C-Lightning PRs #2541, #2545, and #2546 implement multiple changes to the gossip subsystem used for tracking which channels are available and calculating routes across them. This work was motivated by the million channels project and performance results from that project are included in many of the commit messages. If Optech is interpreting the results correctly, the difference between the first commit in the series and the last commit is an 79% reduction in memory use, from 2.6 GiB to 0.6 GiB, and an 80% reduction in the time to build a route to a randomly-selected node (within 20 hops) from 60 seconds to 12 seconds. (If even the improved values seem high, recall this is for a simulation network more than 25 times the size of the current mainnet network and 1,000 times the size of the network a bit over a year ago.) A notable part of this change is C-Lightning switching from its rather unique Bellman-Ford-Gibson (BFG) routing algorithm to a slightly-customized version of Dijkstra.
C-Lightning #2554 changes the default invoice expiration from one hour to one week. This is the time after which the node will automatically reject attempts to pay the invoice. Services that want to minimize exchange rate risk will need to pass a lower expiry value when using the invoiceRPC.
C-Lightning #2540 adds an invoice hook that’s called whenever a “valid payment for an unpaid invoice has arrived.” Among other tasks that can be performed when a payment is received, this can be used by a plugin to implement “hold invoices” as previously implemented in LND (see our description of LND #2022 in Newsletter #38).
C-Lightning #2506 adds a min-capacity-sat configuration parameter to reject channel open requests below a certain value. This replaces a hardcoded minimum of 0.00001 BTC previously in the code.
C-Lightning #2470 modifies the recently-added setchannelfee RPC so that “all” can be passed instead of a specific node’s id in order to set the routing fee for all channels.