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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* accompanied this code).
*
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package jdk.nashorn.internal.runtime.linker;
/**
* <p>
* Implements the name mangling and demangling as specified by John Rose's
* <a href="https://blogs.oracle.com/jrose/entry/symbolic_freedom_in_the_vm"
* target="_blank">"Symbolic Freedom in the VM"</a> article. Normally, you would
* mangle the names in the call sites as you're generating bytecode, and then
* demangle them when you receive them in bootstrap methods.
* </p>
* <p>
* This code is derived from sun.invoke.util.BytecodeName. Apart from subsetting that
* class, we don't want to create dependency between non-exported package from java.base
* to nashorn module.
* </p>
*
* <h3>Comment from BytecodeName class reproduced here:</h3>
*
* Includes universal mangling rules for the JVM.
*
* <h3>Avoiding Dangerous Characters </h3>
*
* <p>
* The JVM defines a very small set of characters which are illegal
* in name spellings. We will slightly extend and regularize this set
* into a group of <cite>dangerous characters</cite>.
* These characters will then be replaced, in mangled names, by escape sequences.
* In addition, accidental escape sequences must be further escaped.
* Finally, a special prefix will be applied if and only if
* the mangling would otherwise fail to begin with the escape character.
* This happens to cover the corner case of the null string,
* and also clearly marks symbols which need demangling.
* </p>
* <p>
* Dangerous characters are the union of all characters forbidden
* or otherwise restricted by the JVM specification,
* plus their mates, if they are brackets
* (<code><big><b>[</b></big></code> and <code><big><b>]</b></big></code>,
* <code><big><b><</b></big></code> and <code><big><b>></b></big></code>),
* plus, arbitrarily, the colon character <code><big><b>:</b></big></code>.
* There is no distinction between type, method, and field names.
* This makes it easier to convert between mangled names of different
* types, since they do not need to be decoded (demangled).
* </p>
* <p>
* The escape character is backslash <code><big><b>\</b></big></code>
* (also known as reverse solidus).
* This character is, until now, unheard of in bytecode names,
* but traditional in the proposed role.
*
* </p>
* <h3> Replacement Characters </h3>
*
*
* <p>
* Every escape sequence is two characters
* (in fact, two UTF8 bytes) beginning with
* the escape character and followed by a
* <cite>replacement character</cite>.
* (Since the replacement character is never a backslash,
* iterated manglings do not double in size.)
* </p>
* <p>
* Each dangerous character has some rough visual similarity
* to its corresponding replacement character.
* This makes mangled symbols easier to recognize by sight.
* </p>
* <p>
* The dangerous characters are
* <code><big><b>/</b></big></code> (forward slash, used to delimit package components),
* <code><big><b>.</b></big></code> (dot, also a package delimiter),
* <code><big><b>;</b></big></code> (semicolon, used in signatures),
* <code><big><b>$</b></big></code> (dollar, used in inner classes and synthetic members),
* <code><big><b><</b></big></code> (left angle),
* <code><big><b>></b></big></code> (right angle),
* <code><big><b>[</b></big></code> (left square bracket, used in array types),
* <code><big><b>]</b></big></code> (right square bracket, reserved in this scheme for language use),
* and <code><big><b>:</b></big></code> (colon, reserved in this scheme for language use).
* Their replacements are, respectively,
* <code><big><b>|</b></big></code> (vertical bar),
* <code><big><b>,</b></big></code> (comma),
* <code><big><b>?</b></big></code> (question mark),
* <code><big><b>%</b></big></code> (percent),
* <code><big><b>^</b></big></code> (caret),
* <code><big><b>_</b></big></code> (underscore), and
* <code><big><b>{</b></big></code> (left curly bracket),
* <code><big><b>}</b></big></code> (right curly bracket),
* <code><big><b>!</b></big></code> (exclamation mark).
* In addition, the replacement character for the escape character itself is
* <code><big><b>-</b></big></code> (hyphen),
* and the replacement character for the null prefix is
* <code><big><b>=</b></big></code> (equal sign).
* </p>
* <p>
* An escape character <code><big><b>\</b></big></code>
* followed by any of these replacement characters
* is an escape sequence, and there are no other escape sequences.
* An equal sign is only part of an escape sequence
* if it is the second character in the whole string, following a backslash.
* Two consecutive backslashes do <em>not</em> form an escape sequence.
* </p>
* <p>
* Each escape sequence replaces a so-called <cite>original character</cite>
* which is either one of the dangerous characters or the escape character.
* A null prefix replaces an initial null string, not a character.
* </p>
* <p>
* All this implies that escape sequences cannot overlap and may be
* determined all at once for a whole string. Note that a spelling
* string can contain <cite>accidental escapes</cite>, apparent escape
* sequences which must not be interpreted as manglings.
* These are disabled by replacing their leading backslash with an
* escape sequence (<code><big><b>\-</b></big></code>). To mangle a string, three logical steps
* are required, though they may be carried out in one pass:
* </p>
* <ol>
* <li>In each accidental escape, replace the backslash with an escape sequence
* (<code><big><b>\-</b></big></code>).</li>
* <li>Replace each dangerous character with an escape sequence
* (<code><big><b>\|</b></big></code> for <code><big><b>/</b></big></code>, etc.).</li>
* <li>If the first two steps introduced any change, <em>and</em>
* if the string does not already begin with a backslash, prepend a null prefix (<code><big><b>\=</b></big></code>).</li>
* </ol>
*
* To demangle a mangled string that begins with an escape,
* remove any null prefix, and then replace (in parallel)
* each escape sequence by its original character.
* <p>Spelling strings which contain accidental
* escapes <em>must</em> have them replaced, even if those
* strings do not contain dangerous characters.
* This restriction means that mangling a string always
* requires a scan of the string for escapes.
* But then, a scan would be required anyway,
* to check for dangerous characters.
*
* </p>
* <h3> Nice Properties </h3>
*
* <p>
* If a bytecode name does not contain any escape sequence,
* demangling is a no-op: The string demangles to itself.
* Such a string is called <cite>self-mangling</cite>.
* Almost all strings are self-mangling.
* In practice, to demangle almost any name “found in nature”,
* simply verify that it does not begin with a backslash.
* </p>
* <p>
* Mangling is a one-to-one function, while demangling
* is a many-to-one function.
* A mangled string is defined as <cite>validly mangled</cite> if
* it is in fact the unique mangling of its spelling string.
* Three examples of invalidly mangled strings are <code><big><b>\=foo</b></big></code>,
* <code><big><b>\-bar</b></big></code>, and <code><big><b>baz\!</b></big></code>, which demangle to <code><big><b>foo</b></big></code>, <code><big><b>\bar</b></big></code>, and
* <code><big><b>baz\!</b></big></code>, but then remangle to <code><big><b>foo</b></big></code>, <code><big><b>\bar</b></big></code>, and <code><big><b>\=baz\-!</b></big></code>.
* If a language back-end or runtime is using mangled names,
* it should never present an invalidly mangled bytecode
* name to the JVM. If the runtime encounters one,
* it should also report an error, since such an occurrence
* probably indicates a bug in name encoding which
* will lead to errors in linkage.
* However, this note does not propose that the JVM verifier
* detect invalidly mangled names.
* </p>
* <p>
* As a result of these rules, it is a simple matter to
* compute validly mangled substrings and concatenations
* of validly mangled strings, and (with a little care)
* these correspond to corresponding operations on their
* spelling strings.
* </p>
* <ul>
* <li>Any prefix of a validly mangled string is also validly mangled,
* although a null prefix may need to be removed.</li>
* <li>Any suffix of a validly mangled string is also validly mangled,
* although a null prefix may need to be added.</li>
* <li>Two validly mangled strings, when concatenated,
* are also validly mangled, although any null prefix
* must be removed from the second string,
* and a trailing backslash on the first string may need escaping,
* if it would participate in an accidental escape when followed
* by the first character of the second string.</li>
* </ul>
* <p>If languages that include non-Java symbol spellings use this
* mangling convention, they will enjoy the following advantages:
* </p>
* <ul>
* <li>They can interoperate via symbols they share in common.</li>
* <li>Low-level tools, such as backtrace printers, will have readable displays.</li>
* <li>Future JVM and language extensions can safely use the dangerous characters
* for structuring symbols, but will never interfere with valid spellings.</li>
* <li>Runtimes and compilers can use standard libraries for mangling and demangling.</li>
* <li>Occasional transliterations and name composition will be simple and regular,
* for classes, methods, and fields.</li>
* <li>Bytecode names will continue to be compact.
* When mangled, spellings will at most double in length, either in
* UTF8 or UTF16 format, and most will not change at all.</li>
* </ul>
*
*
* <h3> Suggestions for Human Readable Presentations </h3>
*
*
* <p>
* For human readable displays of symbols,
* it will be better to present a string-like quoted
* representation of the spelling, because JVM users
* are generally familiar with such tokens.
* We suggest using single or double quotes before and after
* mangled symbols which are not valid Java identifiers,
* with quotes, backslashes, and non-printing characters
* escaped as if for literals in the Java language.
* </p>
* <p>
* For example, an HTML-like spelling
* <code><big><b><pre></b></big></code> mangles to
* <code><big><b>\^pre\_</b></big></code> and could
* display more cleanly as
* <code><big><b>'<pre>'</b></big></code>,
* with the quotes included.
* Such string-like conventions are <em>not</em> suitable
* for mangled bytecode names, in part because
* dangerous characters must be eliminated, rather
* than just quoted. Otherwise internally structured
* strings like package prefixes and method signatures
* could not be reliably parsed.
* </p>
* <p>
* In such human-readable displays, invalidly mangled
* names should <em>not</em> be demangled and quoted,
* for this would be misleading. Likewise, JVM symbols
* which contain dangerous characters (like dots in field
* names or brackets in method names) should not be
* simply quoted. The bytecode names
* <code><big><b>\=phase\,1</b></big></code> and
* <code><big><b>phase.1</b></big></code> are distinct,
* and in demangled displays they should be presented as
* <code><big><b>'phase.1'</b></big></code> and something like
* <code><big><b>'phase'.1</b></big></code>, respectively.
* </p>
*/
public final class NameCodec {
private NameCodec() {
}
private static final char ESCAPE_C = '\\';
// empty escape sequence to avoid a null name or illegal prefix
private static final char NULL_ESCAPE_C = '=';
private static final String NULL_ESCAPE = ESCAPE_C+""+NULL_ESCAPE_C;
/**
* Canonical encoding for the empty name.
*/
public static final String EMPTY_NAME = new String(new char[] { ESCAPE_C, NULL_ESCAPE_C });
/**
* Encodes ("mangles") an unencoded symbolic name.
* @param name the symbolic name to mangle
* @return the mangled form of the symbolic name.
*/
public static String encode(final String name) {
final String bn = mangle(name);
assert((Object)bn == name || looksMangled(bn)) : bn;
assert(name.equals(decode(bn))) : name;
return bn;
}
/**
* Decodes ("demangles") an encoded symbolic name.
* @param name the symbolic name to demangle
* @return the demangled form of the symbolic name.
*/
public static String decode(final String name) {
String sn = name;
if (!sn.isEmpty() && looksMangled(name)) {
sn = demangle(name);
assert(name.equals(mangle(sn))) : name+" => "+sn+" => "+mangle(sn);
}
return sn;
}
private static boolean looksMangled(final String s) {
return s.charAt(0) == ESCAPE_C;
}
private static String mangle(final String s) {
if (s.length() == 0)
return NULL_ESCAPE;
// build this lazily, when we first need an escape:
StringBuilder sb = null;
for (int i = 0, slen = s.length(); i < slen; i++) {
final char c = s.charAt(i);
boolean needEscape = false;
if (c == ESCAPE_C) {
if (i+1 < slen) {
final char c1 = s.charAt(i+1);
if ((i == 0 && c1 == NULL_ESCAPE_C)
|| c1 != originalOfReplacement(c1)) {
// an accidental escape
needEscape = true;
}
}
} else {
needEscape = isDangerous(c);
}
if (!needEscape) {
if (sb != null) sb.append(c);
continue;
}
// build sb if this is the first escape
if (sb == null) {
sb = new StringBuilder(s.length()+10);
// mangled names must begin with a backslash:
if (s.charAt(0) != ESCAPE_C && i > 0)
sb.append(NULL_ESCAPE);
// append the string so far, which is unremarkable:
sb.append(s, 0, i);
}
// rewrite \ to \-, / to \|, etc.
sb.append(ESCAPE_C);
sb.append(replacementOf(c));
}
if (sb != null) return sb.toString();
return s;
}
private static String demangle(final String s) {
// build this lazily, when we first meet an escape:
StringBuilder sb = null;
int stringStart = 0;
if (s.startsWith(NULL_ESCAPE))
stringStart = 2;
for (int i = stringStart, slen = s.length(); i < slen; i++) {
char c = s.charAt(i);
if (c == ESCAPE_C && i+1 < slen) {
// might be an escape sequence
final char rc = s.charAt(i+1);
final char oc = originalOfReplacement(rc);
if (oc != rc) {
// build sb if this is the first escape
if (sb == null) {
sb = new StringBuilder(s.length());
// append the string so far, which is unremarkable:
sb.append(s, stringStart, i);
}
++i; // skip both characters
c = oc;
}
}
if (sb != null)
sb.append(c);
}
if (sb != null) return sb.toString();
return s.substring(stringStart);
}
private static final String DANGEROUS_CHARS = "\\/.;:$[]<>"; // \\ must be first
private static final String REPLACEMENT_CHARS = "-|,?!%{}^_";
private static final int DANGEROUS_CHAR_FIRST_INDEX = 1; // index after \\
private static final long[] SPECIAL_BITMAP = new long[2]; // 128 bits
static {
final String SPECIAL = DANGEROUS_CHARS + REPLACEMENT_CHARS;
for (final char c : SPECIAL.toCharArray()) {
SPECIAL_BITMAP[c >>> 6] |= 1L << c;
}
}
private static boolean isSpecial(final char c) {
if ((c >>> 6) < SPECIAL_BITMAP.length)
return ((SPECIAL_BITMAP[c >>> 6] >> c) & 1) != 0;
else
return false;
}
private static char replacementOf(final char c) {
if (!isSpecial(c)) return c;
final int i = DANGEROUS_CHARS.indexOf(c);
if (i < 0) return c;
return REPLACEMENT_CHARS.charAt(i);
}
private static char originalOfReplacement(final char c) {
if (!isSpecial(c)) return c;
final int i = REPLACEMENT_CHARS.indexOf(c);
if (i < 0) return c;
return DANGEROUS_CHARS.charAt(i);
}
private static boolean isDangerous(final char c) {
if (!isSpecial(c)) return false;
return (DANGEROUS_CHARS.indexOf(c) >= DANGEROUS_CHAR_FIRST_INDEX);
}
}