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/*******************************************************************************
* Copyright (c) 2015 Jeff Martin.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the GNU Lesser General Public
* License v3.0 which accompanies this distribution, and is available at
* http://www.gnu.org/licenses/lgpl.html
* <p>
* Contributors:
* Jeff Martin - initial API and implementation
******************************************************************************/
package cuchaz.enigma.bytecode;
import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javassist.bytecode.AttributeInfo;
import javassist.bytecode.ConstPool;
import javassist.bytecode.MethodInfo;
public class MethodParametersAttribute extends AttributeInfo {
private MethodParametersAttribute(ConstPool pool, List<Integer> parameterNameIndices) {
super(pool, "MethodParameters", writeStruct(parameterNameIndices));
}
public static void updateClass(MethodInfo info, List<String> names) {
// add the names to the class const pool
ConstPool constPool = info.getConstPool();
List<Integer> parameterNameIndices = new ArrayList<Integer>();
for (String name : names) {
if (name != null) {
parameterNameIndices.add(constPool.addUtf8Info(name));
} else {
parameterNameIndices.add(0);
}
}
// add the attribute to the method
info.addAttribute(new MethodParametersAttribute(constPool, parameterNameIndices));
}
private static byte[] writeStruct(List<Integer> parameterNameIndices) {
// JVM 8 Spec says the struct looks like this:
// http://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.24
// uint8 num_params
// for each param:
// uint16 name_index -> points to UTF8 entry in constant pool, or 0 for no entry
// uint16 access_flags -> don't care, just set to 0
ByteArrayOutputStream buf = new ByteArrayOutputStream();
DataOutputStream out = new DataOutputStream(buf);
// NOTE: java hates unsigned integers, so we have to be careful here
// the writeShort(), writeByte() methods will read 16,8 low-order bits from the int argument
// as long as the int argument is in range of the unsigned short/byte type, it will be written as an unsigned short/byte
// if the int is out of range, the byte stream won't look the way we want and weird things will happen
final int SIZEOF_UINT8 = 1;
final int SIZEOF_UINT16 = 2;
final int MAX_UINT8 = (1 << 8) - 1;
final int MAX_UINT16 = (1 << 16) - 1;
try {
assert (parameterNameIndices.size() >= 0 && parameterNameIndices.size() <= MAX_UINT8);
out.writeByte(parameterNameIndices.size());
for (Integer index : parameterNameIndices) {
assert (index >= 0 && index <= MAX_UINT16);
out.writeShort(index);
// just write 0 for the access flags
out.writeShort(0);
}
out.close();
byte[] data = buf.toByteArray();
assert (data.length == SIZEOF_UINT8 + parameterNameIndices.size() * (SIZEOF_UINT16 + SIZEOF_UINT16));
return data;
} catch (IOException ex) {
throw new Error(ex);
}
}
}
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