​ This crate provides Terra-specific bindings to enable your CosmWasm smart contracts to interact with the Terra blockchain by exposing messages and queriers that can be emitted and used from within your contract. ​

​ Add the following to your smart contract's Cargo.toml: ​

[dependencies]
terra-cosmwasm = { version = "1.2" }

​

​ Currently, the Terra bindings include: ​

• Query support for:
  • Market
    • swap rate between 2 currencies at market price
  • Treasury
    • current tax cap for a denomination
    • current tax rate
  • Oracle
    • exchange rates for the given base_denom / quote_denoms ​
• Messages
  • MsgSwap
  • MsgSwapSend ​

​

​ In order to use the query functions enabled by the bindings, create a TerraQuerier instance within your contract logic -- in either init(), handle(), or query() entrypoints. You can access all the enabled queries through this object. ​

// src/contract.rs
use cosmwasm_std::Coin;
use terra_cosmwasm::{ TerraQuerier, SwapResponse, TaxRateResponse, TaxCapResponse, ExchangeRatesResponse };
​
...
​
// handler
pub fn try_something<S: Storage, A: Api, Q: Querier>(
    deps: &mut Extern<S, A, Q>,
    env: Env,
    offer: &Coin
) -> StdResult<HandleResponse> {
    let querier = TerraQuerier::new(&deps.querier);
    let swap_rate: SwapResponse = querier.query_swap(offer.clone(), "uusd")?;
    let tax_cap: TaxCapResponse = querier.query_tax_cap("usdr")?;
    let tax_rate: TaxRateResponse = querier.query_tax_rate()?;
    let exchange_rates: ExchangeRatesResponse = querier.query_exchange_rates("uusd", vec!["uluna", "ukrw"])?;
    ...
}

​

​ NOTE: The Terra bindings do not cover messages that have already been implemented by the CosmWasm team, such as staking-related messages and fundamental ones like MsgSend. ​ You may want your contract to perform messages such as MsgSwap and MsgSwapSend operations at the end of its execution. To do this, create a message using the predefined functions: ​

• create_swap_msg
• create_swap_send_msg ​ And add it to the vector of messages in your HandleResponse before you return Ok. ​

use cosmwasm_std::CosmosMsg;
use terra_cosmwasm::{create_swap_msg, TerraMsgWrapper};
​
...
​
pub fn try_something<S: Storage, A: Api, Q: Querier>(
    deps: &mut Extern<S, A, Q>,
    env: Env,
    offer: &Coin
) -> StdResult<HandleResponse<TerraMsgWrapper>> {
    ...
​
    let msg: CosmosMsg<TerraMsgWrapper> = create_swap_msg(contract_addr, offer_coin, ask_denom);
    let res = HandleResponse {
        messages: vec![msg],
        log: vec![],
        data: None
    };
    Ok(res)
}