Nifi Custom Processor errors with a "ControllerService found was not a WebSocket ControllerService but a com.sun.proxy.$Proxy75" - websocket

Question

*** Update: I have changed my approach as described in my answer to the question, due to which the original issue reported becomes moot. ***
I'm trying to develop a Nifi application that provides a WebSocket interface to Kakfa. I could not accomplish this using the standard Nifi components as I have tried below (it may not make sense but intuitively this is what I want to accomplish):
I have now created a custom Processor "ReadFromKafka" that I intend to use as shown in the image below. "ReadFromKafka" would use the same implementation as the standard "PutWebSocket" component but would read messages from a Kafka Topic and send as response to the WebSocket client.
I have provided a code snippet of the implementation below:
#SystemResourceConsideration(resource = SystemResource.MEMORY)
public class ReadFromKafka extends AbstractProcessor {
public static final PropertyDescriptor PROP_WS_SESSION_ID = new PropertyDescriptor.Builder()
.name("websocket-session-id")
.displayName("WebSocket Session Id")
.description("A NiFi Expression to retrieve the session id. If not specified, a message will be " +
"sent to all connected WebSocket peers for the WebSocket controller service endpoint.")
.required(true)
.addValidator(StandardValidators.NON_BLANK_VALIDATOR)
.expressionLanguageSupported(ExpressionLanguageScope.FLOWFILE_ATTRIBUTES)
.defaultValue("${" + ATTR_WS_SESSION_ID + "}")
.build();
public static final PropertyDescriptor PROP_WS_CONTROLLER_SERVICE_ID = new PropertyDescriptor.Builder()
.name("websocket-controller-service-id")
.displayName("WebSocket ControllerService Id")
.description("A NiFi Expression to retrieve the id of a WebSocket ControllerService.")
.required(true)
.addValidator(StandardValidators.NON_BLANK_VALIDATOR)
.expressionLanguageSupported(ExpressionLanguageScope.FLOWFILE_ATTRIBUTES)
.defaultValue("${" + ATTR_WS_CS_ID + "}")
.build();
public static final PropertyDescriptor PROP_WS_CONTROLLER_SERVICE_ENDPOINT = new PropertyDescriptor.Builder()
.name("websocket-endpoint-id")
.displayName("WebSocket Endpoint Id")
.description("A NiFi Expression to retrieve the endpoint id of a WebSocket ControllerService.")
.required(true)
.addValidator(StandardValidators.NON_BLANK_VALIDATOR)
.expressionLanguageSupported(ExpressionLanguageScope.FLOWFILE_ATTRIBUTES)
.defaultValue("${" + ATTR_WS_ENDPOINT_ID + "}")
.build();
public static final PropertyDescriptor PROP_WS_MESSAGE_TYPE = new PropertyDescriptor.Builder()
.name("websocket-message-type")
.displayName("WebSocket Message Type")
.description("The type of message content: TEXT or BINARY")
.required(true)
.addValidator(StandardValidators.NON_BLANK_VALIDATOR)
.defaultValue(WebSocketMessage.Type.TEXT.toString())
.expressionLanguageSupported(ExpressionLanguageScope.FLOWFILE_ATTRIBUTES)
.build();
public static final Relationship REL_SUCCESS = new Relationship.Builder()
.name("success")
.description("FlowFiles that are sent successfully to the destination are transferred to this relationship.")
.build();
public static final Relationship REL_FAILURE = new Relationship.Builder()
.name("failure")
.description("FlowFiles that failed to send to the destination are transferred to this relationship.")
.build();
private static final List<PropertyDescriptor> descriptors;
private static final Set<Relationship> relationships;
static{
final List<PropertyDescriptor> innerDescriptorsList = new ArrayList<>();
innerDescriptorsList.add(PROP_WS_SESSION_ID);
innerDescriptorsList.add(PROP_WS_CONTROLLER_SERVICE_ID);
innerDescriptorsList.add(PROP_WS_CONTROLLER_SERVICE_ENDPOINT);
innerDescriptorsList.add(PROP_WS_MESSAGE_TYPE);
descriptors = Collections.unmodifiableList(innerDescriptorsList);
final Set<Relationship> innerRelationshipsSet = new HashSet<>();
innerRelationshipsSet.add(REL_SUCCESS);
innerRelationshipsSet.add(REL_FAILURE);
relationships = Collections.unmodifiableSet(innerRelationshipsSet);
}
#Override
public Set<Relationship> getRelationships() {
return relationships;
}
#Override
public final List<PropertyDescriptor> getSupportedPropertyDescriptors() {
return descriptors;
}
#Override
public void onTrigger(final ProcessContext context, final ProcessSession processSession) throws ProcessException {
final FlowFile flowfile = processSession.get();
if (flowfile == null) {
return;
}
final String sessionId = context.getProperty(PROP_WS_SESSION_ID)
.evaluateAttributeExpressions(flowfile).getValue();
final String webSocketServiceId = context.getProperty(PROP_WS_CONTROLLER_SERVICE_ID)
.evaluateAttributeExpressions(flowfile).getValue();
final String webSocketServiceEndpoint = context.getProperty(PROP_WS_CONTROLLER_SERVICE_ENDPOINT)
.evaluateAttributeExpressions(flowfile).getValue();
final String messageTypeStr = context.getProperty(PROP_WS_MESSAGE_TYPE)
.evaluateAttributeExpressions(flowfile).getValue();
final WebSocketMessage.Type messageType = WebSocketMessage.Type.valueOf(messageTypeStr);
if (StringUtils.isEmpty(sessionId)) {
getLogger().debug("Specific SessionID not specified. Message will be broadcast to all connected clients.");
}
if (StringUtils.isEmpty(webSocketServiceId)
|| StringUtils.isEmpty(webSocketServiceEndpoint)) {
transferToFailure(processSession, flowfile, "Required WebSocket attribute was not found.");
return;
}
final ControllerService controllerService = context.getControllerServiceLookup().getControllerService(webSocketServiceId);
if (controllerService == null) {
getLogger().debug("ControllerService is NULL");
transferToFailure(processSession, flowfile, "WebSocket ControllerService was not found.");
return;
} else if (!(controllerService instanceof WebSocketService)) {
getLogger().debug("ControllerService is not instance of WebSocketService");
transferToFailure(processSession, flowfile, "The ControllerService found was not a WebSocket ControllerService but a "
+ controllerService.getClass().getName());
return;
}
...
processSession.getProvenanceReporter().send(updatedFlowFile, transitUri.get(), transmissionMillis);
processSession.transfer(updatedFlowFile, REL_SUCCESS);
processSession.commit();
} catch (WebSocketConfigurationException|IllegalStateException|IOException e) {
// WebSocketConfigurationException: If the corresponding WebSocketGatewayProcessor has been stopped.
// IllegalStateException: Session is already closed or not found.
// IOException: other IO error.
getLogger().error("Failed to send message via WebSocket due to " + e, e);
transferToFailure(processSession, flowfile, e.toString());
}
}
private FlowFile transferToFailure(final ProcessSession processSession, FlowFile flowfile, final String value) {
flowfile = processSession.putAttribute(flowfile, ATTR_WS_FAILURE_DETAIL, value);
processSession.transfer(flowfile, REL_FAILURE);
return flowfile;
}
}
I have deployed the custom processor and when I connect to it using the Chrome "Simple Web Socket Client" I can see the following message in the logs:
ControllerService found was not a WebSocket ControllerService but a com.sun.proxy.$Proxy75
I'm using the exact same code as in PutWebSocket and can't figure out why it would behave any different when I use my custom Processor. I have configured "JettyWebSocketServer" as the ControllerService under "ListenWebSocket" as shown in the image below.
Additional exception details seen in the log are provided below:
java.lang.ClassCastException: class com.sun.proxy.$Proxy75 cannot be cast to class org.apache.nifi.websocket.WebSocketService (com.sun.proxy.$Proxy75 is in unnamed module of loader org.apache.nifi.nar.InstanceClassLoader #35c646b5; org.apache.nifi.websocket.WebSocketService is in unnamed module of loader org.apache.nifi.nar.NarClassLoader #361abd01)

Answer 1

I ended up modifying my flow to utilize out-of-box ListenWebSocket, PutWebSocket Processors, and a custom "FetchFromKafka" Processor that is a modified version of ConsumeKafkaRecord. With this I'm able to provide a WebSocket interface to Kafka. I have provided a screenshot of the updated flow below. More work needs to be done with the custom Processor to support multiple sessions.