001/* 002 * Copyright (C) 2009 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 005 * in compliance with the License. You may obtain a copy of the License at 006 * 007 * http://www.apache.org/licenses/LICENSE-2.0 008 * 009 * Unless required by applicable law or agreed to in writing, software distributed under the License 010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 011 * or implied. See the License for the specific language governing permissions and limitations under 012 * the License. 013 */ 014 015package com.google.common.escape; 016 017import static com.google.common.base.Preconditions.checkNotNull; 018 019import com.google.common.annotations.Beta; 020import com.google.common.annotations.GwtCompatible; 021import java.util.Map; 022import javax.annotation.Nullable; 023 024/** 025 * A {@link UnicodeEscaper} that uses an array to quickly look up replacement characters for a given 026 * code point. An additional safe range is provided that determines whether code points without 027 * specific replacements are to be considered safe and left unescaped or should be escaped in a 028 * general way. 029 * 030 * <p>A good example of usage of this class is for HTML escaping where the replacement array 031 * contains information about the named HTML entities such as {@code &} and {@code "} while 032 * {@link #escapeUnsafe} is overridden to handle general escaping of the form {@code &#NNNNN;}. 033 * 034 * <p>The size of the data structure used by {@link ArrayBasedUnicodeEscaper} is proportional to the 035 * highest valued code point that requires escaping. For example a replacement map containing the 036 * single character '{@code \}{@code u1000}' will require approximately 16K of memory. If you need 037 * to create multiple escaper instances that have the same character replacement mapping consider 038 * using {@link ArrayBasedEscaperMap}. 039 * 040 * @author David Beaumont 041 * @since 15.0 042 */ 043@Beta 044@GwtCompatible 045public abstract class ArrayBasedUnicodeEscaper extends UnicodeEscaper { 046 // The replacement array (see ArrayBasedEscaperMap). 047 private final char[][] replacements; 048 // The number of elements in the replacement array. 049 private final int replacementsLength; 050 // The first code point in the safe range. 051 private final int safeMin; 052 // The last code point in the safe range. 053 private final int safeMax; 054 055 // Cropped values used in the fast path range checks. 056 private final char safeMinChar; 057 private final char safeMaxChar; 058 059 /** 060 * Creates a new ArrayBasedUnicodeEscaper instance with the given replacement map and specified 061 * safe range. If {@code safeMax < safeMin} then no code points are considered safe. 062 * 063 * <p>If a code point has no mapped replacement then it is checked against the safe range. If it 064 * lies outside that, then {@link #escapeUnsafe} is called, otherwise no escaping is performed. 065 * 066 * @param replacementMap a map of characters to their escaped representations 067 * @param safeMin the lowest character value in the safe range 068 * @param safeMax the highest character value in the safe range 069 * @param unsafeReplacement the default replacement for unsafe characters or null if no default 070 * replacement is required 071 */ 072 protected ArrayBasedUnicodeEscaper( 073 Map<Character, String> replacementMap, 074 int safeMin, 075 int safeMax, 076 @Nullable String unsafeReplacement) { 077 this(ArrayBasedEscaperMap.create(replacementMap), safeMin, safeMax, unsafeReplacement); 078 } 079 080 /** 081 * Creates a new ArrayBasedUnicodeEscaper instance with the given replacement map and specified 082 * safe range. If {@code safeMax < safeMin} then no code points are considered safe. This 083 * initializer is useful when explicit instances of ArrayBasedEscaperMap are used to allow the 084 * sharing of large replacement mappings. 085 * 086 * <p>If a code point has no mapped replacement then it is checked against the safe range. If it 087 * lies outside that, then {@link #escapeUnsafe} is called, otherwise no escaping is performed. 088 * 089 * @param escaperMap the map of replacements 090 * @param safeMin the lowest character value in the safe range 091 * @param safeMax the highest character value in the safe range 092 * @param unsafeReplacement the default replacement for unsafe characters or null if no default 093 * replacement is required 094 */ 095 protected ArrayBasedUnicodeEscaper( 096 ArrayBasedEscaperMap escaperMap, 097 int safeMin, 098 int safeMax, 099 @Nullable String unsafeReplacement) { 100 checkNotNull(escaperMap); // GWT specific check (do not optimize) 101 this.replacements = escaperMap.getReplacementArray(); 102 this.replacementsLength = replacements.length; 103 if (safeMax < safeMin) { 104 // If the safe range is empty, set the range limits to opposite extremes 105 // to ensure the first test of either value will fail. 106 safeMax = -1; 107 safeMin = Integer.MAX_VALUE; 108 } 109 this.safeMin = safeMin; 110 this.safeMax = safeMax; 111 112 // This is a bit of a hack but lets us do quicker per-character checks in 113 // the fast path code. The safe min/max values are very unlikely to extend 114 // into the range of surrogate characters, but if they do we must not test 115 // any values in that range. To see why, consider the case where: 116 // safeMin <= {hi,lo} <= safeMax 117 // where {hi,lo} are characters forming a surrogate pair such that: 118 // codePointOf(hi, lo) > safeMax 119 // which would result in the surrogate pair being (wrongly) considered safe. 120 // If we clip the safe range used during the per-character tests so it is 121 // below the values of characters in surrogate pairs, this cannot occur. 122 // This approach does mean that we break out of the fast path code in cases 123 // where we don't strictly need to, but this situation will almost never 124 // occur in practice. 125 if (safeMin >= Character.MIN_HIGH_SURROGATE) { 126 // The safe range is empty or the all safe code points lie in or above the 127 // surrogate range. Either way the character range is empty. 128 this.safeMinChar = Character.MAX_VALUE; 129 this.safeMaxChar = 0; 130 } else { 131 // The safe range is non empty and contains values below the surrogate 132 // range but may extend above it. We may need to clip the maximum value. 133 this.safeMinChar = (char) safeMin; 134 this.safeMaxChar = (char) Math.min(safeMax, Character.MIN_HIGH_SURROGATE - 1); 135 } 136 } 137 138 /* 139 * This is overridden to improve performance. Rough benchmarking shows that this almost doubles 140 * the speed when processing strings that do not require any escaping. 141 */ 142 @Override 143 public final String escape(String s) { 144 checkNotNull(s); // GWT specific check (do not optimize) 145 for (int i = 0; i < s.length(); i++) { 146 char c = s.charAt(i); 147 if ((c < replacementsLength && replacements[c] != null) 148 || c > safeMaxChar 149 || c < safeMinChar) { 150 return escapeSlow(s, i); 151 } 152 } 153 return s; 154 } 155 156 /* Overridden for performance. */ 157 @Override 158 protected final int nextEscapeIndex(CharSequence csq, int index, int end) { 159 while (index < end) { 160 char c = csq.charAt(index); 161 if ((c < replacementsLength && replacements[c] != null) 162 || c > safeMaxChar 163 || c < safeMinChar) { 164 break; 165 } 166 index++; 167 } 168 return index; 169 } 170 171 /** 172 * Escapes a single Unicode code point using the replacement array and safe range values. If the 173 * given character does not have an explicit replacement and lies outside the safe range then 174 * {@link #escapeUnsafe} is called. 175 */ 176 @Override 177 protected final char[] escape(int cp) { 178 if (cp < replacementsLength) { 179 char[] chars = replacements[cp]; 180 if (chars != null) { 181 return chars; 182 } 183 } 184 if (cp >= safeMin && cp <= safeMax) { 185 return null; 186 } 187 return escapeUnsafe(cp); 188 } 189 190 /** 191 * Escapes a code point that has no direct explicit value in the replacement array and lies 192 * outside the stated safe range. Subclasses should override this method to provide generalized 193 * escaping for code points if required. 194 * 195 * <p>Note that arrays returned by this method must not be modified once they have been returned. 196 * However it is acceptable to return the same array multiple times (even for different input 197 * characters). 198 * 199 * @param cp the Unicode code point to escape 200 * @return the replacement characters, or {@code null} if no escaping was required 201 */ 202 protected abstract char[] escapeUnsafe(int cp); 203}