| /* |
| * Copyright (C) 2008 The Guava Authors |
| * |
| * 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.common.escape; |
| |
| import static com.google.common.base.Preconditions.checkNotNull; |
| |
| import com.google.common.annotations.Beta; |
| import com.google.common.annotations.GwtCompatible; |
| |
| /** |
| * An {@link Escaper} that converts literal text into a format safe for inclusion in a particular |
| * context (such as an XML document). Typically (but not always), the inverse process of |
| * "unescaping" the text is performed automatically by the relevant parser. |
| * |
| * <p>For example, an XML escaper would convert the literal string {@code "Foo<Bar>"} into {@code |
| * "Foo<Bar>"} to prevent {@code "<Bar>"} from being confused with an XML tag. When the |
| * resulting XML document is parsed, the parser API will return this text as the original literal |
| * string {@code "Foo<Bar>"}. |
| * |
| * <p><b>Note:</b> This class is similar to {@link CharEscaper} but with one very important |
| * difference. A CharEscaper can only process Java <a |
| * href="http://en.wikipedia.org/wiki/UTF-16">UTF16</a> characters in isolation and may not cope |
| * when it encounters surrogate pairs. This class facilitates the correct escaping of all Unicode |
| * characters. |
| * |
| * <p>As there are important reasons, including potential security issues, to handle Unicode |
| * correctly if you are considering implementing a new escaper you should favor using UnicodeEscaper |
| * wherever possible. |
| * |
| * <p>A {@code UnicodeEscaper} instance is required to be stateless, and safe when used concurrently |
| * by multiple threads. |
| * |
| * <p>Popular escapers are defined as constants in classes like {@link |
| * com.google.common.html.HtmlEscapers} and {@link com.google.common.xml.XmlEscapers}. To create |
| * your own escapers extend this class and implement the {@link #escape(int)} method. |
| * |
| * @author David Beaumont |
| * @since 15.0 |
| */ |
| @Beta |
| @GwtCompatible |
| public abstract class UnicodeEscaper extends Escaper { |
| /** The amount of padding (chars) to use when growing the escape buffer. */ |
| private static final int DEST_PAD = 32; |
| |
| /** Constructor for use by subclasses. */ |
| protected UnicodeEscaper() {} |
| |
| /** |
| * Returns the escaped form of the given Unicode code point, or {@code null} if this code point |
| * does not need to be escaped. When called as part of an escaping operation, the given code point |
| * is guaranteed to be in the range {@code 0 <= cp <= Character#MAX_CODE_POINT}. |
| * |
| * <p>If an empty array is returned, this effectively strips the input character from the |
| * resulting text. |
| * |
| * <p>If the character does not need to be escaped, this method should return {@code null}, rather |
| * than an array containing the character representation of the code point. This enables the |
| * escaping algorithm to perform more efficiently. |
| * |
| * <p>If the implementation of this method cannot correctly handle a particular code point then it |
| * should either throw an appropriate runtime exception or return a suitable replacement |
| * character. It must never silently discard invalid input as this may constitute a security risk. |
| * |
| * @param cp the Unicode code point to escape if necessary |
| * @return the replacement characters, or {@code null} if no escaping was needed |
| */ |
| protected abstract char[] escape(int cp); |
| |
| /** |
| * Returns the escaped form of a given literal string. |
| * |
| * <p>If you are escaping input in arbitrary successive chunks, then it is not generally safe to |
| * use this method. If an input string ends with an unmatched high surrogate character, then this |
| * method will throw {@link IllegalArgumentException}. You should ensure your input is valid <a |
| * href="http://en.wikipedia.org/wiki/UTF-16">UTF-16</a> before calling this method. |
| * |
| * <p><b>Note:</b> When implementing an escaper it is a good idea to override this method for |
| * efficiency by inlining the implementation of {@link #nextEscapeIndex(CharSequence, int, int)} |
| * directly. Doing this for {@link com.google.common.net.PercentEscaper} more than doubled the |
| * performance for unescaped strings (as measured by {@code CharEscapersBenchmark}). |
| * |
| * @param string the literal string to be escaped |
| * @return the escaped form of {@code string} |
| * @throws NullPointerException if {@code string} is null |
| * @throws IllegalArgumentException if invalid surrogate characters are encountered |
| */ |
| @Override |
| public String escape(String string) { |
| checkNotNull(string); |
| int end = string.length(); |
| int index = nextEscapeIndex(string, 0, end); |
| return index == end ? string : escapeSlow(string, index); |
| } |
| |
| /** |
| * Scans a sub-sequence of characters from a given {@link CharSequence}, returning the index of |
| * the next character that requires escaping. |
| * |
| * <p><b>Note:</b> When implementing an escaper, it is a good idea to override this method for |
| * efficiency. The base class implementation determines successive Unicode code points and invokes |
| * {@link #escape(int)} for each of them. If the semantics of your escaper are such that code |
| * points in the supplementary range are either all escaped or all unescaped, this method can be |
| * implemented more efficiently using {@link CharSequence#charAt(int)}. |
| * |
| * <p>Note however that if your escaper does not escape characters in the supplementary range, you |
| * should either continue to validate the correctness of any surrogate characters encountered or |
| * provide a clear warning to users that your escaper does not validate its input. |
| * |
| * <p>See {@link com.google.common.net.PercentEscaper} for an example. |
| * |
| * @param csq a sequence of characters |
| * @param start the index of the first character to be scanned |
| * @param end the index immediately after the last character to be scanned |
| * @throws IllegalArgumentException if the scanned sub-sequence of {@code csq} contains invalid |
| * surrogate pairs |
| */ |
| protected int nextEscapeIndex(CharSequence csq, int start, int end) { |
| int index = start; |
| while (index < end) { |
| int cp = codePointAt(csq, index, end); |
| if (cp < 0 || escape(cp) != null) { |
| break; |
| } |
| index += Character.isSupplementaryCodePoint(cp) ? 2 : 1; |
| } |
| return index; |
| } |
| |
| /** |
| * Returns the escaped form of a given literal string, starting at the given index. This method is |
| * called by the {@link #escape(String)} method when it discovers that escaping is required. It is |
| * protected to allow subclasses to override the fastpath escaping function to inline their |
| * escaping test. See {@link CharEscaperBuilder} for an example usage. |
| * |
| * <p>This method is not reentrant and may only be invoked by the top level {@link |
| * #escape(String)} method. |
| * |
| * @param s the literal string to be escaped |
| * @param index the index to start escaping from |
| * @return the escaped form of {@code string} |
| * @throws NullPointerException if {@code string} is null |
| * @throws IllegalArgumentException if invalid surrogate characters are encountered |
| */ |
| protected final String escapeSlow(String s, int index) { |
| int end = s.length(); |
| |
| // Get a destination buffer and setup some loop variables. |
| char[] dest = Platform.charBufferFromThreadLocal(); |
| int destIndex = 0; |
| int unescapedChunkStart = 0; |
| |
| while (index < end) { |
| int cp = codePointAt(s, index, end); |
| if (cp < 0) { |
| throw new IllegalArgumentException("Trailing high surrogate at end of input"); |
| } |
| // It is possible for this to return null because nextEscapeIndex() may |
| // (for performance reasons) yield some false positives but it must never |
| // give false negatives. |
| char[] escaped = escape(cp); |
| int nextIndex = index + (Character.isSupplementaryCodePoint(cp) ? 2 : 1); |
| if (escaped != null) { |
| int charsSkipped = index - unescapedChunkStart; |
| |
| // This is the size needed to add the replacement, not the full |
| // size needed by the string. We only regrow when we absolutely must. |
| int sizeNeeded = destIndex + charsSkipped + escaped.length; |
| if (dest.length < sizeNeeded) { |
| int destLength = sizeNeeded + (end - index) + DEST_PAD; |
| dest = growBuffer(dest, destIndex, destLength); |
| } |
| // If we have skipped any characters, we need to copy them now. |
| if (charsSkipped > 0) { |
| s.getChars(unescapedChunkStart, index, dest, destIndex); |
| destIndex += charsSkipped; |
| } |
| if (escaped.length > 0) { |
| System.arraycopy(escaped, 0, dest, destIndex, escaped.length); |
| destIndex += escaped.length; |
| } |
| // If we dealt with an escaped character, reset the unescaped range. |
| unescapedChunkStart = nextIndex; |
| } |
| index = nextEscapeIndex(s, nextIndex, end); |
| } |
| |
| // Process trailing unescaped characters - no need to account for escaped |
| // length or padding the allocation. |
| int charsSkipped = end - unescapedChunkStart; |
| if (charsSkipped > 0) { |
| int endIndex = destIndex + charsSkipped; |
| if (dest.length < endIndex) { |
| dest = growBuffer(dest, destIndex, endIndex); |
| } |
| s.getChars(unescapedChunkStart, end, dest, destIndex); |
| destIndex = endIndex; |
| } |
| return new String(dest, 0, destIndex); |
| } |
| |
| /** |
| * Returns the Unicode code point of the character at the given index. |
| * |
| * <p>Unlike {@link Character#codePointAt(CharSequence, int)} or {@link String#codePointAt(int)} |
| * this method will never fail silently when encountering an invalid surrogate pair. |
| * |
| * <p>The behaviour of this method is as follows: |
| * |
| * <ol> |
| * <li>If {@code index >= end}, {@link IndexOutOfBoundsException} is thrown. |
| * <li><b>If the character at the specified index is not a surrogate, it is returned.</b> |
| * <li>If the first character was a high surrogate value, then an attempt is made to read the |
| * next character. |
| * <ol> |
| * <li><b>If the end of the sequence was reached, the negated value of the trailing high |
| * surrogate is returned.</b> |
| * <li><b>If the next character was a valid low surrogate, the code point value of the |
| * high/low surrogate pair is returned.</b> |
| * <li>If the next character was not a low surrogate value, then {@link |
| * IllegalArgumentException} is thrown. |
| * </ol> |
| * <li>If the first character was a low surrogate value, {@link IllegalArgumentException} is |
| * thrown. |
| * </ol> |
| * |
| * @param seq the sequence of characters from which to decode the code point |
| * @param index the index of the first character to decode |
| * @param end the index beyond the last valid character to decode |
| * @return the Unicode code point for the given index or the negated value of the trailing high |
| * surrogate character at the end of the sequence |
| */ |
| protected static int codePointAt(CharSequence seq, int index, int end) { |
| checkNotNull(seq); |
| if (index < end) { |
| char c1 = seq.charAt(index++); |
| if (c1 < Character.MIN_HIGH_SURROGATE || c1 > Character.MAX_LOW_SURROGATE) { |
| // Fast path (first test is probably all we need to do) |
| return c1; |
| } else if (c1 <= Character.MAX_HIGH_SURROGATE) { |
| // If the high surrogate was the last character, return its inverse |
| if (index == end) { |
| return -c1; |
| } |
| // Otherwise look for the low surrogate following it |
| char c2 = seq.charAt(index); |
| if (Character.isLowSurrogate(c2)) { |
| return Character.toCodePoint(c1, c2); |
| } |
| throw new IllegalArgumentException( |
| "Expected low surrogate but got char '" |
| + c2 |
| + "' with value " |
| + (int) c2 |
| + " at index " |
| + index |
| + " in '" |
| + seq |
| + "'"); |
| } else { |
| throw new IllegalArgumentException( |
| "Unexpected low surrogate character '" |
| + c1 |
| + "' with value " |
| + (int) c1 |
| + " at index " |
| + (index - 1) |
| + " in '" |
| + seq |
| + "'"); |
| } |
| } |
| throw new IndexOutOfBoundsException("Index exceeds specified range"); |
| } |
| |
| /** |
| * Helper method to grow the character buffer as needed, this only happens once in a while so it's |
| * ok if it's in a method call. If the index passed in is 0 then no copying will be done. |
| */ |
| private static char[] growBuffer(char[] dest, int index, int size) { |
| if (size < 0) { // overflow - should be OutOfMemoryError but GWT/j2cl don't support it |
| throw new AssertionError("Cannot increase internal buffer any further"); |
| } |
| char[] copy = new char[size]; |
| if (index > 0) { |
| System.arraycopy(dest, 0, copy, 0, index); |
| } |
| return copy; |
| } |
| } |