CosmWasm: A Rust Framework Tutorial/Course 10

In previous chapter, we learnt how increment the counter value by 1. Before learning to reset the counter, let’s take a look at how to only read the underlying storage on the blockchain.

#[cfg_attr(not(feature = "library"), entry_point)]
pub fn query(deps: Deps, _env: Env, msg: QueryMsg) -> StdResult<Binary> {
    match msg {
        QueryMsg::GetCount {} => to_binary(&query::count(deps)?),
    }
}

The above code defines the 3rd entry point for the CosmWasm contract. It looks quite similar to the earlier entry point which was execute. The main difference is that return type has changed and we return the response in a binary. Binary is often used when working with low-level data. The possible values of the incoming message are defined in msg.rs

#[cw_serde]
#[derive(QueryResponses)]
pub enum QueryMsg {
    // GetCount returns the current count as a json-encoded number
    #[returns(GetCountResponse)]
    GetCount {},
}

// We define a custom struct for each query response
#[cw_serde]
pub struct GetCountResponse {
    pub count: i32,
}

A simple variant of enum QueryMsg is defined which is going to return response of type GetCountResponse. GetCountResponse has only one field i.e count of type integer

pub mod query {
    use super::*;

    pub fn count(deps: Deps) -> StdResult<GetCountResponse> {
        let state = STATE.load(deps.storage)?;
        Ok(GetCountResponse { count: state.count })
    }
}

The function count responsible for dealing with GetCount message simply loads the value of STATE and returns the value wrapped in Ok. Last but not least let’s take a look at the test to check whether correct value of count is not only being stored but returned as well.

   #[test]
    fn increment() {
        let mut deps = mock_dependencies();

        let msg = InstantiateMsg { count: 17 };
        let info = mock_info("creator", &coins(2, "token"));
        let _res = instantiate(deps.as_mut(), mock_env(), info, msg).unwrap();

        // beneficiary can release it
        let info = mock_info("anyone", &coins(2, "token"));
        let msg = ExecuteMsg::Increment {};
        let res = execute(deps.as_mut(), mock_env(), info, msg).unwrap();

        // should increase counter by 1
        let res = query(deps.as_ref(), mock_env(), QueryMsg::GetCount {}).unwrap();
        let value: GetCountResponse = from_binary(&res).unwrap();
        assert_eq!(18, value.count);
    }

Following lines have been added to our previous written test.

	    // should increase counter by 1
        let res = query(deps.as_ref(), mock_env(), QueryMsg::GetCount {}).unwrap();
        let value: GetCountResponse = from_binary(&res).unwrap();
        assert_eq!(18, value.count);

These lines simply send the GetCount variant of QueryMsg and then convert it from binary to compare it with desired value.