alexander on Warpcast

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https://warpcast.com/~/channel/miniapps

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I'm glad we're alpha testing because we've already mitigated a flaw in the prediction market contract I'm building. https://warpcast.com/attar/0xb61066f4

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We encountered a critical issue during the finalization of our game contracts: Uniswap V3's "OLD" error disrupted our 24-hour TWAP calculations. Here's a concise breakdown:

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1/ Post-Mortem: Uniswap V3 'OLD' Error During Game Finalization Our game contract, referencing a Uniswap V3 pool for 24-hour TWAP calculations, failed at finalization due to an 'OLD' error.

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2/ Cause of the Error Uniswap V3 pools store price observations in a fixed-size ring buffer. If the buffer isn't large enough for the entire TWAP period, older observations get overwritten. Attempting to retrieve a 24-hour TWAP without the necessary data triggers the 'OLD' error.

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3/ Why This Wasn't Immediately Apparent No Visible Shrinking: The buffer size remains constant, but older data is silently overwritten by newer observations. Initial Success: Our contract's validation logic checked the pool's history during game creation. Early calls to observe(86400) succeeded because the buffer contained 24 hours of data. However, as more trades occurred, older observations were overwritten, leading to the error upon finalization.

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4/ Impact on the Game With essential data overwritten, the contract couldn't finalize the 24-hour TWAP. Participants who paid to join were unable to claim potential winnings.

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5/ Resolution Steps Immediate Action: Manually compensated winners by sending direct transactions with the correct prize amounts. Future Measures: Increase Observation Capacity: Before initiating a game, we'll use increaseObservationCardinalityNext to expand the pool's observation buffer, ensuring it can store the full TWAP period's data. https://docs.uniswap.org/contracts/v3/reference/core/UniswapV3Pool Implement Fallback Mechanism: Introduce an admin fallback function to finalize games using a shorter TWAP if necessary, accompanied by a script to determine the maximum available observation window.

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6/ Key Takeaway When relying on Uniswap V3's TWAP for extended periods, ensure the pool's observation buffer is sufficiently large to prevent data overwriting during finalization.

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7/ Learned a lot over the last day. These docs, in particular, helped me implement and deploy a fix: https://docs.uniswap.org/sdk/v3/guides/advanced/price-oracle#:~:text=Observations%20are%20only%20stored%20when,to%20the%20value%20we%20desire.

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8/ Looking Ahead I'd love to build something similar with Uniswap V4, but currently, these tokens are more frequently deployed in V3 pools, so that's why I'm using V3 at the moment!

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