fix(anvil): guard against the blockchain advancing while checking latest block

[alexghr]

Motivation

Our tests sometimes flake with a BlockRangeOutOfRangeError when calling eth_call with the latest block tag. IIUC, this should not be possible.

I had a look at the code in order to see if a newer version of Anvil would fix the flake. I think there is a race condition in this code if the call is made right as a block was being produced:

  pub async fn ensure_block_number<T: Into<BlockId>>(More actions
        &self,
        block_id: Option<T>,
    ) -> Result<u64, BlockchainError> {
        let current = self.best_number(); // <- returns 20
        let requested =
            match block_id.map(Into::into).unwrap_or(BlockId::Number(BlockNumber::Latest)) {
                // ...
                BlockId::Number(num) => match num {
                    BlockNumber::Latest | BlockNumber::Pending => self.best_number(), // <- returns 21
                    // ...
                },
            };

        if requested > current { // if 21 > 20
            Err(BlockchainError::BlockOutOfRange(current, requested))
        } else {
            Ok(requested)
        }
  }

See issue #10709 for context

Solution

Instead of calling self.best_number() twice, which could return different values if a block is built at the same time, the code now uses the pinned block at the beginning of the function.

I'm not sure how best to test this fix since this is code is heavily dependent on async operations. I'd appreciate some help here :)

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

Fix #10709

[grandizzy]

thank you, ooh, right, race could happen, not sure though how to test. CC @mattsse @yash-atreya mind to have a look before merging? thanks!

[mattsse]

ah this makes sense, ty!