Callback function getting issue

Question

I have two contracts , contract A and Contract B. This is my contract B where I have defined a callback function that will return sp.some("test") when called.

import smartpy as sp


t_balance_of_params = sp.TRecord(
    callback=sp.TContract(sp.TOption(sp.TString)),
    requests=sp.TString,
).layout(("requests", "callback"))

class ContractB(sp.Contract):
    def __init__(self, value):
        self.init()


    @sp.entry_point
    def get_String(self, params):
        sp.set_type(params, t_balance_of_params)
        sp.transfer(
           sp.some("test"), sp.mutez(0), params.callback
        )

Here is the contract A, where I am trying to access the contract B callback function and update my contract A initial storage value,

class ContractA(sp.Contract):
    def __init__(self, value):
        self.init(updated_balance = value, 
                 str_test = sp.some(sp.string("initial")))

    @sp.entry_point
    def getBalance(self, contract_address):
        fa2_contract = sp.contract(
            sp.TRecord(
                callback=sp.TContract(sp.TString),
                requests=sp.TString,
            ).layout(("callback", "requests"))
        , contract_address, entry_point="get_String").open_some()

        x  = sp.transfer(sp.record(callback=sp.self_entry_point("test_balance"), 
                               requests= "Nooo"),
                    sp.tez(0),
                    fa2_contract)

    @sp.entry_point
    def test_balance(self, balance):
        sp.set_type(balance, sp.TString)
        self.data.str_test = sp.some(balance)

Here both of the contracts are being compiled and deployed but somehow when i do the transaction on contract A getBalance function , my assumptions was it should have saved sp.some("test") on self.data.str_test , but the transaction is giving error. What am i doing wrong here ?

Answer 1

get_String is returning an option of string: sp.some("...").

So test_balance is receiving an option of string, not a string.

You can return a string or change the set_balance entrypoint parameter type to be an option.

import smartpy as sp

t_balance_of_params = sp.TRecord(
    callback=sp.TContract(sp.TOption(sp.TString)),
    requests=sp.TString,
).layout(("requests", "callback"))

class ContractA(sp.Contract):
    def __init__(self):
        self.init(str_test = sp.none)

    @sp.entry_point
    def getBalance(self, contract_address):
        fa2_contract = sp.contract(t_balance_of_params, contract_address, entry_point="get_String").open_some()
        sp.transfer(
            sp.record(callback=sp.self_entry_point("test_balance"), requests= "Nooo"),
            sp.tez(0),
            fa2_contract)

    @sp.entry_point
    def test_balance(self, balance):
        sp.set_type(balance, sp.TOption(sp.TString))
        self.data.str_test = balance

class ContractB(sp.Contract):
    @sp.entry_point
    def get_String(self, params):
        sp.set_type(params, t_balance_of_params)
        sp.transfer(
           sp.some("test"), sp.mutez(0), params.callback
        )

if "templates" not in __name__:
    @sp.add_test(name="MyContract")
    def test():
        sc = sp.test_scenario()
        c1 = ContractA()
        sc += c1
        c2 = ContractB()
        sc += c2
        c1.getBalance(c2.address)
        sc.verify(c1.data.str_test == sp.some("test"))

Another remark: always check that the callback sp.sender is the good one.

You can see examples here: https://smartpy.io/ide?template=inter_contract_calls.py