From 2ff9ddc4f10d9f0eae32be72143b81a7b48b8183 Mon Sep 17 00:00:00 2001
From: torlando-tech <torlando-tech@users.noreply.github.com>
Date: Tue, 25 Nov 2025 18:18:22 -0500
Subject: [PATCH] fix: HW_MTU instance attribute and MTU/identity race
 condition
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Two critical fixes ported from Android testing:

1. HW_MTU instance attribute fix:
   - Base Interface.__init__() sets self.HW_MTU = None
   - BLEInterface.HW_MTU = 500 is a CLASS attribute, not instance
   - After super().__init__(), self.HW_MTU is None (instance shadows class)
   - BLEPeerInterface copies: self.HW_MTU = parent.HW_MTU (gets None)
   - When HW_MTU is None, Transport.py truncates packet.data incorrectly
   - Result: Link establishment fails with mismatched link_id
   - Fix: Explicitly set self.HW_MTU = BLEInterface.HW_MTU after super().__init__()

2. MTU/identity race condition fix:
   - MTU negotiation can complete before identity is received
   - Previously: Warning logged, fragmenter not created
   - Now: Store pending MTU, create fragmenter when identity arrives
   - Adds pending_mtu dict to track deferred MTU values
   - _device_connected_callback checks for pending MTU after storing identity

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
---
 src/RNS/Interfaces/BLEInterface.py | 41 +++++++++++++++++++++++++++---
 1 file changed, 38 insertions(+), 3 deletions(-)

diff --git a/src/RNS/Interfaces/BLEInterface.py b/src/RNS/Interfaces/BLEInterface.py
index b89dd69..bcc551b 100644
--- a/src/RNS/Interfaces/BLEInterface.py
+++ b/src/RNS/Interfaces/BLEInterface.py
@@ -284,6 +284,26 @@ class BLEInterface(Interface):
 
         super().__init__()
 
+        # CRITICAL: Set HW_MTU as instance attribute after super().__init__()
+        #
+        # Bug explanation:
+        # - Base Interface.__init__() sets self.HW_MTU = None
+        # - BLEInterface.HW_MTU = 500 is a CLASS attribute, not instance
+        # - After super().__init__(), self.HW_MTU is None (instance shadows class)
+        # - BLEPeerInterface copies: self.HW_MTU = parent.HW_MTU (gets None)
+        #
+        # Impact when HW_MTU is None:
+        # - Transport.py line ~1855 checks: if packet.receiving_interface.HW_MTU == None
+        # - If true, it TRUNCATES packet.data by 3 bytes (LINK_MTU_SIZE) before
+        #   passing to Link.validate_request()
+        # - Link.link_id_from_lr_packet() uses len(packet.data) to compute truncation
+        # - Since packet.data was pre-truncated, it computes WRONG link_id
+        # - Link proof's destination_hash won't match pending link's link_id
+        # - Result: Links time out despite proof arriving correctly
+        #
+        # This bug ONLY affects BLE because other interfaces set HW_MTU in __init__
+        self.HW_MTU = BLEInterface.HW_MTU
+
         # Parse configuration
         c = Interface.get_config_obj(configuration)
 
@@ -364,6 +384,7 @@ class BLEInterface(Interface):
         self.fragmenters = {}  # address -> BLEFragmenter (per MTU)
         self.reassemblers = {}  # address -> BLEReassembler
         self.frag_lock = threading.Lock()
+        self.pending_mtu = {}  # address -> mtu (for MTU/identity race condition)
 
         # Discovery state with prioritization
 
@@ -751,7 +772,7 @@ class BLEInterface(Interface):
         role = self.driver.get_peer_role(address)
 
         if peer_identity is not None:
-            # Central mode: identity provided by driver
+            # Identity provided by driver (central mode direct, peripheral mode via late callback)
             if len(peer_identity) == 16:
                 identity_hash = self._compute_identity_hash(peer_identity)
 
@@ -759,8 +780,15 @@ class BLEInterface(Interface):
                 self.address_to_identity[address] = peer_identity
                 self.identity_to_address[identity_hash] = address
 
-                RNS.log(f"{self} connected to {address} as CENTRAL, received identity: {identity_hash}", RNS.LOG_INFO)
+                role_str = role.upper() if role else "UNKNOWN"
+                RNS.log(f"{self} connected to {address} as {role_str}, received identity: {identity_hash}", RNS.LOG_INFO)
                 self._record_connection_success(address)
+
+                # Check for pending MTU (race condition: MTU negotiated before identity)
+                if address in self.pending_mtu:
+                    pending_mtu = self.pending_mtu.pop(address)
+                    RNS.log(f"{self} creating deferred fragmenter for {address} (MTU={pending_mtu})", RNS.LOG_DEBUG)
+                    self._mtu_negotiated_callback(address, pending_mtu)
             else:
                 RNS.log(f"{self} invalid identity from {address} (wrong length), disconnecting", RNS.LOG_WARNING)
                 self.driver.disconnect(address)
@@ -819,7 +847,10 @@ class BLEInterface(Interface):
         # Get peer identity
         peer_identity = self.address_to_identity.get(address)
         if not peer_identity:
-            RNS.log(f"{self} no identity for {address}, cannot create fragmenter", RNS.LOG_WARNING)
+            # Race condition: MTU negotiated before identity received
+            # Store pending MTU and create fragmenter when identity arrives
+            RNS.log(f"{self} no identity for {address}, storing pending MTU {mtu}", RNS.LOG_DEBUG)
+            self.pending_mtu[address] = mtu
             return
 
         # Create or update fragmenter
@@ -980,6 +1011,10 @@ class BLEInterface(Interface):
                 if frag_key in self.reassemblers:
                     del self.reassemblers[frag_key]
 
+        # Clean up pending MTU (from MTU/identity race condition)
+        if address in self.pending_mtu:
+            del self.pending_mtu[address]
+
     def _error_callback(self, severity: str, message: str, exc: Exception = None):
         """
         Driver callback: Handle driver errors.