update

examples/walkthrough.md

@@ -514,6 +514,7 @@ class SensorSender:
         
         data = [("reading", reading.to_dict(), "dictionary")]
         
+        # Default: is_publish=True (automatically publishes to NATS)
         smartsend(
             f"/sensors/{sensor_id}",
             data,
@@ -521,6 +522,31 @@ class SensorSender:
             fileserver_url=self.fileserver_url
         )
         
+    def prepare_message_only(self, sensor_id: str, value: float, unit: str):
+        """Prepare a message without publishing (is_publish=False)."""
+        reading = SensorReading(
+            sensor_id=sensor_id,
+            timestamp=datetime.now().isoformat(),
+            value=value,
+            unit=unit
+        )
+        
+        data = [("reading", reading.to_dict(), "dictionary")]
+        
+        # With is_publish=False, returns (envelope, json_str) without publishing
+        env, msg_json_str = smartsend(
+            f"/sensors/{sensor_id}/prepare",
+            data,
+            nats_url=self.nats_url,
+            fileserver_url=self.fileserver_url,
+            is_publish=False
+        )
+        
+        # Now you can publish manually using NATS request-reply pattern
+        # nc.request(subject, msg_json_str, reply_to=reply_to_topic)
+        
+        return env, msg_json_str
+        
     def send_batch(self, readings: List[SensorReading]):
         batch = SensorBatch()
         for reading in readings: