Clarify get_update_*_htlc docs and tweak one case slightly

diff --git a/src/ln/channel.rs b/src/ln/channel.rs
index b9a81f6ebc0465cf34396eb44073b790fd7c3925..25e981d7daa3e170c3214254b9303da0d2edf2e9 100644 (file)
--- a/src/ln/channel.rs
+++ b/src/ln/channel.rs
@@ -1122,8 +1122,9 @@ impl Channel {
                Ok(our_sig)
        }
 
-       /// May return an IgnoreError, but should not, and will always return Ok(_) when
-       /// debug_assertions are turned on
+       /// Per HTLC, only one get_update_fail_htlc or get_update_fulfill_htlc call may be made.
+       /// In such cases we debug_assert!(false) and return an IgnoreError. Thus, will always return
+       /// Ok(_) if debug assertions are turned on and preconditions are met.
        fn get_update_fulfill_htlc(&mut self, htlc_id_arg: u64, payment_preimage_arg: [u8; 32]) -> Result<(Option<msgs::UpdateFulfillHTLC>, Option<ChannelMonitor>), HandleError> {
                // Either ChannelFunded got set (which means it wont bet unset) or there is no way any
                // caller thought we could have something claimed (cause we wouldn't have accepted in an
@@ -1175,7 +1176,9 @@ impl Channel {
                                        &HTLCUpdateAwaitingACK::FailHTLC { htlc_id, .. } => {
                                                if htlc_id_arg == htlc_id {
                                                        debug_assert!(false, "Tried to fulfill an HTLC we already had a holding-cell failure on");
-                                                       return Err(HandleError{err: "Unable to find a pending HTLC which matched the given HTLC ID", action: Some(msgs::ErrorAction::IgnoreError)});
+                                                       // Return the new channel monitor in a last-ditch effort to hit the
+                                                       // chain and claim the funds
+                                                       return Ok((None, Some(self.channel_monitor.clone())));
                                                }
                                        },
                                        _ => {}
@@ -1215,8 +1218,9 @@ impl Channel {
                }
        }
 
-       /// May return an IgnoreError, but should not, and will always return Ok(_) when
-       /// debug_assertions are turned on
+       /// Per HTLC, only one get_update_fail_htlc or get_update_fulfill_htlc call may be made.
+       /// In such cases we debug_assert!(false) and return an IgnoreError. Thus, will always return
+       /// Ok(_) if debug assertions are turned on and preconditions are met.
        pub fn get_update_fail_htlc(&mut self, htlc_id_arg: u64, err_packet: msgs::OnionErrorPacket) -> Result<Option<msgs::UpdateFailHTLC>, HandleError> {
                if (self.channel_state & (ChannelState::ChannelFunded as u32)) != (ChannelState::ChannelFunded as u32) {
                        panic!("Was asked to fail an HTLC when channel was not in an operational state");