From 9b1bc9fd79581d0d11d002520eea74a81bba7d48 Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@lightning.engineering>
Date: Tue, 23 Apr 2019 20:05:47 -0700
Subject: [PATCH] watchtower/wtwire/create_session_reply: return last applied

---
 watchtower/wtserver/create_session.go     | 22 ++++++++++++----------
 watchtower/wtwire/create_session_reply.go |  8 ++++++++
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/watchtower/wtserver/create_session.go b/watchtower/wtserver/create_session.go
index 53cc9cf6..2f89b85a 100644
--- a/watchtower/wtserver/create_session.go
+++ b/watchtower/wtserver/create_session.go
@@ -29,14 +29,14 @@ func (s *Server) handleCreateSession(peer Peer, id *wtdb.SessionID,
 		log.Debugf("Already have session for %s", id)
 		return s.replyCreateSession(
 			peer, id, wtwire.CreateSessionCodeAlreadyExists,
-			existingInfo.RewardAddress,
+			existingInfo.LastApplied, existingInfo.RewardAddress,
 		)
 
 	// Some other database error occurred, return a temporary failure.
 	case err != wtdb.ErrSessionNotFound:
 		log.Errorf("unable to load session info for %s", id)
 		return s.replyCreateSession(
-			peer, id, wtwire.CodeTemporaryFailure, nil,
+			peer, id, wtwire.CodeTemporaryFailure, 0, nil,
 		)
 	}
 
@@ -45,7 +45,8 @@ func (s *Server) handleCreateSession(peer Peer, id *wtdb.SessionID,
 		log.Debugf("Rejecting CreateSession from %s, unsupported blob "+
 			"type %s", id, req.BlobType)
 		return s.replyCreateSession(
-			peer, id, wtwire.CreateSessionCodeRejectBlobType, nil,
+			peer, id, wtwire.CreateSessionCodeRejectBlobType, 0,
+			nil,
 		)
 	}
 
@@ -61,7 +62,7 @@ func (s *Server) handleCreateSession(peer Peer, id *wtdb.SessionID,
 			log.Errorf("Unable to generate reward addr for %s: %v",
 				id, err)
 			return s.replyCreateSession(
-				peer, id, wtwire.CodeTemporaryFailure, nil,
+				peer, id, wtwire.CodeTemporaryFailure, 0, nil,
 			)
 		}
 
@@ -72,7 +73,7 @@ func (s *Server) handleCreateSession(peer Peer, id *wtdb.SessionID,
 			log.Errorf("Unable to generate reward script for "+
 				"%s: %v", id, err)
 			return s.replyCreateSession(
-				peer, id, wtwire.CodeTemporaryFailure, nil,
+				peer, id, wtwire.CodeTemporaryFailure, 0, nil,
 			)
 		}
 	}
@@ -99,14 +100,14 @@ func (s *Server) handleCreateSession(peer Peer, id *wtdb.SessionID,
 	if err != nil {
 		log.Errorf("unable to create session for %s", id)
 		return s.replyCreateSession(
-			peer, id, wtwire.CodeTemporaryFailure, nil,
+			peer, id, wtwire.CodeTemporaryFailure, 0, nil,
 		)
 	}
 
 	log.Infof("Accepted session for %s", id)
 
 	return s.replyCreateSession(
-		peer, id, wtwire.CodeOK, rewardScript,
+		peer, id, wtwire.CodeOK, 0, rewardScript,
 	)
 }
 
@@ -115,11 +116,12 @@ func (s *Server) handleCreateSession(peer Peer, id *wtdb.SessionID,
 // Otherwise, this method returns a connection error to ensure we don't continue
 // communication with the client.
 func (s *Server) replyCreateSession(peer Peer, id *wtdb.SessionID,
-	code wtwire.ErrorCode, data []byte) error {
+	code wtwire.ErrorCode, lastApplied uint16, data []byte) error {
 
 	msg := &wtwire.CreateSessionReply{
-		Code: code,
-		Data: data,
+		Code:        code,
+		LastApplied: lastApplied,
+		Data:        data,
 	}
 
 	err := s.sendMessage(peer, msg)
diff --git a/watchtower/wtwire/create_session_reply.go b/watchtower/wtwire/create_session_reply.go
index 9b63b08c..82d2b6ab 100644
--- a/watchtower/wtwire/create_session_reply.go
+++ b/watchtower/wtwire/create_session_reply.go
@@ -43,6 +43,12 @@ type CreateSessionReply struct {
 	// Code will be non-zero if the watchtower rejected the session init.
 	Code CreateSessionCode
 
+	// LastApplied is the tower's last accepted sequence number for the
+	// session. This is useful when the session already exists but the
+	// client doesn't realize it's already used the session, such as after a
+	// restoration.
+	LastApplied uint16
+
 	// Data is a byte slice returned the caller of the message, and is to be
 	// interpreted according to the error Code. When the response is
 	// CreateSessionCodeOK, data encodes the reward address to be included in
@@ -63,6 +69,7 @@ var _ Message = (*CreateSessionReply)(nil)
 func (m *CreateSessionReply) Decode(r io.Reader, pver uint32) error {
 	return ReadElements(r,
 		&m.Code,
+		&m.LastApplied,
 		&m.Data,
 	)
 }
@@ -74,6 +81,7 @@ func (m *CreateSessionReply) Decode(r io.Reader, pver uint32) error {
 func (m *CreateSessionReply) Encode(w io.Writer, pver uint32) error {
 	return WriteElements(w,
 		m.Code,
+		m.LastApplied,
 		m.Data,
 	)
 }