Adds liquidity hints for the sending capabilities of routing channels in the
graph. The channel blacklist is incorporated into liquidity hints.
Liquidity hints are updated when a payment fails with a temporary
channel failure or when it succeeds. Liquidity hints are used to give a
penalty in the _edge_cost heuristics used by the pathfinding algorithm.
The base penalty in (_edge_cost) is removed because it is now part of the
liquidity penalty. We don't return early from get_distances, as we want
to explore all channels.
We pass the private edges to lnrouter, and let it find routes end-to-end.
Previously the edge_cost heuristics didn't apply to the private edges
and we were just randomly picking one of the route hints and use that.
So e.g. cheaper private edges were not preferred, but they are now.
PathEdge now stores both start_node and end_node; not just end_node.
Note that for a required feature, BOLT-09 allows setting either:
- only the REQ bit
- both the REQ bit and the OPT bit
Hence, when checking if a feature is supported by e.g. an invoice, both
bits should be checked.
Note that in lnpeer.py, in self.features specifically, REQ implies OPT,
as it is set by ln_compare_features.
- trampoline is enabled by default in config, to prevent download of `gossip_db`.
(if disabled, `gossip_db` will be downloaded, regardless of the existence of channels)
- if trampoline is enabled:
- the wallet can only open channels with trampoline nodes
- already-existing channels with non-trampoline nodes are frozen for sending.
- there are two types of trampoline payments: legacy and end-to-end (e2e).
- we decide to perform legacy or e2e based on the invoice:
- we use trampoline_routing_opt in features to detect Eclair and Phoenix invoices
- we use trampoline_routing_hints to detect Electrum invoices
- when trying a legacy payment, we add a second trampoline to the path to preserve privacy.
(we fall back to a single trampoline if the payment fails for all trampolines)
- the trampoline list is hardcoded, it will remain so until `trampoline_routing_opt` feature flag is in INIT.
- there are currently only two nodes in the hardcoded list, it would be nice to have more.
- similar to Phoenix, we find the fee/cltv by trial-and-error.
- if there is a second trampoline in the path, we use the same fee for both.
- the final spec should add fee info in error messages, so we will be able to fine-tune fees
Old estimate was heavily biased towards simply minimising CLTV sum.
(fees had a too low weight; typically they were ~noise)
Now also take payment_amount into account.
Previously we would put fake chan announcement and fake outgoing chan upd
for own channels into db (to make path finding work). See Peer.add_own_channel().
Now, instead of above, we pass a "my_channels" param to the relevant ChannelDB methods.
