text: /*
   * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  package jdk.internal.jrtfs;
  
  import java.io.IOException;
  import java.net.URISyntaxException;
  import java.net.URL;
  import java.nio.file.Files;
  import java.nio.file.FileSystem;
  import java.nio.file.FileSystems;
  import java.nio.file.FileSystemNotFoundException;
  import java.nio.file.Path;
  import java.nio.file.Paths;
  import java.security.AccessController;
  import java.security.CodeSource;
  import java.security.PrivilegedAction;
  
  import jdk.internal.jimage.ImageReader;
  import jdk.internal.jimage.ImageReader.Node;
  
  /**
   * @implNote This class needs to maintain JDK 8 source compatibility.
   *
   * It is used internally in the JDK to implement jimage/jrtfs access,
   * but also compiled and delivered as part of the jrtfs.jar to support access
   * to the jimage file provided by the shipped JDK by tools running on JDK 8.
   */
  abstract class SystemImage {
  
      abstract Node findNode(String path) throws IOException;
      abstract byte[] getResource(Node node) throws IOException;
      abstract void close() throws IOException;
  
      static SystemImage open() throws IOException {
          if (modulesImageExists) {
              // open a .jimage and build directory structure
              final ImageReader image = ImageReader.open(moduleImageFile);
              image.getRootDirectory();
              return new SystemImage() {
                  @Override
                  Node findNode(String path) throws IOException {
                      return image.findNode(path);
                  }
                  @Override
                  byte[] getResource(Node node) throws IOException {
                      return image.getResource(node);
                  }
                  @Override
                  void close() throws IOException {
                      image.close();
                  }
              };
          }
          if (Files.notExists(explodedModulesDir))
              throw new FileSystemNotFoundException(explodedModulesDir.toString());
          return new ExplodedImage(explodedModulesDir);
      }
  
      static final String RUNTIME_HOME;
      // "modules" jimage file Path
      final static Path moduleImageFile;
      // "modules" jimage exists or not?
      final static boolean modulesImageExists;
      // <JAVA_HOME>/modules directory Path
      static final Path explodedModulesDir;
  
      static {
          PrivilegedAction<String> pa = SystemImage::findHome;
          RUNTIME_HOME = AccessController.doPrivileged(pa);
  
          FileSystem fs = FileSystems.getDefault();
          moduleImageFile = fs.getPath(RUNTIME_HOME, "lib", "modules");
          explodedModulesDir = fs.getPath(RUNTIME_HOME, "modules");
  
          modulesImageExists = AccessController.doPrivileged(
              new PrivilegedAction<Boolean>() {
                  @Override
                  public Boolean run() {
                      return Files.isRegularFile(moduleImageFile);
                  }
              });
      }
  
      /**
       * Returns the appropriate JDK home for this usage of the FileSystemProvider.
       * When the CodeSource is null (null loader) then jrt:/ is the current runtime,
       * otherwise the JDK home is located relative to jrt-fs.jar.
       */
      private static String findHome() {
          CodeSource cs = SystemImage.class.getProtectionDomain().getCodeSource();
          if (cs == null)
              return System.getProperty("java.home");
  
          // assume loaded from $TARGETJDK/lib/jrt-fs.jar
          URL url = cs.getLocation();
          if (!url.getProtocol().equalsIgnoreCase("file"))
              throw new InternalError(url + " loaded in unexpected way");
          try {
              Path lib = Paths.get(url.toURI()).getParent();
              if (!lib.getFileName().toString().equals("lib"))
                  throw new InternalError(url + " unexpected path");
  
              return lib.getParent().toString();
          } catch (URISyntaxException e) {
              throw new InternalError(e);
          }
      }
  }
  