Share the K1 live scene template and preserve idle media channels

src/k1link/device_plugins/xgrids_k1/node_sensor.py

@@ -151,9 +151,21 @@ class NodeK1Sensor:
             await self.peers.close(params.get("peer_id"))
             return {"ok": True}
         if action == "offer":
-            if item["snapshot"]["acquisition"] != "streaming":
-                raise ValueError("Acquisition is not active")
-            return await self.peers.offer(params)
+            acquisition_id = item["control"]["acquisition_id"]
+            if (item["snapshot"]["acquisition"] != "streaming" or not acquisition_id
+                    or params.get("acquisition_id") != acquisition_id):
+                raise ValueError("Acquisition is not active or changed")
+            answer = await self.peers.offer(params)
+            # Signalling may outlive STOP or a replacement acquisition. Retire
+            # that disposable preview instead of attaching it to another run.
+            current = project_sensor(await self.raw_state(), node_id)
+            if (current is None or current["snapshot"]["acquisition"] != "streaming"
+                    or current["snapshot"]["context"]["session_id"]
+                    != command["session"]["session_id"]
+                    or current["control"]["acquisition_id"] != acquisition_id):
+                await self.peers.close(answer["peer_id"])
+                raise ValueError("Acquisition changed during preview signalling")
+            return answer
         async with self.bridge.lock:
             if datetime.fromisoformat(command["deadline_at"]) <= datetime.now(UTC):
                 raise ValueError("Command expired before dispatch")

src/k1link/viewer/node_media.py

@@ -13,7 +13,7 @@ from uuid import uuid4
 import aioice.ice
 from aiortc import RTCConfiguration, RTCPeerConnection, RTCSessionDescription
 
-MEDIA_PROTOCOL = "missioncore.node-preview/v1"
+MEDIA_PROTOCOL = "missioncore.node-preview/v2"
 MAX_PAYLOAD = 8 * 1024 * 1024
 FRAGMENT_BYTES = 16384
 logger = logging.getLogger(__name__)
@@ -175,6 +175,10 @@ class NodeMediaPeers:
                     break
                 if payload:
                     await self.send(channel, payload)
+                    if subscriber:
+                        # Ordered after native bytes. Age is source arrival age,
+                        # not time spent replaying an encoded preview backlog.
+                        channel.send(json.dumps(subscriber.snapshot()))
         except asyncio.CancelledError:
             pass
         except Exception as error:

src/k1link/viewer/node_rerun.py

@@ -5,14 +5,19 @@ Latest-value queues discard decoded preview frames before encoding; encoded
 RRD bytes are never dropped inside a stream. Slow viewers are closed instead.
 """
 
+import logging
 import queue
 import threading
+import time
 from contextlib import suppress
 from uuid import uuid4
 
+from k1link.data_plane import DecodedPointCloudView
 from k1link.viewer.rerun_bridge import RerunBridge
 
 MAX_ENCODED_CHUNK = 8 * 1024 * 1024
+LIVE_FRAME_MAX_AGE_SECONDS = 2.0
+logger = logging.getLogger(__name__)
 
 
 class RrdSubscriber:
@@ -21,6 +26,7 @@ class RrdSubscriber:
         self.inputs = queue.Queue(maxsize=2)
         self.output = queue.Queue(maxsize=2)
         self.settings_provider = settings_provider
+        self.last_frame = None
         self.thread = threading.Thread(target=self.run, name="node-rerun-view", daemon=True)
         self.thread.start()
 
@@ -41,6 +47,12 @@ class RrdSubscriber:
         except queue.Empty:
             return b""
 
+    def snapshot(self):
+        frame = self.last_frame
+        return {"type": "lidar-state", "sequence": frame[0] if frame else 0,
+                "age_ms": max(0, (time.monotonic_ns() - frame[1]) / 1_000_000) if frame else None,
+                "points": frame[2] if frame else 0}
+
     def close(self):
         self.closed.set()
 
@@ -58,7 +70,9 @@ class RrdSubscriber:
             bridge.begin_session()
             while not self.closed.is_set():
                 payload = binary.read()
-                if len(payload) > MAX_ENCODED_CHUNK:
+                # The SDK returns None while its live sink has no new bytes.
+                # An idle read is not EOF and must not retire the media peer.
+                if payload and len(payload) > MAX_ENCODED_CHUNK:
                     break
                 if payload:
                     # Bound both bytes and waiting time. The archive/producer
@@ -68,9 +82,20 @@ class RrdSubscriber:
                     envelope = self.inputs.get(timeout=0.1)
                 except queue.Empty:
                     continue
+                received = envelope.context.received_monotonic_ns
+                if (received is not None
+                        and (time.monotonic_ns() - received) / 1_000_000_000
+                        > LIVE_FRAME_MAX_AGE_SECONDS):
+                    continue
                 bridge.process(envelope)
-        except Exception:
-            pass
+                if isinstance(envelope, DecodedPointCloudView):
+                    self.last_frame = (
+                        envelope.context.sequence,
+                        envelope.context.received_monotonic_ns or time.monotonic_ns(),
+                        envelope.point_count,
+                    )
+        except Exception as error:
+            logger.warning("Node RRD subscriber failed exception=%s", type(error).__name__)
         finally:
             self.closed.set()
             if bridge is not None:
@@ -98,7 +123,7 @@ class NodeRerunBridge(RerunBridge):
         # It is continuously drained even when no viewer is attached.
         self.binary.read()
         with self.lock:
-            self.latest[type(envelope)] = envelope
+            self.latest[type(envelope)] = (time.monotonic(), envelope)
             self.subscribers = [v for v in self.subscribers if not v.closed.is_set()]
             for subscriber in self.subscribers:
                 subscriber.offer(envelope)
@@ -113,8 +138,9 @@ class NodeRerunBridge(RerunBridge):
             if self._closed or len(self.subscribers) >= 2:
                 raise RuntimeError("Live viewer unavailable")
             subscriber = RrdSubscriber(self._settings_provider)
-            for envelope in self.latest.values():
-                subscriber.offer(envelope)
+            for observed, envelope in self.latest.values():
+                if time.monotonic() - observed <= LIVE_FRAME_MAX_AGE_SECONDS:
+                    subscriber.offer(envelope)
             self.subscribers.append(subscriber)
             return subscriber