Add ChannelError::NotFound variant

When moving ChannelPhase logic from ChannelManager into Channel, it is
useful to error when a Channel is not in the expected state. Add a
ChannelError::NotFound variant for this purpose, which results in
sending an error message without closing the channel.

Author: jkczyz

lightning/src/ln/channel.rs

@@ -713,6 +713,7 @@ pub(super) enum ChannelError {
 	Ignore(String),
 	Warn(String),
 	Close((String, ClosureReason)),
+	NotFound(String),
 }
 
 impl fmt::Debug for ChannelError {
@@ -721,6 +722,7 @@ impl fmt::Debug for ChannelError {
 			&ChannelError::Ignore(ref e) => write!(f, "Ignore : {}", e),
 			&ChannelError::Warn(ref e) => write!(f, "Warn : {}", e),
 			&ChannelError::Close((ref e, _)) => write!(f, "Close : {}", e),
+			&ChannelError::NotFound(ref e) => write!(f, "Not Found : {}", e),
 		}
 	}
 }
@@ -731,6 +733,7 @@ impl fmt::Display for ChannelError {
 			&ChannelError::Ignore(ref e) => write!(f, "{}", e),
 			&ChannelError::Warn(ref e) => write!(f, "{}", e),
 			&ChannelError::Close((ref e, _)) => write!(f, "{}", e),
+			&ChannelError::NotFound(ref e) => write!(f, "{}", e),
 		}
 	}
 }

lightning/src/ln/channelmanager.rs

@@ -792,7 +792,7 @@ impl MsgHandleErrInternal {
 					err: msg,
 					action: msgs::ErrorAction::IgnoreError,
 				},
-				ChannelError::Close((msg, _reason)) => LightningError {
+				ChannelError::Close((msg, _)) | ChannelError::NotFound(msg) => LightningError {
 					err: msg.clone(),
 					action: msgs::ErrorAction::SendErrorMessage {
 						msg: msgs::ErrorMessage {
@@ -3022,6 +3022,9 @@ macro_rules! convert_channel_err {
 					MsgHandleErrInternal::from_finish_shutdown(msg, *$channel_id, shutdown_res, $channel_update);
 				(true, err)
 			},
+			ChannelError::NotFound(msg) => {
+				(false, MsgHandleErrInternal::from_chan_no_close(ChannelError::NotFound(msg), *$channel_id))
+			},
 		}
 	};
 	($self: ident, $peer_state: expr, $err: expr, $funded_channel: expr, $channel_id: expr, FUNDED_CHANNEL) => {