NIFI-14571: Add VerifiableFlowRegistryClient interface to verify Flow Registry Client implementations

Author: mattyb149

src/main/java/org/apache/nifi/controller/VerifiableFlowRegistryClientService.java

@@ -0,0 +1,67 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.nifi.controller;
+
+import org.apache.nifi.components.ConfigVerificationResult;
+import org.apache.nifi.logging.ComponentLog;
+import org.apache.nifi.registry.flow.FlowRegistryClientConfigurationContext;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * <p>
+ *     Any Flow Registry Client that implements this interface will be provided the opportunity to verify
+ *     a given configuration of the Flow Registry Client. This allows the Flow Registry Client to provide meaningful feedback
+ *     to users when configuring the dataflow.
+ * </p>
+ *
+ * <p>
+ *     Generally speaking, verification differs from validation in that validation is expected to be very
+ *     quick and run often. If a Flow Registry Client is not valid, it cannot be started. However, verification may be
+ *     more expensive or time-consuming to complete. For example, validation may ensure that a username is
+ *     provided for connecting to an external service but should not perform any sort of network connection
+ *     in order to verify that the username is accurate. Verification, on the other hand, may create resources
+ *     such as network connections, may be more expensive to complete, and may be run only when a user invokes
+ *     the action (though verification may later occur at other stages, such as when starting a component).
+ * </p>
+ *
+ * <p>
+ *     Verification is allowed to be run only when a Flow Registry Client is fully disabled.
+ *     Therefore, any initialization logic that may need to be performed
+ *     before the Flow Registry Client is triggered may also be required for verification. However, the framework is not responsible
+ *     for triggering the Lifecycle management stages, such as @OnScheduled before triggering the verification. Such
+ *     methods should be handled by the {@link #verify(FlowRegistryClientConfigurationContext, ComponentLog, Map)} itself.
+ *     The {@link #verify(FlowRegistryClientConfigurationContext, ComponentLog, Map)} method will only be called if the configuration is valid according to the
+ *     validation rules (i.e., all Property Descriptors' validators and customValidate methods have indicated that the configuration is valid).
+ * </p>
+ */
+public interface VerifiableFlowRegistryClientService {
+
+    /**
+     * Verifies that the configuration defined by the given FlowRegistryClientConfigurationContext is valid.
+     * @param context the FlowRegistryClientConfigurationContext that contains the necessary configuration
+     * @param verificationLogger a logger that can be used during verification. While the typical logger can be used, doing so may result
+     * in producing bulletins, which can be confusing.
+     * @param variables a Map of key/value pairs that can be used to resolve variables referenced in property values via Expression Language
+     *
+     * @return a List of ConfigVerificationResults, each illustrating one step of the verification process that was completed
+     */
+    List<ConfigVerificationResult> verify(FlowRegistryClientConfigurationContext context, ComponentLog verificationLogger, Map<String, String> variables);
+
+}