Host Communication

One of the things that your contract will probably do is to query the host for some information - what is the current time? Who called me? Following example shows how to do this:

examples/src/features/host_functions.rs

use odra::Variable;
use odra::types::{BlockTime, Address};

#[odra::module]
pub struct HostContract {
    name: Variable<String>,
    created_at: Variable<BlockTime>,
    created_by: Variable<Address>,
}

#[odra::module]
impl HostContract {
    #[odra(init)]
    pub fn init(&mut self, name: String) {
        self.name.set(name);
        self.created_at.set(odra::contract_env::get_block_time());
        self.created_by.set(odra::contract_env::caller())
    }

    pub fn name(&self) -> String {
        self.name.get_or_default()
    }
}

As you can see, we are calling functions from odra::contract_env. get_block_time() will return the current block time wrapped in Odra type BlockTime. caller() will return an Odra Address of a caller (this can be an external caller or another contract).

info

You will learn more functions that Odra exposes from host and types it uses in further articles.

What's next

In the next article, we'll dive into testing your contracts with Odra, so you can check that the code we presented in fact works!