xref: /openjdk9/nashorn/src/jdk.dynalink/share/classes/jdk/dynalink/linker/support/DefaultInternalObjectFilter.java

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/*
 * This file is available under and governed by the GNU General Public
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 * However, the following notice accompanied the original version of this
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/*
   Copyright 2009-2015 Attila Szegedi

   Licensed under both the Apache License, Version 2.0 (the "Apache License")
   and the BSD License (the "BSD License"), with licensee being free to
   choose either of the two at their discretion.

   You may not use this file except in compliance with either the Apache
   License or the BSD License.

   If you choose to use this file in compliance with the Apache License, the
   following notice applies to you:

       You may obtain a copy of the Apache 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.

   If you choose to use this file in compliance with the BSD License, the
   following notice applies to you:

       Redistribution and use in source and binary forms, with or without
       modification, are permitted provided that the following conditions are
       met:
       * Redistributions of source code must retain the above copyright
         notice, this list of conditions and the following disclaimer.
       * Redistributions in binary form must reproduce the above copyright
         notice, this list of conditions and the following disclaimer in the
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       * Neither the name of the copyright holder nor the names of
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         this software without specific prior written permission.

       THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
       IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
       TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
       PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL COPYRIGHT HOLDER
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package jdk.dynalink.linker.support;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import jdk.dynalink.DynamicLinkerFactory;
import jdk.dynalink.linker.MethodHandleTransformer;

/**
 * Default implementation for a
 * {@link DynamicLinkerFactory#setInternalObjectsFilter(MethodHandleTransformer)}
 * that delegates to a pair of filtering method handles. It takes a method
 * handle of {@code Object(Object)} type for filtering parameter values and
 * another one of the same type for filtering return values. It applies them as
 * parameter and return value filters on method handles passed to its
 * {@link #transform(MethodHandle)} method, on those parameters and return values
 * that are declared to have type {@link Object}. Also handles
 * {@link MethodHandle#isVarargsCollector() method handles that support variable
 * arity calls} with a last {@code Object[]} parameter. You can broadly think of
 * the parameter filter as being a wrapping method for exposing internal runtime
 * objects wrapped into an adapter with some public interface, and the return
 * value filter as being its inverse unwrapping method.
 */
public class DefaultInternalObjectFilter implements MethodHandleTransformer {
    private static final MethodHandle FILTER_VARARGS = new Lookup(MethodHandles.lookup()).findStatic(
            DefaultInternalObjectFilter.class, "filterVarArgs", MethodType.methodType(Object[].class, MethodHandle.class, Object[].class));

    private final MethodHandle parameterFilter;
    private final MethodHandle returnFilter;
    private final MethodHandle varArgFilter;

    /**
     * Creates a new filter.
     * @param parameterFilter the filter for method parameters. Must be of type
     * {@code Object(Object)}, or {@code null}.
     * @param returnFilter the filter for return values. Must be of type
     * {@code Object(Object)}, or {@code null}.
     * @throws IllegalArgumentException if one or both filters are not of the
     * expected type.
     */
    public DefaultInternalObjectFilter(final MethodHandle parameterFilter, final MethodHandle returnFilter) {
        this.parameterFilter = checkHandle(parameterFilter, "parameterFilter");
        this.returnFilter = checkHandle(returnFilter, "returnFilter");
        this.varArgFilter = parameterFilter == null ? null : FILTER_VARARGS.bindTo(parameterFilter);
    }

    @Override
    public MethodHandle transform(final MethodHandle target) {
        assert target != null;
        MethodHandle[] filters = null;
        final MethodType type = target.type();
        final boolean isVarArg = target.isVarargsCollector();
        final int paramCount = type.parameterCount();
        final MethodHandle paramsFiltered;
        // Filter parameters
        if (parameterFilter != null) {
            int firstFilter = -1;
            // Ignore receiver, start from argument 1
            for(int i = 1; i < paramCount; ++i) {
                final Class<?> paramType = type.parameterType(i);
                final boolean filterVarArg = isVarArg && i == paramCount - 1 && paramType == Object[].class;
                if (filterVarArg || paramType == Object.class) {
                    if (filters == null) {
                        firstFilter = i;
                        filters = new MethodHandle[paramCount - firstFilter];
                    }
                    filters[i - firstFilter] = filterVarArg ? varArgFilter : parameterFilter;
                }
            }
            paramsFiltered = filters != null ? MethodHandles.filterArguments(target, firstFilter, filters) : target;
        } else {
            paramsFiltered = target;
        }
        // Filter return value if needed
        final MethodHandle returnFiltered = returnFilter != null && type.returnType() == Object.class ? MethodHandles.filterReturnValue(paramsFiltered, returnFilter) : paramsFiltered;
        // Preserve varargs collector state
        return isVarArg && !returnFiltered.isVarargsCollector() ? returnFiltered.asVarargsCollector(type.parameterType(paramCount - 1)) : returnFiltered;

    }

    private static MethodHandle checkHandle(final MethodHandle handle, final String handleKind) {
        if (handle != null) {
            final MethodType objectObjectType = MethodType.methodType(Object.class, Object.class);
            if (!handle.type().equals(objectObjectType)) {
                throw new IllegalArgumentException("Method type for " + handleKind + " must be " + objectObjectType);
            }
        }
        return handle;
    }

    @SuppressWarnings("unused")
    private static Object[] filterVarArgs(final MethodHandle parameterFilter, final Object[] args) throws Throwable {
        Object[] newArgs = null;
        for(int i = 0; i < args.length; ++i) {
            final Object arg = args[i];
            final Object newArg = parameterFilter.invokeExact(arg);
            if (arg != newArg) {
                if (newArgs == null) {
                    newArgs = args.clone();
                }
                newArgs[i] = newArg;
            }
        }
        return newArgs == null ? args : newArgs;
    }
}