2023 Jan 10

• Apparently a good book on computer networking suggested by the LDK discord

• Finally learned about macros in Rust. They are honestly fairly straight forward, at least conceptually. This is my first real introduction to meta-programming, which I had heard a lot about but never really learned myself.

• Also realized there are a lot of books for Rust stuff. There’s a reference book for more in-depth documentation of the language structure. Seems like a good section on macros.

• Review: OP_CLTV (check lock time verify) is absolute, OP_CSV (check sequence verify) is relative to the confirmed block the transaction appears in.

• Trying to dig into a PR: https://github.com/lightningdevkit/rust-lightning/pull/1878

  • In the issue it mentions this is important for people doing (submarine) swaps: why?

    • Review: Submarine swaps. Can be used for…

      1. Alice wants to pay Bob on-chain, Bob wants to receive payment off-chain on lightning, so they use a third person (or some intermediary route) Claire that has the necessary liquidity to pay Bob on lightning. Here, Bob generates a secret, and sends the hash to Alice—essentially just Bob creating a Lightning invoice for Alice. Alice creates an HTLC to send money to Claire (Claire can take funds within time frame with preimage/secret, after cltv_expiry Alice can reclaim funds). Claire creates an HTLC to send money to Bob on their payment channel (only after Alice’s HTLC has been broadcasted on-chain to ensure she can’t double spend it). If Bob claims the payment, he shares the preimage/secret, and Claire is able to claim the funds from Alice.

      2. Alice is paying Bob on-chain to receive off-chain assets. Happens similarly to above but now both Alice and Bob are senders and receivers.

  • What is all this about packing the custom_cltv_expiry_time into the payment secret metadata?

  • What is this PR doing: changelog at the bottom was probably the most helpful for this.