// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// http://code.google.com/p/protobuf/
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package com.google.protobuf;
/**
* 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, "UTF-8").getBytes("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>.
*
* <p>This class supports decoding of partial byte sequences, so that the
* bytes in a complete UTF-8 byte sequences can be stored in multiple
* segments. Methods typically return {@link #MALFORMED} if the partial
* byte sequence is definitely not well-formed, {@link #COMPLETE} if it is
* well-formed in the absence of additional input, or if the byte sequence
* apparently terminated in the middle of a character, an opaque integer
* "state" value containing enough information to decode the character when
* passed to a subsequent invocation of a partial decoding method.
*
* @author martinrb@google.com (Martin Buchholz)
*/
final class Utf8 {
private Utf8() {}
/**
* State value indicating that the byte sequence is well-formed and
* complete (no further bytes are needed to complete a character).
*/
public static final int COMPLETE = 0;
/**
* State value indicating that the byte sequence is definitely not
* well-formed.
*/
public static final int MALFORMED = -1;
// Other state values include the partial bytes of the incomplete
// character to be decoded in the simplest way: we pack the bytes
// into the state int in little-endian order. For example:
//
// int state = byte1 ^ (byte2 << 8) ^ (byte3 << 16);
//
// Such a state is unpacked thus (note the ~ operation for byte2 to
// undo byte1's sign-extension bits):
//
// int byte1 = (byte) state;
// int byte2 = (byte) ~(state >> 8);
// int byte3 = (byte) (state >> 16);
//
// We cannot store a zero byte in the state because it would be
// indistinguishable from the absence of a byte. But we don't need
// to, because partial bytes must always be negative. When building
// a state, we ensure that byte1 is negative and subsequent bytes
// are valid trailing bytes.
/**
* Returns {@code true} if the given byte array is a well-formed
* UTF-8 byte sequence.
*
* <p>This is a convenience method, equivalent to a call to {@code
* isValidUtf8(bytes, 0, bytes.length)}.
*/
public static boolean isValidUtf8(byte[] bytes) {
return isValidUtf8(bytes, 0, bytes.length);
}
/**
* Returns {@code true} if the given byte array slice is a
* well-formed UTF-8 byte sequence. The range of bytes to be
* checked extends from index {@code index}, inclusive, to {@code
* limit}, exclusive.
*
* <p>This is a convenience method, equivalent to {@code
* partialIsValidUtf8(bytes, index, limit) == Utf8.COMPLETE}.
*/
public static boolean isValidUtf8(byte[] bytes, int index, int limit) {
return partialIsValidUtf8(bytes, index, limit) == COMPLETE;
}
/**
* Tells whether the given byte array slice is a well-formed,
* malformed, or incomplete UTF-8 byte sequence. The range of bytes
* to be checked extends from index {@code index}, inclusive, to
* {@code limit}, exclusive.
*
* @param state either {@link Utf8#COMPLETE} (if this is the initial decoding
* operation) or the value returned from a call to a partial decoding method
* for the previous bytes
*
* @return {@link #MALFORMED} if the partial byte sequence is
* definitely not well-formed, {@link #COMPLETE} if it is well-formed
* (no additional input needed), or if the byte sequence is
* "incomplete", i.e. apparently terminated in the middle of a character,
* an opaque integer "state" value containing enough information to
* decode the character when passed to a subsequent invocation of a
* partial decoding method.
*/
public static int partialIsValidUtf8(
int state, byte[] bytes, int index, int limit) {
if (state != COMPLETE) {
// The previous decoding operation was incomplete (or malformed).
// We look for a well-formed sequence consisting of bytes from
// the previous decoding operation (stored in state) together
// with bytes from the array slice.
//
// We expect such "straddler characters" to be rare.
if (index >= limit) { // No bytes? No progress.
return state;
}
int byte1 = (byte) state;
// byte1 is never ASCII.
if (byte1 < (byte) 0xE0) {
// two-byte form
// Simultaneously checks for illegal trailing-byte in
// leading position and overlong 2-byte form.
if (byte1 < (byte) 0xC2 ||
// byte2 trailing-byte test
bytes[index++] > (byte) 0xBF) {
return MALFORMED;
}
} else if (byte1 < (byte) 0xF0) {
// three-byte form
// Get byte2 from saved state or array
int byte2 = (byte) ~(state >> 8);
if (byte2 == 0) {
byte2 = bytes[index++];
if (index >= limit) {
return incompleteStateFor(byte1, byte2);
}
}
if (byte2 > (byte) 0xBF ||
// overlong? 5 most significant bits must not all be zero
(byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0) ||
// illegal surrogate codepoint?
(byte1 == (byte) 0xED && byte2 >= (byte) 0xA0) ||
// byte3 trailing-byte test
bytes[index++] > (byte) 0xBF) {
return MALFORMED;
}
} else {
// four-byte form
// Get byte2 and byte3 from saved state or array
int byte2 = (byte) ~(state >> 8);
int byte3 = 0;
if (byte2 == 0) {
byte2 = bytes[index++];
if (index >= limit) {
return incompleteStateFor(byte1, byte2);
}
} else {
byte3 = (byte) (state >> 16);
}
if (byte3 == 0) {
byte3 = bytes[index++];
if (index >= limit) {
return incompleteStateFor(byte1, byte2, byte3);
}
}
// If we were called with state == MALFORMED, then byte1 is 0xFF,
// which never occurs in well-formed UTF-8, and so we will return
// MALFORMED again below.
if (byte2 > (byte) 0xBF ||
// Check that 1 <= plane <= 16. Tricky optimized form of:
// if (byte1 > (byte) 0xF4 ||
// byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
// byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
(((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0 ||
// byte3 trailing-byte test
byte3 > (byte) 0xBF ||
// byte4 trailing-byte test
bytes[index++] > (byte) 0xBF) {
return MALFORMED;
}
}
}
return partialIsValidUtf8(bytes, index, limit);
}
/**
* Tells whether the given byte array slice is a well-formed,
* malformed, or incomplete UTF-8 byte sequence. The range of bytes
* to be checked extends from index {@code index}, inclusive, to
* {@code limit}, exclusive.
*
* <p>This is a convenience method, equivalent to a call to {@code
* partialIsValidUtf8(Utf8.COMPLETE, bytes, index, limit)}.
*
* @return {@link #MALFORMED} if the partial byte sequence is
* definitely not well-formed, {@link #COMPLETE} if it is well-formed
* (no additional input needed), or if the byte sequence is
* "incomplete", i.e. apparently terminated in the middle of a character,
* an opaque integer "state" value containing enough information to
* decode the character when passed to a subsequent invocation of a
* partial decoding method.
*/
public static int partialIsValidUtf8(
byte[] bytes, int index, int limit) {
// Optimize for 100% ASCII.
// Hotspot loves small simple top-level loops like this.
while (index < limit && bytes[index] >= 0) {
index++;
}
return (index >= limit) ? COMPLETE :
partialIsValidUtf8NonAscii(bytes, index, limit);
}
private static int partialIsValidUtf8NonAscii(
byte[] bytes, int index, int limit) {
for (;;) {
int byte1, byte2;
// Optimize for interior runs of ASCII bytes.
do {
if (index >= limit) {
return COMPLETE;
}
} while ((byte1 = bytes[index++]) >= 0);
if (byte1 < (byte) 0xE0) {
// two-byte form
if (index >= limit) {
return byte1;
}
// Simultaneously checks for illegal trailing-byte in
// leading position and overlong 2-byte form.
if (byte1 < (byte) 0xC2 ||
bytes[index++] > (byte) 0xBF) {
return MALFORMED;
}
} else if (byte1 < (byte) 0xF0) {
// three-byte form
if (index >= limit - 1) { // incomplete sequence
return incompleteStateFor(bytes, index, limit);
}
if ((byte2 = bytes[index++]) > (byte) 0xBF ||
// 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) ||
// byte3 trailing-byte test
bytes[index++] > (byte) 0xBF) {
return MALFORMED;
}
} else {
// four-byte form
if (index >= limit - 2) { // incomplete sequence
return incompleteStateFor(bytes, index, limit);
}
if ((byte2 = bytes[index++]) > (byte) 0xBF ||
// Check that 1 <= plane <= 16. Tricky optimized form of:
// if (byte1 > (byte) 0xF4 ||
// byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 ||
// byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F)
(((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0 ||
// byte3 trailing-byte test
bytes[index++] > (byte) 0xBF ||
// byte4 trailing-byte test
bytes[index++] > (byte) 0xBF) {
return MALFORMED;
}
}
}
}
private static int incompleteStateFor(int byte1) {
return (byte1 > (byte) 0xF4) ?
MALFORMED : byte1;
}
private static int incompleteStateFor(int byte1, int byte2) {
return (byte1 > (byte) 0xF4 ||
byte2 > (byte) 0xBF) ?
MALFORMED : byte1 ^ (byte2 << 8);
}
private static int incompleteStateFor(int byte1, int byte2, int byte3) {
return (byte1 > (byte) 0xF4 ||
byte2 > (byte) 0xBF ||
byte3 > (byte) 0xBF) ?
MALFORMED : byte1 ^ (byte2 << 8) ^ (byte3 << 16);
}
private static int incompleteStateFor(byte[] bytes, int index, int limit) {
int byte1 = bytes[index - 1];
switch (limit - index) {
case 0: return incompleteStateFor(byte1);
case 1: return incompleteStateFor(byte1, bytes[index]);
case 2: return incompleteStateFor(byte1, bytes[index], bytes[index + 1]);
default: throw new AssertionError();
}
}
}