Add ROFL query to example and docs

Show how EVM queries to Sapphire can be used in ROFL.

Taken from the ROFL example, sth like this may work to fetch the last submitted observation:

let res = env.client().query(
            0,
            "evm.SimulateCall",
            module_evm::types::SimulateCallQuery {
                gas_price: 10_000.into(),
                gas_limit: 100_000,
                caller: module_evm::derive_caller::from_sigspec(&SignatureAddressSpec::Secp256k1Eth(sdk_pub_key)).unwrap(),
                address: Some(ORACLE_CONTRACT_ADDRESS.parse().unwrap()),
                value: 0.into(),
                 data: [
                   ethabi::short_signature("getLastObservation", &[]).to_vec(),
                   ethabi::encode(&[]),
                 ].concat(),
            },
        ).await?;
        println!("{:?}", res);

Based on this code https://github.com/oasisprotocol/oasis-sdk/blob/main/runtime-sdk/modules/evm/src/mock.rs#L168-L179

This is the working code snippet to read the getLastObservation view function from the ROFL oracle example.

async fn get_last_observation(self: Arc<Self>, env: Environment<Self>) -> Result<(u128, u64)> {
    let data: Vec<u8> = [
        ethabi::short_signature("getLastObservation", &[]).to_vec(),
        ethabi::encode(&[]),
    ]
    .concat();

    let sdk_pub_key =
        secp256k1::PublicKey::from_bytes(env.signer().public_key().as_bytes()).unwrap();

    let caller = module_evm::derive_caller::from_sigspec(&SignatureAddressSpec::Secp256k1Eth(
        sdk_pub_key,
    ))
    .unwrap();

    let res: Vec<u8> = env
        .client()
        .query(
            env.client().latest_round().await?.into(),
            "evm.SimulateCall",
            module_evm::types::SimulateCallQuery {
                gas_price: 10_000.into(),
                gas_limit: 100_000,
                caller,
                address: Some(ORACLE_CONTRACT_ADDRESS.parse().unwrap()),
                value: 0.into(),
                data,
            },
        )
        .await?;

    let decoded = ethabi::decode(
        &[
            ethabi::ParamType::Uint(128), // _value
            ethabi::ParamType::Uint(256), // _block
        ],
        &res,
    )
    .map_err(|e| anyhow::anyhow!("Failed to decode response: {}", e))?;

    let value = decoded[0].clone().into_uint().unwrap().as_u128();
    let block = decoded[1].clone().into_uint().unwrap().as_u64();

    Ok((value, block))
}

match self.get_last_observation(env).await {
    Ok((value, block)) => {
        let price = value as f64 / 1_000_000.0;
        println!(
            "Last observation: ${:.6} ROSE/USDT at block {}",
            price, block
        );
    }
    Err(err) => println!("Failed to get last observation: {:?}", err),
}

oasisprotocol / oasis-sdk

Add ROFL query to example and docs #1999