/*
* 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 javax.annotation.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.
*
* <p>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;}.
*
* <p>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.
*
* <p>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<Character, String> 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.
*
* <p>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;
}
/* 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 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);
}
/**
* 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.
*
* <p>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);
}