[Core Protocol] Need to add L1 confirmation checker.

[maodaishan]

Issue Description

On Arbitrum , there's a useful service: L1 confirmation checker.
I can't find familiar service on Optimism. I think it's useful and important, wish the official team could develop it, thanks.
https://github.com/OffchainLabs/arbitrum-tutorials/tree/master/packages/l1-confirmation-checker

Here's an important use case:
e.g. I'm considering to deploy a L3 , which rollup to Optimism L2. My question is : How could to consider the security of L3 blocks?
If a new block was built on L3, before it was rolledup to L2, we think it's unsafe, when it's rolledup to L2, can we think it's safe? Because it only get the promise from L2 Sequencer, it's possible that block be dropped and won't be rolledup to L1. But if we require that when the L2 block containing the L3 DA be rolled up to L1 as safe, how could the L3 nodes know it ? Because it's hard to ask the DApps on L3 to run a L2 node.
With the L1 confirmation checker, I think this maybe handled. On L3, we could store the L2 transaction containing the L3 rollup, then we could use the L1 confirmation checker to confirm the L2 transaction state, then we can know how secure is our L3 block.

Additional Information

No response

[sbvegan]

That is a helpful tool! I'm not aware of a similar one we have at the moment. The root of what you're looking for is the different block tags (safe, unsafe, and finalized).

• safe means all of the data to derive a L2 block has been included on L1. safe blocks only reorg if L1 reorg happens.
• unsafe means all of the data to derive a L2 block has been included on L1. unsafe blocks can reorg if the L1 reorgs or there was an issue sequencer.
• finalized means all of the data to derive a L2 block has been finalized on L1. No finalized block can be reorged.

This is information I gathered from our specs.

So to get the behavior you're looking for, you can check what block the transaction is in and then compare that against the block tags.

[maodaishan]

Thanks @sbvegan , Will Optimism official team develop such service? Or I need to develop it myself?

[sbvegan]

At the moment, you'll need to implement it yourself. I will flag this to our developer experience team so its on their radar.

[maodaishan]

Got it, thank you @sbvegan

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