/*
* Copyright 2008 Google Inc.
*
* 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.gwt.dev.js;
import com.google.gwt.dev.js.ast.JsName;
import com.google.gwt.dev.js.ast.JsProgram;
import com.google.gwt.dev.js.ast.JsRootScope;
import com.google.gwt.dev.js.ast.JsScope;
import java.util.Iterator;
import java.util.List;
/**
* A namer that uses short, unrecognizable idents to minimize generated code
* size.
*/
public class JsObfuscateNamer {
/**
* A lookup table of base-64 chars we use to encode idents.
*/
private static final char[] sBase64Chars = new char[] {
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B',
'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '$', '_', '0', '1',
'2', '3', '4', '5', '6', '7', '8', '9'};
public static void exec(JsProgram program) {
new JsObfuscateNamer(program).execImpl();
}
/**
* Communicates to a parent scope the maximum id used by any of its children.
*/
private int maxChildId = 0;
private final JsProgram program;
/**
* A temp buffer big enough to hold at least 32 bits worth of base-64 chars.
*/
private final char[] sIdentBuf = new char[6];
public JsObfuscateNamer(JsProgram program) {
this.program = program;
}
private void execImpl() {
visit(program.getRootScope());
}
private boolean isLegal(JsScope scope, String newIdent) {
if (JsKeywords.isKeyword(newIdent)) {
return false;
}
/*
* Never obfuscate a name into an identifier that conflicts with an existing
* unobfuscatable name! It's okay if it conflicts with an existing
* obfuscatable name, since that name will get obfuscated to something else
* anyway.
*/
return (scope.findExistingUnobfuscatableName(newIdent) == null);
}
private String makeObfuscatedIdent(int id) {
// Use base-54 for the first character of the identifier,
// so that we don't use any numbers (which are illegal at
// the beginning of an identifier).
//
int i = 0;
sIdentBuf[i++] = sBase64Chars[id % 54];
id /= 54;
// Use base-64 for the rest of the identifier.
//
while (id != 0) {
sIdentBuf[i++] = sBase64Chars[id & 0x3f];
id >>= 6;
}
return new String(sIdentBuf, 0, i);
}
private void visit(JsScope scope) {
// Save off the maxChildId which is currently being computed for my parent.
int mySiblingsMaxId = maxChildId;
/*
* Visit my children first. Reset maxChildId so that my children will get a
* clean slate: I do not communicate to my children.
*/
maxChildId = 0;
List<JsScope> children = scope.getChildren();
for (Iterator<JsScope> it = children.iterator(); it.hasNext();) {
visit(it.next());
}
// maxChildId is now the max of all of my children's ids
JsRootScope rootScope = program.getRootScope();
if (scope == rootScope) {
return;
}
// Visit my idents.
int curId = maxChildId;
for (Iterator<JsName> it = scope.getAllNames(); it.hasNext();) {
JsName name = it.next();
if (!name.isObfuscatable()) {
// Unobfuscatable names become themselves.
name.setShortIdent(name.getIdent());
continue;
}
String newIdent;
while (true) {
// Get the next possible obfuscated name
newIdent = makeObfuscatedIdent(curId++);
if (isLegal(scope, newIdent)) {
break;
}
}
name.setShortIdent(newIdent);
}
maxChildId = Math.max(mySiblingsMaxId, curId);
}
}