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/*
* Copyright 2014 Google Inc. All rights reserved.
*
* 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 com.google.flatbuffers;
import java.nio.ByteBuffer;
import static java.lang.Character.MAX_SURROGATE;
import static java.lang.Character.MIN_SURROGATE;
import static java.lang.Character.MIN_HIGH_SURROGATE;
import static java.lang.Character.MIN_LOW_SURROGATE;
import static java.lang.Character.MIN_SUPPLEMENTARY_CODE_POINT;
import static java.lang.Character.isSurrogatePair;
import static java.lang.Character.toCodePoint;
public abstract class Utf8 {
/**
* Returns the number of bytes in the UTF-8-encoded form of {@code sequence}. For a string,
* this method is equivalent to {@code string.getBytes(UTF_8).length}, but is more efficient in
* both time and space.
*
* @throws IllegalArgumentException if {@code sequence} contains ill-formed UTF-16 (unpaired
* surrogates)
*/
public abstract int encodedLength(CharSequence sequence);
/**
* Encodes the given characters to the target {@link ByteBuffer} using UTF-8 encoding.
*
* Selects an optimal algorithm based on the type of {@link ByteBuffer} (i.e. heap or direct)
* and the capabilities of the platform.
*
* @param in the source string to be encoded
* @param out the target buffer to receive the encoded string.
*/
public abstract void encodeUtf8(CharSequence in, ByteBuffer out);
/**
* Decodes the given UTF-8 portion of the {@link ByteBuffer} into a {@link String}.
*
* @throws IllegalArgumentException if the input is not valid UTF-8.
*/
public abstract String decodeUtf8(ByteBuffer buffer, int offset, int length);
private static Utf8 DEFAULT;
/**
* Get the default UTF-8 processor.
* @return the default processor
*/
public static Utf8 getDefault() {
if (DEFAULT == null) {
DEFAULT = new Utf8Safe();
}
return DEFAULT;
}
/**
* Set the default instance of the UTF-8 processor.
* @param instance the new instance to use
*/
public static void setDefault(Utf8 instance) {
DEFAULT = instance;
}
/**
* Encode a Java's CharSequence UTF8 codepoint into a byte array.
* @param in CharSequence to be encoded
* @param start start position of the first char in the codepoint
* @param out byte array of 4 bytes to be filled
* @return return the amount of bytes occupied by the codepoint
*/
public static int encodeUtf8CodePoint(CharSequence in, int start, byte[] out) {
// utf8 codepoint needs at least 4 bytes
assert out.length >= 4;
final int inLength = in.length();
if (start >= inLength) {
return 0;
}
char c = in.charAt(start);
if (c < 0x80) {
// One byte (0xxx xxxx)
out[0] = (byte) c;
return 1;
} else if (c < 0x800) {
// Two bytes (110x xxxx 10xx xxxx)
out[0] = (byte) (0xC0 | (c >>> 6));
out[1] = (byte) (0x80 | (0x3F & c));
return 2;
} else if (c < MIN_SURROGATE || MAX_SURROGATE < c) {
// Three bytes (1110 xxxx 10xx xxxx 10xx xxxx)
// Maximum single-char code point is 0xFFFF, 16 bits.
out[0] = (byte) (0xE0 | (c >>> 12));
out[1] =(byte) (0x80 | (0x3F & (c >>> 6)));
out[2] = (byte) (0x80 | (0x3F & c));
return 3;
} else {
// Four bytes (1111 xxxx 10xx xxxx 10xx xxxx 10xx xxxx)
// Minimum code point represented by a surrogate pair is 0x10000, 17 bits, four UTF-8
// bytes
final char low;
if (start + 1 == inLength || !isSurrogatePair(c, (low = in.charAt(start+1)))) {
throw new UnpairedSurrogateException(start, inLength);
}
int codePoint = toCodePoint(c, low);
out[0] = (byte) ((0xF << 4) | (codePoint >>> 18));
out[1] = (byte) (0x80 | (0x3F & (codePoint >>> 12)));
out[2] = (byte) (0x80 | (0x3F & (codePoint >>> 6)));
out[3] = (byte) (0x80 | (0x3F & codePoint));
return 4;
}
}
/**
* Utility methods for decoding bytes into {@link String}. Callers are responsible for extracting
* bytes (possibly using Unsafe methods), and checking remaining bytes. All other UTF-8 validity
* checks and codepoint conversion happen in this class.
*/
static class DecodeUtil {
/**
* Returns whether this is a single-byte codepoint (i.e., ASCII) with the form '0XXXXXXX'.
*/
static boolean isOneByte(byte b) {
return b >= 0;
}
/**
* Returns whether this is a two-byte codepoint with the form '10XXXXXX'.
*/
static boolean isTwoBytes(byte b) {
return b < (byte) 0xE0;
}
/**
* Returns whether this is a three-byte codepoint with the form '110XXXXX'.
*/
static boolean isThreeBytes(byte b) {
return b < (byte) 0xF0;
}
static void handleOneByte(byte byte1, char[] resultArr, int resultPos) {
resultArr[resultPos] = (char) byte1;
}
static void handleTwoBytes(
byte byte1, byte byte2, char[] resultArr, int resultPos)
throws IllegalArgumentException {
// Simultaneously checks for illegal trailing-byte in leading position (<= '11000000') and
// overlong 2-byte, '11000001'.
if (byte1 < (byte) 0xC2) {
throw new IllegalArgumentException("Invalid UTF-8: Illegal leading byte in 2 bytes utf");
}
if (isNotTrailingByte(byte2)) {
throw new IllegalArgumentException("Invalid UTF-8: Illegal trailing byte in 2 bytes utf");
}
resultArr[resultPos] = (char) (((byte1 & 0x1F) << 6) | trailingByteValue(byte2));
}
static void handleThreeBytes(
byte byte1, byte byte2, byte byte3, char[] resultArr, int resultPos)
throws IllegalArgumentException {
if (isNotTrailingByte(byte2)
// overlong? 5 most significant bits must not all be zero
|| (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0)
// check for illegal surrogate codepoints
|| (byte1 == (byte) 0xED && byte2 >= (byte) 0xA0)
|| isNotTrailingByte(byte3)) {
throw new IllegalArgumentException("Invalid UTF-8");
}
resultArr[resultPos] = (char)
(((byte1 & 0x0F) << 12) | (trailingByteValue(byte2) << 6) | trailingByteValue(byte3));
}
static void handleFourBytes(
byte byte1, byte byte2, byte byte3, byte byte4, char[] resultArr, int resultPos)
throws IllegalArgumentException{
if (isNotTrailingByte(byte2)
// Check that 1 <= plane <= 16. Tricky optimized form of:
// valid 4-byte leading byte?
// if (byte1 > (byte) 0xF4 ||
// overlong? 4 most significant bits must not all be zero
// byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
// codepoint larger than the highest code point (U+10FFFF)?
// byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
|| (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0
|| isNotTrailingByte(byte3)
|| isNotTrailingByte(byte4)) {
throw new IllegalArgumentException("Invalid UTF-8");
}
int codepoint = ((byte1 & 0x07) << 18)
| (trailingByteValue(byte2) << 12)
| (trailingByteValue(byte3) << 6)
| trailingByteValue(byte4);
resultArr[resultPos] = DecodeUtil.highSurrogate(codepoint);
resultArr[resultPos + 1] = DecodeUtil.lowSurrogate(codepoint);
}
/**
* Returns whether the byte is not a valid continuation of the form '10XXXXXX'.
*/
private static boolean isNotTrailingByte(byte b) {
return b > (byte) 0xBF;
}
/**
* Returns the actual value of the trailing byte (removes the prefix '10') for composition.
*/
private static int trailingByteValue(byte b) {
return b & 0x3F;
}
private static char highSurrogate(int codePoint) {
return (char) ((MIN_HIGH_SURROGATE - (MIN_SUPPLEMENTARY_CODE_POINT >>> 10))
+ (codePoint >>> 10));
}
private static char lowSurrogate(int codePoint) {
return (char) (MIN_LOW_SURROGATE + (codePoint & 0x3ff));
}
}
// These UTF-8 handling methods are copied from Guava's Utf8Unsafe class with a modification to throw
// a protocol buffer local exception. This exception is then caught in CodedOutputStream so it can
// fallback to more lenient behavior.
static class UnpairedSurrogateException extends IllegalArgumentException {
UnpairedSurrogateException(int index, int length) {
super("Unpaired surrogate at index " + index + " of " + length);
}
}
}