1 files changed, 80 insertions, 0 deletions

diff --git a/src/cuchaz/enigma/bytecode/MethodParametersAttribute.java b/src/cuchaz/enigma/bytecode/MethodParametersAttribute.java
new file mode 100644
index 0000000..0b29403
--- /dev/null
+++ b/src/cuchaz/enigma/bytecode/MethodParametersAttribute.java
@@ -0,0 +1,80 @@
+/*******************************************************************************
+ * 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.List;
+
+import javassist.bytecode.AttributeInfo;
+import javassist.bytecode.ConstPool;
+
+public class MethodParametersAttribute extends AttributeInfo
+{
+        public MethodParametersAttribute( ConstPool pool, int attributeNameIndex, List<Integer> parameterNameIndices )
+        {
+                super( pool, "MethodParameters", writeStruct( attributeNameIndex, parameterNameIndices ) );
+        }
+        
+        private static byte[] writeStruct( int attributeNameIndex, List<Integer> parameterNameIndices )
+        {
+                // JVM 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
+                // uint16 name_index -> points to UTF8 entry in constant pool that says "MethodParameters"
+                // uint32 length -> length of this struct, minus 6 bytes (ie, length of num_params and parameter array)
+                // 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_UINT16 = 2;
+                final int MAX_UINT8 = ( 1 << 8 ) - 1;
+                final int MAX_UINT16 = ( 1 << 16 ) - 1;
+                final long MAX_UINT32 = ( 1 << 32 ) - 1;
+                
+                try
+                {
+                        assert( attributeNameIndex >= 0 && attributeNameIndex <= MAX_UINT16 );
+                        out.writeShort( attributeNameIndex );
+                        
+                        long length = SIZEOF_UINT16 + parameterNameIndices.size()*( SIZEOF_UINT16 + SIZEOF_UINT16 );
+                        assert( length >= 0 && length <= MAX_UINT32 );
+                        out.writeInt( (int)length );
+                        
+                        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();
+                        return buf.toByteArray();
+                }
+                catch( IOException ex )
+                {
+                        throw new Error( ex );
+                }
+        }
+}