minifi-nar-bundles/minifi-framework-bundle/minifi-framework/minifi-runtime/src/main/java/org/apache/nifi/minifi/FlowParser.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.minifi;

import org.apache.commons.io.IOUtils;
import org.apache.nifi.util.LoggingXmlParserErrorHandler;
import org.apache.nifi.util.file.FileUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.ArrayList;
import java.util.List;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;

/**
 * Parses a flow from its xml.gz format into an XML {@link Document}.  This class is primarily toward utilities for assisting
 * with the handling of component bundles.
 * <p>
 * Provides auxiliary methods to aid in evaluating and manipulating the flow.
 */
public class FlowParser {

    private static final Logger logger = LoggerFactory.getLogger(FlowParser.class);

    /**
     * Generates a {@link Document} from the flow configuration file provided
     */
    public Document parse(final File flowConfigurationFile) {
        if (flowConfigurationFile == null) {
            logger.debug("Flow Configuration file was null");
            return null;
        }

        // if the flow doesn't exist or is 0 bytes, then return null
        final Path flowPath = flowConfigurationFile.toPath();
        try {
            if (!Files.exists(flowPath) || Files.size(flowPath) == 0) {
                logger.warn("Flow Configuration does not exist or was empty");
                return null;
            }
        } catch (IOException e) {
            logger.error("An error occurred determining the size of the Flow Configuration file");
            return null;
        }

        // otherwise create the appropriate input streams to read the file
        try (final InputStream in = Files.newInputStream(flowPath, StandardOpenOption.READ);
             final InputStream gzipIn = new GZIPInputStream(in)) {

            final byte[] flowBytes = IOUtils.toByteArray(gzipIn);
            if (flowBytes == null || flowBytes.length == 0) {
                logger.warn("Could not extract root group id because Flow Configuration File was empty");
                return null;
            }

            final DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
            docFactory.setNamespaceAware(true);
            docFactory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);

            // parse the flow
            final DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
            docBuilder.setErrorHandler(new LoggingXmlParserErrorHandler("Flow Configuration", logger));
            final Document document = docBuilder.parse(new ByteArrayInputStream(flowBytes));
            return document;

        } catch (final SAXException | ParserConfigurationException | IOException ex) {
            logger.error("Unable to parse flow {} due to {}", new Object[]{flowPath.toAbsolutePath(), ex});
            return null;
        }
    }


    /**
     * Writes a given XML Flow out to the specified path.
     *
     * @param flowDocument flowDocument of the associated XML content to write to disk
     * @param flowXmlPath  path on disk to write the flow
     * @throws IOException if there are issues in accessing the target destination for the flow
     * @throws TransformerException if there are issues in the xml transformation process
     */
    public void writeFlow(final Document flowDocument, final Path flowXmlPath) throws IOException, TransformerException {
        final ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        final Source xmlSource = new DOMSource(flowDocument);
        final Result outputTarget = new StreamResult(outputStream);
        TransformerFactory.newInstance().newTransformer().transform(xmlSource, outputTarget);
        final InputStream is = new ByteArrayInputStream(outputStream.toByteArray());

        try (final OutputStream output = Files.newOutputStream(flowXmlPath, StandardOpenOption.WRITE, StandardOpenOption.CREATE);
             final OutputStream gzipOut = new GZIPOutputStream(output);) {
            FileUtils.copy(is, gzipOut);
        }
    }

    /**
     * Finds child elements with the given tagName.
     *
     * @param element the parent element
     * @param tagName the child element name to find
     * @return a list of matching child elements
     */
    public static List<Element> getChildrenByTagName(final Element element, final String tagName) {
        final List<Element> matches = new ArrayList<>();
        final NodeList nodeList = element.getChildNodes();
        for (int i = 0; i < nodeList.getLength(); i++) {
            final Node node = nodeList.item(i);
            if (!(node instanceof Element)) {
                continue;
            }
            final Element child = (Element) nodeList.item(i);
            if (child.getNodeName().equals(tagName)) {
                matches.add(child);
            }
        }
        return matches;
    }

}