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/*******************************************************************************
* Copyright (c) 2014 Jeff Martin.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the GNU Public License v3.0
* which accompanies this distribution, and is available at
* http://www.gnu.org/licenses/gpl.html
*
* 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://cr.openjdk.java.net/~mr/se/8/java-se-8-fr-spec-01/java-se-8-jvms-fr-diffs.pdf
// 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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