Fix fee mismatch without htlc

We allow disagreeing on fees while the channel doesn't contain any htlc,
because no funds can be at risk in that case. But we used the latest signed
fee when adding a new HTLC, whereas we must also take into account the
latest proposed (unsigned) fee.

eclair-core/src/main/scala/fr/acinq/eclair/channel/Commitments.scala

@@ -276,8 +276,10 @@ object Commitments {
 
     // we allowed mismatches between our feerates and our remote's as long as commitments didn't contain any HTLC at risk
     // we need to verify that we're not disagreeing on feerates anymore before offering new HTLCs
+    // NB: there may be a pending update_fee that hasn't been signed yet that needs to be taken into account
+    val currentFeeratePerKw = commitments.remoteChanges.proposed.collect { case f: UpdateFee => f.feeratePerKw }.lastOption.getOrElse(commitments.localCommit.spec.feeratePerKw)
     val localFeeratePerKw = feeConf.getCommitmentFeerate(commitments.channelVersion, commitments.capacity, None)
-    if (feeConf.maxFeerateMismatchFor(commitments.remoteNodeId).isFeeDiffTooHigh(commitments.channelVersion, localFeeratePerKw, commitments.localCommit.spec.feeratePerKw)) {
+    if (feeConf.maxFeerateMismatchFor(commitments.remoteNodeId).isFeeDiffTooHigh(commitments.channelVersion, localFeeratePerKw, currentFeeratePerKw)) {
       return Left(FeerateTooDifferent(commitments.channelId, localFeeratePerKw = localFeeratePerKw, remoteFeeratePerKw = commitments.localCommit.spec.feeratePerKw))
     }
 
@@ -337,8 +339,10 @@ object Commitments {
 
     // we allowed mismatches between our feerates and our remote's as long as commitments didn't contain any HTLC at risk
     // we need to verify that we're not disagreeing on feerates anymore before accepting new HTLCs
+    // NB: there may be a pending update_fee that hasn't been signed yet that needs to be taken into account
+    val currentFeeratePerKw = commitments.remoteChanges.proposed.collect { case f: UpdateFee => f.feeratePerKw }.lastOption.getOrElse(commitments.localCommit.spec.feeratePerKw)
     val localFeeratePerKw = feeConf.getCommitmentFeerate(commitments.channelVersion, commitments.capacity, None)
-    if (feeConf.maxFeerateMismatchFor(commitments.remoteNodeId).isFeeDiffTooHigh(commitments.channelVersion, localFeeratePerKw, commitments.localCommit.spec.feeratePerKw)) {
+    if (feeConf.maxFeerateMismatchFor(commitments.remoteNodeId).isFeeDiffTooHigh(commitments.channelVersion, localFeeratePerKw, currentFeeratePerKw)) {
       return Left(FeerateTooDifferent(commitments.channelId, localFeeratePerKw = localFeeratePerKw, remoteFeeratePerKw = commitments.localCommit.spec.feeratePerKw))
     }