/*
 * Copyright (c) 2015, 2016, 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.loader;

import java.io.File;
import java.io.FilePermission;
import java.io.IOException;
import java.io.InputStream;
import java.lang.module.ModuleDescriptor;
import java.lang.module.ModuleReference;
import java.lang.module.ModuleReader;
import java.lang.ref.SoftReference;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URL;
import java.nio.ByteBuffer;
import java.security.AccessController;
import java.security.CodeSigner;
import java.security.CodeSource;
import java.security.Permission;
import java.security.PermissionCollection;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.security.SecureClassLoader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.jar.Attributes;
import java.util.jar.Manifest;
import java.util.stream.Stream;

import jdk.internal.misc.VM;
import jdk.internal.module.ModulePatcher.PatchedModuleReader;
import jdk.internal.module.SystemModules;
import jdk.internal.module.Resources;


The platform or application class loader. Resources loaded from modules
defined to the boot class loader are also loaded via an instance of this
ClassLoader type.
 This ClassLoader supports loading of classes and resources from modules. Modules are defined to the ClassLoader by invoking the loadModule method. Defining a module to this ClassLoader has the effect of making the types in the module visible. 
 This ClassLoader also supports loading of classes and resources from a
class path of URLs that are specified to the ClassLoader at construction
time. The class path may expand at runtime (the Class-Path attribute in JAR
files or via instrumentation agents). 
 The delegation model used by this ClassLoader differs to the regular
delegation model. When requested to load a class then this ClassLoader first
maps the class name to its package name. If there is a module defined to a
BuiltinClassLoader containing this package then the class loader delegates
directly to that class loader. If there isn't a module containing the
package then it delegates the search to the parent class loader and if not
found in the parent then it searches the class path. The main difference
between this and the usual delegation model is that it allows the platform
class loader to delegate to the application class loader, important with
upgraded modules defined to the platform class loader.
/**
 * The platform or application class loader. Resources loaded from modules
 * defined to the boot class loader are also loaded via an instance of this
 * ClassLoader type.
 *
 * <p> This ClassLoader supports loading of classes and resources from modules.
 * Modules are defined to the ClassLoader by invoking the {@link #loadModule}
 * method. Defining a module to this ClassLoader has the effect of making the
 * types in the module visible. </p>
 *
 * <p> This ClassLoader also supports loading of classes and resources from a
 * class path of URLs that are specified to the ClassLoader at construction
 * time. The class path may expand at runtime (the Class-Path attribute in JAR
 * files or via instrumentation agents). </p>
 *
 * <p> The delegation model used by this ClassLoader differs to the regular
 * delegation model. When requested to load a class then this ClassLoader first
 * maps the class name to its package name. If there is a module defined to a
 * BuiltinClassLoader containing this package then the class loader delegates
 * directly to that class loader. If there isn't a module containing the
 * package then it delegates the search to the parent class loader and if not
 * found in the parent then it searches the class path. The main difference
 * between this and the usual delegation model is that it allows the platform
 * class loader to delegate to the application class loader, important with
 * upgraded modules defined to the platform class loader.
 */

public class BuiltinClassLoader
    extends SecureClassLoader
{
    static {
        if (!ClassLoader.registerAsParallelCapable())
            throw new InternalError("Unable to register as parallel capable");
    }

    // parent ClassLoader
    private final BuiltinClassLoader parent;

    // the URL class path or null if there is no class path
    private final URLClassPath ucp;


    
A module defined/loaded by a built-in class loader.
A LoadedModule encapsulates a ModuleReference along with its CodeSource
URL to avoid needing to create this URL when defining classes.
/**
     * A module defined/loaded by a built-in class loader.
     *
     * A LoadedModule encapsulates a ModuleReference along with its CodeSource
     * URL to avoid needing to create this URL when defining classes.
     */
    private static class LoadedModule {
        private final BuiltinClassLoader loader;
        private final ModuleReference mref;
        private final URL codeSourceURL;          // may be null

        LoadedModule(BuiltinClassLoader loader, ModuleReference mref) {
            URL url = null;
            if (mref.location().isPresent()) {
                try {
                    url = mref.location().get().toURL();
                } catch (MalformedURLException | IllegalArgumentException e) { }
            }
            this.loader = loader;
            this.mref = mref;
            this.codeSourceURL = url;
        }

        BuiltinClassLoader loader() { return loader; }
        ModuleReference mref() { return mref; }
        String name() { return mref.descriptor().name(); }
        URL codeSourceURL() { return codeSourceURL; }
    }


    // maps package name to loaded module for modules in the boot layer
    private static final Map<String, LoadedModule> packageToModule
        = new ConcurrentHashMap<>(SystemModules.PACKAGES_IN_BOOT_LAYER);

    // maps a module name to a module reference
    private final Map<String, ModuleReference> nameToModule;

    // maps a module reference to a module reader
    private final Map<ModuleReference, ModuleReader> moduleToReader;

    // cache of resource name -> list of URLs.
    // used only for resources that are not in module packages
    private volatile SoftReference<Map<String, List<URL>>> resourceCache;

    
Create a new instance.
/**
     * Create a new instance.
     */
    BuiltinClassLoader(String name, BuiltinClassLoader parent, URLClassPath ucp) {
        // ensure getParent() returns null when the parent is the boot loader
        super(name, parent == null || parent == ClassLoaders.bootLoader() ? null : parent);

        this.parent = parent;
        this.ucp = ucp;

        this.nameToModule = new ConcurrentHashMap<>();
        this.moduleToReader = new ConcurrentHashMap<>();
    }

    
Returns true if there is a class path associated with this class loader. /**
     * Returns {@code true} if there is a class path associated with this
     * class loader.
     */
    boolean hasClassPath() {
        return ucp != null;
    }

    
Register a module this class loader. This has the effect of making the
types in the module visible.
/**
     * Register a module this class loader. This has the effect of making the
     * types in the module visible.
     */
    public void loadModule(ModuleReference mref) {
        String mn = mref.descriptor().name();
        if (nameToModule.putIfAbsent(mn, mref) != null) {
            throw new InternalError(mn + " already defined to this loader");
        }

        LoadedModule loadedModule = new LoadedModule(this, mref);
        for (String pn : mref.descriptor().packages()) {
            LoadedModule other = packageToModule.putIfAbsent(pn, loadedModule);
            if (other != null) {
                throw new InternalError(pn + " in modules " + mn + " and "
                                        + other.mref().descriptor().name());
            }
        }

        // clear resources cache if VM is already initialized
        if (VM.isModuleSystemInited() && resourceCache != null) {
            resourceCache = null;
        }
    }

    
Returns the ModuleReference for the named module defined to this class loader; or null if not defined. 
Params:
name – The name of the module to find/**
     * Returns the {@code ModuleReference} for the named module defined to
     * this class loader; or {@code null} if not defined.
     *
     * @param name The name of the module to find
     */
    protected ModuleReference findModule(String name) {
        return nameToModule.get(name);
    }


    // -- finding resources

    
Returns a URL to a resource of the given name in a module defined to
this class loader.
/**
     * Returns a URL to a resource of the given name in a module defined to
     * this class loader.
     */
    @Override
    public URL findResource(String mn, String name) throws IOException {
        URL url = null;

        if (mn != null) {
            // find in module
            ModuleReference mref = nameToModule.get(mn);
            if (mref != null) {
                url = findResource(mref, name);
            }
        } else {
            // find on class path
            url = findResourceOnClassPath(name);
        }

        return checkURL(url);  // check access before returning
    }

    
Returns an input stream to a resource of the given name in a module
defined to this class loader.
/**
     * Returns an input stream to a resource of the given name in a module
     * defined to this class loader.
     */
    public InputStream findResourceAsStream(String mn, String name)
        throws IOException
    {
        // Need URL to resource when running with a security manager so that
        // the right permission check is done.
        if (System.getSecurityManager() != null || mn == null) {
            URL url = findResource(mn, name);
            return (url != null) ? url.openStream() : null;
        }

        // find in module defined to this loader, no security manager
        ModuleReference mref = nameToModule.get(mn);
        if (mref != null) {
            return moduleReaderFor(mref).open(name).orElse(null);
        } else {
            return null;
        }
    }

    
Finds a resource with the given name in the modules defined to this
class loader or its class path.
/**
     * Finds a resource with the given name in the modules defined to this
     * class loader or its class path.
     */
    @Override
    public URL findResource(String name) {
        String pn = Resources.toPackageName(name);
        LoadedModule module = packageToModule.get(pn);
        if (module != null) {

            // resource is in a package of a module defined to this loader
            if (module.loader() == this) {
                URL url;
                try {
                    url = findResource(module.name(), name); // checks URL
                } catch (IOException ioe) {
                    return null;
                }
                if (url != null
                    && (name.endsWith(".class")
                        || url.toString().endsWith("/")
                        || isOpen(module.mref(), pn))) {
                    return url;
                }
            }

        } else {

            // not in a module package but may be in module defined to this loader
            try {
                List<URL> urls = findMiscResource(name);
                if (!urls.isEmpty()) {
                    URL url = urls.get(0);
                    if (url != null) {
                        return checkURL(url); // check access before returning
                    }
                }
            } catch (IOException ioe) {
                return null;
            }

        }

        // search class path
        URL url = findResourceOnClassPath(name);
        return checkURL(url);
    }

    
Returns an enumeration of URL objects to all the resources with the
given name in modules defined to this class loader or on the class
path of this loader.
/**
     * Returns an enumeration of URL objects to all the resources with the
     * given name in modules defined to this class loader or on the class
     * path of this loader.
     */
    @Override
    public Enumeration<URL> findResources(String name) throws IOException {
        List<URL> checked = new ArrayList<>();  // list of checked URLs

        String pn = Resources.toPackageName(name);
        LoadedModule module = packageToModule.get(pn);
        if (module != null) {

            // resource is in a package of a module defined to this loader
            if (module.loader() == this) {
                URL url = findResource(module.name(), name); // checks URL
                if (url != null
                    && (name.endsWith(".class")
                        || url.toString().endsWith("/")
                        || isOpen(module.mref(), pn))) {
                    checked.add(url);
                }
            }

        } else {
            // not in a package of a module defined to this loader
            for (URL url : findMiscResource(name)) {
                url = checkURL(url);
                if (url != null) {
                    checked.add(url);
                }
            }
        }

        // class path (not checked)
        Enumeration<URL> e = findResourcesOnClassPath(name);

        // concat the checked URLs and the (not checked) class path
        return new Enumeration<>() {
            final Iterator<URL> iterator = checked.iterator();
            URL next;
            private boolean hasNext() {
                if (next != null) {
                    return true;
                } else if (iterator.hasNext()) {
                    next = iterator.next();
                    return true;
                } else {
                    // need to check each URL
                    while (e.hasMoreElements() && next == null) {
                        next = checkURL(e.nextElement());
                    }
                    return next != null;
                }
            }
            @Override
            public boolean hasMoreElements() {
                return hasNext();
            }
            @Override
            public URL nextElement() {
                if (hasNext()) {
                    URL result = next;
                    next = null;
                    return result;
                } else {
                    throw new NoSuchElementException();
                }
            }
        };

    }

    
Returns the list of URLs to a "miscellaneous" resource in modules
defined to this loader. A miscellaneous resource is not in a module
package, e.g. META-INF/services/p.S.
The cache used by this method avoids repeated searching of all modules.
/**
     * Returns the list of URLs to a "miscellaneous" resource in modules
     * defined to this loader. A miscellaneous resource is not in a module
     * package, e.g. META-INF/services/p.S.
     *
     * The cache used by this method avoids repeated searching of all modules.
     */
    private List<URL> findMiscResource(String name) throws IOException {
        SoftReference<Map<String, List<URL>>> ref = this.resourceCache;
        Map<String, List<URL>> map = (ref != null) ? ref.get() : null;
        if (map == null) {
            map = new ConcurrentHashMap<>();
            this.resourceCache = new SoftReference<>(map);
        } else {
            List<URL> urls = map.get(name);
            if (urls != null)
                return urls;
        }

        // search all modules for the resource
        List<URL> urls;
        try {
            urls = AccessController.doPrivileged(
                new PrivilegedExceptionAction<>() {
                    @Override
                    public List<URL> run() throws IOException {
                        List<URL> result = null;
                        for (ModuleReference mref : nameToModule.values()) {
                            URI u = moduleReaderFor(mref).find(name).orElse(null);
                            if (u != null) {
                                try {
                                    if (result == null)
                                        result = new ArrayList<>();
                                    result.add(u.toURL());
                                } catch (MalformedURLException |
                                         IllegalArgumentException e) {
                                }
                            }
                        }
                        return (result != null) ? result : Collections.emptyList();
                    }
                });
        } catch (PrivilegedActionException pae) {
            throw (IOException) pae.getCause();
        }

        // only cache resources after VM is fully initialized
        if (VM.isModuleSystemInited()) {
            map.putIfAbsent(name, urls);
        }

        return urls;
    }

    
Returns the URL to a resource in a module or null if not found. /**
     * Returns the URL to a resource in a module or {@code null} if not found.
     */
    private URL findResource(ModuleReference mref, String name) throws IOException {
        URI u;
        if (System.getSecurityManager() == null) {
            u = moduleReaderFor(mref).find(name).orElse(null);
        } else {
            try {
                u = AccessController.doPrivileged(new PrivilegedExceptionAction<> () {
                    @Override
                    public URI run() throws IOException {
                        return moduleReaderFor(mref).find(name).orElse(null);
                    }
                });
            } catch (PrivilegedActionException pae) {
                throw (IOException) pae.getCause();
            }
        }
        if (u != null) {
            try {
                return u.toURL();
            } catch (MalformedURLException | IllegalArgumentException e) { }
        }
        return null;
    }

    
Returns the URL to a resource in a module. Returns null if not found or an I/O error occurs. /**
     * Returns the URL to a resource in a module. Returns {@code null} if not found
     * or an I/O error occurs.
     */
    private URL findResourceOrNull(ModuleReference mref, String name) {
        try {
            return findResource(mref, name);
        } catch (IOException ignore) {
            return null;
        }
    }

    
Returns a URL to a resource on the class path.
/**
     * Returns a URL to a resource on the class path.
     */
    private URL findResourceOnClassPath(String name) {
        if (hasClassPath()) {
            if (System.getSecurityManager() == null) {
                return ucp.findResource(name, false);
            } else {
                PrivilegedAction<URL> pa = () -> ucp.findResource(name, false);
                return AccessController.doPrivileged(pa);
            }
        } else {
            // no class path
            return null;
        }
    }

    
Returns the URLs of all resources of the given name on the class path.
/**
     * Returns the URLs of all resources of the given name on the class path.
     */
    private Enumeration<URL> findResourcesOnClassPath(String name) {
        if (hasClassPath()) {
            if (System.getSecurityManager() == null) {
                return ucp.findResources(name, false);
            } else {
                PrivilegedAction<Enumeration<URL>> pa;
                pa = () -> ucp.findResources(name, false);
                return AccessController.doPrivileged(pa);
            }
        } else {
            // no class path
            return Collections.emptyEnumeration();
        }
    }

    // -- finding/loading classes

    
Finds the class with the specified binary name.
/**
     * Finds the class with the specified binary name.
     */
    @Override
    protected Class<?> findClass(String cn) throws ClassNotFoundException {
        // no class loading until VM is fully initialized
        if (!VM.isModuleSystemInited())
            throw new ClassNotFoundException(cn);

        // find the candidate module for this class
        LoadedModule loadedModule = findLoadedModule(cn);

        Class<?> c = null;
        if (loadedModule != null) {

            // attempt to load class in module defined to this loader
            if (loadedModule.loader() == this) {
                c = findClassInModuleOrNull(loadedModule, cn);
            }

        } else {

            // search class path
            if (hasClassPath()) {
                c = findClassOnClassPathOrNull(cn);
            }

        }

        // not found
        if (c == null)
            throw new ClassNotFoundException(cn);

        return c;
    }

    
Finds the class with the specified binary name in a module. This method returns null if the class cannot be found or not defined in the specified module. /**
     * Finds the class with the specified binary name in a module.
     * This method returns {@code null} if the class cannot be found
     * or not defined in the specified module.
     */
    @Override
    protected Class<?> findClass(String mn, String cn) {
        if (mn != null) {
            // find the candidate module for this class
            LoadedModule loadedModule = findLoadedModule(mn, cn);
            if (loadedModule == null) {
                return null;
            }

            // attempt to load class in module defined to this loader
            assert loadedModule.loader() == this;
            return findClassInModuleOrNull(loadedModule, cn);
        }

        // search class path
        if (hasClassPath()) {
            return findClassOnClassPathOrNull(cn);
        }

        return null;
    }

    
Loads the class with the specified binary name.
/**
     * Loads the class with the specified binary name.
     */
    @Override
    protected Class<?> loadClass(String cn, boolean resolve)
        throws ClassNotFoundException
    {
        Class<?> c = loadClassOrNull(cn, resolve);
        if (c == null)
            throw new ClassNotFoundException(cn);
        return c;
    }

    
A variation of loadCass to load a class with the specified binary name. This method returns null when the class is not found. /**
     * A variation of {@code loadCass} to load a class with the specified
     * binary name. This method returns {@code null} when the class is not
     * found.
     */
    protected Class<?> loadClassOrNull(String cn, boolean resolve) {
        synchronized (getClassLoadingLock(cn)) {
            // check if already loaded
            Class<?> c = findLoadedClass(cn);

            if (c == null) {

                // find the candidate module for this class
                LoadedModule loadedModule = findLoadedModule(cn);
                if (loadedModule != null) {

                    // package is in a module
                    BuiltinClassLoader loader = loadedModule.loader();
                    if (loader == this) {
                        if (VM.isModuleSystemInited()) {
                            c = findClassInModuleOrNull(loadedModule, cn);
                        }
                    } else {
                        // delegate to the other loader
                        c = loader.loadClassOrNull(cn);
                    }

                } else {

                    // check parent
                    if (parent != null) {
                        c = parent.loadClassOrNull(cn);
                    }

                    // check class path
                    if (c == null && hasClassPath() && VM.isModuleSystemInited()) {
                        c = findClassOnClassPathOrNull(cn);
                    }
                }

            }

            if (resolve && c != null)
                resolveClass(c);

            return c;
        }
    }

    
A variation of loadCass to load a class with the specified binary name. This method returns null when the class is not found. /**
     * A variation of {@code loadCass} to load a class with the specified
     * binary name. This method returns {@code null} when the class is not
     * found.
     */
    protected  Class<?> loadClassOrNull(String cn) {
        return loadClassOrNull(cn, false);
    }

    
Find the candidate loaded module for the given class name. Returns null if none of the modules defined to this class loader contain the API package for the class. /**
     * Find the candidate loaded module for the given class name.
     * Returns {@code null} if none of the modules defined to this
     * class loader contain the API package for the class.
     */
    private LoadedModule findLoadedModule(String cn) {
        int pos = cn.lastIndexOf('.');
        if (pos < 0)
            return null; // unnamed package

        String pn = cn.substring(0, pos);
        return packageToModule.get(pn);
    }

    
Find the candidate loaded module for the given class name in the named module. Returns null if the named module is not defined to this class loader or does not contain the API package for the class. /**
     * Find the candidate loaded module for the given class name
     * in the named module.  Returns {@code null} if the named module
     * is not defined to this class loader or does not contain
     * the API package for the class.
     */
    private LoadedModule findLoadedModule(String mn, String cn) {
        LoadedModule loadedModule = findLoadedModule(cn);
        if (loadedModule != null && mn.equals(loadedModule.name())) {
            return loadedModule;
        } else {
            return null;
        }
    }

    
Finds the class with the specified binary name if in a module
defined to this ClassLoader.
Returns:
the resulting Class or null if not found/**
     * Finds the class with the specified binary name if in a module
     * defined to this ClassLoader.
     *
     * @return the resulting Class or {@code null} if not found
     */
    private Class<?> findClassInModuleOrNull(LoadedModule loadedModule, String cn) {
        if (System.getSecurityManager() == null) {
            return defineClass(cn, loadedModule);
        } else {
            PrivilegedAction<Class<?>> pa = () -> defineClass(cn, loadedModule);
            return AccessController.doPrivileged(pa);
        }
    }

    
Finds the class with the specified binary name on the class path.
Returns:
the resulting Class or null if not found/**
     * Finds the class with the specified binary name on the class path.
     *
     * @return the resulting Class or {@code null} if not found
     */
    private Class<?> findClassOnClassPathOrNull(String cn) {
        String path = cn.replace('.', '/').concat(".class");
        if (System.getSecurityManager() == null) {
            Resource res = ucp.getResource(path, false);
            if (res != null) {
                try {
                    return defineClass(cn, res);
                } catch (IOException ioe) {
                    // TBD on how I/O errors should be propagated
                }
            }
            return null;
        } else {
            // avoid use of lambda here
            PrivilegedAction<Class<?>> pa = new PrivilegedAction<>() {
                public Class<?> run() {
                    Resource res = ucp.getResource(path, false);
                    if (res != null) {
                        try {
                            return defineClass(cn, res);
                        } catch (IOException ioe) {
                            // TBD on how I/O errors should be propagated
                        }
                    }
                    return null;
                }
            };
            return AccessController.doPrivileged(pa);
        }
    }

    
Defines the given binary class name to the VM, loading the class
bytes from the given module.
Returns:
the resulting Class or null if an I/O error occurs/**
     * Defines the given binary class name to the VM, loading the class
     * bytes from the given module.
     *
     * @return the resulting Class or {@code null} if an I/O error occurs
     */
    private Class<?> defineClass(String cn, LoadedModule loadedModule) {
        ModuleReference mref = loadedModule.mref();
        ModuleReader reader = moduleReaderFor(mref);

        try {
            ByteBuffer bb = null;
            URL csURL = null;

            // locate class file, special handling for patched modules to
            // avoid locating the resource twice
            String rn = cn.replace('.', '/').concat(".class");
            if (reader instanceof PatchedModuleReader) {
                Resource r = ((PatchedModuleReader)reader).findResource(rn);
                if (r != null) {
                    bb = r.getByteBuffer();
                    csURL = r.getCodeSourceURL();
                }
            } else {
                bb = reader.read(rn).orElse(null);
                csURL = loadedModule.codeSourceURL();
            }

            if (bb == null) {
                // class not found
                return null;
            }

            CodeSource cs = new CodeSource(csURL, (CodeSigner[]) null);
            try {
                // define class to VM
                return defineClass(cn, bb, cs);

            } finally {
                reader.release(bb);
            }

        } catch (IOException ioe) {
            // TBD on how I/O errors should be propagated
            return null;
        }
    }

    
Defines the given binary class name to the VM, loading the class
bytes via the given Resource object.
Throws:
IOException – if reading the resource fails
SecurityException – if there is a sealing violation (JAR spec)
Returns:
the resulting Class/**
     * Defines the given binary class name to the VM, loading the class
     * bytes via the given Resource object.
     *
     * @return the resulting Class
     * @throws IOException if reading the resource fails
     * @throws SecurityException if there is a sealing violation (JAR spec)
     */
    private Class<?> defineClass(String cn, Resource res) throws IOException {
        URL url = res.getCodeSourceURL();

        // if class is in a named package then ensure that the package is defined
        int pos = cn.lastIndexOf('.');
        if (pos != -1) {
            String pn = cn.substring(0, pos);
            Manifest man = res.getManifest();
            defineOrCheckPackage(pn, man, url);
        }

        // defines the class to the runtime
        ByteBuffer bb = res.getByteBuffer();
        if (bb != null) {
            CodeSigner[] signers = res.getCodeSigners();
            CodeSource cs = new CodeSource(url, signers);
            return defineClass(cn, bb, cs);
        } else {
            byte[] b = res.getBytes();
            CodeSigner[] signers = res.getCodeSigners();
            CodeSource cs = new CodeSource(url, signers);
            return defineClass(cn, b, 0, b.length, cs);
        }
    }


    // -- packages

    
Defines a package in this ClassLoader. If the package is already defined
then its sealing needs to be checked if sealed by the legacy sealing
mechanism.
Throws:
SecurityException – if there is a sealing violation (JAR spec)/**
     * Defines a package in this ClassLoader. If the package is already defined
     * then its sealing needs to be checked if sealed by the legacy sealing
     * mechanism.
     *
     * @throws SecurityException if there is a sealing violation (JAR spec)
     */
    protected Package defineOrCheckPackage(String pn, Manifest man, URL url) {
        Package pkg = getAndVerifyPackage(pn, man, url);
        if (pkg == null) {
            try {
                if (man != null) {
                    pkg = definePackage(pn, man, url);
                } else {
                    pkg = definePackage(pn, null, null, null, null, null, null, null);
                }
            } catch (IllegalArgumentException iae) {
                // defined by another thread so need to re-verify
                pkg = getAndVerifyPackage(pn, man, url);
                if (pkg == null)
                    throw new InternalError("Cannot find package: " + pn);
            }
        }
        return pkg;
    }

    
Get the Package with the specified package name. If defined
then verify that it against the manifest and code source.
Throws:
SecurityException – if there is a sealing violation (JAR spec)/**
     * Get the Package with the specified package name. If defined
     * then verify that it against the manifest and code source.
     *
     * @throws SecurityException if there is a sealing violation (JAR spec)
     */
    private Package getAndVerifyPackage(String pn, Manifest man, URL url) {
        Package pkg = getDefinedPackage(pn);
        if (pkg != null) {
            if (pkg.isSealed()) {
                if (!pkg.isSealed(url)) {
                    throw new SecurityException(
                        "sealing violation: package " + pn + " is sealed");
                }
            } else {
                // can't seal package if already defined without sealing
                if ((man != null) && isSealed(pn, man)) {
                    throw new SecurityException(
                        "sealing violation: can't seal package " + pn +
                        ": already defined");
                }
            }
        }
        return pkg;
    }

    
Defines a new package in this ClassLoader. The attributes in the specified
Manifest are use to get the package version and sealing information.
Throws:
IllegalArgumentException – if the package name duplicates an
existing package either in this class loader or one of its ancestors/**
     * Defines a new package in this ClassLoader. The attributes in the specified
     * Manifest are use to get the package version and sealing information.
     *
     * @throws IllegalArgumentException if the package name duplicates an
     * existing package either in this class loader or one of its ancestors
     */
    private Package definePackage(String pn, Manifest man, URL url) {
        String specTitle = null;
        String specVersion = null;
        String specVendor = null;
        String implTitle = null;
        String implVersion = null;
        String implVendor = null;
        String sealed = null;
        URL sealBase = null;

        if (man != null) {
            Attributes attr = man.getAttributes(pn.replace('.', '/').concat("/"));
            if (attr != null) {
                specTitle = attr.getValue(Attributes.Name.SPECIFICATION_TITLE);
                specVersion = attr.getValue(Attributes.Name.SPECIFICATION_VERSION);
                specVendor = attr.getValue(Attributes.Name.SPECIFICATION_VENDOR);
                implTitle = attr.getValue(Attributes.Name.IMPLEMENTATION_TITLE);
                implVersion = attr.getValue(Attributes.Name.IMPLEMENTATION_VERSION);
                implVendor = attr.getValue(Attributes.Name.IMPLEMENTATION_VENDOR);
                sealed = attr.getValue(Attributes.Name.SEALED);
            }

            attr = man.getMainAttributes();
            if (attr != null) {
                if (specTitle == null)
                    specTitle = attr.getValue(Attributes.Name.SPECIFICATION_TITLE);
                if (specVersion == null)
                    specVersion = attr.getValue(Attributes.Name.SPECIFICATION_VERSION);
                if (specVendor == null)
                    specVendor = attr.getValue(Attributes.Name.SPECIFICATION_VENDOR);
                if (implTitle == null)
                    implTitle = attr.getValue(Attributes.Name.IMPLEMENTATION_TITLE);
                if (implVersion == null)
                    implVersion = attr.getValue(Attributes.Name.IMPLEMENTATION_VERSION);
                if (implVendor == null)
                    implVendor = attr.getValue(Attributes.Name.IMPLEMENTATION_VENDOR);
                if (sealed == null)
                    sealed = attr.getValue(Attributes.Name.SEALED);
            }

            // package is sealed
            if ("true".equalsIgnoreCase(sealed))
                sealBase = url;
        }
        return definePackage(pn,
                specTitle,
                specVersion,
                specVendor,
                implTitle,
                implVersion,
                implVendor,
                sealBase);
    }

    
Returns true if the specified package name is sealed according to the given manifest. /**
     * Returns {@code true} if the specified package name is sealed according to
     * the given manifest.
     */
    private boolean isSealed(String pn, Manifest man) {
        String path = pn.replace('.', '/').concat("/");
        Attributes attr = man.getAttributes(path);
        String sealed = null;
        if (attr != null)
            sealed = attr.getValue(Attributes.Name.SEALED);
        if (sealed == null && (attr = man.getMainAttributes()) != null)
            sealed = attr.getValue(Attributes.Name.SEALED);
        return "true".equalsIgnoreCase(sealed);
    }

    // -- permissions

    
Returns the permissions for the given CodeSource.
/**
     * Returns the permissions for the given CodeSource.
     */
    @Override
    protected PermissionCollection getPermissions(CodeSource cs) {
        PermissionCollection perms = super.getPermissions(cs);

        // add the permission to access the resource
        URL url = cs.getLocation();
        if (url == null)
            return perms;
        Permission p = null;
        try {
            p = url.openConnection().getPermission();
            if (p != null) {
                // for directories then need recursive access
                if (p instanceof FilePermission) {
                    String path = p.getName();
                    if (path.endsWith(File.separator)) {
                        path += "-";
                        p = new FilePermission(path, "read");
                    }
                }
                perms.add(p);
            }
        } catch (IOException ioe) { }

        return perms;
    }


    // -- miscellaneous supporting methods

    
Returns the ModuleReader for the given module.
/**
     * Returns the ModuleReader for the given module.
     */
    private ModuleReader moduleReaderFor(ModuleReference mref) {
        return moduleToReader.computeIfAbsent(mref, BuiltinClassLoader::createModuleReader);
    }

    
Creates a ModuleReader for the given module.
/**
     * Creates a ModuleReader for the given module.
     */
    private static ModuleReader createModuleReader(ModuleReference mref) {
        try {
            return mref.open();
        } catch (IOException e) {
            // Return a null module reader to avoid a future class load
            // attempting to open the module again.
            return new NullModuleReader();
        }
    }

    
A ModuleReader that doesn't read any resources.
/**
     * A ModuleReader that doesn't read any resources.
     */
    private static class NullModuleReader implements ModuleReader {
        @Override
        public Optional<URI> find(String name) {
            return Optional.empty();
        }
        @Override
        public Stream<String> list() {
            return Stream.empty();
        }
        @Override
        public void close() {
            throw new InternalError("Should not get here");
        }
    };

    
Returns true if the given module opens the given package
unconditionally.
Implementation Note:
This method currently iterates over each of the open
packages. This will be replaced once the ModuleDescriptor.Opens
API is updated./**
     * Returns true if the given module opens the given package
     * unconditionally.
     *
     * @implNote This method currently iterates over each of the open
     * packages. This will be replaced once the ModuleDescriptor.Opens
     * API is updated.
     */
    private boolean isOpen(ModuleReference mref, String pn) {
        ModuleDescriptor descriptor = mref.descriptor();
        if (descriptor.isOpen() || descriptor.isAutomatic())
            return true;
        for (ModuleDescriptor.Opens opens : descriptor.opens()) {
            String source = opens.source();
            if (!opens.isQualified() && source.equals(pn)) {
                return true;
            }
        }
        return false;
    }

    
Checks access to the given URL. We use URLClassPath for consistent
checking with java.net.URLClassLoader.
/**
     * Checks access to the given URL. We use URLClassPath for consistent
     * checking with java.net.URLClassLoader.
     */
    private static URL checkURL(URL url) {
        return URLClassPath.checkURL(url);
    }
}