do not append on empty buffer (#268)

Co-authored-by: Linwei Shang <[email protected]>

e2e-tests/canisters/reverse.rs

@@ -6,5 +6,9 @@ fn reverse() {
     assert_eq!(arg_bytes.len(), arg_data_raw_size());
     reply_raw(arg_bytes.into_iter().rev().collect::<Vec<_>>().as_ref());
 }
+#[export_name = "canister_update empty_call"]
+fn empty_call() {
+    reply_raw(&[]);
+}
 
 fn main() {}

e2e-tests/tests/e2e.rs

@@ -126,6 +126,11 @@ fn test_raw_api() {
 
     let result = env.query(canister_id, "reverse", vec![1, 2, 3, 4]).unwrap();
     assert_eq!(result, WasmResult::Reply(vec![4, 3, 2, 1]));
+
+    let result = env
+        .execute_ingress(canister_id, "empty_call", Default::default())
+        .unwrap();
+    assert_eq!(result, WasmResult::Reply(Default::default()));
 }
 
 #[test]

src/ic-cdk/CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - Use explicitly type u8 in vector initialization (#264)
+- Make `reply_raw` avoid writing empty replies
 - Uses new format for candid environment variables in import macros. Requires DFX >=0.9.2 (#270)
 
 ## [0.5.1] - 2022-05-16

src/ic-cdk/src/api/call.rs

@@ -573,7 +573,9 @@ pub fn arg_data_raw_size() -> usize {
 /// Replies with the bytes passed
 pub fn reply_raw(buf: &[u8]) {
     unsafe {
-        ic0::msg_reply_data_append(buf.as_ptr() as i32, buf.len() as i32);
+        if !buf.is_empty() {
+            ic0::msg_reply_data_append(buf.as_ptr() as i32, buf.len() as i32)
+        };
         ic0::msg_reply();
     }
 }