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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.search.yql;
class StringUnescaper {
private static boolean lookaheadOctal(String v, int point) {
return point < v.length() && "01234567".indexOf(v.charAt(point)) != -1;
}
public static String unquote(String token) {
if (null == token || !(token.startsWith("'") && token.endsWith("'") || token.startsWith("\"") && token.endsWith("\""))) {
return token;
}
// remove quotes from around string and unescape it
String value = token.substring(1, token.length() - 1);
// first quickly check to see if \ is present -- if not then there's no escaping and we're done
int idx = value.indexOf('\\');
if (idx == -1) {
return value;
}
// the output string will be no bigger than the input string, since escapes add characters
StringBuilder result = new StringBuilder(value.length());
int start = 0;
while (idx != -1) {
result.append(value.subSequence(start, idx));
start = idx + 1;
switch (value.charAt(start)) {
case 'b':
result.append('\b');
++start;
break;
case 't':
result.append('\t');
++start;
break;
case 'n':
result.append('\n');
++start;
break;
case 'f':
result.append('\f');
++start;
break;
case 'r':
result.append('\r');
++start;
break;
case '"':
result.append('"');
++start;
break;
case '\'':
result.append('\'');
++start;
break;
case '\\':
result.append('\\');
++start;
break;
case '/':
result.append('/');
++start;
break;
case 'u':
// hex hex hex hex
++start;
result.append((char) Integer.parseInt(value.substring(start, start + 4), 16));
start += 4;
break;
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
// octal escape
// 1, 2, or 3 bytes
// peek ahead
if (lookaheadOctal(value, start + 1) && lookaheadOctal(value, start + 2)) {
result.append((char) Integer.parseInt(value.substring(start, start + 3), 8));
start += 3;
} else if (lookaheadOctal(value, start + 1)) {
result.append((char) Integer.parseInt(value.substring(start, start + 2), 8));
start += 2;
} else {
result.append((char) Integer.parseInt(value.substring(start, start + 1), 8));
start += 1;
}
break;
default:
// the lexer should be ensuring there are no malformed escapes here, so we'll just blow up
throw new IllegalArgumentException("Unknown escape sequence in token: " + token);
}
idx = value.indexOf('\\', start);
}
result.append(value.subSequence(start, value.length()));
return result.toString();
}
public static String escape(String value) {
int idx = value.indexOf('\'');
if (idx == -1) {
return "\'" + value + "\'";
}
StringBuilder result = new StringBuilder(value.length() + 5);
result.append("'");
// right now we only escape ' on output
int start = 0;
while (idx != -1) {
result.append(value.subSequence(start, idx));
start = idx + 1;
result.append("\\'");
idx = value.indexOf('\\', start);
}
result.append(value.subSequence(start, value.length()));
result.append("'");
return result.toString();
}
}
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