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Diffstat (limited to 'java/src/main/java/com/google/protobuf/Utf8.java')
-rw-r--r-- | java/src/main/java/com/google/protobuf/Utf8.java | 349 |
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diff --git a/java/src/main/java/com/google/protobuf/Utf8.java b/java/src/main/java/com/google/protobuf/Utf8.java new file mode 100644 index 0000000..4d0ef53 --- /dev/null +++ b/java/src/main/java/com/google/protobuf/Utf8.java @@ -0,0 +1,349 @@ +// 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 +// "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 THE COPYRIGHT +// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + +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(); + } + } +} |