From fdd3ad314957da4330340d0ac80c1141d5916bc6 Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@mit.edu>
Date: Tue, 23 Oct 2018 18:28:27 -0700
Subject: [PATCH] watchtower/wtwire/state_update: sends encrypted blobs

---
 watchtower/wtwire/state_update.go | 88 +++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 watchtower/wtwire/state_update.go

diff --git a/watchtower/wtwire/state_update.go b/watchtower/wtwire/state_update.go
new file mode 100644
index 00000000..ab51ed38
--- /dev/null
+++ b/watchtower/wtwire/state_update.go
@@ -0,0 +1,88 @@
+package wtwire
+
+import "io"
+
+// StateUpdate transmits an encrypted state update from the client to the
+// watchtower. Each state update is tied to particular session, identified by
+// the client's brontine key used to make the request.
+type StateUpdate struct {
+	// SeqNum is a 1-indexed, monotonically incrementing sequence number.
+	// This number represents to the client's expected sequence number when
+	// sending updates sent to the watchtower. This value must always be
+	// less or equal than the negotiated MaxUpdates for the session, and
+	// greater than the LastApplied sent in the same message.
+	SeqNum uint16
+
+	// LastApplied echos the LastApplied value returned from watchtower,
+	// allowing the tower to detect faulty clients. This allow provides a
+	// feedback mechanism for the tower if updates are allowed to stream in
+	// an async fashion.
+	LastApplied uint16
+
+	// IsComplete is 1 if the watchtower should close the connection after
+	// responding, and 0 otherwise.
+	IsComplete uint8
+
+	// Hint is the 16-byte prefix of the revoked commitment transaction ID
+	// for which the encrypted blob can exact justice.
+	Hint [16]byte
+
+	// EncryptedBlob is the serialized ciphertext containing all necessary
+	// information to sweep the commitment transaction corresponding to the
+	// Hint. The ciphertext is to be encrypted using the full transaction ID
+	// of the revoked commitment transaction.
+	//
+	// The plaintext MUST be encoded using the negotiated Version for
+	// this session. In addition, the signatures must be computed over a
+	// sweep transaction honoring the decided SweepFeeRate, RewardRate, and
+	// (possibly) reward address returned in the SessionInitReply.
+	EncryptedBlob []byte
+}
+
+// A compile time check to ensure StateUpdate implements the wtwire.Message
+// interface.
+var _ Message = (*StateUpdate)(nil)
+
+// Decode deserializes a serialized StateUpdate message stored in the passed
+// io.Reader observing the specified protocol version.
+//
+// This is part of the wtwire.Message interface.
+func (m *StateUpdate) Decode(r io.Reader, pver uint32) error {
+	return ReadElements(r,
+		&m.SeqNum,
+		&m.LastApplied,
+		&m.IsComplete,
+		&m.Hint,
+		&m.EncryptedBlob,
+	)
+}
+
+// Encode serializes the target StateUpdate into the passed io.Writer
+// observing the protocol version specified.
+//
+// This is part of the wtwire.Message interface.
+func (m *StateUpdate) Encode(w io.Writer, pver uint32) error {
+	return WriteElements(w,
+		m.SeqNum,
+		m.LastApplied,
+		m.IsComplete,
+		m.Hint,
+		m.EncryptedBlob,
+	)
+}
+
+// MsgType returns the integer uniquely identifying this message type on the
+// wire.
+//
+// This is part of the wtwire.Message interface.
+func (m *StateUpdate) MsgType() MessageType {
+	return MsgStateUpdate
+}
+
+// MaxPayloadLength returns the maximum allowed payload size for a StateUpdate
+// complete message observing the specified protocol version.
+//
+// This is part of the wtwire.Message interface.
+func (m *StateUpdate) MaxPayloadLength(uint32) uint32 {
+	return MaxMessagePayload
+}