ln: add TrampolineForward SendHTLCId variant
What the developer wrote
Authored by Carla Kirk-Cohen
ln: add TrampolineForward SendHTLCId variant
This commit adds a SendHTLCId for trampoline forwards, identified by
their session_priv. As with an OutboundRoute, we can expect our HTLC
to be uniquely identified by a randomly generated session_priv.
TrampolineForward could also be identified by the set of all previous
outbound scid/htlc id pairs that represent its incoming HTLC(s). We
choose the 32 byte session_priv to fix the size of this identifier
rather than 16 byte scid/id pairs that will grow with the number of
incoming htlcs.
What changed, and why it matters
This commit adds a new internal identifier type for tracking forwarded Lightning payments that use Trampoline routing. It is a small, structural code change that does not appear to fix or introduce a security vulnerability on its own. It simply lets the software distinguish Trampoline forwards from other kinds of payment routes when recording which HTLCs were sent.
No security action required. Review as part of normal Trampoline routing feature development and ensure downstream code that matches on SentHTLCId handles the new variant.
Security signals we found
No memory-safety issues visible in diff
No input validation changes
No cryptographic operation changes
No privilege or authorization changes
No existing variant behavior modified
Purely additive enum/serialization change
Evidence from the diff
The patch extends the SentHTLCId enum in lightning/src/ln/channelmanager.rs with a TrampolineForward { session_priv: [u8; 32] } variant and adds corresponding serialization logic. This identifier is used internally to correlate outbound HTLCs with their source. The change is additive and does not modify existing variant handling, bounds checks, or cryptographic operations.
Changed components
lightning/src/ln/channelmanager.rsSentHTLCId enum serializationInspect captured patch +4 / −0
diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index 2520d68..19322ba 100644
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -756,6 +756,7 @@ impl Default for OptionalOfferPaymentParams {
pub(crate) enum SentHTLCId {
PreviousHopData { prev_outbound_scid_alias: u64, htlc_id: u64 },
OutboundRoute { session_priv: [u8; SECRET_KEY_SIZE] },
+ TrampolineForward { session_priv: [u8; SECRET_KEY_SIZE] },
}
impl SentHTLCId {
pub(crate) fn from_source(source: &HTLCSource) -> Self {
@@ -778,6 +779,9 @@ impl_writeable_tlv_based_enum!(SentHTLCId,
(2, OutboundRoute) => {
(0, session_priv, required),
},
+ (4, TrampolineForward) => {
+ (0, session_priv, required),
+ },
);
type FailedHTLCForward = (HTLCSource, PaymentHash, HTLCFailReason, HTLCHandlingFailureType);
Why this scored 18/100
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