Add helpers for code replacement

Author: ago1024

src/launcher/org/gotti/wurmunlimited/modloader/classhooks/CodeReplacer.java

@@ -0,0 +1,77 @@
+package org.gotti.wurmunlimited.modloader.classhooks;
+
+import javassist.NotFoundException;
+import javassist.bytecode.BadBytecode;
+import javassist.bytecode.CodeAttribute;
+import javassist.bytecode.CodeIterator;
+
+/**
+ * Replace byte code fragments with other byte code.
+ */
+public class CodeReplacer {
+
+	private CodeAttribute codeAttribute;
+
+	/**
+	 * Initialize code replace.
+	 * 
+	 * @param codeAttribute
+	 */
+	public CodeReplacer(CodeAttribute codeAttribute) {
+		this.codeAttribute = codeAttribute;
+	}
+
+	/**
+	 * Replace the code
+	 * @param search Code to replace
+	 * @param replacement Replacement
+	 * @throws NotFoundException The code to replace was not found
+	 * @throws BadBytecode Something was wrong with the byte code
+	 */
+	public void replaceCode(byte[] search, byte[] replacement) throws NotFoundException, BadBytecode {
+		int pos = findCode(search);
+		
+		if (replacement.length <= search.length) {
+			// Replacement is shorter or the same length as the code to replace
+			// Replace the code and insert nops at the end
+			writeWithNops(pos, replacement, search.length - replacement.length);
+		} else {
+			// Replacement is longer than the original code
+			// Insert nops first, then write the replacement over nops and code to replace
+			writeOverlapping(pos, replacement, replacement.length - search.length);
+		}
+	}
+
+	private void writeOverlapping(int pos, byte[] replacement, int overlapping) throws BadBytecode {
+		CodeIterator codeIterator = codeAttribute.iterator();
+		codeIterator.insertGap(pos, overlapping);
+		codeIterator.write(replacement, pos);
+	}
+
+	private void writeWithNops(int pos, byte[] replacement, int gap) {
+		byte[] nops = new byte[gap];
+		CodeIterator codeIterator = codeAttribute.iterator();
+		codeIterator.write(replacement, pos);
+		codeIterator.write(nops, pos + replacement.length); 
+	}
+
+	// Find the code fragment
+	private int findCode(byte[] search) throws NotFoundException {
+		byte[] code = codeAttribute.getCode();
+		for (int i = 0, j = 0, backtrack = 0; i < code.length && j < search.length; i++) {
+			if (code[i] == search[j]) {
+				if (j == 0) {
+					backtrack = i;
+				}
+				j++;
+				if (j == search.length) {
+					return backtrack;
+				}
+			} else if (j > 0) {
+				i = backtrack;
+				j = 0;
+			}
+		}
+		throw new NotFoundException("code");
+	}
+}

src/launcher/org/gotti/wurmunlimited/modloader/classhooks/LocalNameLookup.java

@@ -0,0 +1,26 @@
+package org.gotti.wurmunlimited.modloader.classhooks;
+
+import javassist.NotFoundException;
+import javassist.bytecode.LocalVariableAttribute;
+
+public class LocalNameLookup {
+
+	private LocalVariableAttribute attr;
+
+	public LocalNameLookup(LocalVariableAttribute attribute) {
+		this.attr = attribute;
+	}
+
+	public int get(String name) throws NotFoundException {
+		if (name == null) {
+			throw new NotFoundException(name);
+		}
+		for (int i = 0; i < attr.tableLength(); i++) {
+			if (name.equals(attr.variableName(i))) {
+				return attr.index(i);
+			}
+		}
+		throw new NotFoundException(name);
+	}
+
+}