Issue #105 - Store last packet on backend; send only changes to front…

… end

ait/gui/__init__.py

@@ -682,6 +682,33 @@ def handle():
         pass
 
 
+last_packets = { }
+def get_packet_delta(pkt_defn, packet):
+    """
+    Keeps track of last packets recieved of all types recieved
+    and checks returns only fields that have changed since last
+    packet.
+
+    Params:
+        pkt_defn:  Packet definition
+        packet:    Packet in JSON format
+    Returns:
+        delta:     JSON of packet fields that have changed
+    """
+    if pkt_defn.name not in last_packets:
+        last_packets[pkt_defn.name] = packet
+        delta = packet
+    else:
+        delta = { }
+        for field, new_value in packet.items():
+            last_value = last_packets[pkt_defn.name][field]
+            if new_value != last_value:
+                delta[field] = new_value
+                last_packets[pkt_defn.name][field] = new_value
+
+    return delta
+
+
 @App.route('/tlm/realtime')
 def handle():
     """Return telemetry packets in realtime to client"""
@@ -704,9 +731,12 @@ def handle():
                             pkt_defn = v
                             break
 
+                    json_pkt = ait.core.tlm.Packet(pkt_defn, data=data).toJSON()
+                    delta = get_packet_delta(pkt_defn, json_pkt)
+
                     wsock.send(json.dumps({
                         'packet': pkt_defn.name,
-                        'data': ait.core.tlm.Packet(pkt_defn, data=data).toJSON()
+                        'data': delta
                     }))
 
                 except IndexError: