Implement try-state Hook

Severity: High

Description

In Substrate, hooks are specialized lifecycle methods that allow pallets to perform operations at specific points during the blockchain runtime's execution cycle. Common hooks include on_initialize, on_finalize, and offchain_worker, each serving a distinct purpose, such as initializing block-specific logic, finalizing block-level operations, or executing off-chain tasks.

The try-state hook is a specialized hook used exclusively during try-runtime builds. Unlike other hooks that are part of normal runtime operations, try-state is designed to validate storage state without altering it. This makes it an invaluable tool for debugging and testing, as it enables developers to simulate runtime upgrades, migrations, and other critical changes in a controlled environment.

The absence of try-state hooks prevents runtime sanity checks, making it harder to ensure that the storage state is sensible after upgrades or other critical operations. These hooks are executed only when the runtime is built with the try-runtime feature and provide a mechanism to validate state without altering storage, ensuring consistency and correctness. It is a best practice to run try-runtime prior to any migration to catch potential issues in a controlled environment.

What should be avoided

Skipping sanity checks during runtime upgrades or migrations can leave storage inconsistencies unnoticed, leading to potential bugs:

#![allow(unused)]
fn main() {
fn on_runtime_upgrade() {
    // No validation of state consistency
    SomeStorage::<T>::mutate(|state| {
        *state = new_state;
    });
}
}

Best practice

Implement the try-state hook to perform thorough state checks without altering storage. Use try-runtime to simulate migrations and validate state consistency before deploying updates:

#![allow(unused)]
fn main() {
#[pallet::hooks]
impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
    #[cfg(feature = "try-runtime")]
    fn try_state(_n: BlockNumber) -> Result<(), TryRuntimeError> {
        // Example: Ensure a storage map is non-empty.
        // No need to worry about weight consumption here.
        ensure!(!SomeStorage::<T>::iter().count().is_zero(), "Storage map is empty");

        // Add more sanity checks as needed.
        Ok(())
    }
}
}

The key benefits of this approach are:

1. Controlled Validation: The try-state hook ensures that the state is checked rigorously without altering storage, making it safe for runtime use.
2. Integration with try-runtime: When the node is built with the try-runtime feature, these hooks enable testing in a controlled environment, simulating runtime upgrades and migrations to catch potential issues early.
3. Prevention of Errors: Running try-runtime before deploying migrations reduces the risk of deploying a broken runtime, ensuring system stability.

By implementing try-state hooks and leveraging try-runtime, developers can validate and maintain storage consistency while catching potential issues early in the development cycle.