Interchain Module Communication

Introduction

Interchain Abstract Accounts allow for executing actions on behalf of an Account on another chain. However, this mechanism doesn’t allow modules installed on these Accounts to communicate securely by default. To clarify this statement, imagine an Abstract module “X” on a chain. This module wants to send a message to another module “Y” on a remote chain. The module on the remote chain wants to ensure that the message was sent by module X.

In order to do so, the developer could attempt to send his message through the user’s Account using the Account IBC infrastructure. However, using this method it is impossible for module Y to verify that the content of the message was indeed sent by the origin module X. Executing actions through the Account is great for permissionless actions (like depositing assets into a protocol) but is unsuited for permissioned entry-points. So what now?

Secure Interchain Module Communication

To allow modules to send messages securely to other modules across IBC, we have developed an Interchain Module Communication (IMC) protocol. IMC allows developers to send messages from a module directly to another module on a different chain. The module that receives the IBC message can then access the source module details. This way IMC allows interoperable permissioned actions between all Abstract modules.

flowchart
    subgraph Module IBC
        direction TB
        subgraph Chain A
        Mod1[Module] ==> A1[Account]
        end

        subgraph Chain B
        Mod2[Module] ==> A2[Account]
        end
        Mod1 <-.IBC.-> Mod2
    end

Let’s see how to create a contract with IMC capabilities by following the ping-pong example app that you can find here.

Sending a message

In order to send a message, a module needs to interact with the ibc-client module. You can use the IbcClient API to interact with the ibc-client. The example below shows how the ping-pong app sends a message to an instance of itself on another chain.

#![allow(unused)]
fn main() {
    let self_module_info = module.module_info()?;
    let ibc_client: IbcClient<_> = module.ibc_client(deps.as_ref());
    let ibc_action: CosmosMsg = ibc_client.module_ibc_action(
        opponent_chain.clone(),
        self_module_info,
        // Start by playing a Ping
        &PingPongIbcMsg {
            hand: PingOrPong::Ping,
        },
        Some(Callback::new(&PingPongCallbackMsg::Pinged {
            opponent_chain,
        })?),
    )?;
}

• opponent_chain is the TruncatedChainId of the destination chain where the app is expected to be installed.
• target_module describes the module on which the message will be executed on the remote chain. In this case, it is another instance of the ping-pong app.
• msg is the message that will be executed on the remote module via a custom endpoint. We explain in the section about receiving a message how this message is used by the targeted module.
• callback_info is used to request a callback once the packet has been received and acknowledged. We explain more about this behavior in the acks and callbacks section

Receiving a message

In order for a module to receive a message coming from a remote Module, it needs to implement the module-ibc endpoint. The function signature for this endpoint is:

#![allow(unused)]
fn main() {
pub fn module_ibc(deps: DepsMut, env: Env, module: Module, source_module: ModuleIbcInfo, msg: Binary) -> Result<Response, Error>;
}

The deps, env and module variables are identical to the execute endpoint and should be clear to you by now. If not here are some links to more documentation:

• deps and env are described in the CosmWasm documentation
• module (or App or Adapter usually) are described in the Abstract SDK section of our docs

The msg variable contains the msg constructed by the module on the source chain. In this case the PingPongIbcMsg.

The source_module variable contains information about the module that sent the message, as well as the source chain information. This information can be used to assert the source of a message, like so:

#![allow(unused)]
fn main() {
pub fn receive_module_ibc(
    deps: DepsMut,
    env: Env,
    module: App,
    source_module: ModuleIbcInfo,
    msg: Binary,
) -> AppResult<Response> {
    let this_module_info = module.module_info()?;
    ensure_eq!(
        source_module.module,
        this_module_info,
        AppError::NotPingPong {
            source_module: source_module.module.clone()
        }
    );
    let ping_msg: PingPongIbcMsg = from_json(msg)?;
}

For example, the above code will return an error if the source module doesn’t match the receiving module. This way only other ping-pong apps can call this ping-pong app!

Callbacks

As mentioned callbacks can be added to the IBC flow progress or revert your contract’s state depending on the packets execution result.

Callback Execution

If a callback was requested when sending a module IBC message, the callback will be executed wether the execution was successful or not. A callback message will be executed on the ̀ibc_callback endpoint of the calling module. The function signature for this endpoint is:

#![allow(unused)]
fn main() {
pub fn ibc_callback(deps: DepsMut, env: Env, module: Module, callback: Callback, result: IbcResult,) -> Result<Response, Error>;
}

The callback variable contains a msg: Binary that is the encoded callback message that was provided to the callback on construction. In the ping-pong case this was PingPongCallbackMsg::Pinged.

The result contains the result data from the IBC packet execution. You can match against this result to assert that the remote execution was successful and roll back state if it was not.

Specification of Interchain Module Communication

This part is not yet done. This is an outstanding TODO for the Abstract Team. If you’re a module developer, you should have all the information you need in the previous sections. Good luck! 🚀