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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.
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/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.javascript.serialize;

import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
import java.util.StringTokenizer;

import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.ScriptableObject;
import org.mozilla.javascript.UniqueTag;

/**
 * Class ScriptableOutputStream is an ObjectOutputStream used
 * to serialize JavaScript objects and functions. Note that
 * compiled functions currently cannot be serialized, only
 * interpreted functions. The top-level scope containing the
 * object is not written out, but is instead replaced with
 * another top-level object when the ScriptableInputStream
 * reads in this object. Also, object corresponding to names
 * added to the exclude list are not written out but instead
 * are looked up during deserialization. This approach avoids
 * the creation of duplicate copies of standard objects
 * during deserialization.
 *
 * @author Norris Boyd
 */

// API class

public class ScriptableOutputStream extends ObjectOutputStream {

    /**
     * ScriptableOutputStream constructor.
     * Creates a ScriptableOutputStream for use in serializing
     * JavaScript objects. Calls excludeStandardObjectNames.
     *
     * @param out the OutputStream to write to.
     * @param scope the scope containing the object.
     */
    public ScriptableOutputStream(OutputStream out, Scriptable scope)
        throws IOException
    {
        super(out);
        this.scope = scope;
        table = new HashMap();
        table.put(scope, "");
        enableReplaceObject(true);
        excludeStandardObjectNames(); // XXX
    }

    public void excludeAllIds(Object[] ids) {
        for (Object id: ids) {
            if (id instanceof String &&
                (scope.get((String) id, scope) instanceof Scriptable))
            {
                this.addExcludedName((String)id);
            }
        }
    }

    /**
     * Adds a qualified name to the list of object to be excluded from
     * serialization. Names excluded from serialization are looked up
     * in the new scope and replaced upon deserialization.
     * @param name a fully qualified name (of the form "a.b.c", where
     *             "a" must be a property of the top-level object). The object
     *             need not exist, in which case the name is ignored.
     * @throws IllegalArgumentException if the object is not a
     *         {@link Scriptable}.
     */
    public void addOptionalExcludedName(String name) {
        Object obj = lookupQualifiedName(scope, name);
        if(obj != null && obj != UniqueTag.NOT_FOUND) {
            if (!(obj instanceof Scriptable)) {
                throw new IllegalArgumentException(
                        "Object for excluded name " + name +
                        " is not a Scriptable, it is " +
                        obj.getClass().getName());
            }
            table.put(obj, name);
        }
    }

    /**
     * Adds a qualified name to the list of objects to be excluded from
     * serialization. Names excluded from serialization are looked up
     * in the new scope and replaced upon deserialization.
     * @param name a fully qualified name (of the form "a.b.c", where
     *             "a" must be a property of the top-level object)
     * @throws IllegalArgumentException if the object is not found or is not
     *         a {@link Scriptable}.
     */
    public void addExcludedName(String name) {
        Object obj = lookupQualifiedName(scope, name);
        if (!(obj instanceof Scriptable)) {
            throw new IllegalArgumentException("Object for excluded name " +
                                               name + " not found.");
        }
        table.put(obj, name);
    }

    /**
     * Returns true if the name is excluded from serialization.
     */
    public boolean hasExcludedName(String name) {
        return table.get(name) != null;
    }

    /**
     * Removes a name from the list of names to exclude.
     */
    public void removeExcludedName(String name) {
        table.remove(name);
    }

    /**
     * Adds the names of the standard objects and their
     * prototypes to the list of excluded names.
     */
    public void excludeStandardObjectNames() {
        String[] names = { "Object", "Object.prototype",
                           "Function", "Function.prototype",
                           "String", "String.prototype",
                           "Math",  // no Math.prototype
                           "Array", "Array.prototype",
                           "Error", "Error.prototype",
                           "Number", "Number.prototype",
                           "Date", "Date.prototype",
                           "RegExp", "RegExp.prototype",
                           "Script", "Script.prototype",
                           "Continuation", "Continuation.prototype",
                         };
        for (int i=0; i < names.length; i++) {
            addExcludedName(names[i]);
        }

        String[] optionalNames = {
                "XML", "XML.prototype",
                "XMLList", "XMLList.prototype",
        };
        for (int i=0; i < optionalNames.length; i++) {
            addOptionalExcludedName(optionalNames[i]);
        }
    }

    static Object lookupQualifiedName(Scriptable scope,
                                      String qualifiedName)
    {
        StringTokenizer st = new StringTokenizer(qualifiedName, ".");
        Object result = scope;
        while (st.hasMoreTokens()) {
            String s = st.nextToken();
            result = ScriptableObject.getProperty((Scriptable)result, s);
            if (result == null || !(result instanceof Scriptable))
                break;
        }
        return result;
    }

    static class PendingLookup implements Serializable
    {
        private static final long serialVersionUID = -2692990309789917727L;

        PendingLookup(String name) { this.name = name; }

        String getName() { return name; }

        private String name;
    }

    @Override
    protected Object replaceObject(Object obj) throws IOException
    {
        if (false) throw new IOException(); // suppress warning
        String name = table.get(obj);
        if (name == null)
            return obj;
        return new PendingLookup(name);
    }

    private Scriptable scope;
    private Map table;
}