Support decoding HTLC onions once fully committed#2845
Merged
TheBlueMatt merged 15 commits intolightningdevkit:mainfrom Mar 28, 2024
Merged
Support decoding HTLC onions once fully committed#2845TheBlueMatt merged 15 commits intolightningdevkit:mainfrom
TheBlueMatt merged 15 commits intolightningdevkit:mainfrom
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Currently, we decode HTLC onions immediately upon receiving an
update_add_htlc. Doing so determines what we should do with the HTLC: forward it, or immediately fail it back if it cannot be accepted. This action is tracked until the HTLC is fully committed to by both sides, and a new commitment in the latter case is proposed to fully remove the HTLC. While this has worked so far, it has some minor privacy implications, as forwarding/failing back do not go through the usualPendingHTLCsForwardableflow. It also presents issues with the quiescence handshake, as failures through this path do not go through the holding cell abstraction, leading to a potential violation of the protocol by sending anupdate_fail_*after already having sentstfu.This PR aims to support, but does not enable, decoding incoming HTLC onions once HTLCs are fully committed to by both sides instead. Unfortunately, switching over is not a forwards compatible change, so we'll need to do so over multiple releases.