// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// 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 documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package com.google.protobuf;

import java.lang.reflect.Field;
import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.security.AccessController;
import java.security.PrivilegedExceptionAction;
import java.util.logging.Level;
import java.util.logging.Logger;

/** Utility class for working with unsafe operations. */
final class UnsafeUtil {
  private static final Logger logger = Logger.getLogger(UnsafeUtil.class.getName());
  private static final sun.misc.Unsafe UNSAFE = getUnsafe();
  private static final MemoryAccessor MEMORY_ACCESSOR = getMemoryAccessor();
  private static final boolean HAS_UNSAFE_BYTEBUFFER_OPERATIONS =
      supportsUnsafeByteBufferOperations();
  private static final boolean HAS_UNSAFE_ARRAY_OPERATIONS = supportsUnsafeArrayOperations();
  private static final boolean HAS_UNSAFE_COPY_MEMORY = supportsUnsafeCopyMemory();
  private static final long ARRAY_BASE_OFFSET = byteArrayBaseOffset();
  private static final long BUFFER_ADDRESS_OFFSET = fieldOffset(bufferAddressField());

  private UnsafeUtil() {}

  static boolean hasUnsafeArrayOperations() {
    return HAS_UNSAFE_ARRAY_OPERATIONS;
  }

  static boolean hasUnsafeCopyMemory() {
    return HAS_UNSAFE_COPY_MEMORY;
  }

  static boolean hasUnsafeByteBufferOperations() {
    return HAS_UNSAFE_BYTEBUFFER_OPERATIONS;
  }

  static long objectFieldOffset(Field field) {
    return MEMORY_ACCESSOR.objectFieldOffset(field);
  }

  static long getArrayBaseOffset() {
    return ARRAY_BASE_OFFSET;
  }

  static byte getByte(Object target, long offset) {
    return MEMORY_ACCESSOR.getByte(target, offset);
  }

  static void putByte(Object target, long offset, byte value) {
    MEMORY_ACCESSOR.putByte(target, offset, value);
  }

  static int getInt(Object target, long offset) {
    return MEMORY_ACCESSOR.getInt(target, offset);
  }

  static void putInt(Object target, long offset, int value) {
    MEMORY_ACCESSOR.putInt(target, offset, value);
  }

  static long getLong(Object target, long offset) {
    return MEMORY_ACCESSOR.getLong(target, offset);
  }

  static void putLong(Object target, long offset, long value) {
    MEMORY_ACCESSOR.putLong(target, offset, value);
  }

  static boolean getBoolean(Object target, long offset) {
    return MEMORY_ACCESSOR.getBoolean(target, offset);
  }

  static void putBoolean(Object target, long offset, boolean value) {
    MEMORY_ACCESSOR.putBoolean(target, offset, value);
  }

  static float getFloat(Object target, long offset) {
    return MEMORY_ACCESSOR.getFloat(target, offset);
  }

  static void putFloat(Object target, long offset, float value) {
    MEMORY_ACCESSOR.putFloat(target, offset, value);
  }

  static double getDouble(Object target, long offset) {
    return MEMORY_ACCESSOR.getDouble(target, offset);
  }

  static void putDouble(Object target, long offset, double value) {
    MEMORY_ACCESSOR.putDouble(target, offset, value);
  }

  static Object getObject(Object target, long offset) {
    return MEMORY_ACCESSOR.getObject(target, offset);
  }

  static void putObject(Object target, long offset, Object value) {
    MEMORY_ACCESSOR.putObject(target, offset, value);
  }

  static void copyMemory(
      Object src, long srcOffset, Object target, long targetOffset, long length) {
    MEMORY_ACCESSOR.copyMemory(src, srcOffset, target, targetOffset, length);
  }

  static byte getByte(long address) {
    return MEMORY_ACCESSOR.getByte(address);
  }

  static void putByte(long address, byte value) {
    MEMORY_ACCESSOR.putByte(address, value);
  }

  static int getInt(long address) {
    return MEMORY_ACCESSOR.getInt(address);
  }

  static void putInt(long address, int value) {
    MEMORY_ACCESSOR.putInt(address, value);
  }

  static long getLong(long address) {
    return MEMORY_ACCESSOR.getLong(address);
  }

  static void putLong(long address, long value) {
    MEMORY_ACCESSOR.putLong(address, value);
  }

  static void copyMemory(long srcAddress, long targetAddress, long length) {
    MEMORY_ACCESSOR.copyMemory(srcAddress, targetAddress, length);
  }

  /**
   * Gets the offset of the {@code address} field of the given direct {@link ByteBuffer}.
   */
  static long addressOffset(ByteBuffer buffer) {
    return MEMORY_ACCESSOR.getLong(buffer, BUFFER_ADDRESS_OFFSET);
  }

  static Object getStaticObject(Field field) {
    return MEMORY_ACCESSOR.getStaticObject(field);
  }

  /**
   * Gets the {@code sun.misc.Unsafe} instance, or {@code null} if not available on this platform.
   */
  private static sun.misc.Unsafe getUnsafe() {
    sun.misc.Unsafe unsafe = null;
    try {
      unsafe =
          AccessController.doPrivileged(
              new PrivilegedExceptionAction<sun.misc.Unsafe>() {
                @Override
                public sun.misc.Unsafe run() throws Exception {
                  Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;

                  for (Field f : k.getDeclaredFields()) {
                    f.setAccessible(true);
                    Object x = f.get(null);
                    if (k.isInstance(x)) {
                      return k.cast(x);
                    }
                  }
                  // The sun.misc.Unsafe field does not exist.
                  return null;
                }
              });
    } catch (Throwable e) {
      // Catching Throwable here due to the fact that Google AppEngine raises NoClassDefFoundError
      // for Unsafe.
    }
    return unsafe;
  }

  /** Get a {@link MemoryAccessor} appropriate for the platform, or null if not supported. */
  private static MemoryAccessor getMemoryAccessor() {
    if (UNSAFE == null) {
      return null;
    }
    return new JvmMemoryAccessor(UNSAFE);
  }

  /** Indicates whether or not unsafe array operations are supported on this platform. */
  private static boolean supportsUnsafeArrayOperations() {
    if (UNSAFE == null) {
      return false;
    }
    try {
      Class<?> clazz = UNSAFE.getClass();
      clazz.getMethod("objectFieldOffset", Field.class);
      clazz.getMethod("arrayBaseOffset", Class.class);
      clazz.getMethod("getInt", Object.class, long.class);
      clazz.getMethod("putInt", Object.class, long.class, int.class);
      clazz.getMethod("getLong", Object.class, long.class);
      clazz.getMethod("putLong", Object.class, long.class, long.class);
      clazz.getMethod("getObject", Object.class, long.class);
      clazz.getMethod("putObject", Object.class, long.class, Object.class);
      clazz.getMethod("getByte", Object.class, long.class);
      clazz.getMethod("putByte", Object.class, long.class, byte.class);
      clazz.getMethod("getBoolean", Object.class, long.class);
      clazz.getMethod("putBoolean", Object.class, long.class, boolean.class);
      clazz.getMethod("getFloat", Object.class, long.class);
      clazz.getMethod("putFloat", Object.class, long.class, float.class);
      clazz.getMethod("getDouble", Object.class, long.class);
      clazz.getMethod("putDouble", Object.class, long.class, double.class);

      return true;
    } catch (Throwable e) {
      logger.log(
          Level.WARNING,
          "platform method missing - proto runtime falling back to safer methods: " + e);
    }
    return false;
  }

  /**
   * Indicates whether or not unsafe copyMemory(object, long, object, long, long) operations are
   * supported on this platform.
   */
  private static boolean supportsUnsafeCopyMemory() {
    if (UNSAFE == null) {
      return false;
    }
    try {
      Class<?> clazz = UNSAFE.getClass();
      clazz.getMethod("copyMemory", Object.class, long.class, Object.class, long.class, long.class);

      return true;
    } catch (Throwable e) {
      logger.log(
          Level.WARNING,
          "copyMemory is missing from platform - proto runtime falling back to safer methods.");
    }
    return false;
  }

  private static boolean supportsUnsafeByteBufferOperations() {
    if (UNSAFE == null) {
      return false;
    }
    try {
      Class<?> clazz = UNSAFE.getClass();
      // Methods for getting direct buffer address.
      clazz.getMethod("objectFieldOffset", Field.class);
      clazz.getMethod("getLong", Object.class, long.class);

      clazz.getMethod("getByte", long.class);
      clazz.getMethod("putByte", long.class, byte.class);
      clazz.getMethod("getInt", long.class);
      clazz.getMethod("putInt", long.class, int.class);
      clazz.getMethod("getLong", long.class);
      clazz.getMethod("putLong", long.class, long.class);
      clazz.getMethod("copyMemory", long.class, long.class, long.class);
      return true;
    } catch (Throwable e) {
      logger.log(
          Level.WARNING,
          "platform method missing - proto runtime falling back to safer methods: " + e);
    }
    return false;
  }


  @SuppressWarnings("unchecked")
  private static <T> Class<T> getClassForName(String name) {
    try {
      return (Class<T>) Class.forName(name);
    } catch (Throwable e) {
      return null;
    }
  }

  /** Finds the address field within a direct {@link Buffer}. */
  private static Field bufferAddressField() {
    return field(Buffer.class, "address");
  }

  /**
   * Get the base offset for byte arrays, or {@code -1} if {@code sun.misc.Unsafe} is not available.
   */
  private static int byteArrayBaseOffset() {
    return HAS_UNSAFE_ARRAY_OPERATIONS ? MEMORY_ACCESSOR.arrayBaseOffset(byte[].class) : -1;
  }

  /**
   * Returns the offset of the provided field, or {@code -1} if {@code sun.misc.Unsafe} is not
   * available.
   */
  private static long fieldOffset(Field field) {
    return field == null || MEMORY_ACCESSOR == null ? -1 : MEMORY_ACCESSOR.objectFieldOffset(field);
  }

  /**
   * Gets the field with the given name within the class, or {@code null} if not found. If found,
   * the field is made accessible.
   */
  private static Field field(Class<?> clazz, String fieldName) {
    Field field;
    try {
      field = clazz.getDeclaredField(fieldName);
      field.setAccessible(true);
    } catch (Throwable t) {
      // Failed to access the fields.
      field = null;
    }
    return field;
  }

  private abstract static class MemoryAccessor {

    sun.misc.Unsafe unsafe;

    MemoryAccessor(sun.misc.Unsafe unsafe) {
      this.unsafe = unsafe;
    }

    public final long objectFieldOffset(Field field) {
      return unsafe.objectFieldOffset(field);
    }

    public abstract byte getByte(Object target, long offset);

    public abstract void putByte(Object target, long offset, byte value);

    public final int getInt(Object target, long offset) {
      return unsafe.getInt(target, offset);
    }

    public final void putInt(Object target, long offset, int value) {
      unsafe.putInt(target, offset, value);
    }

    public final long getLong(Object target, long offset) {
      return unsafe.getLong(target, offset);
    }

    public final void putLong(Object target, long offset, long value) {
      unsafe.putLong(target, offset, value);
    }

    public abstract boolean getBoolean(Object target, long offset);

    public abstract void putBoolean(Object target, long offset, boolean value);

    public abstract float getFloat(Object target, long offset);

    public abstract void putFloat(Object target, long offset, float value);

    public abstract double getDouble(Object target, long offset);

    public abstract void putDouble(Object target, long offset, double value);

    public final Object getObject(Object target, long offset) {
      return unsafe.getObject(target, offset);
    }

    public final void putObject(Object target, long offset, Object value) {
      unsafe.putObject(target, offset, value);
    }

    public final int arrayBaseOffset(Class<?> clazz) {
      return unsafe.arrayBaseOffset(clazz);
    }

    public abstract byte getByte(long address);

    public abstract void putByte(long address, byte value);

    public abstract int getInt(long address);

    public abstract void putInt(long address, int value);

    public abstract long getLong(long address);

    public abstract void putLong(long address, long value);

    public abstract void copyMemory(long srcAddress, long targetAddress, long length);

    public abstract void copyMemory(
        Object src, long srcOffset, Object target, long targetOffset, long length);

    public abstract Object getStaticObject(Field field);
  }

  private static final class JvmMemoryAccessor extends MemoryAccessor {

    JvmMemoryAccessor(sun.misc.Unsafe unsafe) {
      super(unsafe);
    }

    @Override
    public byte getByte(long address) {
      return unsafe.getByte(address);
    }

    @Override
    public void putByte(long address, byte value) {
      unsafe.putByte(address, value);
    }

    @Override
    public int getInt(long address) {
      return unsafe.getInt(address);
    }

    @Override
    public void putInt(long address, int value) {
      unsafe.putInt(address, value);
    }

    @Override
    public long getLong(long address) {
      return unsafe.getLong(address);
    }

    @Override
    public void putLong(long address, long value) {
      unsafe.putLong(address, value);
    }

    @Override
    public byte getByte(Object target, long offset) {
      return unsafe.getByte(target, offset);
    }

    @Override
    public void putByte(Object target, long offset, byte value) {
      unsafe.putByte(target, offset, value);
    }

    @Override
    public boolean getBoolean(Object target, long offset) {
      return unsafe.getBoolean(target, offset);
    }

    @Override
    public void putBoolean(Object target, long offset, boolean value) {
      unsafe.putBoolean(target, offset, value);
    }

    @Override
    public float getFloat(Object target, long offset) {
      return unsafe.getFloat(target, offset);
    }

    @Override
    public void putFloat(Object target, long offset, float value) {
      unsafe.putFloat(target, offset, value);
    }

    @Override
    public double getDouble(Object target, long offset) {
      return unsafe.getDouble(target, offset);
    }

    @Override
    public void putDouble(Object target, long offset, double value) {
      unsafe.putDouble(target, offset, value);
    }

    @Override
    public void copyMemory(
        Object src, long srcOffset, Object target, long targetOffset, long length) {
      unsafe.copyMemory(src, srcOffset, target, targetOffset, length);
    }

    @Override
    public void copyMemory(long srcAddress, long targetAddress, long length) {
      unsafe.copyMemory(srcAddress, targetAddress, length);
    }

    @Override
    public Object getStaticObject(Field field) {
      return getObject(unsafe.staticFieldBase(field), unsafe.staticFieldOffset(field));
    }
  }

}
