Refactor and comment ComposeInitiatorHandshakeMessage

lib/transport/ntcp/outgoing_handshake.go

@@ -28,20 +28,47 @@ func (c *NTCP2Session) ComposeInitiatorHandshakeMessage(
 	handshakeState *noise.HandshakeState,
 	err error,
 ) {
-	// Create session request
+	// Create session request with obfuscated ephemeral key
 	request, err := c.CreateSessionRequest()
 	if err != nil {
 		return nil, nil, nil, err
 	}
 
+	// Initialize negotiation data with NTCP2 protocol specifics
+	negotiationData = initNegotiationData(nil)
+
 	// Buffer for the complete message
 	buf := new(bytes.Buffer)
 
-	// Write obfuscated key
-	buf.Write(request.ObfuscatedKey)
+	// Write obfuscated key - this has already been obfuscated in CreateSessionRequest()
+	if _, err := buf.Write(request.ObfuscatedKey); err != nil {
+		return nil, nil, nil, err
+	}
 
-	// Write timestamp
-	binary.BigEndian.PutUint32(buf.Next(4), request.Timestamp)
+	// Create options block - 16 bytes
+	options := make([]byte, 16)
+
+	// Set network ID (2 for production I2P)
+	options[0] = 2
+	// Set protocol version (2 for NTCP2)
+	options[1] = NTCP_PROTOCOL_VERSION
+
+	// Set padding length (bytes 2-3, big endian)
+	binary.BigEndian.PutUint16(options[2:4], uint16(len(request.Padding)))
+
+	// Set message 3 part 2 length (bytes 4-5) - placeholder for now
+	// This is the size of the second AEAD frame in SessionConfirmed
+	binary.BigEndian.PutUint16(options[4:6], 0) // Will need to be updated with actual size
+
+	// Set timestamp (bytes 8-11, big endian)
+	binary.BigEndian.PutUint32(options[8:12], request.Timestamp)
+
+	// Reserved bytes (6-7, 12-15) should be set to 0
+
+	// Write options block
+	if _, err := buf.Write(options); err != nil {
+		return nil, nil, nil, err
+	}
 
 	// Initialize Noise
 	config := noise.Config{
@@ -49,6 +76,7 @@ func (c *NTCP2Session) ComposeInitiatorHandshakeMessage(
 		Pattern:       noise.HandshakeXK,
 		Initiator:     true,
 		StaticKeypair: localStatic,
+		PeerStatic:    remoteStatic, // Add the peer's static key
 		Random:        rand.Reader,
 	}
 
@@ -57,7 +85,8 @@ func (c *NTCP2Session) ComposeInitiatorHandshakeMessage(
 		return nil, nil, nil, err
 	}
 
-	// Create Noise message
+	// Create Noise message - this contains the encrypted payload (options block)
+	// WriteMessage encrypts the payload and returns the message
 	handshakeMessage, _, _, err = handshakeState.WriteMessage(nil, buf.Bytes())
 	if err != nil {
 		return nil, nil, nil, err
@@ -66,6 +95,6 @@ func (c *NTCP2Session) ComposeInitiatorHandshakeMessage(
 	// Add padding
 	handshakeMessage = append(handshakeMessage, request.Padding...)
 
-	// Ensure entire message is written at once
-	return nil, handshakeMessage, handshakeState, nil
+	// Return the complete handshake message
+	return negotiationData, handshakeMessage, handshakeState, nil
 }