JarEntry entry = sourceZip.getJarEntry(jarName);
byte[] vanillaBytes = entry != null ? ByteStreams.toByteArray(sourceZip.getInputStream(entry)) : new byte[0];
byte[] patchedBytes = Files.toByteArray(targetFile);
byte[] diff = delta.compute(vanillaBytes, patchedBytes);
ByteArrayDataOutput diffOut = ByteStreams.newDataOutput(diff.length + 50);
// Original name
diffOut.writeUTF(name);