Cross-Contract execution in Ink contracts

Question

    #[ink(message)]
    pub fn test_cross_contract_call(
        &mut self,
        calls_count: u64,
    ) {
        let selector: Selector = Selector::new([0x6b, 0x25, 0xcb, 0x19]);
        let response: Result<u64> = build_call::<DefaultEnvironment>()
                .call_type(
                    Call::new()
                        .callee(self.env().account_id())
                        .transferred_value(0)
                        .gas_limit(50000),
                )
                .call_flags(ink::env::CallFlags::default().set_allow_reentry(true))
                .exec_input(
                    ExecutionInput::new(selector)
                        .push_arg(calls_count)
                )
                .returns::<u64>()
                .fire();
        self.value = response.unwrap();
    }

    #[ink(message, selector = 0x6b25cb19)]
    pub fn dummy_function(
        &mut self,
        value: u64,
    ) -> u64 {
        return 45 * value;
    }

This is my contract code snippet. I am trying to test cross-contract call with simplest computation. But I am getting Contracts.ContractTrapped error. I also updated the dummy_fuction selector to "_" to check if i was passing wrong selector. But then also I am getting the same error. DO we have some examples on how to call cross contract calls to self or other contract? And Can someone explain what wrong i am doing in my code?

Answer 1

Instead of cross contract calling, what you are doing here is Reentrancy guard which is the process to prevent specific type of attack (i.e reentrancy attack where attacker can repeatedly call function without expected condition met) whereas cross contract calling is the process of interacting with other smart contract.

In order to do cross contract call you can view this offical doc tutorial and this repo. There is delegator example code which is advance concept for corss contract calling.