Account storage capacity overflow

[onflow]

Account storage capacity overflow

[janezpodhostnik]

@turbolent can this be done with the current version of cadence?

the function is: (

flow-core-contracts/contracts/FlowStorageFees.cdc

Line 63 in c327df1

pub fun calculateAccountCapacity(_ accountAddress: Address): UFix64 {

)

    // Returns megabytes
    pub fun calculateAccountCapacity(_ accountAddress: Address): UFix64 {
        let balanceRef = getAccount(accountAddress)
            .getCapability<&FlowToken.Vault{FungibleToken.Balance}>(/public/flowTokenBalance)!
            .borrow() ?? panic("Could not borrow FLOW balance capability")

        // get address token balance
        if balanceRef.balance < self.minimumStorageReservation {
            // if < then minimum return 0
            return 0.0
        } else {
            // return balance multiplied with megabytes per flow 
            return balanceRef.balance * self.storageMegaBytesPerReservedFLOW
        }
    }

The last part balanceRef.balance * self.storageMegaBytesPerReservedFLOW should return max UFix64 if the multiplication result is more than max UFix64.

[turbolent]

I think what we would want is saturating multiply, that results in the min/max value instead of underflowing/overflow. We don't have that in Cadence, but it could be easily added. For example, Rust has saturating_mul: https://doc.rust-lang.org/std/primitive.u32.html#method.saturating_mul

Alternatively, the same behaviour could be implemented by dividing from the max value and checking if the multiplication would result in an overflow. There are currently no max/min constants of number types exposed (e.g. UFix.max), but again this could be easily added, and alternatively defined as a constant in the Cadence program itself (e.g. let UFix64Max = ....

I'll create issues for both.