/*
* 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.net;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.escape.UnicodeEscaper;
/**
* A {@code UnicodeEscaper} that escapes some set of Java characters using a
* UTF-8 based percent encoding scheme. The set of safe characters (those which
* remain unescaped) can be specified on construction.
*
* <p>This class is primarily used for creating URI escapers in {@link
* UrlEscapers} but can be used directly if required. While URI escapers impose
* specific semantics on which characters are considered 'safe', this class has
* a minimal set of restrictions.
*
* <p>When escaping a String, the following rules apply:
* <ul>
* <li>All specified safe characters remain unchanged.
* <li>If {@code plusForSpace} was specified, the space character " " is
* converted into a plus sign {@code "+"}.
* <li>All other characters are converted into one or more bytes using UTF-8
* encoding and each byte is then represented by the 3-character string
* "%XX", where "XX" is the two-digit, uppercase, hexadecimal representation
* of the byte value.
* </ul>
*
* <p>For performance reasons the only currently supported character encoding of
* this class is UTF-8.
*
* <p><b>Note:</b> This escaper produces uppercase hexadecimal sequences. From
* <a href="http://www.ietf.org/rfc/rfc3986.txt">RFC 3986</a>:<br>
* <i>"URI producers and normalizers should use uppercase hexadecimal digits
* for all percent-encodings."</i>
*
* @author David Beaumont
* @since 15.0
*/
@Beta
@GwtCompatible
public final class PercentEscaper extends UnicodeEscaper {
// In some escapers spaces are escaped to '+'
private static final char[] PLUS_SIGN = { '+' };
// Percent escapers output upper case hex digits (uri escapers require this).
private static final char[] UPPER_HEX_DIGITS =
"0123456789ABCDEF".toCharArray();
/**
* If true we should convert space to the {@code +} character.
*/
private final boolean plusForSpace;
/**
* An array of flags where for any {@code char c} if {@code safeOctets[c]} is
* true then {@code c} should remain unmodified in the output. If
* {@code c > safeOctets.length} then it should be escaped.
*/
private final boolean[] safeOctets;
/**
* Constructs a percent escaper with the specified safe characters and
* optional handling of the space character.
*
* <p>Not that it is allowed, but not necessarily desirable to specify {@code %}
* as a safe character. This has the effect of creating an escaper which has no
* well defined inverse but it can be useful when escaping additional characters.
*
* @param safeChars a non null string specifying additional safe characters
* for this escaper (the ranges 0..9, a..z and A..Z are always safe and
* should not be specified here)
* @param plusForSpace true if ASCII space should be escaped to {@code +}
* rather than {@code %20}
* @throws IllegalArgumentException if any of the parameters were invalid
*/
public PercentEscaper(String safeChars, boolean plusForSpace) {
// TODO(user): Switch to static factory methods for creation now that class is final.
// TODO(user): Support escapers where alphanumeric chars are not safe.
checkNotNull(safeChars); // eager for GWT.
// Avoid any misunderstandings about the behavior of this escaper
if (safeChars.matches(".*[0-9A-Za-z].*")) {
throw new IllegalArgumentException(
"Alphanumeric characters are always 'safe' and should not be " +
"explicitly specified");
}
safeChars += "abcdefghijklmnopqrstuvwxyz" +
"ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
"0123456789";
// Avoid ambiguous parameters. Safe characters are never modified so if
// space is a safe character then setting plusForSpace is meaningless.
if (plusForSpace && safeChars.contains(" ")) {
throw new IllegalArgumentException(
"plusForSpace cannot be specified when space is a 'safe' character");
}
this.plusForSpace = plusForSpace;
this.safeOctets = createSafeOctets(safeChars);
}
/**
* Creates a boolean array with entries corresponding to the character values
* specified in safeChars set to true. The array is as small as is required to
* hold the given character information.
*/
private static boolean[] createSafeOctets(String safeChars) {
int maxChar = -1;
char[] safeCharArray = safeChars.toCharArray();
for (char c : safeCharArray) {
maxChar = Math.max(c, maxChar);
}
boolean[] octets = new boolean[maxChar + 1];
for (char c : safeCharArray) {
octets[c] = true;
}
return octets;
}
/*
* Overridden for performance. For unescaped strings this improved the
* performance of the uri escaper from ~760ns to ~400ns as measured by
* {@link CharEscapersBenchmark}.
*/
@Override
protected int nextEscapeIndex(CharSequence csq, int index, int end) {
checkNotNull(csq);
for (; index < end; index++) {
char c = csq.charAt(index);
if (c >= safeOctets.length || !safeOctets[c]) {
break;
}
}
return index;
}
/*
* Overridden for performance. For unescaped strings this improved the
* performance of the uri escaper from ~400ns to ~170ns as measured by
* {@link CharEscapersBenchmark}.
*/
@Override
public String escape(String s) {
checkNotNull(s);
int slen = s.length();
for (int index = 0; index < slen; index++) {
char c = s.charAt(index);
if (c >= safeOctets.length || !safeOctets[c]) {
return escapeSlow(s, index);
}
}
return s;
}
/**
* Escapes the given Unicode code point in UTF-8.
*/
@Override
protected char[] escape(int cp) {
// We should never get negative values here but if we do it will throw an
// IndexOutOfBoundsException, so at least it will get spotted.
if (cp < safeOctets.length && safeOctets[cp]) {
return null;
} else if (cp == ' ' && plusForSpace) {
return PLUS_SIGN;
} else if (cp <= 0x7F) {
// Single byte UTF-8 characters
// Start with "%--" and fill in the blanks
char[] dest = new char[3];
dest[0] = '%';
dest[2] = UPPER_HEX_DIGITS[cp & 0xF];
dest[1] = UPPER_HEX_DIGITS[cp >>> 4];
return dest;
} else if (cp <= 0x7ff) {
// Two byte UTF-8 characters [cp >= 0x80 && cp <= 0x7ff]
// Start with "%--%--" and fill in the blanks
char[] dest = new char[6];
dest[0] = '%';
dest[3] = '%';
dest[5] = UPPER_HEX_DIGITS[cp & 0xF];
cp >>>= 4;
dest[4] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)];
cp >>>= 2;
dest[2] = UPPER_HEX_DIGITS[cp & 0xF];
cp >>>= 4;
dest[1] = UPPER_HEX_DIGITS[0xC | cp];
return dest;
} else if (cp <= 0xffff) {
// Three byte UTF-8 characters [cp >= 0x800 && cp <= 0xffff]
// Start with "%E-%--%--" and fill in the blanks
char[] dest = new char[9];
dest[0] = '%';
dest[1] = 'E';
dest[3] = '%';
dest[6] = '%';
dest[8] = UPPER_HEX_DIGITS[cp & 0xF];
cp >>>= 4;
dest[7] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)];
cp >>>= 2;
dest[5] = UPPER_HEX_DIGITS[cp & 0xF];
cp >>>= 4;
dest[4] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)];
cp >>>= 2;
dest[2] = UPPER_HEX_DIGITS[cp];
return dest;
} else if (cp <= 0x10ffff) {
char[] dest = new char[12];
// Four byte UTF-8 characters [cp >= 0xffff && cp <= 0x10ffff]
// Start with "%F-%--%--%--" and fill in the blanks
dest[0] = '%';
dest[1] = 'F';
dest[3] = '%';
dest[6] = '%';
dest[9] = '%';
dest[11] = UPPER_HEX_DIGITS[cp & 0xF];
cp >>>= 4;
dest[10] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)];
cp >>>= 2;
dest[8] = UPPER_HEX_DIGITS[cp & 0xF];
cp >>>= 4;
dest[7] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)];
cp >>>= 2;
dest[5] = UPPER_HEX_DIGITS[cp & 0xF];
cp >>>= 4;
dest[4] = UPPER_HEX_DIGITS[0x8 | (cp & 0x3)];
cp >>>= 2;
dest[2] = UPPER_HEX_DIGITS[cp & 0x7];
return dest;
} else {
// If this ever happens it is due to bug in UnicodeEscaper, not bad input.
throw new IllegalArgumentException(
"Invalid unicode character value " + cp);
}
}
}