/
Utf8Safe.java
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/
Utf8Safe.java
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package com.google.flatbuffers;
import java.nio.ByteBuffer;
import static java.lang.Character.MAX_SURROGATE;
import static java.lang.Character.MIN_SUPPLEMENTARY_CODE_POINT;
import static java.lang.Character.MIN_SURROGATE;
import static java.lang.Character.isSurrogatePair;
import static java.lang.Character.toCodePoint;
/**
* A set of low-level, high-performance static utility methods related
* to the UTF-8 character encoding. This class has no dependencies
* outside of the core JDK libraries.
*
* <p>There are several variants of UTF-8. The one implemented by
* this class is the restricted definition of UTF-8 introduced in
* Unicode 3.1, which mandates the rejection of "overlong" byte
* sequences as well as rejection of 3-byte surrogate codepoint byte
* sequences. Note that the UTF-8 decoder included in Oracle's JDK
* has been modified to also reject "overlong" byte sequences, but (as
* of 2011) still accepts 3-byte surrogate codepoint byte sequences.
*
* <p>The byte sequences considered valid by this class are exactly
* those that can be roundtrip converted to Strings and back to bytes
* using the UTF-8 charset, without loss: <pre> {@code
* Arrays.equals(bytes, new String(bytes, Internal.UTF_8).getBytes(Internal.UTF_8))
* }</pre>
*
* <p>See the Unicode Standard,</br>
* Table 3-6. <em>UTF-8 Bit Distribution</em>,</br>
* Table 3-7. <em>Well Formed UTF-8 Byte Sequences</em>.
*/
final public class Utf8Safe extends 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)
*/
private static int computeEncodedLength(CharSequence sequence) {
// Warning to maintainers: this implementation is highly optimized.
int utf16Length = sequence.length();
int utf8Length = utf16Length;
int i = 0;
// This loop optimizes for pure ASCII.
while (i < utf16Length && sequence.charAt(i) < 0x80) {
i++;
}
// This loop optimizes for chars less than 0x800.
for (; i < utf16Length; i++) {
char c = sequence.charAt(i);
if (c < 0x800) {
utf8Length += ((0x7f - c) >>> 31); // branch free!
} else {
utf8Length += encodedLengthGeneral(sequence, i);
break;
}
}
if (utf8Length < utf16Length) {
// Necessary and sufficient condition for overflow because of maximum 3x expansion
throw new IllegalArgumentException("UTF-8 length does not fit in int: "
+ (utf8Length + (1L << 32)));
}
return utf8Length;
}
private static int encodedLengthGeneral(CharSequence sequence, int start) {
int utf16Length = sequence.length();
int utf8Length = 0;
for (int i = start; i < utf16Length; i++) {
char c = sequence.charAt(i);
if (c < 0x800) {
utf8Length += (0x7f - c) >>> 31; // branch free!
} else {
utf8Length += 2;
// jdk7+: if (Character.isSurrogate(c)) {
if (Character.MIN_SURROGATE <= c && c <= Character.MAX_SURROGATE) {
// Check that we have a well-formed surrogate pair.
int cp = Character.codePointAt(sequence, i);
if (cp < MIN_SUPPLEMENTARY_CODE_POINT) {
throw new Utf8Safe.UnpairedSurrogateException(i, utf16Length);
}
i++;
}
}
}
return utf8Length;
}
public static String decodeUtf8Array(byte[] bytes, int index, int size) {
// Bitwise OR combines the sign bits so any negative value fails the check.
if ((index | size | bytes.length - index - size) < 0) {
throw new ArrayIndexOutOfBoundsException(
String.format("buffer length=%d, index=%d, size=%d", bytes.length, index, size));
}
int offset = index;
final int limit = offset + size;
// The longest possible resulting String is the same as the number of input bytes, when it is
// all ASCII. For other cases, this over-allocates and we will truncate in the end.
char[] resultArr = new char[size];
int resultPos = 0;
// Optimize for 100% ASCII (Hotspot loves small simple top-level loops like this).
// This simple loop stops when we encounter a byte >= 0x80 (i.e. non-ASCII).
while (offset < limit) {
byte b = bytes[offset];
if (!DecodeUtil.isOneByte(b)) {
break;
}
offset++;
DecodeUtil.handleOneByte(b, resultArr, resultPos++);
}
while (offset < limit) {
byte byte1 = bytes[offset++];
if (DecodeUtil.isOneByte(byte1)) {
DecodeUtil.handleOneByte(byte1, resultArr, resultPos++);
// It's common for there to be multiple ASCII characters in a run mixed in, so add an
// extra optimized loop to take care of these runs.
while (offset < limit) {
byte b = bytes[offset];
if (!DecodeUtil.isOneByte(b)) {
break;
}
offset++;
DecodeUtil.handleOneByte(b, resultArr, resultPos++);
}
} else if (DecodeUtil.isTwoBytes(byte1)) {
if (offset >= limit) {
throw new IllegalArgumentException("Invalid UTF-8");
}
DecodeUtil.handleTwoBytes(byte1, /* byte2 */ bytes[offset++], resultArr, resultPos++);
} else if (DecodeUtil.isThreeBytes(byte1)) {
if (offset >= limit - 1) {
throw new IllegalArgumentException("Invalid UTF-8");
}
DecodeUtil.handleThreeBytes(
byte1,
/* byte2 */ bytes[offset++],
/* byte3 */ bytes[offset++],
resultArr,
resultPos++);
} else {
if (offset >= limit - 2) {
throw new IllegalArgumentException("Invalid UTF-8");
}
DecodeUtil.handleFourBytes(
byte1,
/* byte2 */ bytes[offset++],
/* byte3 */ bytes[offset++],
/* byte4 */ bytes[offset++],
resultArr,
resultPos++);
// 4-byte case requires two chars.
resultPos++;
}
}
return new String(resultArr, 0, resultPos);
}
public static String decodeUtf8Buffer(ByteBuffer buffer, int offset,
int length) {
// Bitwise OR combines the sign bits so any negative value fails the check.
if ((offset | length | buffer.limit() - offset - length) < 0) {
throw new ArrayIndexOutOfBoundsException(
String.format("buffer limit=%d, index=%d, limit=%d", buffer.limit(),
offset, length));
}
final int limit = offset + length;
// The longest possible resulting String is the same as the number of input bytes, when it is
// all ASCII. For other cases, this over-allocates and we will truncate in the end.
char[] resultArr = new char[length];
int resultPos = 0;
// Optimize for 100% ASCII (Hotspot loves small simple top-level loops like this).
// This simple loop stops when we encounter a byte >= 0x80 (i.e. non-ASCII).
while (offset < limit) {
byte b = buffer.get(offset);
if (!DecodeUtil.isOneByte(b)) {
break;
}
offset++;
DecodeUtil.handleOneByte(b, resultArr, resultPos++);
}
while (offset < limit) {
byte byte1 = buffer.get(offset++);
if (DecodeUtil.isOneByte(byte1)) {
DecodeUtil.handleOneByte(byte1, resultArr, resultPos++);
// It's common for there to be multiple ASCII characters in a run mixed in, so add an
// extra optimized loop to take care of these runs.
while (offset < limit) {
byte b = buffer.get(offset);
if (!DecodeUtil.isOneByte(b)) {
break;
}
offset++;
DecodeUtil.handleOneByte(b, resultArr, resultPos++);
}
} else if (DecodeUtil.isTwoBytes(byte1)) {
if (offset >= limit) {
throw new IllegalArgumentException("Invalid UTF-8");
}
DecodeUtil.handleTwoBytes(
byte1, /* byte2 */ buffer.get(offset++), resultArr, resultPos++);
} else if (DecodeUtil.isThreeBytes(byte1)) {
if (offset >= limit - 1) {
throw new IllegalArgumentException("Invalid UTF-8");
}
DecodeUtil.handleThreeBytes(
byte1,
/* byte2 */ buffer.get(offset++),
/* byte3 */ buffer.get(offset++),
resultArr,
resultPos++);
} else {
if (offset >= limit - 2) {
throw new IllegalArgumentException("Invalid UTF-8");
}
DecodeUtil.handleFourBytes(
byte1,
/* byte2 */ buffer.get(offset++),
/* byte3 */ buffer.get(offset++),
/* byte4 */ buffer.get(offset++),
resultArr,
resultPos++);
// 4-byte case requires two chars.
resultPos++;
}
}
return new String(resultArr, 0, resultPos);
}
@Override
public int encodedLength(CharSequence in) {
return computeEncodedLength(in);
}
/**
* Decodes the given UTF-8 portion of the {@link ByteBuffer} into a {@link String}.
*
* @throws IllegalArgumentException if the input is not valid UTF-8.
*/
@Override
public String decodeUtf8(ByteBuffer buffer, int offset, int length)
throws IllegalArgumentException {
if (buffer.hasArray()) {
return decodeUtf8Array(buffer.array(), buffer.arrayOffset() + offset, length);
} else {
return decodeUtf8Buffer(buffer, offset, length);
}
}
private static void encodeUtf8Buffer(CharSequence in, ByteBuffer out) {
final int inLength = in.length();
int outIx = out.position();
int inIx = 0;
// Since ByteBuffer.putXXX() already checks boundaries for us, no need to explicitly check
// access. Assume the buffer is big enough and let it handle the out of bounds exception
// if it occurs.
try {
// Designed to take advantage of
// https://wikis.oracle.com/display/HotSpotInternals/RangeCheckElimination
for (char c; inIx < inLength && (c = in.charAt(inIx)) < 0x80; ++inIx) {
out.put(outIx + inIx, (byte) c);
}
if (inIx == inLength) {
// Successfully encoded the entire string.
out.position(outIx + inIx);
return;
}
outIx += inIx;
for (char c; inIx < inLength; ++inIx, ++outIx) {
c = in.charAt(inIx);
if (c < 0x80) {
// One byte (0xxx xxxx)
out.put(outIx, (byte) c);
} else if (c < 0x800) {
// Two bytes (110x xxxx 10xx xxxx)
// Benchmarks show put performs better than putShort here (for HotSpot).
out.put(outIx++, (byte) (0xC0 | (c >>> 6)));
out.put(outIx, (byte) (0x80 | (0x3F & c)));
} 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.
// Benchmarks show put performs better than putShort here (for HotSpot).
out.put(outIx++, (byte) (0xE0 | (c >>> 12)));
out.put(outIx++, (byte) (0x80 | (0x3F & (c >>> 6))));
out.put(outIx, (byte) (0x80 | (0x3F & c)));
} 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 (inIx + 1 == inLength || !isSurrogatePair(c, (low = in.charAt(++inIx)))) {
throw new UnpairedSurrogateException(inIx, inLength);
}
// TODO(nathanmittler): Consider using putInt() to improve performance.
int codePoint = toCodePoint(c, low);
out.put(outIx++, (byte) ((0xF << 4) | (codePoint >>> 18)));
out.put(outIx++, (byte) (0x80 | (0x3F & (codePoint >>> 12))));
out.put(outIx++, (byte) (0x80 | (0x3F & (codePoint >>> 6))));
out.put(outIx, (byte) (0x80 | (0x3F & codePoint)));
}
}
// Successfully encoded the entire string.
out.position(outIx);
} catch (IndexOutOfBoundsException e) {
// TODO(nathanmittler): Consider making the API throw IndexOutOfBoundsException instead.
// If we failed in the outer ASCII loop, outIx will not have been updated. In this case,
// use inIx to determine the bad write index.
int badWriteIndex = out.position() + Math.max(inIx, outIx - out.position() + 1);
throw new ArrayIndexOutOfBoundsException(
"Failed writing " + in.charAt(inIx) + " at index " + badWriteIndex);
}
}
private static int encodeUtf8Array(CharSequence in, byte[] out,
int offset, int length) {
int utf16Length = in.length();
int j = offset;
int i = 0;
int limit = offset + length;
// Designed to take advantage of
// https://wikis.oracle.com/display/HotSpotInternals/RangeCheckElimination
for (char c; i < utf16Length && i + j < limit && (c = in.charAt(i)) < 0x80; i++) {
out[j + i] = (byte) c;
}
if (i == utf16Length) {
return j + utf16Length;
}
j += i;
for (char c; i < utf16Length; i++) {
c = in.charAt(i);
if (c < 0x80 && j < limit) {
out[j++] = (byte) c;
} else if (c < 0x800 && j <= limit - 2) { // 11 bits, two UTF-8 bytes
out[j++] = (byte) ((0xF << 6) | (c >>> 6));
out[j++] = (byte) (0x80 | (0x3F & c));
} else if ((c < Character.MIN_SURROGATE || Character.MAX_SURROGATE < c) && j <= limit - 3) {
// Maximum single-char code point is 0xFFFF, 16 bits, three UTF-8 bytes
out[j++] = (byte) ((0xF << 5) | (c >>> 12));
out[j++] = (byte) (0x80 | (0x3F & (c >>> 6)));
out[j++] = (byte) (0x80 | (0x3F & c));
} else if (j <= limit - 4) {
// Minimum code point represented by a surrogate pair is 0x10000, 17 bits,
// four UTF-8 bytes
final char low;
if (i + 1 == in.length()
|| !Character.isSurrogatePair(c, (low = in.charAt(++i)))) {
throw new UnpairedSurrogateException((i - 1), utf16Length);
}
int codePoint = Character.toCodePoint(c, low);
out[j++] = (byte) ((0xF << 4) | (codePoint >>> 18));
out[j++] = (byte) (0x80 | (0x3F & (codePoint >>> 12)));
out[j++] = (byte) (0x80 | (0x3F & (codePoint >>> 6)));
out[j++] = (byte) (0x80 | (0x3F & codePoint));
} else {
// If we are surrogates and we're not a surrogate pair, always throw an
// UnpairedSurrogateException instead of an ArrayOutOfBoundsException.
if ((Character.MIN_SURROGATE <= c && c <= Character.MAX_SURROGATE)
&& (i + 1 == in.length()
|| !Character.isSurrogatePair(c, in.charAt(i + 1)))) {
throw new UnpairedSurrogateException(i, utf16Length);
}
throw new ArrayIndexOutOfBoundsException("Failed writing " + c + " at index " + j);
}
}
return j;
}
/**
* Encodes the given characters to the target {@link ByteBuffer} using UTF-8 encoding.
*
* <p>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.
*/
@Override
public void encodeUtf8(CharSequence in, ByteBuffer out) {
if (out.hasArray()) {
int start = out.arrayOffset();
int end = encodeUtf8Array(in, out.array(), start + out.position(),
out.remaining());
out.position(end - start);
} else {
encodeUtf8Buffer(in, out);
}
}
// These UTF-8 handling methods are copied from Guava's Utf8Unsafe class with
// a modification to throw a local exception. This exception can be caught
// to fallback to more lenient behavior.
static class UnpairedSurrogateException extends IllegalArgumentException {
UnpairedSurrogateException(int index, int length) {
super("Unpaired surrogate at index " + index + " of " + length);
}
}
}