# Unsafe unwrap

## Description

- Category: `Validations and error handling`
- Severity: `Minor`
- Detectors: [`unsafe-unwrap`](https://github.com/CoinFabrik/scout-soroban/tree/main/detectors/unsafe-unwrap)
- Test Cases: [`unsafe-unwrap-1`](https://github.com/CoinFabrik/scout-soroban/tree/main/test-cases/unsafe-unwrap/unsafe-unwrap-1) [`unsafe-unwrap-2`](https://github.com/CoinFabrik/scout-soroban/tree/main/test-cases/unsafe-unwrap/unsafe-unwrap-2) [`unsafe-unwrap-3`](https://github.com/CoinFabrik/scout-soroban/tree/main/test-cases/unsafe-unwrap/unsafe-unwrap-3) [`unsafe-unwrap-4`](https://github.com/CoinFabrik/scout-soroban/tree/main/test-cases/unsafe-unwrap/unsafe-unwrap-4) [`unsafe-unwrap-5`](https://github.com/CoinFabrik/scout-soroban/tree/main/test-cases/unsafe-unwrap/unsafe-unwrap-5) [`unsafe-unwrap-6`](https://github.com/CoinFabrik/scout-soroban/tree/main/test-cases/unsafe-unwrap/unsafe-unwrap-6)

In Rust, the `unwrap` method is commonly used for error handling. It retrieves the inner value of an `Option` or `Result`. If an error or `None` occurs, it calls `panic!` without a custom error message.

## Why is this bad?

`.unwrap()` might panic if the result value is an error or `None`. It is recommended to avoid this, because it stops its execution, which might lead the contract to an inconsistent state if the panic occurs in the middle of state changes. Additionally, the panic could cause a transaction to fail.

## Issue example

Consider the following `Soroban` contract:

#[contractimpl]
impl UnsafeUnwrap {
    pub fn unwrap(n: u64) -> u64 {
        let result = Self::non_zero_or_error(n);
        result.unwrap()
    }

    pub fn non_zero_or_error(n: u64) -> Result<u64, Error> {
        if n == 0 {
            return Err(Error::CustomError);
        }
        Ok(n)
    }
}

In this contract, the `unwrap` function uses the `unwrap` method to save the result of the `non_zero_or_error` function. If the function returns `Err`, the contract will panic and halt execution, potentially leading to malicious exploitation to disrupt the contract's operation.

The code example can be found [here](https://github.com/CoinFabrik/scout-soroban/tree/main/test-cases/unsafe-unwrap/unsafe-unwrap-1/vulnerable-example).

## Remediated example

Instead of using `unwrap`, use a safer method for error handling. In this case, if the function returns `Err`, it will return a default value (like `0`).

#[contractimpl]
impl UnsafeUnwrap {
    pub fn unwrap_or_default(n: u64) -> u64 {
        let result = Self::non_zero_or_error(n);
        result.unwrap_or(0)
    }

    pub fn non_zero_or_error(n: u64) -> Result<u64, Error> {
        if n == 0 {
            return Err(Error::CustomError);
        }
        Ok(n)
    }
}

The remediated code example can be found [here](https://github.com/CoinFabrik/scout-soroban/tree/main/test-cases/unsafe-unwrap/unsafe-unwrap-1/remediated-example).

## How is it detected?

Checks for usage of .unwrap()

## References

[Rust documentation: `unwrap`](https://doc.rust-lang.org/std/option/enum.Option.html#method.unwrap)