1 files changed, 86 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..512e65a
--- /dev/null
+++ b/src/cuchaz/enigma/bytecode/MethodParametersAttribute.java
@@ -0,0 +1,86 @@
+/*******************************************************************************
+ * 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
+ * 
+ * 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);
+                }
+        }
+}