extra test and method encode fix

ipc/tests/examples.rs

@@ -45,4 +45,16 @@ mod tests {
 		assert_eq!(vec![0, 0, 0, 0, 0, 5], service_proxy.socket().borrow().write_buffer.clone());
 		assert_eq!(10, result);
 	}
+
+	#[test]
+	fn call_service_proxy_optional() {
+		let mut socket = TestSocket::new();
+		socket.read_buffer = vec![0, 0, 0, 10];
+		let service_proxy = ServiceProxy::new(socket);
+
+		let result = service_proxy.rollback(Some(5), 10);
+
+		assert_eq!(vec![0, 1, 1, 0, 0, 0, 5, 0, 0, 0, 10], service_proxy.socket().borrow().write_buffer.clone());
+		assert_eq!(10, result);
+	}
 }

ipc/tests/service.rs.in

@@ -29,10 +29,11 @@ impl Service {
 		*lock = *lock + f as usize;
 		f
 	}
-	pub fn rollback(&self, a: u32, b: u32) -> i32 {
+	pub fn rollback(&self, a: Option<u32>, b: u32) -> i32 {
+		let a_0 = a.unwrap_or_else(|| 0);
 		let mut lock = self.rollbacks.write().unwrap();
-		*lock = *lock + a as usize - b as usize;
-		(a - b) as i32
+		*lock = *lock + a_0 as usize - b as usize;
+		(a_0 - b) as i32
 	}
 }