your provider connector and logging webserver are still running, we can re-use the existing assets and contract definitions stored on provider side. If not, set up your assets and contract definitions as described in the Negotiation chapter.

1. Build & launch the consumer with listener extension

This consumer connector is based on a different build file, hence a new JAR file will be built. Make sure to terminate your current consumer connector from the previous chapters. That way we unblock the ports and can reuse the known configuration files and API calls.

Run this to build and launch the consumer with listener extension:

./gradlew transfer:transfer-04-event-consumer:consumer-with-listener:build
java -Dedc.keystore=transfer/transfer-00-prerequisites/resources/certs/cert.pfx -Dedc.keystore.password=123456 -Dedc.fs.config=transfer/transfer-00-prerequisites/resources/configuration/consumer-configuration.properties -jar transfer/transfer-04-event-consumer/consumer-with-listener/build/libs/connector.jar

2. Negotiate a new contract

curl -d @transfer/transfer-01-negotiation/resources/negotiate-contract.json \
  -X POST -H 'content-type: application/json' http://localhost:29193/management/v3/contractnegotiations \
  -s | jq

3. Get the contract agreement id

curl -X GET "http://localhost:29193/management/v3/contractnegotiations/{{contract-negotiation-id}}" \
    --header 'Content-Type: application/json' \
    -s | jq

4. Perform a file transfer

Replace the contractId property inside the request body with the contract agreement id from the previous call. Afterward run:

curl -X POST "http://localhost:29193/management/v3/transferprocesses" \
  -H "Content-Type: application/json" \
  -d @transfer/transfer-02-consumer-pull/resources/start-transfer.json \
  -s | jq

5. Inspect the logs

The consumer should spew out logs similar to:

DEBUG 2023-10-16T09:29:45.316908 [TransferProcessManagerImpl] TransferProcess 762b5a0c-43fb-4b8b-8022-669043c8fa81 is now in state REQUESTED
DEBUG 2023-10-16T09:29:46.269998 DSP: Incoming TransferStartMessage for class org.eclipse.edc.connector.controlplane.transfer.spi.types.TransferProcess process: 762b5a0c-43fb-4b8b-8022-669043c8fa81
DEBUG 2023-10-16T09:29:46.271592 TransferProcessStartedListener received STARTED event   <----------------------------
DEBUG 2023-10-16T09:29:46.27174 TransferProcess 762b5a0c-43fb-4b8b-8022-669043c8fa81 is now in state STARTED

If you see the TransferProcessStartedListener received STARTED event log message, it means that your event consumer has been configured successfully.

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