2023 Jan 09

• Watched this video on Rust 2024. I didn’t even really consider that there is still so much development to do on Rust, and that some of the “accidental complexity” scenarios that were mentioned existed.

• SCID stands for short channel ID.

• Looking into this issue: https://github.com/lightningdevkit/rust-lightning/issues/1570

  • This is kind of tough. I feel like it’s not that bad, but I just am not familiar with the whole repo so I don’t know what exists and where things are.

  • I’m looking at pub fn fail_htlc_backwards(&self, payment_hash: &PaymentHash) on ChannelManager. This seems to be what the issue is talking about, i.e. an exposed function for the user to tell the ChannelManager to fail back a payment. From what I understand, this function removes the payment from the ChannelManager’s claimable_payments–the (inbound) payments it thinks are able to be/in the midst of being claimed, then for each source of the payment (can be multiple for a MPP) it “fails back” HTLCs to free up resources on channels along the path from here to the original sender.

    • Purpose of the function: Indicates that the preimage for payment_hash is unknown or the received amount is incorrect after a PaymentClaimable event, failing the HTLC back to its origin and freeing resources along the path (including in our own channel on which we received it).

    • For each source currently, it marks the reason as HTLCFailReason::reason(0x4000 | 15, htlc_msat_height_data); which I don’t really get, however I believe this might be something we would change to allow the user to input?

  • Have a lot more to say, left my summarized thoughts as a comment.

• Trying to go about my first issue is leaving me with a good amount of questions that I’m realizing could probably be answered by doing a lot of review. Definitely going to prioritize trying to do that tomorrow.