Cross calls

To show how to handle calls between contracts, first, let's implement two of them:

examples/src/features/cross_calls.rs

use odra::prelude::*;

#[odra::module]
pub struct CrossContract {
    pub math_engine: External<MathEngineContractRef>
}

#[odra::module]
impl CrossContract {
    pub fn init(&mut self, math_engine_address: Address) {
        self.math_engine.set(math_engine_address);
    }

    pub fn add_using_another(&self) -> u32 {
        self.math_engine.add(3, 5)
    }
}

#[odra::module]
pub struct MathEngine;

#[odra::module]
impl MathEngine {
    pub fn add(&self, n1: u32, n2: u32) -> u32 {
        n1 + n2
    }
}

MathEngine contract can add two numbers. CrossContract takes an Address in its init function and saves it in storage for later use. If we deploy the MathEngine first and take note of its address, we can then deploy CrossContract and use MathEngine to perform complicated calculations for us!

To perform a cross-contact call, we use the External module component and wrap the {{ModuleName}}ContractRef that was created for us by Odra:

examples/src/features/cross_calls.rs

pub struct CrossContract {
    pub math_engine: External<MathEngineContractRef>
}

and then we use the math_engine like any other contract/module:

examples/src/features/cross_calls.rs

self.math_engine.add(3, 5)

Alternatively, we could store a raw Address, then use the {{ModuleName}}ContractRef directly:

examples/src/features/cross_calls.rs

MathEngineContractRef::new(self.env(), math_engine_address).add(3, 5)

Contract Ref

We mentioned HostRef already in our Testing article - a host side reference to already deployed contract.

In the module context we use a ContractRef instead, to call other contracts.

Similarly to the HostRef trait implemetation for the module, the {{ModuleName}}ContractRef is generated automatically, by the #[odra::module] attribute.

The reference implements all the public endpoints to the contract (those marked as pub in #[odra::module] impl), and the {{ModuleName}}ContractRef::address() function, which returns the address of the contract.

External Contracts

Sometimes in our contract, we would like to interact with a someone else's contract, already deployed onto the blockchain. The only thing we know about the contract is the ABI.

For that purpose, we use #[odra:external_contract] attribute. This attribute should be applied to a trait. The trait defines the part of the ABI we would like to take advantage of.

Let's pretend the MathEngine we defined is an external contract. There is a contract with add() function that adds two numbers somewhere.

#[odra::external_contract]
pub trait Adder {
    fn add(&self, n1: u32, n2: u32) -> u32;
}

Odra automatically creates the AdderContractRef struct. Having an address, in the module context we can call:

struct Contract {
    adder: External<AdderContractRef>
}
// in some function
self.adder.add(3, 5)

// or

struct Contract {
    adder: Var<Address>
}
// in some function
AdderContractRef::new(self.env(), address).add(3, 5)

Loading the contract

Sometimes it is useful to load the deployed contract instead of deploying it by ourselves. This is especially useful when we want to test our contracts in Livenet backend. We can load the contract using load method on the Deployer:

examples/bin/erc20_on_livenet.rs

fn _load(env: &HostEnv) -> Erc20HostRef {
    let address = "hash-d26fcbd2106e37be975d2045c580334a6d7b9d0a241c2358a4db970dfd516945";
    let address = Address::from_str(address).unwrap();
    Erc20::load(env, address)
}

Testing

Let's see how we can test our cross calls using this knowledge:

examples/src/features/cross_calls.rs

#[cfg(test)]
mod tests {
    use super::{CrossContract, CrossContractInitArgs, MathEngineHostRef};
    use odra::host::{Deployer, HostRef, NoArgs};

    #[test]
    fn test_cross_calls() {
        let test_env = odra_test::env();
        let math_engine_contract = MathEngine::deploy(&test_env, NoArgs);
        let cross_contract = CrossContract::deploy(
            &test_env,
            CrossContractInitArgs {
                math_engine_address: *math_engine_contract.address()
            }
        );
        assert_eq!(cross_contract.add_using_another(), 8);
    }
}

Each test begins with a clean instance of the blockchain, with no contracts deployed. To test an external contract, we first deploy a MathEngine contract, although we won't directly utilize it. Instead, we only extract its address. Let's continue assuming there is a contract featuring the add() function that we intend to utilize.

#[cfg(test)]
mod tests {
    use super::*;
    use odra::{host::{Deployer, HostRef, NoArgs}};
    
    #[test]
    fn test_ext() {
        let test_env = odra_test::env();
        let adder = Adder::new(&test_env, get_adder_address(&test_env)).add(3, 5)
        assert_eq!(adder.add(1, 2), 3);
    }

    fn get_adder_address(test_env: &HostEnv) -> Address {
        let contract = MathEngine::deploy(test_env, NoArgs);
        *contract.address()
    }
}