Support chat validation

chat/sign/session.go

@@ -1,6 +1,8 @@
 package sign
 
 import (
+	"crypto/sha256"
+	"encoding/binary"
 	"io"
 
 	"github.com/google/uuid"
@@ -11,40 +13,81 @@ import (
 )
 
 type Message struct {
-	Link struct {
-		Index   int
-		Sender  uuid.UUID
-		Session uuid.UUID
-	}
-	Signature []byte
-	PackedMessageBody
+	Prev      Prev
+	Signature *Signature
+	*MessageBody
 	Unsigned *chat.Message
 	FilterMask
 }
 
+type Prev struct {
+	Index   int
+	Sender  uuid.UUID
+	Session uuid.UUID
+}
+
 type Session struct {
-	sessionID uuid.UUID
-	publicKey user.PublicKey
+	SessionID uuid.UUID
+	PublicKey user.PublicKey
+
+	valid   bool
+	lastMsg *Message
 }
 
 func (s Session) WriteTo(w io.Writer) (n int64, err error) {
-	n1, err := pk.UUID(s.sessionID).WriteTo(w)
+	n1, err := pk.UUID(s.SessionID).WriteTo(w)
 	if err != nil {
 		return n1, err
 	}
-	n2, err := s.publicKey.WriteTo(w)
+	n2, err := s.PublicKey.WriteTo(w)
 	return n1 + n2, err
 }
 
 func (s *Session) ReadFrom(r io.Reader) (n int64, err error) {
-	n1, err := ((*pk.UUID)(&s.sessionID)).ReadFrom(r)
+	n1, err := ((*pk.UUID)(&s.SessionID)).ReadFrom(r)
 	if err != nil {
 		return n1, err
 	}
-	n2, err := s.publicKey.ReadFrom(r)
+	n2, err := s.PublicKey.ReadFrom(r)
 	return n1 + n2, err
 }
 
-func (s *Session) Update(msg Message) bool {
-	panic("todo")
+func (s *Session) InitValidate() {
+	s.valid = true
+	s.lastMsg = nil
+}
+
+func (s *Session) VerifyAndUpdate(msg *Message) bool {
+	s.valid = s.valid && s.verifyHash(msg) && s.verifyChain(msg)
+	if s.valid {
+		s.lastMsg = msg
+		return true
+	}
+	return false
+}
+
+func (s *Session) verifyHash(msg *Message) bool {
+	h := sha256.New()
+	// 1
+	_ = binary.Write(h, binary.BigEndian, int32(1))
+	// Prev
+	_, _ = h.Write(msg.Prev.Sender[:])
+	_, _ = h.Write(msg.Prev.Session[:])
+	_ = binary.Write(h, binary.BigEndian, msg.Prev.Index)
+	// Body
+	_ = binary.Write(h, binary.BigEndian, msg.Salt)
+	_ = binary.Write(h, binary.BigEndian, msg.Timestamp.Unix())
+	content := []byte(msg.PlainMsg)
+	_ = binary.Write(h, binary.BigEndian, int32(len(content)))
+	_, _ = h.Write(content)
+	// Body.LastSeen
+	_ = binary.Write(h, binary.BigEndian, int32(len(msg.LastSeen)))
+	for _, v := range msg.LastSeen {
+		_, _ = h.Write((*v)[:])
+	}
+	return s.PublicKey.VerifyMessage(h.Sum(nil), msg.Signature[:]) == nil
+}
+
+func (s *Session) verifyChain(msg *Message) bool {
+	return s.lastMsg != nil && (msg.Prev.Index < s.lastMsg.Prev.Index || msg.Prev.Sender != s.lastMsg.Prev.Sender || msg.Prev.Session != s.lastMsg.Prev.Session)
 }