src/java.base/share/classes/jdk/internal/module/ModulePatcher.java - platform/libcore - Git at Google

 /*
  * Copyright (c) 2015, 2017, 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.module;

 import java.io.Closeable;
 import java.io.File;
 import java.io.IOError;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.UncheckedIOException;
 import java.lang.module.ModuleDescriptor;
 import java.lang.module.ModuleDescriptor.Builder;
 import java.lang.module.ModuleReader;
 import java.lang.module.ModuleReference;
 import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URL;
 import java.nio.ByteBuffer;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;

 import jdk.internal.loader.Resource;
 import jdk.internal.misc.JavaLangModuleAccess;
 import jdk.internal.misc.SharedSecrets;
 import sun.net.www.ParseUtil;


 /**
  * Provides support for patching modules, mostly the boot layer.
  */

 public final class ModulePatcher {

     private static final JavaLangModuleAccess JLMA
         = SharedSecrets.getJavaLangModuleAccess();

     // module name -> sequence of patches (directories or JAR files)
     private final Map<String, List<Path>> map;

     /**
      * Initialize the module patcher with the given map. The map key is
      * the module name, the value is a list of path strings.
      */
     public ModulePatcher(Map<String, List<String>> input) {
         if (input.isEmpty()) {
             this.map = Map.of();
         } else {
             Map<String, List<Path>> map = new HashMap<>();
             for (Map.Entry<String, List<String>> e : input.entrySet()) {
                 String mn = e.getKey();
                 List<Path> paths = e.getValue().stream()
                         .map(Paths::get)
                         .collect(Collectors.toList());
                 map.put(mn, paths);
             }
             this.map = map;
         }
     }

     /**
      * Returns a module reference that interposes on the given module if
      * needed. If there are no patches for the given module then the module
      * reference is simply returned. Otherwise the patches for the module
      * are scanned (to find any new packages) and a new module reference is
      * returned.
      *
      * @throws UncheckedIOException if an I/O error is detected
      */
     public ModuleReference patchIfNeeded(ModuleReference mref) {
         // if there are no patches for the module then nothing to do
         ModuleDescriptor descriptor = mref.descriptor();
         String mn = descriptor.name();
         List<Path> paths = map.get(mn);
         if (paths == null)
             return mref;

         // Scan the JAR file or directory tree to get the set of packages.
         // For automatic modules then packages that do not contain class files
         // must be ignored.
         Set<String> packages = new HashSet<>();
         boolean isAutomatic = descriptor.isAutomatic();
         try {
             for (Path file : paths) {
                 if (Files.isRegularFile(file)) {

                     // JAR file - do not open as a multi-release JAR as this
                     // is not supported by the boot class loader
                     try (JarFile jf = new JarFile(file.toString())) {
                         jf.stream()
                           .filter(e -> !e.isDirectory()
                                   && (!isAutomatic || e.getName().endsWith(".class")))
                           .map(e -> toPackageName(file, e))
                           .filter(Checks::isPackageName)
                           .forEach(packages::add);
                     }

                 } else if (Files.isDirectory(file)) {

                     // exploded directory without following sym links
                     Path top = file;
                     Files.find(top, Integer.MAX_VALUE,
                                ((path, attrs) -> attrs.isRegularFile()))
                             .filter(path -> (!isAutomatic
                                     || path.toString().endsWith(".class"))
                                     && !isHidden(path))
                             .map(path -> toPackageName(top, path))
                             .filter(Checks::isPackageName)
                             .forEach(packages::add);

                 }
             }

         } catch (IOException ioe) {
             throw new UncheckedIOException(ioe);
         }

         // if there are new packages then we need a new ModuleDescriptor
         packages.removeAll(descriptor.packages());
         if (!packages.isEmpty()) {
             Builder builder = JLMA.newModuleBuilder(descriptor.name(),
                                                     /*strict*/ false,
                                                     descriptor.modifiers());
             if (!descriptor.isAutomatic()) {
                 descriptor.requires().forEach(builder::requires);
                 descriptor.exports().forEach(builder::exports);
                 descriptor.opens().forEach(builder::opens);
                 descriptor.uses().forEach(builder::uses);
             }
             descriptor.provides().forEach(builder::provides);

             descriptor.version().ifPresent(builder::version);
             descriptor.mainClass().ifPresent(builder::mainClass);

             // original + new packages
             builder.packages(descriptor.packages());
             builder.packages(packages);

             descriptor = builder.build();
         }

         // return a module reference to the patched module
         URI location = mref.location().orElse(null);

         ModuleTarget target = null;
         ModuleHashes recordedHashes = null;
         ModuleHashes.HashSupplier hasher = null;
         ModuleResolution mres = null;
         if (mref instanceof ModuleReferenceImpl) {
             ModuleReferenceImpl impl = (ModuleReferenceImpl)mref;
             target = impl.moduleTarget();
             recordedHashes = impl.recordedHashes();
             hasher = impl.hasher();
             mres = impl.moduleResolution();
         }

         return new ModuleReferenceImpl(descriptor,
                                        location,
                                        () -> new PatchedModuleReader(paths, mref),
                                        this,
                                        target,
                                        recordedHashes,
                                        hasher,
                                        mres);

     }

     /**
      * Returns true is this module patcher has patches.
      */
     public boolean hasPatches() {
         return !map.isEmpty();
     }

     /*
      * Returns the names of the patched modules.
      */
     Set<String> patchedModules() {
         return map.keySet();
     }

     /**
      * A ModuleReader that reads resources from a patched module.
      *
      * This class is public so as to expose the findResource method to the
      * built-in class loaders and avoid locating the resource twice during
      * class loading (once to locate the resource, the second to gets the
      * URL for the CodeSource).
      */
     public static class PatchedModuleReader implements ModuleReader {
         private final List<ResourceFinder> finders;
         private final ModuleReference mref;
         private final URL delegateCodeSourceURL;
         private volatile ModuleReader delegate;

         /**
          * Creates the ModuleReader to reads resources in a patched module.
          */
         PatchedModuleReader(List<Path> patches, ModuleReference mref) {
             List<ResourceFinder> finders = new ArrayList<>();
             boolean initialized = false;
             try {
                 for (Path file : patches) {
                     if (Files.isRegularFile(file)) {
                         finders.add(new JarResourceFinder(file));
                     } else {
                         finders.add(new ExplodedResourceFinder(file));
                     }
                 }
                 initialized = true;
             } catch (IOException ioe) {
                 throw new UncheckedIOException(ioe);
             } finally {
                 // close all ResourceFinder in the event of an error
                 if (!initialized) closeAll(finders);
             }

             this.finders = finders;
             this.mref = mref;
             this.delegateCodeSourceURL = codeSourceURL(mref);
         }

         /**
          * Closes all resource finders.
          */
         private static void closeAll(List<ResourceFinder> finders) {
             for (ResourceFinder finder : finders) {
                 try { finder.close(); } catch (IOException ioe) { }
             }
         }

         /**
          * Returns the code source URL for the given module.
          */
         private static URL codeSourceURL(ModuleReference mref) {
             try {
                 Optional<URI> ouri = mref.location();
                 if (ouri.isPresent())
                     return ouri.get().toURL();
             } catch (MalformedURLException e) { }
             return null;
         }

         /**
          * Returns the ModuleReader to delegate to when the resource is not
          * found in a patch location.
          */
         private ModuleReader delegate() throws IOException {
             ModuleReader r = delegate;
             if (r == null) {
                 synchronized (this) {
                     r = delegate;
                     if (r == null) {
                         delegate = r = mref.open();
                     }
                 }
             }
             return r;
         }

         /**
          * Finds a resources in the patch locations. Returns null if not found
          * or the name is "module-info.class" as that cannot be overridden.
          */
         private Resource findResourceInPatch(String name) throws IOException {
             if (!name.equals("module-info.class")) {
                 for (ResourceFinder finder : finders) {
                     Resource r = finder.find(name);
                     if (r != null)
                         return r;
                 }
             }
             return null;
         }

         /**
          * Finds a resource of the given name in the patched module.
          */
         public Resource findResource(String name) throws IOException {

             // patch locations
             Resource r = findResourceInPatch(name);
             if (r != null)
                 return r;

             // original module
             ByteBuffer bb = delegate().read(name).orElse(null);
             if (bb == null)
                 return null;

             return new Resource() {
                 private <T> T shouldNotGetHere(Class<T> type) {
                     throw new InternalError("should not get here");
                 }
                 @Override
                 public String getName() {
                     return shouldNotGetHere(String.class);
                 }
                 @Override
                 public URL getURL() {
                     return shouldNotGetHere(URL.class);
                 }
                 @Override
                 public URL getCodeSourceURL() {
                     return delegateCodeSourceURL;
                 }
                 @Override
                 public ByteBuffer getByteBuffer() throws IOException {
                     return bb;
                 }
                 @Override
                 public InputStream getInputStream() throws IOException {
                     return shouldNotGetHere(InputStream.class);
                 }
                 @Override
                 public int getContentLength() throws IOException {
                     return shouldNotGetHere(int.class);
                 }
             };
         }

         @Override
         public Optional<URI> find(String name) throws IOException {
             Resource r = findResourceInPatch(name);
             if (r != null) {
                 URI uri = URI.create(r.getURL().toString());
                 return Optional.of(uri);
             } else {
                 return delegate().find(name);
             }
         }

         @Override
         public Optional<InputStream> open(String name) throws IOException {
             Resource r = findResourceInPatch(name);
             if (r != null) {
                 return Optional.of(r.getInputStream());
             } else {
                 return delegate().open(name);
             }
         }

         @Override
         public Optional<ByteBuffer> read(String name) throws IOException {
             Resource r = findResourceInPatch(name);
             if (r != null) {
                 ByteBuffer bb = r.getByteBuffer();
                 assert !bb.isDirect();
                 return Optional.of(bb);
             } else {
                 return delegate().read(name);
             }
         }

         @Override
         public void release(ByteBuffer bb) {
             if (bb.isDirect()) {
                 try {
                     delegate().release(bb);
                 } catch (IOException ioe) {
                     throw new InternalError(ioe);
                 }
             }
         }

         @Override
         public Stream<String> list() throws IOException {
             Stream<String> s = delegate().list();
             for (ResourceFinder finder : finders) {
                 s = Stream.concat(s, finder.list());
             }
             return s.distinct();
         }

         @Override
         public void close() throws IOException {
             closeAll(finders);
             delegate().close();
         }
     }


     /**
      * A resource finder that find resources in a patch location.
      */
     private static interface ResourceFinder extends Closeable {
         Resource find(String name) throws IOException;
         Stream<String> list() throws IOException;
     }


     /**
      * A ResourceFinder that finds resources in a JAR file.
      */
     private static class JarResourceFinder implements ResourceFinder {
         private final JarFile jf;
         private final URL csURL;

         JarResourceFinder(Path path) throws IOException {
             this.jf = new JarFile(path.toString());
             this.csURL = path.toUri().toURL();
         }

         @Override
         public void close() throws IOException {
             jf.close();
         }

         @Override
         public Resource find(String name) throws IOException {
             JarEntry entry = jf.getJarEntry(name);
             if (entry == null)
                 return null;

             return new Resource() {
                 @Override
                 public String getName() {
                     return name;
                 }
                 @Override
                 public URL getURL() {
                     String encodedPath = ParseUtil.encodePath(name, false);
                     try {
                         return new URL("jar:" + csURL + "!/" + encodedPath);
                     } catch (MalformedURLException e) {
                         return null;
                     }
                 }
                 @Override
                 public URL getCodeSourceURL() {
                     return csURL;
                 }
                 @Override
                 public ByteBuffer getByteBuffer() throws IOException {
                     byte[] bytes = getInputStream().readAllBytes();
                     return ByteBuffer.wrap(bytes);
                 }
                 @Override
                 public InputStream getInputStream() throws IOException {
                     return jf.getInputStream(entry);
                 }
                 @Override
                 public int getContentLength() throws IOException {
                     long size = entry.getSize();
                     return (size > Integer.MAX_VALUE) ? -1 : (int) size;
                 }
             };
         }

         @Override
         public Stream<String> list() throws IOException {
             return jf.stream().map(JarEntry::getName);
         }
     }


     /**
      * A ResourceFinder that finds resources on the file system.
      */
     private static class ExplodedResourceFinder implements ResourceFinder {
         private final Path dir;

         ExplodedResourceFinder(Path dir) {
             this.dir = dir;
         }

         @Override
         public void close() { }

         @Override
         public Resource find(String name) throws IOException {
             Path file = Resources.toFilePath(dir, name);
             if (file != null) {
                 return newResource(name, dir, file);
             } else {
                 return null;
             }
         }

         private Resource newResource(String name, Path top, Path file) {
             return new Resource() {
                 @Override
                 public String getName() {
                     return name;
                 }
                 @Override
                 public URL getURL() {
                     try {
                         return file.toUri().toURL();
                     } catch (IOException | IOError e) {
                         return null;
                     }
                 }
                 @Override
                 public URL getCodeSourceURL() {
                     try {
                         return top.toUri().toURL();
                     } catch (IOException | IOError e) {
                         return null;
                     }
                 }
                 @Override
                 public ByteBuffer getByteBuffer() throws IOException {
                     return ByteBuffer.wrap(Files.readAllBytes(file));
                 }
                 @Override
                 public InputStream getInputStream() throws IOException {
                     return Files.newInputStream(file);
                 }
                 @Override
                 public int getContentLength() throws IOException {
                     long size = Files.size(file);
                     return (size > Integer.MAX_VALUE) ? -1 : (int)size;
                 }
             };
         }

         @Override
         public Stream<String> list() throws IOException {
             return Files.walk(dir, Integer.MAX_VALUE)
                         .map(f -> Resources.toResourceName(dir, f))
                         .filter(s -> !s.isEmpty());
         }
     }


     /**
      * Derives a package name from the file path of an entry in an exploded patch
      */
     private static String toPackageName(Path top, Path file) {
         Path entry = top.relativize(file);
         Path parent = entry.getParent();
         if (parent == null) {
             return warnIfModuleInfo(top, entry.toString());
         } else {
             return parent.toString().replace(File.separatorChar, '.');
         }
     }

     /**
      * Returns true if the given file exists and is a hidden file
      */
     private boolean isHidden(Path file) {
         try {
             return Files.isHidden(file);
         } catch (IOException ioe) {
             return false;
         }
     }

     /**
      * Derives a package name from the name of an entry in a JAR file.
      */
     private static String toPackageName(Path file, JarEntry entry) {
         String name = entry.getName();
         int index = name.lastIndexOf("/");
         if (index == -1) {
             return warnIfModuleInfo(file, name);
         } else {
             return name.substring(0, index).replace('/', '.');
         }
     }

     private static String warnIfModuleInfo(Path file, String e) {
         if (e.equals("module-info.class"))
             System.err.println("WARNING: " + e + " ignored in patch: " + file);
         return "";
     }
 }
	/*
	* Copyright (c) 2015, 2017, 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.module;

	import java.io.Closeable;
	import java.io.File;
	import java.io.IOError;
	import java.io.IOException;
	import java.io.InputStream;
	import java.io.UncheckedIOException;
	import java.lang.module.ModuleDescriptor;
	import java.lang.module.ModuleDescriptor.Builder;
	import java.lang.module.ModuleReader;
	import java.lang.module.ModuleReference;
	import java.net.MalformedURLException;
	import java.net.URI;
	import java.net.URL;
	import java.nio.ByteBuffer;
	import java.nio.file.Files;
	import java.nio.file.Path;
	import java.nio.file.Paths;
	import java.util.ArrayList;
	import java.util.HashMap;
	import java.util.HashSet;
	import java.util.List;
	import java.util.Map;
	import java.util.Optional;
	import java.util.Set;
	import java.util.jar.JarEntry;
	import java.util.jar.JarFile;
	import java.util.stream.Collectors;
	import java.util.stream.Stream;

	import jdk.internal.loader.Resource;
	import jdk.internal.misc.JavaLangModuleAccess;
	import jdk.internal.misc.SharedSecrets;
	import sun.net.www.ParseUtil;


	/**
	* Provides support for patching modules, mostly the boot layer.
	*/

	public final class ModulePatcher {

	private static final JavaLangModuleAccess JLMA
	= SharedSecrets.getJavaLangModuleAccess();

	// module name -> sequence of patches (directories or JAR files)
	private final Map<String, List<Path>> map;

	/**
	* Initialize the module patcher with the given map. The map key is
	* the module name, the value is a list of path strings.
	*/
	public ModulePatcher(Map<String, List<String>> input) {
	if (input.isEmpty()) {
	this.map = Map.of();
	} else {
	Map<String, List<Path>> map = new HashMap<>();
	for (Map.Entry<String, List<String>> e : input.entrySet()) {
	String mn = e.getKey();
	List<Path> paths = e.getValue().stream()
	.map(Paths::get)
	.collect(Collectors.toList());
	map.put(mn, paths);
	}
	this.map = map;
	}
	}

	/**
	* Returns a module reference that interposes on the given module if
	* needed. If there are no patches for the given module then the module
	* reference is simply returned. Otherwise the patches for the module
	* are scanned (to find any new packages) and a new module reference is
	* returned.
	*
	* @throws UncheckedIOException if an I/O error is detected
	*/
	public ModuleReference patchIfNeeded(ModuleReference mref) {
	// if there are no patches for the module then nothing to do
	ModuleDescriptor descriptor = mref.descriptor();
	String mn = descriptor.name();
	List<Path> paths = map.get(mn);
	if (paths == null)
	return mref;

	// Scan the JAR file or directory tree to get the set of packages.
	// For automatic modules then packages that do not contain class files
	// must be ignored.
	Set<String> packages = new HashSet<>();
	boolean isAutomatic = descriptor.isAutomatic();
	try {
	for (Path file : paths) {
	if (Files.isRegularFile(file)) {

	// JAR file - do not open as a multi-release JAR as this
	// is not supported by the boot class loader
	try (JarFile jf = new JarFile(file.toString())) {
	jf.stream()
	.filter(e -> !e.isDirectory()
	&& (!isAutomatic \|\| e.getName().endsWith(".class")))
	.map(e -> toPackageName(file, e))
	.filter(Checks::isPackageName)
	.forEach(packages::add);
	}

	} else if (Files.isDirectory(file)) {

	// exploded directory without following sym links
	Path top = file;
	Files.find(top, Integer.MAX_VALUE,
	((path, attrs) -> attrs.isRegularFile()))
	.filter(path -> (!isAutomatic
	\|\| path.toString().endsWith(".class"))
	&& !isHidden(path))
	.map(path -> toPackageName(top, path))
	.filter(Checks::isPackageName)
	.forEach(packages::add);

	}
	}

	} catch (IOException ioe) {
	throw new UncheckedIOException(ioe);
	}

	// if there are new packages then we need a new ModuleDescriptor
	packages.removeAll(descriptor.packages());
	if (!packages.isEmpty()) {
	Builder builder = JLMA.newModuleBuilder(descriptor.name(),
	/strict/ false,
	descriptor.modifiers());
	if (!descriptor.isAutomatic()) {
	descriptor.requires().forEach(builder::requires);
	descriptor.exports().forEach(builder::exports);
	descriptor.opens().forEach(builder::opens);
	descriptor.uses().forEach(builder::uses);
	}
	descriptor.provides().forEach(builder::provides);

	descriptor.version().ifPresent(builder::version);
	descriptor.mainClass().ifPresent(builder::mainClass);

	// original + new packages
	builder.packages(descriptor.packages());
	builder.packages(packages);

	descriptor = builder.build();
	}

	// return a module reference to the patched module
	URI location = mref.location().orElse(null);

	ModuleTarget target = null;
	ModuleHashes recordedHashes = null;
	ModuleHashes.HashSupplier hasher = null;
	ModuleResolution mres = null;
	if (mref instanceof ModuleReferenceImpl) {
	ModuleReferenceImpl impl = (ModuleReferenceImpl)mref;
	target = impl.moduleTarget();
	recordedHashes = impl.recordedHashes();
	hasher = impl.hasher();
	mres = impl.moduleResolution();
	}

	return new ModuleReferenceImpl(descriptor,
	location,
	() -> new PatchedModuleReader(paths, mref),
	this,
	target,
	recordedHashes,
	hasher,
	mres);

	}

	/**
	* Returns true is this module patcher has patches.
	*/
	public boolean hasPatches() {
	return !map.isEmpty();
	}

	/*
	* Returns the names of the patched modules.
	*/
	Set<String> patchedModules() {
	return map.keySet();
	}

	/**
	* A ModuleReader that reads resources from a patched module.
	*
	* This class is public so as to expose the findResource method to the
	* built-in class loaders and avoid locating the resource twice during
	* class loading (once to locate the resource, the second to gets the
	* URL for the CodeSource).
	*/
	public static class PatchedModuleReader implements ModuleReader {
	private final List<ResourceFinder> finders;
	private final ModuleReference mref;
	private final URL delegateCodeSourceURL;
	private volatile ModuleReader delegate;

	/**
	* Creates the ModuleReader to reads resources in a patched module.
	*/
	PatchedModuleReader(List<Path> patches, ModuleReference mref) {
	List<ResourceFinder> finders = new ArrayList<>();
	boolean initialized = false;
	try {
	for (Path file : patches) {
	if (Files.isRegularFile(file)) {
	finders.add(new JarResourceFinder(file));
	} else {
	finders.add(new ExplodedResourceFinder(file));
	}
	}
	initialized = true;
	} catch (IOException ioe) {
	throw new UncheckedIOException(ioe);
	} finally {
	// close all ResourceFinder in the event of an error
	if (!initialized) closeAll(finders);
	}

	this.finders = finders;
	this.mref = mref;
	this.delegateCodeSourceURL = codeSourceURL(mref);
	}

	/**
	* Closes all resource finders.
	*/
	private static void closeAll(List<ResourceFinder> finders) {
	for (ResourceFinder finder : finders) {
	try { finder.close(); } catch (IOException ioe) { }
	}
	}

	/**
	* Returns the code source URL for the given module.
	*/
	private static URL codeSourceURL(ModuleReference mref) {
	try {
	Optional<URI> ouri = mref.location();
	if (ouri.isPresent())
	return ouri.get().toURL();
	} catch (MalformedURLException e) { }
	return null;
	}

	/**
	* Returns the ModuleReader to delegate to when the resource is not
	* found in a patch location.
	*/
	private ModuleReader delegate() throws IOException {
	ModuleReader r = delegate;
	if (r == null) {
	synchronized (this) {
	r = delegate;
	if (r == null) {
	delegate = r = mref.open();
	}
	}
	}
	return r;
	}

	/**
	* Finds a resources in the patch locations. Returns null if not found
	* or the name is "module-info.class" as that cannot be overridden.
	*/
	private Resource findResourceInPatch(String name) throws IOException {
	if (!name.equals("module-info.class")) {
	for (ResourceFinder finder : finders) {
	Resource r = finder.find(name);
	if (r != null)
	return r;
	}
	}
	return null;
	}

	/**
	* Finds a resource of the given name in the patched module.
	*/
	public Resource findResource(String name) throws IOException {

	// patch locations
	Resource r = findResourceInPatch(name);
	if (r != null)
	return r;

	// original module
	ByteBuffer bb = delegate().read(name).orElse(null);
	if (bb == null)
	return null;

	return new Resource() {
	private <T> T shouldNotGetHere(Class<T> type) {
	throw new InternalError("should not get here");
	}
	@Override
	public String getName() {
	return shouldNotGetHere(String.class);
	}
	@Override
	public URL getURL() {
	return shouldNotGetHere(URL.class);
	}
	@Override
	public URL getCodeSourceURL() {
	return delegateCodeSourceURL;
	}
	@Override
	public ByteBuffer getByteBuffer() throws IOException {
	return bb;
	}
	@Override
	public InputStream getInputStream() throws IOException {
	return shouldNotGetHere(InputStream.class);
	}
	@Override
	public int getContentLength() throws IOException {
	return shouldNotGetHere(int.class);
	}
	};
	}

	@Override
	public Optional<URI> find(String name) throws IOException {
	Resource r = findResourceInPatch(name);
	if (r != null) {
	URI uri = URI.create(r.getURL().toString());
	return Optional.of(uri);
	} else {
	return delegate().find(name);
	}
	}

	@Override
	public Optional<InputStream> open(String name) throws IOException {
	Resource r = findResourceInPatch(name);
	if (r != null) {
	return Optional.of(r.getInputStream());
	} else {
	return delegate().open(name);
	}
	}

	@Override
	public Optional<ByteBuffer> read(String name) throws IOException {
	Resource r = findResourceInPatch(name);
	if (r != null) {
	ByteBuffer bb = r.getByteBuffer();
	assert !bb.isDirect();
	return Optional.of(bb);
	} else {
	return delegate().read(name);
	}
	}

	@Override
	public void release(ByteBuffer bb) {
	if (bb.isDirect()) {
	try {
	delegate().release(bb);
	} catch (IOException ioe) {
	throw new InternalError(ioe);
	}
	}
	}

	@Override
	public Stream<String> list() throws IOException {
	Stream<String> s = delegate().list();
	for (ResourceFinder finder : finders) {
	s = Stream.concat(s, finder.list());
	}
	return s.distinct();
	}

	@Override
	public void close() throws IOException {
	closeAll(finders);
	delegate().close();
	}
	}


	/**
	* A resource finder that find resources in a patch location.
	*/
	private static interface ResourceFinder extends Closeable {
	Resource find(String name) throws IOException;
	Stream<String> list() throws IOException;
	}


	/**
	* A ResourceFinder that finds resources in a JAR file.
	*/
	private static class JarResourceFinder implements ResourceFinder {
	private final JarFile jf;
	private final URL csURL;

	JarResourceFinder(Path path) throws IOException {
	this.jf = new JarFile(path.toString());
	this.csURL = path.toUri().toURL();
	}

	@Override
	public void close() throws IOException {
	jf.close();
	}

	@Override
	public Resource find(String name) throws IOException {
	JarEntry entry = jf.getJarEntry(name);
	if (entry == null)
	return null;

	return new Resource() {
	@Override
	public String getName() {
	return name;
	}
	@Override
	public URL getURL() {
	String encodedPath = ParseUtil.encodePath(name, false);
	try {
	return new URL("jar:" + csURL + "!/" + encodedPath);
	} catch (MalformedURLException e) {
	return null;
	}
	}
	@Override
	public URL getCodeSourceURL() {
	return csURL;
	}
	@Override
	public ByteBuffer getByteBuffer() throws IOException {
	byte[] bytes = getInputStream().readAllBytes();
	return ByteBuffer.wrap(bytes);
	}
	@Override
	public InputStream getInputStream() throws IOException {
	return jf.getInputStream(entry);
	}
	@Override
	public int getContentLength() throws IOException {
	long size = entry.getSize();
	return (size > Integer.MAX_VALUE) ? -1 : (int) size;
	}
	};
	}

	@Override
	public Stream<String> list() throws IOException {
	return jf.stream().map(JarEntry::getName);
	}
	}


	/**
	* A ResourceFinder that finds resources on the file system.
	*/
	private static class ExplodedResourceFinder implements ResourceFinder {
	private final Path dir;

	ExplodedResourceFinder(Path dir) {
	this.dir = dir;
	}

	@Override
	public void close() { }

	@Override
	public Resource find(String name) throws IOException {
	Path file = Resources.toFilePath(dir, name);
	if (file != null) {
	return newResource(name, dir, file);
	} else {
	return null;
	}
	}

	private Resource newResource(String name, Path top, Path file) {
	return new Resource() {
	@Override
	public String getName() {
	return name;
	}
	@Override
	public URL getURL() {
	try {
	return file.toUri().toURL();
	} catch (IOException \| IOError e) {
	return null;
	}
	}
	@Override
	public URL getCodeSourceURL() {
	try {
	return top.toUri().toURL();
	} catch (IOException \| IOError e) {
	return null;
	}
	}
	@Override
	public ByteBuffer getByteBuffer() throws IOException {
	return ByteBuffer.wrap(Files.readAllBytes(file));
	}
	@Override
	public InputStream getInputStream() throws IOException {
	return Files.newInputStream(file);
	}
	@Override
	public int getContentLength() throws IOException {
	long size = Files.size(file);
	return (size > Integer.MAX_VALUE) ? -1 : (int)size;
	}
	};
	}

	@Override
	public Stream<String> list() throws IOException {
	return Files.walk(dir, Integer.MAX_VALUE)
	.map(f -> Resources.toResourceName(dir, f))
	.filter(s -> !s.isEmpty());
	}
	}


	/**
	* Derives a package name from the file path of an entry in an exploded patch
	*/
	private static String toPackageName(Path top, Path file) {
	Path entry = top.relativize(file);
	Path parent = entry.getParent();
	if (parent == null) {
	return warnIfModuleInfo(top, entry.toString());
	} else {
	return parent.toString().replace(File.separatorChar, '.');
	}
	}

	/**
	* Returns true if the given file exists and is a hidden file
	*/
	private boolean isHidden(Path file) {
	try {
	return Files.isHidden(file);
	} catch (IOException ioe) {
	return false;
	}
	}

	/**
	* Derives a package name from the name of an entry in a JAR file.
	*/
	private static String toPackageName(Path file, JarEntry entry) {
	String name = entry.getName();
	int index = name.lastIndexOf("/");
	if (index == -1) {
	return warnIfModuleInfo(file, name);
	} else {
	return name.substring(0, index).replace('/', '.');
	}
	}

	private static String warnIfModuleInfo(Path file, String e) {
	if (e.equals("module-info.class"))
	System.err.println("WARNING: " + e + " ignored in patch: " + file);
	return "";
	}
	}