Do not let payload search match redacted direct messages (#174)

* Update CONTRIBUTING.md

* Update CONTRIBUTING.md

* Do not let payload search match redacted direct messages

/api/packets shows the text of a direct message (TEXT_MESSAGE_APP to a
specific node) as "<redacted>". The contains= filter, however, is a LIKE
over the stored packet bytes, which include the decrypted text for
messages on a known channel key. With portnum left out of the request,
contains=<guess> returned the packet when the guess appeared in a redacted
message, so the text could be recovered one substring at a time.

Direct text messages are now excluded from the substring match. Broadcast
messages and all other packet types search exactly as before.

Co-Authored-By: Claude Mythos 5.1 <noreply@anthropic.com>

---------

Co-authored-by: Pablo Revilla <pablorevilla@gmail.com>
Co-authored-by: Nathan <nathan@stonekitty.net>
Co-authored-by: Claude Mythos 5.1 <noreply@anthropic.com>

meshview/store.py

@@ -4,11 +4,14 @@ from datetime import datetime, timedelta, timezone
 from sqlalchemy import Text, and_, cast, func, or_, select
 from sqlalchemy.orm import lazyload
 
+from meshtastic.protobuf.portnums_pb2 import PortNum
 from meshview import database, models
 from meshview.models import Node, Packet, PacketSeen, Traceroute
 
 logger = logging.getLogger(__name__)
 
+BROADCAST_NODE_ID = 0xFFFFFFFF
+
 
 async def get_node(node_id):
     async with database.async_session() as session:
@@ -70,6 +73,14 @@ async def get_packets(
             contains_lower = f"%{contains.lower()}%"
             payload_text = cast(models.Packet.payload, Text)
             conditions.append(func.lower(payload_text).like(contains_lower))
+            # Direct text messages are shown as "<redacted>" by the API, so they must not be
+            # searchable either: a match would reveal their contents one substring at a time.
+            conditions.append(
+                or_(
+                    models.Packet.portnum != PortNum.TEXT_MESSAGE_APP,
+                    models.Packet.to_node_id == BROADCAST_NODE_ID,
+                )
+            )
 
         # Apply WHERE conditions
         if conditions: