README.md

Cross-Contract Hello Contract

The smart contract implements the simplest form of cross-contract calls: it calls the Hello NEAR example to get and set a greeting.

// Public - query external greeting
pub fn query_greeting(&self) -> Promise {
  // Create a promise to call HelloNEAR.get_greeting()
  let promise = hello_near::ext(self.hello_account.clone())
    .with_static_gas(Gas(5*TGAS))
    .get_greeting();
  
  return promise.then( // Create a promise to callback query_greeting_callback
    Self::ext(env::current_account_id())
    .with_static_gas(Gas(5*TGAS))
    .query_greeting_callback()
  )
}

#[private] // Public - but only callable by env::current_account_id()
pub fn query_greeting_callback(&self, #[callback_result] call_result: Result<String, PromiseError>) -> String {
  // Check if the promise succeeded by calling the method outlined in external.rs
  if call_result.is_err() {
    log!("There was an error contacting Hello NEAR");
    return "".to_string();
  }

  // Return the greeting
  let greeting: String = call_result.unwrap();
  greeting
}

// Public - change external greeting
pub fn change_greeting(&mut self, new_greeting: String) -> Promise {
  // Create a promise to call HelloNEAR.set_greeting(message:string)
  hello_near::ext(self.hello_account.clone())
    .with_static_gas(Gas(5*TGAS))
    .set_greeting(new_greeting)
  .then( // Create a callback change_greeting_callback
    Self::ext(env::current_account_id())
    .with_static_gas(Gas(5*TGAS))
    .change_greeting_callback()
  )
}

#[private]
pub fn change_greeting_callback(&mut self, #[callback_result] call_result: Result<(), PromiseError>) -> bool {
  // Return whether or not the promise succeeded using the method outlined in external.rs
  if call_result.is_err() {
    env::log_str("set_greeting was successful!");
    return true;
  } else {
    env::log_str("set_greeting failed...");
    return false;
  }
}

Quickstart

1. Make sure you have installed rust.
2. Install the NEAR CLI

1. Build and Deploy the Contract

You can automatically compile and deploy the contract in the NEAR testnet by running:

./deploy.sh

Once finished, check the neardev/dev-account file to find the address in which the contract was deployed:

cat ./neardev/dev-account  # dev-1659899566943-21539992274727

2. Get the Greeting

query_greeting performs a cross-contract call, calling the get_greeting() method from hello-nearverse.testnet.

Call methods can only be invoked using a NEAR account, since the account needs to pay GAS for the transaction.

# Use near-cli to ask the contract to query the greeting
near call <dev-account> query_greeting --accountId <dev-account>

3. Set a New Greeting

change_greeting performs a cross-contract call, calling the set_greeting({greeting:String}) method from hello-nearverse.testnet.

Call methods can only be invoked using a NEAR account, since the account needs to pay GAS for the transaction.

# Use near-cli to change the greeting
near call <dev-account> change_greeting '{"new_greeting":"XCC Hi"}' --accountId <dev-account>

Tip: If you would like to call change_greeting or query_greeting using your own account, first login into NEAR using:

# Use near-cli to login your NEAR account
near login

and then use the logged account to sign the transaction: --accountId <your-account>.