Initially in lnd, we didn't store the extra TLV data that could be
dangling off of gossip messages. This was fixed initially in lnd v0.5
with this PR: https://github.com/lightningnetwork/lnd/pull/1825.
Within the PR, we incorrect set the `ExtraOpaqueData` (extra TLV blob)
of the `ChannelAnnouncement` to the value stored in `edge`, which is
actually our channel update. As 6-ish years ago we didn't yet have
anything that used the TLV gossip fields, this went unnoticed.
Fast forward to 2024, we shipped an experimental version of inbounbd
fees. This starts to store additional data in the `ExtraOpaqueData`
field, the TLV for the inbound fee. Initially, everything is valid when
the first `ChannelAnnouncement` is sent, but as soon as a user attempts
to set an inbound fee policy, we'd incorrectly swap in that new
serialized TLV for the _channel announcement_:
841e24399c (diff-1eda595bbebe495bd74a6a0431c46b66cb4e8b53beb311067c010feac2665dcbR2560).
Since we're just trying to generate a new `channel_update`, we don't
also regenerate the signature for the `channel_announcement` message. As
a result, we end up storing a `channel_announcement` with an invalid sig
on disk, continuing to broadcast that to peers.
We have existing logic to attempt to reliably send a channel update to
the remote peer. In the wild, we've seen this fail, as it's possible
right when we send the update the peer disconnects.
In this commit, we implement a simple fix which is just to send the chan
update each time we connect to the remote party.
Fixes https://github.com/lightningnetwork/lnd/issues/6870.
When iterating edges, pathfinding checks early whether using an edge
would violate the requested total fee limit for a route. This check is
done on the net amount (an amount the inbound fee is calculated with).
However, a possible next hop's fee discount leads to a reduction in fees
and as such using the net amount leads to assuming a higher cumulative
fee than the route really has, excluding the path erroneously. We
perform the fee limit check on the amount to send, which includes both
inbound and outbound fees. This should be possible as the first hop's
outbound fee is zero and therefore doesn't have to be checked in the
end.
