f - take channel_state lock only when needed

Author: ViktorTigerstrom

lightning/src/ln/channelmanager.rs

@@ -2241,13 +2241,12 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 			}
 		};
 
-		let mut channel_state = self.channel_state.lock().unwrap();
 		if let &PendingHTLCStatus::Forward(PendingHTLCInfo { ref routing, ref amt_to_forward, ref outgoing_cltv_value, .. }) = &pending_forward_info {
 			// If short_channel_id is 0 here, we'll reject the HTLC as there cannot be a channel
 			// with a short_channel_id of 0. This is important as various things later assume
 			// short_channel_id is non-0 in any ::Forward.
 			if let &PendingHTLCRouting::Forward { ref short_channel_id, .. } = routing {
-				let id_option = channel_state.short_to_chan_info.get(&short_channel_id).cloned();
+				let id_option = self.channel_state.lock().unwrap().short_to_chan_info.get(&short_channel_id).cloned();
 				if let Some((err, code, chan_update)) = loop {
 					let forwarding_id_opt = match id_option {
 						None => { // unknown_next_peer
@@ -2262,36 +2261,42 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 						Some((_cp_id, chan_id)) => Some(chan_id.clone()),
 					};
 					let chan_update_opt = if let Some(forwarding_id) = forwarding_id_opt {
-						let chan = channel_state.by_id.get_mut(&forwarding_id).unwrap();
-						if !chan.should_announce() && !self.default_configuration.accept_forwards_to_priv_channels {
-							// Note that the behavior here should be identical to the above block - we
-							// should NOT reveal the existence or non-existence of a private channel if
-							// we don't allow forwards outbound over them.
-							break Some(("Refusing to forward to a private channel based on our config.", 0x4000 | 10, None));
-						}
-						if chan.get_channel_type().supports_scid_privacy() && *short_channel_id != chan.outbound_scid_alias() {
-							// `option_scid_alias` (referred to in LDK as `scid_privacy`) means
-							// "refuse to forward unless the SCID alias was used", so we pretend
-							// we don't have the channel here.
-							break Some(("Refusing to forward over real channel SCID as our counterparty requested.", 0x4000 | 10, None));
-						}
-						let chan_update_opt = self.get_channel_update_for_onion(*short_channel_id, chan).ok();
-
-						// Note that we could technically not return an error yet here and just hope
-						// that the connection is reestablished or monitor updated by the time we get
-						// around to doing the actual forward, but better to fail early if we can and
-						// hopefully an attacker trying to path-trace payments cannot make this occur
-						// on a small/per-node/per-channel scale.
-						if !chan.is_live() { // channel_disabled
-							break Some(("Forwarding channel is not in a ready state.", 0x1000 | 20, chan_update_opt));
-						}
-						if *amt_to_forward < chan.get_counterparty_htlc_minimum_msat() { // amount_below_minimum
-							break Some(("HTLC amount was below the htlc_minimum_msat", 0x1000 | 11, chan_update_opt));
-						}
-						if let Err((err, code)) = chan.htlc_satisfies_config(&msg, *amt_to_forward, *outgoing_cltv_value) {
-							break Some((err, code, chan_update_opt));
+						let mut channel_state = self.channel_state.lock().unwrap();
+						if let Some(chan) = channel_state.by_id.get_mut(&forwarding_id){
+							if !chan.should_announce() && !self.default_configuration.accept_forwards_to_priv_channels {
+								// Note that the behavior here should be identical to the above block - we
+								// should NOT reveal the existence or non-existence of a private channel if
+								// we don't allow forwards outbound over them.
+								break Some(("Refusing to forward to a private channel based on our config.", 0x4000 | 10, None));
+							}
+							if chan.get_channel_type().supports_scid_privacy() && *short_channel_id != chan.outbound_scid_alias() {
+								// `option_scid_alias` (referred to in LDK as `scid_privacy`) means
+								// "refuse to forward unless the SCID alias was used", so we pretend
+								// we don't have the channel here.
+								break Some(("Refusing to forward over real channel SCID as our counterparty requested.", 0x4000 | 10, None));
+							}
+							let chan_update_opt = self.get_channel_update_for_onion(*short_channel_id, chan).ok();
+
+							// Note that we could technically not return an error yet here and just hope
+							// that the connection is reestablished or monitor updated by the time we get
+							// around to doing the actual forward, but better to fail early if we can and
+							// hopefully an attacker trying to path-trace payments cannot make this occur
+							// on a small/per-node/per-channel scale.
+							if !chan.is_live() { // channel_disabled
+								break Some(("Forwarding channel is not in a ready state.", 0x1000 | 20, chan_update_opt));
+							}
+							if *amt_to_forward < chan.get_counterparty_htlc_minimum_msat() { // amount_below_minimum
+								break Some(("HTLC amount was below the htlc_minimum_msat", 0x1000 | 11, chan_update_opt));
+							}
+							if let Err((err, code)) = chan.htlc_satisfies_config(&msg, *amt_to_forward, *outgoing_cltv_value) {
+								break Some((err, code, chan_update_opt));
+							}
+							chan_update_opt
+						} else {
+							// No channel found for the forwarding_id_opt. The channel could have
+							// been dropped before the channel_state_lock was retaken.
+							break Some(("Don't have available channel for forwarding as requested.", 0x4000 | 10, None));
 						}
-						chan_update_opt
 					} else {
 						if (msg.cltv_expiry as u64) < (*outgoing_cltv_value) as u64 + MIN_CLTV_EXPIRY_DELTA as u64 { // incorrect_cltv_expiry
 							break Some((