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/*
 * Copyright (C) 2009 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;
import java.util.Map;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A {@link UnicodeEscaper} that uses an array to quickly look up replacement characters for a given
 * code point. An additional safe range is provided that determines whether code points without
 * specific replacements are to be considered safe and left unescaped or should be escaped in a
 * general way.
 *
 * 

A good example of usage of this class is for HTML escaping where the replacement array * contains information about the named HTML entities such as {@code &} and {@code "} while * {@link #escapeUnsafe} is overridden to handle general escaping of the form {@code &#NNNNN;}. * *

The size of the data structure used by {@link ArrayBasedUnicodeEscaper} is proportional to the * highest valued code point that requires escaping. For example a replacement map containing the * single character '{@code \}{@code u1000}' will require approximately 16K of memory. If you need * to create multiple escaper instances that have the same character replacement mapping consider * using {@link ArrayBasedEscaperMap}. * * @author David Beaumont * @since 15.0 */ @Beta @GwtCompatible public abstract class ArrayBasedUnicodeEscaper extends UnicodeEscaper { // The replacement array (see ArrayBasedEscaperMap). private final char[][] replacements; // The number of elements in the replacement array. private final int replacementsLength; // The first code point in the safe range. private final int safeMin; // The last code point in the safe range. private final int safeMax; // Cropped values used in the fast path range checks. private final char safeMinChar; private final char safeMaxChar; /** * Creates a new ArrayBasedUnicodeEscaper instance with the given replacement map and specified * safe range. If {@code safeMax < safeMin} then no code points are considered safe. * *

If a code point has no mapped replacement then it is checked against the safe range. If it * lies outside that, then {@link #escapeUnsafe} is called, otherwise no escaping is performed. * * @param replacementMap a map of characters to their escaped representations * @param safeMin the lowest character value in the safe range * @param safeMax the highest character value in the safe range * @param unsafeReplacement the default replacement for unsafe characters or null if no default * replacement is required */ protected ArrayBasedUnicodeEscaper( Map replacementMap, int safeMin, int safeMax, @Nullable String unsafeReplacement) { this(ArrayBasedEscaperMap.create(replacementMap), safeMin, safeMax, unsafeReplacement); } /** * Creates a new ArrayBasedUnicodeEscaper instance with the given replacement map and specified * safe range. If {@code safeMax < safeMin} then no code points are considered safe. This * initializer is useful when explicit instances of ArrayBasedEscaperMap are used to allow the * sharing of large replacement mappings. * *

If a code point has no mapped replacement then it is checked against the safe range. If it * lies outside that, then {@link #escapeUnsafe} is called, otherwise no escaping is performed. * * @param escaperMap the map of replacements * @param safeMin the lowest character value in the safe range * @param safeMax the highest character value in the safe range * @param unsafeReplacement the default replacement for unsafe characters or null if no default * replacement is required */ protected ArrayBasedUnicodeEscaper( ArrayBasedEscaperMap escaperMap, int safeMin, int safeMax, @Nullable String unsafeReplacement) { checkNotNull(escaperMap); // GWT specific check (do not optimize) this.replacements = escaperMap.getReplacementArray(); this.replacementsLength = replacements.length; if (safeMax < safeMin) { // If the safe range is empty, set the range limits to opposite extremes // to ensure the first test of either value will fail. safeMax = -1; safeMin = Integer.MAX_VALUE; } this.safeMin = safeMin; this.safeMax = safeMax; // This is a bit of a hack but lets us do quicker per-character checks in // the fast path code. The safe min/max values are very unlikely to extend // into the range of surrogate characters, but if they do we must not test // any values in that range. To see why, consider the case where: // safeMin <= {hi,lo} <= safeMax // where {hi,lo} are characters forming a surrogate pair such that: // codePointOf(hi, lo) > safeMax // which would result in the surrogate pair being (wrongly) considered safe. // If we clip the safe range used during the per-character tests so it is // below the values of characters in surrogate pairs, this cannot occur. // This approach does mean that we break out of the fast path code in cases // where we don't strictly need to, but this situation will almost never // occur in practice. if (safeMin >= Character.MIN_HIGH_SURROGATE) { // The safe range is empty or the all safe code points lie in or above the // surrogate range. Either way the character range is empty. this.safeMinChar = Character.MAX_VALUE; this.safeMaxChar = 0; } else { // The safe range is non empty and contains values below the surrogate // range but may extend above it. We may need to clip the maximum value. this.safeMinChar = (char) safeMin; this.safeMaxChar = (char) Math.min(safeMax, Character.MIN_HIGH_SURROGATE - 1); } } /* * This is overridden to improve performance. Rough benchmarking shows that this almost doubles * the speed when processing strings that do not require any escaping. */ @Override public final String escape(String s) { checkNotNull(s); // GWT specific check (do not optimize) for (int i = 0; i < s.length(); i++) { char c = s.charAt(i); if ((c < replacementsLength && replacements[c] != null) || c > safeMaxChar || c < safeMinChar) { return escapeSlow(s, i); } } return s; } /** * Escapes a single Unicode code point using the replacement array and safe range values. If the * given character does not have an explicit replacement and lies outside the safe range then * {@link #escapeUnsafe} is called. */ @Override protected final char[] escape(int cp) { if (cp < replacementsLength) { char[] chars = replacements[cp]; if (chars != null) { return chars; } } if (cp >= safeMin && cp <= safeMax) { return null; } return escapeUnsafe(cp); } /* Overridden for performance. */ @Override protected final int nextEscapeIndex(CharSequence csq, int index, int end) { while (index < end) { char c = csq.charAt(index); if ((c < replacementsLength && replacements[c] != null) || c > safeMaxChar || c < safeMinChar) { break; } index++; } return index; } /** * Escapes a code point that has no direct explicit value in the replacement array and lies * outside the stated safe range. Subclasses should override this method to provide generalized * escaping for code points if required. * *

Note that arrays returned by this method must not be modified once they have been returned. * However it is acceptable to return the same array multiple times (even for different input * characters). * * @param cp the Unicode code point to escape * @return the replacement characters, or {@code null} if no escaping was required */ protected abstract char[] escapeUnsafe(int cp); }





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