src/main/java/org/apache/nifi/extension/definition/extraction/ExtensionDefinitionFactory.java

/*
 * 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.extension.definition.extraction;

import org.apache.maven.artifact.Artifact;
import org.apache.nifi.extension.definition.ExtensionDefinition;
import org.apache.nifi.extension.definition.ExtensionType;
import org.apache.nifi.extension.definition.ServiceAPIDefinition;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.URL;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class ExtensionDefinitionFactory {
    private static final String SERVICES_DIRECTORY = "META-INF/services/";

    private static final Map<ExtensionType, String> INTERFACE_NAMES = new HashMap<>();
    static {
        INTERFACE_NAMES.put(ExtensionType.PROCESSOR, "org.apache.nifi.processor.Processor");
        INTERFACE_NAMES.put(ExtensionType.CONTROLLER_SERVICE, "org.apache.nifi.controller.ControllerService");
        INTERFACE_NAMES.put(ExtensionType.REPORTING_TASK, "org.apache.nifi.reporting.ReportingTask");
    }

    private final ClassLoader extensionClassLoader;

    public ExtensionDefinitionFactory(final ClassLoader classLoader) {
        this.extensionClassLoader = classLoader;
    }

    public Set<ExtensionDefinition> discoverExtensions(final ExtensionType extensionType) throws IOException {
        final String interfaceName = INTERFACE_NAMES.get(extensionType);
        final Set<String> classNames = discoverClassNames(interfaceName);

        if (classNames.isEmpty()) {
            return Collections.emptySet();
        }

        final Set<ExtensionDefinition> definitions = new HashSet<>();
        for (final String className : classNames) {
            try {
                definitions.add(createExtensionDefinition(extensionType, className));
            } catch (final Exception e) {
                throw new IOException("Failed to create Extension Definition for " + extensionType + " " + className, e);
            }
        }

        return definitions;
    }

    private ExtensionDefinition createExtensionDefinition(final ExtensionType extensionType, final String className) throws ClassNotFoundException {
        final Class<?> extensionClass = Class.forName(className, false, extensionClassLoader);
        final Set<ServiceAPIDefinition> serviceApis = getProvidedServiceAPIs(extensionType, extensionClass);
        return new StandardExtensionDefinition(extensionType, className, serviceApis);
    }

    private Set<ServiceAPIDefinition> getProvidedServiceAPIs(final ExtensionType extensionType, final Class<?> extensionClass) throws ClassNotFoundException {
        if (extensionType != ExtensionType.CONTROLLER_SERVICE) {
            return Collections.emptySet();
        }

        final Set<ServiceAPIDefinition> serviceApis = new HashSet<>();
        final Class<?> controllerServiceClass = Class.forName("org.apache.nifi.controller.ControllerService", false, extensionClassLoader);
        addProvidedServiceAPIs(controllerServiceClass, extensionClass, serviceApis);
        return serviceApis;
    }

    private void addProvidedServiceAPIs(final Class<?> controllerServiceClass, final Class<?> extensionClass, final Set<ServiceAPIDefinition> serviceApis) {
        if (extensionClass.getInterfaces() != null) {
            for (final Class<?> implementedInterface : extensionClass.getInterfaces()) {
                if (controllerServiceClass.isAssignableFrom(implementedInterface) && !controllerServiceClass.equals(implementedInterface)) {
                    final ClassLoader interfaceClassLoader = implementedInterface.getClassLoader();
                    if (interfaceClassLoader instanceof ExtensionClassLoader) {
                        final Artifact interfaceNarArtifact = ((ExtensionClassLoader) interfaceClassLoader).getNarArtifact();

                        final ServiceAPIDefinition serviceDefinition = new StandardServiceAPIDefinition(implementedInterface.getName(),
                                interfaceNarArtifact.getGroupId(), interfaceNarArtifact.getArtifactId(), interfaceNarArtifact.getBaseVersion());

                        serviceApis.add(serviceDefinition);
                    }
                }
            }
        }

        if (extensionClass.getSuperclass() != null) {
            addProvidedServiceAPIs(controllerServiceClass, extensionClass.getSuperclass(), serviceApis);
        }
    }

    private Set<String> discoverClassNames(final String extensionType) throws IOException {
        final Set<String> classNames = new HashSet<>();

        final Enumeration<URL> resources = extensionClassLoader.getResources(SERVICES_DIRECTORY + extensionType);

        while (resources.hasMoreElements()) {
            final URL resourceUrl = resources.nextElement();
            classNames.addAll(discoverClassNames(extensionClassLoader, resourceUrl));
        }

        return classNames;
    }

    private Set<String> discoverClassNames(final ClassLoader classLoader, final URL serviceUrl) throws IOException {
        final Set<String> classNames = new HashSet<>();

        try (final InputStream in = serviceUrl.openStream();
             final Reader rawReader = new InputStreamReader(in);
             final BufferedReader reader = new BufferedReader(rawReader)) {

            String line;
            while ((line = reader.readLine()) != null) {
                line = line.trim();

                if (line.isEmpty() || line.startsWith("#")) {
                    continue;
                }

                classNames.add(line);
            }
        }

        return classNames;
    }

}