State Modifications in View Functions

StarkNet uses the @view decorator to indicate that a function should not modify the state. However, this restriction is not currently enforced by the compiler. Developers should exercise caution when creating view functions and when calling functions in other contracts, as there may be unintended consequences if they accidentally include state modifications.

Example

Consider the following function that is declared as a @view. It might have originally been intended solely as a view function, but was later repurposed to fetch a nonce and increment it in the process to ensure that a nonce is never repeated when creating a signature.

@view
func bad_get_nonce{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr}() -> (
    nonce: felt
) {
    let (user) = get_caller_address();
    let (nonce) = user_nonces.read(user);
    user_nonces.write(user, nonce + 1);

    return (nonce);
}

Mitigations

• Thoroughly review all @view functions, including those in third-party contracts, to make sure they don't unintentionally modify the state.

External Examples