dalvik/system/PathClassLoader.java

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed 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 dalvik.system;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import libcore.io.IoUtils;

/**
 * Provides a simple {@link ClassLoader} implementation that operates on a list
 * of files and directories in the local file system, but does not attempt to
 * load classes from the network. Android uses this class for its system class
 * loader and for its application class loader(s).
 */
public class PathClassLoader extends ClassLoader {

    private final String path;
    private final String libPath;

    /*
     * Parallel arrays for jar/apk files.
     *
     * (could stuff these into an object and have a single array;
     * improves clarity but adds overhead)
     */
    private final String[] mPaths;
    private final File[] mFiles;
    private final ZipFile[] mZips;
    private final DexFile[] mDexs;

    /**
     * Native library path.
     */
    private final List<String> libraryPathElements;

    /**
     * Creates a {@code PathClassLoader} that operates on a given list of files
     * and directories. This method is equivalent to calling
     * {@link #PathClassLoader(String, String, ClassLoader)} with a
     * {@code null} value for the second argument (see description there).
     *
     * @param path
     *            the list of files and directories
     *
     * @param parent
     *            the parent class loader
     */
    public PathClassLoader(String path, ClassLoader parent) {
        this(path, null, parent);
    }

    /**
     * Creates a {@code PathClassLoader} that operates on two given
     * lists of files and directories. The entries of the first list
     * should be one of the following:
     *
     * <ul>
     * <li>Directories containing classes or resources.
     * <li>JAR/ZIP/APK files, possibly containing a "classes.dex" file.
     * <li>"classes.dex" files.
     * </ul>
     *
     * The entries of the second list should be directories containing
     * native library files. Both lists are separated using the
     * character specified by the "path.separator" system property,
     * which, on Android, defaults to ":".
     *
     * @param path
     *            the list of files and directories containing classes and
     *            resources
     *
     * @param libPath
     *            the list of directories containing native libraries
     *
     * @param parent
     *            the parent class loader
     */
    public PathClassLoader(String path, String libPath, ClassLoader parent) {
        super(parent);

        if (path == null) {
            throw new NullPointerException();
        }

        this.path = path;
        this.libPath = libPath;

        mPaths = path.split(":");
        int length = mPaths.length;

        mFiles = new File[length];
        mZips = new ZipFile[length];
        mDexs = new DexFile[length];

        /* open all Zip and DEX files up front */
        for (int i = 0; i < length; i++) {
            File pathFile = new File(mPaths[i]);
            mFiles[i] = pathFile;

            if (pathFile.isFile()) {
                if (!mPaths[i].endsWith(".dex")) {
                    /*
                     * If the name doesn't end with ".dex" assume it's a zip
                     * file of some sort.
                     */
                    try {
                        mZips[i] = new ZipFile(pathFile);
                    }
                    catch (IOException ioex) {
                        // expecting IOException and ZipException
                        //System.out.println("Failed opening '" + pathFile
                        //    + "': " + ioex);
                        //ioex.printStackTrace();
                    }
                }

                /*
                 * If we got a zip file, we still need to extract out
                 * the dex file from it.
                 */
                try {
                    mDexs[i] = new DexFile(pathFile);
                }
                catch (IOException ioex) {
                    // It might be a resource-only zip.
                    //System.out.println("Failed to construct DexFile '"
                    //    + pathFile + "': " + ioex);
                }
            }
        }

        /*
         * Native libraries may exist in both the system and application library
         * paths, so we use this search order for these paths:
         *   1. This class loader's library path for application libraries
         *   2. The VM's library path from the system property for system libraries
         * This order was reversed prior to Gingerbread; see http://b/2933456
         */
        libraryPathElements = new ArrayList<String>();
        if (libPath != null) {
            for (String pathElement : libPath.split(File.pathSeparator)) {
                libraryPathElements.add(cleanupPathElement(pathElement));
            }
        }
        String systemLibraryPath = System.getProperty("java.library.path", ".");
        if (!systemLibraryPath.isEmpty()) {
            for (String pathElement : systemLibraryPath.split(File.pathSeparator)) {
                libraryPathElements.add(cleanupPathElement(pathElement));
            }
        }
    }

    /**
     * Returns a path element that includes a trailing file separator.
     */
    private String cleanupPathElement(String path) {
        return path.endsWith(File.separator) ? path : (path + File.separator);
    }

    /**
     * Finds a class. This method is called by {@code loadClass()} after the
     * parent ClassLoader has failed to find a loaded class of the same name.
     *
     * @param name
     *            The "binary name" of the class to search for, in a
     *            human-readable form like "java.lang.String" or
     *            "java.net.URLClassLoader$3$1".
     * @return the {@link Class} object representing the class
     * @throws ClassNotFoundException
     *             if the class cannot be found
     */
    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        //System.out.println("PathClassLoader " + this + ": findClass '" + name + "'");

        byte[] data = null;
        int length = mPaths.length;

        for (int i = 0; i < length; i++) {
            //System.out.println("My path is: " + mPaths[i]);

            if (mDexs[i] != null) {
                Class clazz = mDexs[i].loadClassBinaryName(name, this);
                if (clazz != null)
                    return clazz;
            } else if (mZips[i] != null) {
                String fileName = name.replace('.', '/') + ".class";
                data = loadFromArchive(mZips[i], fileName);
            } else {
                File pathFile = mFiles[i];
                if (pathFile.isDirectory()) {
                    String fileName =
                        mPaths[i] + "/" + name.replace('.', '/') + ".class";
                    data = loadFromDirectory(fileName);
                } else {
                    //System.out.println("PathClassLoader: can't find '"
                    //    + mPaths[i] + "'");
                }

            }

            /* --this doesn't work in current version of Dalvik--
            if (data != null) {
                System.out.println("--- Found class " + name
                    + " in zip[" + i + "] '" + mZips[i].getName() + "'");
                int dotIndex = name.lastIndexOf('.');
                if (dotIndex != -1) {
                    String packageName = name.substring(0, dotIndex);
                    synchronized (this) {
                        Package packageObj = getPackage(packageName);
                        if (packageObj == null) {
                            definePackage(packageName, null, null,
                                    null, null, null, null, null);
                        }
                    }
                }

                return defineClass(name, data, 0, data.length);
            }
            */
        }

        throw new ClassNotFoundException(name + " in loader " + this);
    }

    /**
     * Finds a resource. This method is called by {@code getResource()} after
     * the parent ClassLoader has failed to find a loaded resource of the same
     * name.
     *
     * @param name
     *            The name of the resource to find
     * @return the location of the resource as a URL, or {@code null} if the
     *         resource is not found.
     */
    @Override
    protected URL findResource(String name) {
        //java.util.logging.Logger.global.severe("findResource: " + name);

        int length = mPaths.length;

        for (int i = 0; i < length; i++) {
            URL result = findResource(name, i);
            if (result != null) {
                return result;
            }
        }

        return null;
    }

    /**
     * Finds an enumeration of URLs for the resource with the specified name.
     *
     * @param resName
     *            the name of the resource to find.
     * @return an enumeration of {@code URL} objects for the requested resource.
     */
    @Override
    protected Enumeration<URL> findResources(String resName) {
        int length = mPaths.length;
        ArrayList<URL> results = new ArrayList<URL>();
        for (int i = 0; i < length; i++) {
            URL result = findResource(resName, i);
            if (result != null) {
                results.add(result);
            }
        }
        return Collections.enumeration(results);
    }

    private URL findResource(String name, int i) {
        File pathFile = mFiles[i];
        ZipFile zip = mZips[i];
        if (zip != null) {
            if (isInArchive(zip, name)) {
                //System.out.println("  found " + name + " in " + pathFile);
                try {
                    // File.toURL() is compliant with RFC 1738 in always
                    // creating absolute path names. If we construct the
                    // URL by concatenating strings, we might end up with
                    // illegal URLs for relative names.
                    return new URL("jar:" + pathFile.toURL() + "!/" + name);
                }
                catch (MalformedURLException e) {
                    throw new RuntimeException(e);
                }
            }
        } else if (pathFile.isDirectory()) {
            File dataFile = new File(mPaths[i] + "/" + name);
            if (dataFile.exists()) {
                //System.out.println("  found resource " + name);
                try {
                    // Same as archive case regarding URL construction.
                    return dataFile.toURL();
                }
                catch (MalformedURLException e) {
                    throw new RuntimeException(e);
                }
            }
        } else if (pathFile.isFile()) {
        } else {
            System.err.println("PathClassLoader: can't find '"
                + mPaths[i] + "'");
        }
        return null;
    }

    /*
     * Load the contents of a file from a file in a directory.
     *
     * Returns null if the class wasn't found.
     */
    private byte[] loadFromDirectory(String path) {
        try {
            return IoUtils.readFileAsByteArray(path);
        } catch (IOException ex) {
            System.err.println("Error reading from " + path);
            // swallow it, return null instead
            return null;
        }
    }

    /*
     * Load a class from a file in an archive.  We currently assume that
     * the file is a Zip archive.
     *
     * Returns null if the class wasn't found.
     */
    private byte[] loadFromArchive(ZipFile zip, String name) {
        ZipEntry entry;

        entry = zip.getEntry(name);
        if (entry == null)
            return null;

        ByteArrayOutputStream byteStream;
        InputStream stream;
        int count;

        /*
         * Copy the data out of the stream.  Because we got the ZipEntry
         * from a ZipFile, the uncompressed size is known, and we can set
         * the initial size of the ByteArrayOutputStream appropriately.
         */
        try {
            stream = zip.getInputStream(entry);
            byteStream = new ByteArrayOutputStream((int) entry.getSize());
            byte[] buf = new byte[4096];
            while ((count = stream.read(buf)) > 0)
                byteStream.write(buf, 0, count);

            stream.close();
        }
        catch (IOException ioex) {
            //System.out.println("Failed extracting '" + archive + "': " +ioex);
            return null;
        }

        //System.out.println("  loaded from Zip");
        return byteStream.toByteArray();
    }

    /*
     * Figure out if "name" is a member of "archive".
     */
    private boolean isInArchive(ZipFile zip, String name) {
        return zip.getEntry(name) != null;
    }

    /**
     * Finds a native library. This class loader first searches its own library
     * path (as specified in the constructor) and then the system library path.
     * In Android 2.2 and earlier, the search order was reversed.
     *
     * @param libname
     *            The name of the library to find
     * @return the complete path of the library, or {@code null} if the library
     *         is not found.
     */
    public String findLibrary(String libname) {
        String fileName = System.mapLibraryName(libname);
        for (String pathElement : libraryPathElements) {
            String pathName = pathElement + fileName;
            File test = new File(pathName);

            if (test.exists()) {
                return pathName;
            }
        }

        return null;
    }

    /**
     * Returns package information for the given package. Unfortunately, the
     * PathClassLoader doesn't really have this information, and as a non-secure
     * ClassLoader, it isn't even required to, according to the spec. Yet, we
     * want to provide it, in order to make all those hopeful callers of
     * <code>myClass.getPackage().getName()</code> happy. Thus we construct a
     * Package object the first time it is being requested and fill most of the
     * fields with dummy values. The Package object is then put into the
     * ClassLoader's Package cache, so we see the same one next time. We don't
     * create Package objects for null arguments or for the default package.
     * <p>
     * There a limited chance that we end up with multiple Package objects
     * representing the same package: It can happen when when a package is
     * scattered across different JAR files being loaded by different
     * ClassLoaders. Rather unlikely, and given that this whole thing is more or
     * less a workaround, probably not worth the effort.
     *
     * @param name
     *            the name of the class
     * @return the package information for the class, or {@code null} if there
     *         is not package information available for it
     */
    @Override
    protected Package getPackage(String name) {
        if (name != null && !name.isEmpty()) {
            synchronized(this) {
                Package pack = super.getPackage(name);

                if (pack == null) {
                    pack = definePackage(name, "Unknown", "0.0", "Unknown", "Unknown", "0.0", "Unknown", null);
                }

                return pack;
            }
        }
        return null;
    }

    public String toString () {
        return getClass().getName() + "[" + path + "]";
    }
}