rich1.0Olaoluwa Osuntokun [ARCHIVE] (npub19h…zkvn4)https://yabu.me/npub19helcfnqgk2jrwzjex2aflq6jwfc8zd9uzzkwlgwhve7lykv23mq5zkvn4njumphttps://yabu.me📅 Original date posted:2022-06-29 📝 Original message: Hi Rusty, Thanks for the feedback! > This is over-design: if you fail to get reliable gossip, your routing will > suffer anyway. Nothing new here. Idk, it's pretty simple: you're already watching for closes, so if a close looks a certain way, it's a splice. When you see that, you can even take note of the _new_ channel size (funds added/removed) and update your pathfinding/blindedpaths/hophints accordingly. If this is an over-designed solution, that I'd categorize _only_ waiting N blocks as wishful thinking, given we have effectively no guarantees w.r.t how long it'll take a message to propagate. If by routing you mean a routing node then: no, a routing node doesn't even really need the graph at all to do their job. If by routing you mean a sender, then imo still no: you don't necessarily need _all_ gossip, just the latest policies of the nodes you route most frequently to. On top of that, since you can get the latest policy each time you incur a routing failure, as you make payments, you'll get the latest policies of the nodes you care about over time. Also consider that you might fail to get "reliable" gossip, simply just due to your peer neighborhood aggressively rate limiting gossip (they only allow 1 update a day for a node, you updated your fee, oops, no splice msg for you). So it appears you don't agree that the "wait N blocks before you close your channels" isn't a fool proof solution? Why 12 blocks, why not 15? Or 144? >From my PoV, the whole point of even signalling that a splice is on going, is for the sender's/receivers: they can continue to send/recv payments over the channel while the splice is in process. It isn't that a node isn't getting any gossip, it's that if the node fails to obtain the gossip message within the N block period of time, then the channel has effectively closed from their PoV, and it may be an hour+ until it's seen as a usable (new) channel again. If there isn't a 100% reliable way to signal that a splice is in progress, then this disincentives its usage, as routers can lose out on potential fee revenue, and sends/receivers may grow to favor only very long lived channels. IMO _only_ having a gossip message simply isn't enough: there're no real guarantees w.r.t _when_ all relevant parties will get your gossip message. So why not give them a 100% reliable on chain signal that: something is in progress here, stay tuned for the gossip message, whenever you receive that. -- Laolu On Tue, Jun 28, 2022 at 6:40 PM Rusty Russell <rusty at rustcorp.com.au> wrote: > Hi Roasbeef, > > This is over-design: if you fail to get reliable gossip, your routing > will suffer anyway. Nothing new here. > > And if you *know* you're missing gossip, you can simply delay onchain > closures for longer: since nodes should respect the old channel ids for > a while anyway. > > Matt's proposal to simply defer treating onchain closes is elegant and > minimal. We could go further and relax requirements to detect onchain > closes at all, and optionally add a perm close message. > > Cheers, > Rusty. > > Olaoluwa Osuntokun <laolu32 at gmail.com> writes: > > Hi y'all, > > > > This mail was inspired by this [1] spec PR from Lisa. At a high level, it > > proposes the nodes add a delay between the time they see a channel > closed on > > chain, to when they remove it from their local channel graph. The motive > > here is to give the gossip message that indicates a splice is in process, > > "enough" time to propagate through the network. If a node can see this > > message before/during the splicing operation, then they'll be able relate > > the old and the new channels, meaning it's usable again by > senders/receiver > > _before_ the entire chain of transactions confirms on chain. > > > > IMO, this sort of arbitrary delay (expressed in blocks) won't actually > > address the issue in practice. The proposal suffers from the following > > issues: > > > > 1. 12 blocks is chosen arbitrarily. If for w/e reason an announcement > > takes longer than 2 hours to reach the "economic majority" of > > senders/receivers, then the channel won't be able to mask the splicing > > downtime. > > > > 2. Gossip propagation delay and offline peers. These days most nodes > > throttle gossip pretty aggressively. As a result, a pair of nodes doing > > several in-flight splices (inputs become double spent or something, so > > they need to try a bunch) might end up being rate limited within the > > network, causing the splice update msg to be lost or delayed > significantly > > (IIRC CLN resets these values after 24 hours). On top of that, if a > peer > > is offline for too long (think mobile senders), then they may miss the > > update all together as most nodes don't do a full historical > > _channel_update_ dump anymore. > > > > In order to resolve these issues, I think instead we need to rely on the > > primary splicing signal being sourced from the chain itself. In other > words, > > if I see a channel close, and a closing transaction "looks" a certain > way, > > then I know it's a splice. This would be used in concert w/ any new > gossip > > messages, as the chain signal is a 100% foolproof way of letting an aware > > peer know that a splice is actually happening (not a normal close). A > chain > > signal doesn't suffer from any of the gossip/time related issues above, > as > > the signal is revealed at the same time a peer learns of a channel > > close/splice. > > > > Assuming, we agree that a chain signal has some sort of role in the > ultimate > > plans for splicing, we'd need to decide on exactly _what_ such a signal > > looks like. Off the top, a few options are: > > > > 1. Stuff something in the annex. Works in theory, but not in practice, > as > > bitcoind (being the dominant full node implementation on the p2p > network, > > as well as what all the miners use) treats annexes as non-standard. > Also > > the annex itself might have some fundamental issues that get in the > way of > > its use all together [2]. > > > > 2. Re-use the anchors for this purpose. Anchor are nice as they allow > for > > 1st/2nd/3rd party CPFP. As a splice might have several inputs and > outputs, > > both sides will want to make sure it gets confirmed in a timely manner. > > Ofc, RBF can be used here, but that requires both sides to be online to > > make adjustments. Pre-signing can work too, but the effectiveness > > (minimizing chain cost while expediting confirmation) would be > dependent > > on the fee step size. > > > > In this case, we'd use a different multi-sig output (both sides can > rotate > > keys if they want to), and then roll the anchors into this splicing > > transaction. Given that all nodes on the network know what the anchor > size > > is (assuming feature bit understanding), they're able to realize that > it's > > actually a splice, and they don't need to remove it from the channel > graph > > (yet). > > > > 3. Related to the above: just re-use the same multi-sig output. If > nodes > > don't care all that much about rotating these keys, then they can just > use > > the same output. This is trivially recognizable by nodes, as they > already > > know the funding keys used, as they're in the channel_announcement. > > > > 4. OP_RETURN (yeh, I had to list it). Self explanatory, push some > bytes in > > an OP_RETURN and use that as the marker. > > > > 5. Fiddle w/ the locktime+sequence somehow to make it identifiable to > > verifiers. This might run into some unintended interactions if the > inputs > > provided have either relative or absolute lock times. There might also > be > > some interaction w/ the main constructing for eltoo (uses the > locktime). > > > > Of all the options, I think #2 makes the most sense: we already use > anchors > > to be able to do fee bumping after-the-fact for closing transactions, so > why > > not inherit them here. They make the splicing transaction slightly > larger, > > so maybe #3 (or something else) is a better choice. > > > > The design space for spicing is preeetty large, so I figure the most > > productive route might be discussing isolated aspects of it at a time. > > Personally, I'm not suuuper caught up w/ what the latest design drafts > are > > (aside from convos at the recent LN Dev Summit), but from my PoV, how to > > communicate the splice to other peers has been an outstanding design > > question. > > > > [1]: https://github.com/lightning/bolts/pull/1004 > > [2]: > > > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-March/020045.html > > > > -- Laolu > > _______________________________________________ > > Lightning-dev mailing list > > Lightning-dev at lists.linuxfoundation.org > > https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev > -------------- next part -------------- An HTML attachment was scrubbed... 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