How to migrate ManualReply to ic_cdk v0.18

Developers Rust
1

I don’t get how to adapt the deprecated ic_cdk::api::call::ManualReply of the ic_cdk v0.18 and I cannot find any description in the migration guide.

Has anyone an example to share?

For example, I would like to adapt:

#[update(guard = "caller_is_admin_controller", manual_reply = true)]
fn reject_proposal(proposal: RejectProposal) -> ManualReply<()> {
    match make_reject_proposal(&proposal) {
        Ok(_) => ManualReply::one(()),
        Err(e) => ManualReply::reject(e.to_string()),
    }
}

And the deprecation notice says Please use std::marker::PhantomData with manual_reply instead, so I tried following:

#[update(guard = "caller_is_admin_controller", manual_reply = true)]
fn reject_proposal(proposal: RejectProposal) -> PhantomData<()> {
    match make_reject_proposal(&proposal) {
        Ok(_) => msg_reply(()),
        Err(e) => msg_reject(e.to_string()),
    }

    PhantomData
}

but then I get the trait AsRef<[u8]> is not implemented for ()

2

The usage of PhantomData with manual_reply is correct.

The error probably came from msg_reply(()). The function signature is pub fn msg_reply<T: AsRef<[u8]>>(data: T). So to reply the call with empty bytes, you can invoke msg_reply(vec![]).

3

Thanks. But that’s not the same, isn’t it? Returning empty bytes is not the same as (), so wouldn’t this produce a different Candid response on the wire and therefore require changes to the definition and my clients to avoid issues (which is unlikely to happen)?

4

To reply the () value, you will need to encode it into bytes first.

let reply_bytes = candid::encode_one(()).unwrap(); 
ic_cdk::api::msg_reply(reply_bytes);
5

encode_one was the key!

I created a util for my code base that basically replicates the implementation of ManualReply and adds the encoded_one. CI passes and I did a quick manual test, therefore seems good to go.

PR if useful to anyone :backhand_index_pointing_right: junobuild/juno#1867

Thanks for the help!