Bugfix/htlc flush shutdown

cmd/lncli/commands.go

@@ -921,6 +921,10 @@ func executeChannelClose(ctxc context.Context, client lnrpc.LightningClient,
 		}
 
 		switch update := resp.Update.(type) {
+		case *lnrpc.CloseStatusUpdate_CloseInstant:
+			if req.NoWait {
+				return nil
+			}
 		case *lnrpc.CloseStatusUpdate_ClosePending:
 			closingHash := update.ClosePending.Txid
 			txid, err := chainhash.NewHash(closingHash)

docs/release-notes/release-notes-0.18.0.md

@@ -65,6 +65,11 @@
 * [Properly handle un-acked updates for exhausted watchtower 
   sessions](https://github.com/lightningnetwork/lnd/pull/8233)
 
+* [Allow `shutdown`s while HTLCs are in-flight](https://github.com/lightningnetwork/lnd/pull/8167).
+  This change fixes an issue where we would force-close channels when receiving
+  a `shutdown` message if there were currently HTLCs on the channel. After this
+  change, the shutdown procedure should be compliant with BOLT2 requirements.
+
 # New Features
 ## Functional Enhancements
 
@@ -123,6 +128,12 @@
   file](https://github.com/lightningnetwork/lnd/pull/8188). The corresponding
   `lncli getdebuginfo` command was also added.
 
+* Add a [new flag](https://github.com/lightningnetwork/lnd/pull/8167) to the
+  `CloseChannel` RPC method that instructs the client to not wait for the
+  closing transaction to be negotiated. This should be used if you don't care
+  about the txid and don't want the calling code to block while the channel
+  drains the active HTLCs.
+
 ## lncli Additions
 
 * Deprecate `bumpclosefee` for `bumpforceclosefee` to accommodate for the fact 

go.mod

@@ -39,7 +39,7 @@ require (
 	github.com/lightningnetwork/lightning-onion v1.2.1-0.20230823005744-06182b1d7d2f
 	github.com/lightningnetwork/lnd/cert v1.2.2
 	github.com/lightningnetwork/lnd/clock v1.1.1
-	github.com/lightningnetwork/lnd/fn v1.0.0
+	github.com/lightningnetwork/lnd/fn v1.0.1
 	github.com/lightningnetwork/lnd/healthcheck v1.2.3
 	github.com/lightningnetwork/lnd/kvdb v1.4.4
 	github.com/lightningnetwork/lnd/queue v1.1.1

go.sum

@@ -449,8 +449,8 @@ github.com/lightningnetwork/lnd/cert v1.2.2/go.mod h1:jQmFn/Ez4zhDgq2hnYSw8r35bq
 github.com/lightningnetwork/lnd/clock v1.0.1/go.mod h1:KnQudQ6w0IAMZi1SgvecLZQZ43ra2vpDNj7H/aasemg=
 github.com/lightningnetwork/lnd/clock v1.1.1 h1:OfR3/zcJd2RhH0RU+zX/77c0ZiOnIMsDIBjgjWdZgA0=
 github.com/lightningnetwork/lnd/clock v1.1.1/go.mod h1:mGnAhPyjYZQJmebS7aevElXKTFDuO+uNFFfMXK1W8xQ=
-github.com/lightningnetwork/lnd/fn v1.0.0 h1:I5VG9AD63mOQ89RMQEu7HRI1r68wn8yz539LoylUIKM=
-github.com/lightningnetwork/lnd/fn v1.0.0/go.mod h1:XV+0vBXSnh3aUjskJUv58TOpsveiXQ+ac8rEnXZDGFc=
+github.com/lightningnetwork/lnd/fn v1.0.1 h1:4nAxKpGKgk4/xRQKxvim3BW0QM34S4BH6QghWZVjsko=
+github.com/lightningnetwork/lnd/fn v1.0.1/go.mod h1:XV+0vBXSnh3aUjskJUv58TOpsveiXQ+ac8rEnXZDGFc=
 github.com/lightningnetwork/lnd/healthcheck v1.2.3 h1:oqhOOy8WmIEa6RBkYKC0mmYZkhl8T2kGD97n9jpML8o=
 github.com/lightningnetwork/lnd/healthcheck v1.2.3/go.mod h1:eDxH3dEwV9DeBW/6inrmlVh1qBOFV0AI14EEPnGt9gc=
 github.com/lightningnetwork/lnd/kvdb v1.4.4 h1:bCv63rVCvzqj1BkagN/EWTov6NDDgYEG/t0z2HepRMk=

htlcswitch/interfaces.go

@@ -134,12 +134,55 @@ type ChannelUpdateHandler interface {
 	// parameter.
 	MayAddOutgoingHtlc(lnwire.MilliSatoshi) error
 
-	// ShutdownIfChannelClean shuts the link down if the channel state is
-	// clean. This can be used with dynamic commitment negotiation or coop
-	// close negotiation which require a clean channel state.
-	ShutdownIfChannelClean() error
+	// EnableAdds sets the ChannelUpdateHandler state to allow
+	// UpdateAddHtlc's in the specified direction. It returns an error if
+	// the state already allowed those adds.
+	EnableAdds(direction LinkDirection) error
+
+	// DiableAdds sets the ChannelUpdateHandler state to allow
+	// UpdateAddHtlc's in the specified direction. It returns an error if
+	// the state already disallowed those adds.
+	DisableAdds(direction LinkDirection) error
+
+	// IsFlushing returns true when UpdateAddHtlc's are disabled in the
+	// direction of the argument.
+	IsFlushing(direction LinkDirection) bool
+
+	// OnFlushedOnce adds a hook that will be called the next time the
+	// channel state reaches zero htlcs. This hook will only ever be called
+	// once. If the channel state already has zero htlcs, then this will be
+	// called immediately.
+	OnFlushedOnce(func())
+
+	// OnCommitOnce adds a hook that will be called the next time a
+	// CommitSig message is sent in the argument's LinkDirection. This hook
+	// will only ever be called once. If no CommitSig is owed in the
+	// argument's LinkDirection, then we will call this hook immediately.
+	OnCommitOnce(LinkDirection, func())
 }
 
+// CommitHookID is a value that is used to uniquely identify hooks in the
+// ChannelUpdateHandler's commitment update lifecycle. You should never need to
+// construct one of these by hand, nor should you try.
+type CommitHookID uint64
+
+// FlushHookID is a value that is used to uniquely identify hooks in the
+// ChannelUpdateHandler's flush lifecycle. You should never need to construct
+// one of these by hand, nor should you try.
+type FlushHookID uint64
+
+// LinkDirection is used to query and change any link state on a per-direction
+// basis.
+type LinkDirection bool
+
+const (
+	// Incoming is the direction from the remote peer to our node.
+	Incoming LinkDirection = false
+
+	// Outgoing is the direction from our node to the remote peer.
+	Outgoing LinkDirection = true
+)
+
 // ChannelLink is an interface which represents the subsystem for managing the
 // incoming htlc requests, applying the changes to the channel, and also
 // propagating/forwarding it to htlc switch.