htlcswitch: forward blinded payments addressed by node_id#10942
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htlcswitch: forward blinded payments addressed by node_id#10942bitromortac wants to merge 5 commits into
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PR Severity: CRITICAL Highest-severity file determines level | 10 files (excl. tests) | ~259 lines changed (excl. tests) CRITICAL files (8):
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Analysis: This PR touches two distinct critical packages (contractcourt and htlcswitch), independently triggering CRITICAL severity. The bulk of changes are in htlcswitch/hop/ and htlcswitch/switch.go, at the heart of Lightning payment forwarding. The large itest addition (lnd_route_blinding_test.go, +417 lines) is excluded as a test file. Expert review of htlcswitch and contractcourt changes is required. To override, add a severity-override-{critical,high,medium,low} label. |
The forwarding next hop is currently always a short channel ID. To allow a blinded route to identify the next hop by node ID instead, change ForwardingInfo.NextHop to fn.Either[lnwire.ShortChannelID, [33]byte], where the Left is the outgoing channel ID and the Right (wired up in a follow-up commit) is the next node's public key. This commit is a pure representational change with no behavioural effect: every next hop is still a channel ID. The Either is encapsulated behind ForwardingInfo methods so callers never destructure it directly: IsExit() is the single source of truth for exit-hop detection (used by the link and the contract court) and NextHopChannel() yields the outgoing SCID.
Some implementations (e.g. Core Lightning) identify the next hop in a blinded route by the next node's ID (next_node_id) instead of a short channel ID. Decode such a hop into a node-ID next hop, the Right of ForwardingInfo.NextHop, holding the next node's public key. The switch resolves that key to one of our channels with the peer in a later commit. BOLT 4 requires a non-final blinded hop to carry exactly one of short_channel_id or next_node_id, so a hop that sets both is rejected.
Fixes lightningnetwork#10937: forward a blinded-route payment when the recipient identifies the next hop by node ID rather than a short channel ID. The htlcPacket carries the decoded next hop to the switch, whose handlePacketAdd resolves the pubkey to the peer's links via getLinks() and lets the existing non-strict forwarding logic load-balance across the peer's channels. outgoingChanID stays a ShortChannelID. It is the persisted CircuitKey and is set to the selected channel after non-strict selection. The circular route check filters candidate channels before selection so a valid forward is never rejected by landing on the incoming channel.
Add integration tests for an lnd introduction node forwarding a blinded
payment whose non-final hops identify the next hop by node ID (next_node_id)
rather than a short channel ID, as produced by other implementations:
- testBlindedRouteNextNodeID: the outgoing channel is public.
- testBlindedRouteNextNodeIDPrivateChannel: the outgoing channel is
private, so the node ID resolves to an SCID alias.
- testBlindedRouteNextNodeIDRestart: the introduction node is restarted
while the HTLC is in flight, exercising forwarding-package replay and
re-decode of the node-ID blinded hop.
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Fixes #10937.
When lnd is the introduction node of a blinded path, the recipient may identify the next hop by next_node_id instead of a short_channel_id. lnd only handled the channel-ID case and failed such forwards with next SCID not set for non-final blinded hop.
The next hop now becomes an
fn.Either[ShortChannelID, pubkey]: decode yields the peer's key when onlynext_node_idis present, and the switch resolves it through the same non-strictgetLinkspath that already load-balances across a peer's channels.outgoingChanID(the circuit key) stays a short channel ID, set once a channel is chosen, so private and alias channels need no special handling.Alternative considered
Resolving the node ID to a channel at decode time is smaller but makes onion decoding depend on live link state and re-implements alias handling the switch already owns. Resolving in the switch keeps decode pure and is correct for alias channels by construction.