Multiple arguments passed as a single tuple in canister-to-canister calls

[sasa-tomic]

This issue documents one problem that we've observed while developing BigMap with the rust-cdk.

In that code we wrote, we're making put update calls from the index canister to the data bucket canisters. The put update call has two arguments fn put (key: Vec<u8>, value: Vec<u8>) - which is likely the source of problems.

Invoking the put function from the user works as expected, e.g. with the dfx canister call command - so all good so far.

However, when the put function is invoked from the index canister, argument parsing fails. By trial and error, I have found that when the index canister invokes data_canister.put(key, value), the data canister instead receives the arguments as fn put((key, value)), i.e., the arguments are not unpacked at the destination canister.

The following work-around works. I've added another method which is invoked from the index canister, and this method receives the argument tuple, unpacks it, and invokes the regular put function.

#[update]
fn put_from_index(key_value: (Key, Val)) -> bool {
    let (key, value) = key_value;
    put(key, value)
}

The sample code which demonstrates this is here: https://github.com/dfinity/bigmap-rs/blob/eefec72442898264ce6d7198b041bb9a64b4128c/src/bigmap_data.rs#L72

[adamspofford-dfinity]

Is this still an issue with the latest CDK version?

[sasa-tomic]

Great question @adamspofford-dfinity -- no idea! :) I haven't worked on Rust BigMap in quite a while and not a lot of other code makes inter-canister calls. Possibly the OpenChat folks do it. But it shouldn't be hard to reproduce with two canisters.