I built op-stack-hooks (https://github.com/AlexBHarley/op-stack-hooks) one of the first OP Stack Mods. op-stack-hooks allows registering listeners on the L2 for events that happen on the L1. ie, - listening and reacting to swaps made on Uniswap- permissionless & automated Chainlink feeds on the L2.The mod includes changes to op-node, for deriving events and an additional predeploy for registering events.
Acts as a nice demonstration for how OP Stack Mods can be written. Previously the only example I could find was Ticking Optimism (https://stack.optimism.io/docs/build/featured/#ticking-optimism) which is fairly rudimentary. This example shows event parsing, L2 state reads and L2 writes.
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