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diff --git a/dalvik/src/main/java/dalvik/system/DexFile.java b/dalvik/src/main/java/dalvik/system/DexFile.java
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+++ b/dalvik/src/main/java/dalvik/system/DexFile.java
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+/*
+ * 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.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.Enumeration;
+import libcore.io.ErrnoException;
+import libcore.io.Libcore;
+import libcore.io.StructStat;
+
+/**
+ * Manipulates DEX files. The class is similar in principle to
+ * {@link java.util.zip.ZipFile}. It is used primarily by class loaders.
+ * <p>
+ * Note we don't directly open and read the DEX file here. They're memory-mapped
+ * read-only by the VM.
+ */
+public final class DexFile {
+    private int mCookie;
+    private final String mFileName;
+    private final CloseGuard guard = CloseGuard.get();
+
+    /**
+     * Opens a DEX file from a given File object. This will usually be a ZIP/JAR
+     * file with a "classes.dex" inside.
+     *
+     * The VM will generate the name of the corresponding file in
+     * /data/dalvik-cache and open it, possibly creating or updating
+     * it first if system permissions allow.  Don't pass in the name of
+     * a file in /data/dalvik-cache, as the named file is expected to be
+     * in its original (pre-dexopt) state.
+     *
+     * @param file
+     *            the File object referencing the actual DEX file
+     *
+     * @throws IOException
+     *             if an I/O error occurs, such as the file not being found or
+     *             access rights missing for opening it
+     */
+    public DexFile(File file) throws IOException {
+        this(file.getPath());
+    }
+
+    /**
+     * Opens a DEX file from a given filename. This will usually be a ZIP/JAR
+     * file with a "classes.dex" inside.
+     *
+     * The VM will generate the name of the corresponding file in
+     * /data/dalvik-cache and open it, possibly creating or updating
+     * it first if system permissions allow.  Don't pass in the name of
+     * a file in /data/dalvik-cache, as the named file is expected to be
+     * in its original (pre-dexopt) state.
+     *
+     * @param fileName
+     *            the filename of the DEX file
+     *
+     * @throws IOException
+     *             if an I/O error occurs, such as the file not being found or
+     *             access rights missing for opening it
+     */
+    public DexFile(String fileName) throws IOException {
+        mCookie = openDexFile(fileName, null, 0);
+        mFileName = fileName;
+        guard.open("close");
+        //System.out.println("DEX FILE cookie is " + mCookie);
+    }
+
+    /**
+     * Opens a DEX file from a given filename, using a specified file
+     * to hold the optimized data.
+     *
+     * @param sourceName
+     *  Jar or APK file with "classes.dex".
+     * @param outputName
+     *  File that will hold the optimized form of the DEX data.
+     * @param flags
+     *  Enable optional features.
+     */
+    private DexFile(String sourceName, String outputName, int flags) throws IOException {
+        if (outputName != null) {
+            try {
+                String parent = new File(outputName).getParent();
+                if (Libcore.os.getuid() != Libcore.os.stat(parent).st_uid) {
+                    throw new IllegalArgumentException("Optimized data directory " + parent
+                            + " is not owned by the current user. Shared storage cannot protect"
+                            + " your application from code injection attacks.");
+                }
+            } catch (ErrnoException ignored) {
+                // assume we'll fail with a more contextual error later
+            }
+        }
+
+        mCookie = openDexFile(sourceName, outputName, flags);
+        mFileName = sourceName;
+        guard.open("close");
+        //System.out.println("DEX FILE cookie is " + mCookie);
+    }
+
+    /**
+     * Open a DEX file, specifying the file in which the optimized DEX
+     * data should be written.  If the optimized form exists and appears
+     * to be current, it will be used; if not, the VM will attempt to
+     * regenerate it.
+     *
+     * This is intended for use by applications that wish to download
+     * and execute DEX files outside the usual application installation
+     * mechanism.  This function should not be called directly by an
+     * application; instead, use a class loader such as
+     * dalvik.system.DexClassLoader.
+     *
+     * @param sourcePathName
+     *  Jar or APK file with "classes.dex".  (May expand this to include
+     *  "raw DEX" in the future.)
+     * @param outputPathName
+     *  File that will hold the optimized form of the DEX data.
+     * @param flags
+     *  Enable optional features.  (Currently none defined.)
+     * @return
+     *  A new or previously-opened DexFile.
+     * @throws IOException
+     *  If unable to open the source or output file.
+     */
+    static public DexFile loadDex(String sourcePathName, String outputPathName,
+        int flags) throws IOException {
+
+        /*
+         * TODO: we may want to cache previously-opened DexFile objects.
+         * The cache would be synchronized with close().  This would help
+         * us avoid mapping the same DEX more than once when an app
+         * decided to open it multiple times.  In practice this may not
+         * be a real issue.
+         */
+        return new DexFile(sourcePathName, outputPathName, flags);
+    }
+
+    /**
+     * Gets the name of the (already opened) DEX file.
+     *
+     * @return the file name
+     */
+    public String getName() {
+        return mFileName;
+    }
+
+    /**
+     * Closes the DEX file.
+     * <p>
+     * This may not be able to release any resources. If classes from this
+     * DEX file are still resident, the DEX file can't be unmapped.
+     *
+     * @throws IOException
+     *             if an I/O error occurs during closing the file, which
+     *             normally should not happen
+     */
+    public void close() throws IOException {
+        guard.close();
+        closeDexFile(mCookie);
+        mCookie = 0;
+    }
+
+    /**
+     * Loads a class. Returns the class on success, or a {@code null} reference
+     * on failure.
+     * <p>
+     * If you are not calling this from a class loader, this is most likely not
+     * going to do what you want. Use {@link Class#forName(String)} instead.
+     * <p>
+     * The method does not throw {@link ClassNotFoundException} if the class
+     * isn't found because it isn't reasonable to throw exceptions wildly every
+     * time a class is not found in the first DEX file we look at.
+     *
+     * @param name
+     *            the class name, which should look like "java/lang/String"
+     *
+     * @param loader
+     *            the class loader that tries to load the class (in most cases
+     *            the caller of the method
+     *
+     * @return the {@link Class} object representing the class, or {@code null}
+     *         if the class cannot be loaded
+     */
+    public Class loadClass(String name, ClassLoader loader) {
+        String slashName = name.replace('.', '/');
+        return loadClassBinaryName(slashName, loader);
+    }
+
+    /**
+     * See {@link #loadClass(String, ClassLoader)}.
+     *
+     * This takes a "binary" class name to better match ClassLoader semantics.
+     *
+     * @hide
+     */
+    public Class loadClassBinaryName(String name, ClassLoader loader) {
+        return defineClass(name, loader, mCookie);
+    }
+
+    private native static Class defineClass(String name, ClassLoader loader, int cookie);
+
+    /**
+     * Enumerate the names of the classes in this DEX file.
+     *
+     * @return an enumeration of names of classes contained in the DEX file, in
+     *         the usual internal form (like "java/lang/String").
+     */
+    public Enumeration<String> entries() {
+        return new DFEnum(this);
+    }
+
+    /*
+     * Helper class.
+     */
+    private class DFEnum implements Enumeration<String> {
+        private int mIndex;
+        private String[] mNameList;
+
+        DFEnum(DexFile df) {
+            mIndex = 0;
+            mNameList = getClassNameList(mCookie);
+        }
+
+        public boolean hasMoreElements() {
+            return (mIndex < mNameList.length);
+        }
+
+        public String nextElement() {
+            return mNameList[mIndex++];
+        }
+    }
+
+    /* return a String array with class names */
+    native private static String[] getClassNameList(int cookie);
+
+    /**
+     * Called when the class is finalized. Makes sure the DEX file is closed.
+     *
+     * @throws IOException
+     *             if an I/O error occurs during closing the file, which
+     *             normally should not happen
+     */
+    @Override protected void finalize() throws Throwable {
+        try {
+            if (guard != null) {
+                guard.warnIfOpen();
+            }
+            close();
+        } finally {
+            super.finalize();
+        }
+    }
+
+    /*
+     * Open a DEX file.  The value returned is a magic VM cookie.  On
+     * failure, an IOException is thrown.
+     */
+    native private static int openDexFile(String sourceName, String outputName,
+        int flags) throws IOException;
+
+    /*
+     * Open a DEX file based on a {@code byte[]}. The value returned
+     * is a magic VM cookie. On failure, a RuntimeException is thrown.
+     */
+    native private static int openDexFile(byte[] fileContents);
+
+    /*
+     * Close DEX file.
+     */
+    native private static void closeDexFile(int cookie);
+
+    /**
+     * Returns true if the VM believes that the apk/jar file is out of date
+     * and should be passed through "dexopt" again.
+     *
+     * @param fileName the absolute path to the apk/jar file to examine.
+     * @return true if dexopt should be called on the file, false otherwise.
+     * @throws java.io.FileNotFoundException if fileName is not readable,
+     *         not a file, or not present.
+     * @throws java.io.IOException if fileName is not a valid apk/jar file or
+     *         if problems occur while parsing it.
+     * @throws java.lang.NullPointerException if fileName is null.
+     * @throws dalvik.system.StaleDexCacheError if the optimized dex file
+     *         is stale but exists on a read-only partition.
+     */
+    native public static boolean isDexOptNeeded(String fileName)
+            throws FileNotFoundException, IOException;
+}