Merge pull request #47 from Moballo-LLC/codex/ocf-multicast-responder

feat(protocol): discover known-host OCF responder ports

README.md

@@ -57,6 +57,10 @@ retransmissions within that same deadline:
 sess.connect(timeout=4.0)
 ```
 
+The deadline stops further setup, retries, and network waits. If OpenSSL
+reports that the handshake completed at the deadline boundary, the completed
+session is retained rather than torn down as a timeout.
+
 Connection attempts can also use a one-way cancellation signal. The signal is
 backed by a socketpair, so setting it wakes the network wait immediately while
 OpenSSL retains control of DTLS retransmission timing:
@@ -171,6 +175,32 @@ the key must be exactly 16 or 32 bytes. `PskAuth` selects only
 or persist credentials. Ownership transfer and credential discovery are
 outside this package.
 
+Code that has already completed an authenticated manufacturer-certificate
+session can derive IoTivity's 128-bit OwnerPSK from the resulting TLS state:
+
+```python
+from smartthings_local.protocol.owner_psk import derive_mfg_certificate_owner_psk
+
+owner_psk = derive_mfg_certificate_owner_psk(
+    master_secret=master_secret,
+    client_random=client_random,
+    server_random=server_random,
+    owner_uuid=owner_uuid,
+    device_uuid=device_uuid,
+    cipher_name=cipher_name,
+    oxm_label=selected_oxm_label,
+)
+```
+
+The caller must supply the exact authenticated TLS values, non-nil raw OCF
+UUIDs, negotiated cipher name, and label for the selected OXM. Use
+`STANDARD_MFG_CERTIFICATE_OXM_LABEL` for `oic.sec.doxm.mfgcert` and
+`CONFIRMED_MFG_CERTIFICATE_OXM_LABEL` for
+`x.org.iotivity.conmfgcert`; do not infer the label from the appliance model.
+The helper performs deterministic key derivation only: it does not access a
+session, discover credentials, choose an ownership method, write security
+resources, run OTM, or persist the result.
+
 ### Classified errors
 
 Runtime transport failures use the public types in
@@ -232,6 +262,34 @@ The resolver retains candidate order and the socket setup tries the next
 candidate after a family, bind, or connect failure. Resolution and socket
 setup failures raise the redacted `EndpointError` documented above.
 
+### Dynamic plaintext OCF response ports
+
+Some OCF devices listen for multicast discovery on UDP 5683 but send their
+response from a different port that changes after a power cycle. A caller that
+already knows the device's IPv4 address can discover those plaintext response
+port candidates on one explicit LAN interface:
+
+```python
+from smartthings_local.protocol.ocf_multicast import (
+    discover_ocf_responder_ports,
+)
+
+result = discover_ocf_responder_ports(
+    "192.0.2.20",
+    interface_address="192.0.2.10",
+)
+for discovery_port in result.ports:
+    pass  # use for a bounded, source-bound /oic/res lookup
+```
+
+The call sends unfiltered current OCF and legacy IoTivity directory requests,
+plus a legacy DOXM-filtered fallback, under one deadline. It accepts only
+token-correlated replies from the expected host, closes its multicast socket
+before returning, and omits addresses and ports from its result representation.
+Returned ports are unauthenticated candidates, not DTLS endpoints; directory
+parsing, DTLS liveness, and authenticated device identity remain separate
+checks.
+
 For a full worked integration, the higher-level `smartthings_local.ocf` layer (`StateCache`, `PollScheduler`, `KeepaliveTask`, `ObserveRefreshTask`) coordinates tiered polling and OBSERVE on top of a session. The MQTT bridge demo below wires all of it together.
 
 ### What the demo bridge gives you
@@ -605,6 +663,7 @@ smartthings_local/                   The installable library — `pip install sm
     dtls_session.py                  DTLS session: handshake, client-cert auth (file or in-memory PEM), Block2, liveness
     dtls_probe.py                    Stateless DTLS liveness + opt-in stateful diagnostic
     dtls_handshake.py                Shared memory-BIO handshake driver, bounded by a monotonic deadline (used by session + probe)
+    owner_psk.py                     Pure manufacturer-certificate OwnerPSK derivation
     ocf_root_ca.pem                  Samsung OCF root CA, bundled for handshake verification
   ocf/                               OCF resource + state layer (reusable)
     __init__.py
@@ -631,7 +690,7 @@ mqtt_demo/                           MQTT bridge demo (consumes smartthings_loca
   .env.example                       Template — copy to .env, fill in
 setup_cert.py                        One-shot cert minting script (live-fetches AC14K_M + UUID)
 pyproject.toml                       Packaging — PyPI dist `smartthings-local`, hatch-vcs versioning
-tests/                               pytest suite (CoAP wire, state cache, import isolation, cert loading, DTLS probe, bridge port resolution, cert signing, certificate profiles, connect deadline, session interruption)
+tests/                               pytest suite (CoAP wire, state cache, import isolation, cert loading, DTLS probe, bridge port resolution, cert signing, certificate profiles, OwnerPSK derivation, connect deadline, session interruption)
 .github/workflows/publish.yml        Build + PyPI Trusted Publishing on `v*` tags
 ```
 

mqtt_demo/__main__.py

@@ -166,7 +166,7 @@ def main():
         stopping.set()
         logger.info("shutting down…")
         for b in bridges:
-            b.stop.set()
+            b.request_stop()
             try: b.set_availability(False)
             except Exception: pass
 

mqtt_demo/bridge.py

@@ -87,6 +87,7 @@ OCF_STANDARD_SECURE_PORT = 5684
 # fixed-source-port reconnect invariant is untouched (see session_once).
 _GATE_RETRIES = 1
 _GATE_TIMEOUT_S = 4.0
+_WORKER_JOIN_TIMEOUT_S = 2.0
 
 
 class PushBridge:
@@ -123,6 +124,8 @@ class PushBridge:
         self.last_cycle_pub = None
         self.last_avail_pub: str | None = None
         self.stop = threading.Event()
+        self._session_stop_lock = threading.Lock()
+        self._session_stop: threading.Event | None = None
         self.started_ts = time.time()
         self.session_started_ts = None
         self.last_change_ts = None
@@ -175,6 +178,13 @@ class PushBridge:
                 app.topic_prefix, shared.HA_DISCOVERY_PREFIX, app.device_name,
                 model=descriptor.name.title()))
 
+    def request_stop(self) -> None:
+        """Stop the bridge and wake workers belonging to its current session."""
+        self.stop.set()
+        with self._session_stop_lock:
+            if self._session_stop is not None:
+                self._session_stop.set()
+
     # ---- cache plumbing ---------------------------------------------
 
     def _on_cache_change(self, changed: bool, source: str) -> None:
@@ -423,25 +433,54 @@ class PushBridge:
         self.keepalive = keepalive
         self.observe_refresh = observe_refresh
 
+        # These workers belong to this DTLS session, not to the bridge
+        # process. A reconnect must retire them before the replacement
+        # session starts or they continue operating on the closed session.
+        session_stop = threading.Event()
+        with self._session_stop_lock:
+            self._session_stop = session_stop
+            # ``request_stop()`` sets the bridge event before taking this
+            # lock. Checking it while publishing the handle prevents a lost
+            # wakeup if shutdown races this session handoff.
+            if self.stop.is_set():
+                session_stop.set()
+
         sched_t = threading.Thread(
-            target=scheduler.run_forever, args=(self.stop,),
+            target=scheduler.run_forever, args=(session_stop,),
             daemon=True, name=f'{self.app.klass}-poll')
         ka_t = threading.Thread(
-            target=keepalive.run_forever, args=(self.stop,),
+            target=keepalive.run_forever, args=(session_stop,),
             daemon=True, name=f'{self.app.klass}-ping')
         ref_t = threading.Thread(
-            target=observe_refresh.run_forever, args=(self.stop,),
+            target=observe_refresh.run_forever, args=(session_stop,),
             daemon=True, name=f'{self.app.klass}-obsref')
-        sched_t.start()
-        ka_t.start()
-        ref_t.start()
+        workers = (sched_t, ka_t, ref_t)
+        started_workers = []
 
         try:
+            for worker in workers:
+                worker.start()
+                started_workers.append(worker)
             sess.join()
         finally:
+            # A worker already inside a tick can finish after the reader
+            # exits. Disable old-session reachability callbacks first so it
+            # cannot change availability after a replacement takes over.
+            keepalive.on_reachable = None
+            keepalive.on_unreachable = None
+            session_stop.set()
+            join_deadline = time.monotonic() + _WORKER_JOIN_TIMEOUT_S
+            for worker in started_workers:
+                worker.join(max(0.0, join_deadline - time.monotonic()))
+                if worker.is_alive():
+                    self.log.warning(
+                        "session worker did not stop: %s", worker.name)
             self.scheduler = None
             self.keepalive = None
             self.observe_refresh = None
+            with self._session_stop_lock:
+                if self._session_stop is session_stop:
+                    self._session_stop = None
 
     def _seed_from_device0(self, sess):
         code, pl = sess.get(self.descriptor.seed_path, timeout=15.0)

mqtt_demo/samples/oven.py

@@ -166,6 +166,14 @@ def flatten(links):
     if temps_items:
         cur_c = _int(temps_items[0].get('x.com.samsung.da.current'))
         des_c = _int(temps_items[0].get('x.com.samsung.da.desired'))
+    # With no cycle set the oven reports desired=0. That means "no
+    # setpoint", not a 0 °C target, and HA rejects it against the Number
+    # entity's 30-270 range on every publish. Anything outside the
+    # settable band is absent, not a value: null lands as unknown on both
+    # the Number and the Setpoint sensor, the way completion_minutes
+    # already reads when idle. _setpoint applies the same bounds on write.
+    if des_c is not None and not (SETPOINT_MIN_C <= des_c <= SETPOINT_MAX_C):
+        des_c = None
 
     # Door
     doors_items = g('/doors/vs/0', 'x.com.samsung.da.items') or []

smartthings_local/protocol/coap.py

@@ -13,6 +13,7 @@ from ..errors import MalformedMessageError
 URI_PATH       = 11
 URI_QUERY      = 15
 OBSERVE        =  6
+ETAG           =  4
 CONTENT_FORMAT = 12
 ACCEPT         = 17
 BLOCK2         = 23
@@ -121,6 +122,14 @@ def block_value(num, more, szx):
     return struct.pack('>I', v)[1:]
 
 
+def block_fields(value):
+    """Decode a CoAP Block-N option value. Inverse of block_value().
+    Returns (num, more, szx). An empty value means block 0, no more,
+    SZX=0 — RFC 7959 §2.2 allows a zero-length option to elide it."""
+    v = int.from_bytes(value, 'big')
+    return v >> 4, (v >> 3) & 1, v & 0x07
+
+
 def fmt_code(c):
     """0x45 → '2.05', 0x84 → '4.04'. Used in log lines."""
     return f"{c >> 5}.{c & 0x1F:02d}"

smartthings_local/protocol/dtls_handshake.py

@@ -34,14 +34,16 @@ def _drive_dtls_handshake(
     bounded only by its deadline, while the diagnostic probe retains its
     explicit retry budget.
 
-    Return ``True`` only when the handshake completes before the deadline.
-    TLS and socket failures are left to the caller to classify.
+    Return ``True`` once OpenSSL reports the handshake complete. The deadline
+    prevents another setup, retry, or network-wait iteration; it does not tear
+    down a session that completed while ``do_handshake()`` was running. TLS and
+    socket failures are left to the caller to classify.
     """
     retransmits = 0
     while time.monotonic() < deadline:
         try:
             connection.do_handshake()
-            return time.monotonic() < deadline
+            return True
         except SSL.WantReadError:
             pass
 

smartthings_local/protocol/dtls_session.py

@@ -12,11 +12,18 @@ Wire-level details that matter (from local-tools/oven-findings.md §17):
     or interleaved one-shot / OBSERVE traffic mis-attributes.
   * Multi-block GET requires the SAME CoAP token across every block
     of the response ("token-stable Block2"). Fresh-token-per-block
-    is silently dropped by the server.
+    is silently dropped by the server, and a transfer that opens at
+    NUM>0 under a token the server has not seen gets no reply at all.
 
 Reader thread owns the UDP socket. Callers issue get()/post() and block
 on a per-token Event the reader signals. OBSERVE notifications are
 delivered via the on_notification callback.
+
+A notification carries only the first block of a large representation
+(RFC 7959 §2.6). Because a continuation cannot borrow the observation's
+token (§3.4) and this server will not continue a transfer it did not
+start, such a notification is withheld and the resource is re-read from
+block 0 on a fresh one-shot token by a worker thread. See #39.
 """
 import errno
 import math
@@ -35,11 +42,12 @@ from ..errors import (
     SessionTimeoutError,
 )
 from .coap import (
-    URI_PATH, URI_QUERY, OBSERVE, CONTENT_FORMAT, ACCEPT, BLOCK2, SIZE2,
+    URI_PATH, URI_QUERY, OBSERVE, ETAG, CONTENT_FORMAT, ACCEPT, BLOCK2, SIZE2,
     TYPE_CON, TYPE_NON, TYPE_ACK, TYPE_RST,
     METHOD_GET, METHOD_POST, CF_CBOR,
     OBSERVE_REGISTER, OBSERVE_DEREGISTER, BLOCK_SZX,
-    encode_options, parse_coap, build_coap, block_value, fmt_code,
+    encode_options, parse_coap, build_coap, block_value, block_fields,
+    fmt_code,
     split_dtls as _split_dtls,
 )
 from .auth import (
@@ -72,6 +80,11 @@ DEBUG_BRIDGE = os.environ.get('DEBUG_BRIDGE') == '1'
 _BLOCK_MAX_ATTEMPTS = 3
 _BLOCK_ACK_TIMEOUT  = 4.0
 
+# How often a block wait re-checks that the reader is still alive. Short
+# enough that a mid-transfer reader death fails fast instead of burning
+# the whole per-block timeout, long enough to stay off the CPU.
+_BLOCK_LIVENESS_POLL_S = 0.25
+
 # Inter-request pacing: minimum seconds between CoAP CON sends on one session.
 # Samsung's RT-OCF stacks drop requests when hit faster than their firmware
 # ceiling (dryer ~14 req/s, oven ~8 req/s, dishwasher unknown). 5 req/s
@@ -79,6 +92,22 @@ _BLOCK_ACK_TIMEOUT  = 4.0
 # once the ceiling is measured empirically.
 _DEFAULT_RATE_LIMIT_RPS = 5.0
 
+# Maximum hrefs held for OBSERVE refetch at once. A notification storm
+# on more resources than this is already past what the 5/s ceiling can
+# drain, so the excess is dropped rather than queued indefinitely.
+_MAX_PENDING_REFETCH = 16
+
+# Timeout for one notification refetch. Generous relative to a poll:
+# the resource is known large (that is why it blocked) and the worker
+# is serialized, so a slow one delays only later refetches.
+_REFETCH_TIMEOUT_S = 15.0
+
+
+class _EtagChanged(Exception):
+    """Internal: the server's ETag changed partway through a Block2
+    transfer, so the blocks in hand are from two different versions."""
+
+
 # ICMP errors a connected UDP socket surfaces on the next recv. On these
 # appliances they show up while the device is rebooting, while it holds an
 # orphaned association, or across a router blip, and the next datagram
@@ -241,6 +270,11 @@ class DtlsCoapSession:
         self.endpoint = None
 
         self._send_lock = threading.Lock()
+        # Guards the MID/token counters and _pending. The refetch worker
+        # makes the session its own second concurrent get() caller, so
+        # two threads can mint tokens at once; without this they can
+        # collide and one transfer silently absorbs the other's blocks.
+        self._state_lock = threading.Lock()
         # Randomize MID and token counter starting points so reconnects
         # don't reuse identifiers from previous sessions — Samsung's
         # RT-OCF appears to remember observer state across DTLS
@@ -257,6 +291,14 @@ class DtlsCoapSession:
         # token (bytes) → href (str)
         self._observe_tokens = {}
 
+        # OBSERVE refetch queue: href → sequence number of the newest
+        # notification that asked for it. Drained by a worker thread
+        # because _dispatch_coap cannot block (see _queue_refetch).
+        self._refetch_cond = threading.Condition()
+        self._refetch_pending = {}
+        self._refetch_seq = 0
+        self._refetch_thread = None
+
         self._stop = threading.Event()
         self._reader_thread = None
         # Set while the reader owns the socket. Cleared when it exits for
@@ -280,13 +322,15 @@ class DtlsCoapSession:
         timeout: float | None = None,
         cancel: ConnectCancellation | None = None,
     ):
-        """Perform a cancellable DTLS handshake within a monotonic deadline.
+        """Perform a cancellable DTLS handshake using a monotonic deadline.
 
         ``timeout`` overrides ``HANDSHAKE_TIMEOUT_S`` for this call. OpenSSL
         owns DTLS retransmission timing while every receive is capped by the
         remaining budget, so wall-clock adjustments cannot change the bound.
-        A ``ConnectCancellation`` wakes the network wait immediately and does
-        not alter an already established session.
+        Once OpenSSL reports completion, that completed session is retained
+        even if the call returns just after the deadline. A
+        ``ConnectCancellation`` wakes the network wait immediately and does not
+        alter an already established session.
         """
         handshake_timeout = _validate_handshake_timeout(
             timeout, self.HANDSHAKE_TIMEOUT_S)
@@ -338,6 +382,7 @@ class DtlsCoapSession:
         io_failed = False
         cancelled = False
         interrupted = False
+        completed = False
         try:
             try:
                 completed = _drive_dtls_handshake(
@@ -359,7 +404,7 @@ class DtlsCoapSession:
         finally:
             if wake_subscription is not None:
                 interrupted = cancel._unsubscribe(*wake_subscription)
-        if cancelled or interrupted:
+        if cancelled or (interrupted and not completed):
             sock.close()
             raise SessionClosedError()
         if backend_failed:
@@ -407,6 +452,8 @@ class DtlsCoapSession:
         """Block until the reader thread exits (i.e. socket dies)."""
         if self._reader_thread is not None:
             self._reader_thread.join()
+        if self._refetch_thread is not None:
+            self._refetch_thread.join()
 
     def _send_observe_dereg(self, tok, path_segs):
         """Send a single OBSERVE deregister GET (Observe option = 1)
@@ -438,6 +485,11 @@ class DtlsCoapSession:
             time.sleep(0.1)
 
         self._stop.set()
+        # Wake the refetch worker so it sees _stop instead of sitting on
+        # its condition for up to a second after the socket is gone.
+        with self._refetch_cond:
+            self._refetch_pending.clear()
+            self._refetch_cond.notify_all()
         if self.conn is not None:
             try:
                 self.conn.shutdown()
@@ -448,10 +500,12 @@ class DtlsCoapSession:
                 self.sock.close()
             except Exception:
                 pass
-        for tok, (ev, container) in list(self._pending.items()):
+        with self._state_lock:
+            pending = list(self._pending.items())
+            self._pending.clear()
+        for tok, (ev, container) in pending:
             container.setdefault('err', SessionClosedError())
             ev.set()
-        self._pending.clear()
         self._observe_tokens.clear()
         self.sock = None
         self.conn = None
@@ -461,27 +515,30 @@ class DtlsCoapSession:
     # ---- send / receive plumbing -------------------------------------
 
     def _next_mid(self):
-        self._mid = (self._mid + 1) & 0xFFFF
-        return self._mid
+        with self._state_lock:
+            self._mid = (self._mid + 1) & 0xFFFF
+            return self._mid
 
     def _next_tok(self):
-        self._tok_counter = (self._tok_counter + 1) & 0xFFFFFFFF
-        # 4-byte tokens — fits within tkl=8 cap with headroom and
-        # avoids collisions across long-running OBSERVE subscriptions.
-        return self._tok_counter.to_bytes(4, 'big')
+        with self._state_lock:
+            self._tok_counter = (self._tok_counter + 1) & 0xFFFFFFFF
+            # 4-byte tokens — fits within tkl=8 cap with headroom and
+            # avoids collisions across long-running OBSERVE subscriptions.
+            return self._tok_counter.to_bytes(4, 'big')
 
     def _next_observe_tok(self):
-        # Single-byte tokens for OBSERVE registrations. Samsung
-        # RT-OCF accepts these but silently drops TKL=4 OBSERVE
-        # registrations. Counter is randomly seeded per session so
-        # reconnects don't collide with stale observer state Samsung
-        # may still be holding from the previous run.
-        self._observe_tok_counter = (self._observe_tok_counter + 1) & 0xFF
-        # Avoid 0x00 — some CoAP stacks treat an all-zero token as
-        # equivalent to "no token" / empty (TKL=0).
-        if self._observe_tok_counter == 0:
-            self._observe_tok_counter = 1
-        return bytes([self._observe_tok_counter])
+        with self._state_lock:
+            # Single-byte tokens for OBSERVE registrations. Samsung
+            # RT-OCF accepts these but silently drops TKL=4 OBSERVE
+            # registrations. Counter is randomly seeded per session so
+            # reconnects don't collide with stale observer state Samsung
+            # may still be holding from the previous run.
+            self._observe_tok_counter = (self._observe_tok_counter + 1) & 0xFF
+            # Avoid 0x00 — some CoAP stacks treat an all-zero token as
+            # equivalent to "no token" / empty (TKL=0).
+            if self._observe_tok_counter == 0:
+                self._observe_tok_counter = 1
+            return bytes([self._observe_tok_counter])
 
     def _send_dgram(self, datagram):
         """Send a CoAP datagram. Holds the send lock for the
@@ -583,9 +640,15 @@ class DtlsCoapSession:
             # Reader no longer owns the socket — callers must fail fast.
             self._reader_running.clear()
             # Make sure pending waiters don't hang if the reader dies.
-            for tok, (ev, container) in list(self._pending.items()):
+            with self._state_lock:
+                pending = list(self._pending.items())
+            for tok, (ev, container) in pending:
                 container.setdefault('err', SessionClosedError())
                 ev.set()
+            # Nothing will answer a refetch now either.
+            with self._refetch_cond:
+                self._refetch_pending.clear()
+                self._refetch_cond.notify_all()
 
     def _dispatch_coap(self, datagram):
         try:
@@ -615,7 +678,8 @@ class DtlsCoapSession:
             return
 
         # Pending one-shot? Resolve and return.
-        rec = self._pending.get(tok)
+        with self._state_lock:
+            rec = self._pending.get(tok)
         if rec is not None:
             ev, container = rec
             container['code']    = code
@@ -633,6 +697,16 @@ class DtlsCoapSession:
                 logger.warning("observe %s: non-2.05 %s",
                                href, fmt_code(code))
                 return
+            # RFC 7959 §2.6: a notification carries only the first block
+            # of the representation. Handing the callback a partial CBOR
+            # buffer is what #39 was about, so anything with M=1 (or a
+            # block past the first) goes to the refetch worker instead.
+            b2 = [v for n, v in ropts if n == BLOCK2]
+            if b2:
+                num, more, _ = block_fields(b2[0])
+                if more or num:
+                    self._queue_refetch(href)
+                    return
             cb = self.on_notification
             if cb is not None:
                 try:
@@ -644,6 +718,110 @@ class DtlsCoapSession:
 
         # Stale token (post-reconnect or unknown) — drop quietly.
 
+    # ---- OBSERVE refetch ---------------------------------------------
+
+    @staticmethod
+    def _log_refetch(msg, *args):
+        """Refetch outcomes are debug-level in normal operation, which is
+        below the bridge's INFO default, so a healthy session stays quiet.
+        DEBUG_BRIDGE=1 promotes them to INFO for hardware validation:
+        that shows which token the re-read used and whether it completed,
+        without also turning on every per-block retransmit line."""
+        (logger.info if DEBUG_BRIDGE else logger.debug)(msg, *args)
+
+    def _queue_refetch(self, href):
+        """Queue a blockwise notification for re-reading.
+
+        Called from the reader thread, so it must not block: _dispatch_coap
+        runs there and _blockwise_get waits on an Event only that same
+        thread can set, which would deadlock the session outright. Latest
+        wins per href — a burst of notifications on one resource collapses
+        into a single re-read of its final state."""
+        with self._refetch_cond:
+            if (href not in self._refetch_pending
+                    and len(self._refetch_pending) >= _MAX_PENDING_REFETCH):
+                self._log_refetch(
+                    "refetch %s dropped: queue full (%d pending)",
+                    href, len(self._refetch_pending))
+                return
+            self._refetch_seq += 1
+            self._refetch_pending[href] = self._refetch_seq
+            self._refetch_cond.notify()
+        self._start_refetch_worker()
+
+    def _start_refetch_worker(self):
+        """Start the refetch worker on first use. Sessions that never see
+        a blockwise notification never grow the thread."""
+        if self._refetch_thread is not None or self._stop.is_set():
+            return
+        with self._state_lock:
+            if self._refetch_thread is not None or self._stop.is_set():
+                return
+            self._refetch_thread = threading.Thread(
+                target=self._refetch_loop, daemon=True,
+                name=f'stl-refetch-{self.host}')
+            self._refetch_thread.start()
+
+    def _refetch_loop(self):
+        """Re-read blockwise-notified resources, one at a time.
+
+        Serialized on purpose. Each re-read is a multi-block transfer and
+        _blockwise_get paces between blocks, so running one at a time is
+        what keeps a notification storm under the firmware's request
+        ceiling."""
+        while self._refetch_alive():
+            with self._refetch_cond:
+                while not self._refetch_pending and self._refetch_alive():
+                    self._refetch_cond.wait(1.0)
+                if not self._refetch_pending:
+                    return
+                href, seq = next(iter(self._refetch_pending.items()))
+                del self._refetch_pending[href]
+            self._refetch_one(href, seq)
+
+    def _refetch_alive(self):
+        """False once the session is closing or the reader has died. A
+        refetch needs the reader to resolve its token, so outliving it
+        would leave join() waiting on a thread with nothing to do."""
+        if self._stop.is_set():
+            return False
+        return self._reader_thread is None or self._reader_running.is_set()
+
+    def _refetch_one(self, href, seq):
+        """Re-read one href from block 0 and deliver it if it is still
+        the freshest thing we know about that resource."""
+        self.pace()
+        segs = [s for s in href.split('/') if s]
+        try:
+            code, payload, blocks, tok = self._blockwise_get(
+                segs, (), _REFETCH_TIMEOUT_S)
+        except Exception as e:
+            # Device silent, session gone, ETag never settled, block cap
+            # hit. Whatever the reason, dropping the notification is the
+            # contract: the poll tiers still carry freshness, and handing
+            # over the first block is the bug this replaced.
+            self._log_refetch("refetch %s failed: %s", href, e)
+            return
+        if code != 0x45:
+            self._log_refetch("refetch %s returned %s", href, fmt_code(code))
+            return
+        with self._refetch_cond:
+            # A newer notification landed while we were reading. That one
+            # has its own refetch queued, so this result is already stale.
+            if self._refetch_pending.get(href, 0) > seq:
+                self._log_refetch(
+                    "refetch %s tok=%s blocks=%d bytes=%d superseded",
+                    href, tok.hex(), blocks, len(payload))
+                return
+        self._log_refetch("refetch %s tok=%s blocks=%d bytes=%d ok",
+                          href, tok.hex(), blocks, len(payload))
+        cb = self.on_notification
+        if cb is not None:
+            try:
+                cb(href, payload)
+            except Exception as e:
+                logger.warning("notification callback %s: %s", href, e)
+
     # ---- request primitives ------------------------------------------
 
     def get(self, path_segs, query=(), timeout=10.0):
@@ -654,76 +832,183 @@ class DtlsCoapSession:
         token, and dropping a fresh token on block 1+ silently drops
         the request."""
         self._check_live()
+        code, blob, _blocks, _tok = self._blockwise_get(
+            path_segs, query, timeout)
+        return code, blob
+
+    def _blockwise_get(self, path_segs, query=(), timeout=10.0):
+        """Shared token-stable Block2 reassembly (RFC 7959 §2.4).
+
+        Returns (code, payload, block_count, token). The last two are
+        diagnostics for the refetch log; get() drops them.
+
+        Mints one fresh 4-byte token and holds it across every block of
+        the transfer. Also the notification-refetch primitive: RFC 7959
+        §3.4 forbids continuing a blockwise notification on the
+        observation's token, and Samsung's RT-OCF drops a transfer that
+        opens at NUM>0 under a token it has not seen, so a truncated
+        notification is recovered by re-reading from block 0 through
+        this same path rather than by a §2.6 continuation.
+
+        Restarts once if the server's ETag changes mid-transfer, then
+        gives up: RFC 7959 §2.4 requires the client to compare ETags
+        when the server supplies them. None of the tested appliances
+        emit option 4, so on those this is inert."""
+        try:
+            return self._blockwise_get_once(path_segs, query, timeout)
+        except _EtagChanged:
+            logger.debug("GET %s /%s: ETag changed mid-transfer, restarting",
+                         self.host, '/'.join(path_segs))
+        try:
+            return self._blockwise_get_once(path_segs, query, timeout)
+        except _EtagChanged:
+            logger.debug(
+                "GET %s /%s: representation kept changing mid-transfer",
+                self.host, '/'.join(path_segs))
+            raise BlockwiseError() from None
+
+    def _blockwise_get_once(self, path_segs, query, timeout):
+        """One attempt at a full Block2 transfer. Raises _EtagChanged if
+        the server's representation changed while we were reassembling."""
         tok = self._next_tok()
         blob = b''
         num = 0
+        blocks = 0
         last_code = None
-        last_opts = []
+        etag = None
         deadline = time.time() + timeout
         szx = BLOCK_SZX   # server may negotiate down; track per-transfer
         while True:
-            if num > 0:
-                self.pace()
-            container = {}
-            for attempt in range(_BLOCK_MAX_ATTEMPTS):
-                ev = threading.Event()
-                container = {}
-                self._pending[tok] = (ev, container)
-                try:
-                    mid = self._next_mid()
-                    opts = [(URI_PATH, s.encode()) for s in path_segs]
-                    for q in query:
-                        opts.append((URI_QUERY, q.encode()))
-                    opts.append((ACCEPT, CF_CBOR))
-                    if num > 0:
-                        opts.append((BLOCK2, block_value(num, 0, szx)))
-                    self._send_dgram(
-                        build_coap(TYPE_CON, METHOD_GET, mid, tok, opts))
-                    per_wait = min(_BLOCK_ACK_TIMEOUT,
-                                   max(0.1, deadline - time.time()))
-                    if ev.wait(per_wait):
-                        break  # got a response
-                    remaining = deadline - time.time()
-                    if remaining <= 0 or attempt == _BLOCK_MAX_ATTEMPTS - 1:
-                        logger.debug(
-                            "GET %s /%s block %d: timed out after %d attempt(s)",
-                            self.host, '/'.join(path_segs), num, attempt + 1,
-                        )
-                        raise SessionTimeoutError()
-                    logger.debug(
-                        "GET %s /%s block %d: attempt %d/%d timeout, retrying",
-                        self.host, '/'.join(path_segs), num,
-                        attempt + 1, _BLOCK_MAX_ATTEMPTS,
-                    )
-                finally:
-                    self._pending.pop(tok, None)
+            self.pace()
+            self._check_live()
+            container = self._exchange_block(
+                tok, path_segs, query, num, szx, deadline)
             if 'err' in container:
                 raise container['err']
+            blocks += 1
 
             code = container['code']
             payload = container['payload']
             ropts = container['options']
             last_code = code
-            last_opts = ropts
-            blob += payload
             # 4.xx / 5.xx responses don't carry Block2 continuation —
             # bail with whatever we got. Caller decides if 4.xx is fatal.
             if code >> 5 != 2:
-                return code, blob
+                return code, blob, blocks, tok
+
+            # RFC 7959 §2.4: compare ETags across blocks, or we splice
+            # two versions of the resource into one buffer.
+            block_etag = next((v for n, v in ropts if n == ETAG), None)
+            if num == 0:
+                etag = block_etag
+            elif etag is not None and block_etag != etag:
+                raise _EtagChanged()
+
+            blob += payload
             b2 = [v for n, v in ropts if n == BLOCK2]
-            more = 0
-            if b2:
-                bv = int.from_bytes(b2[0], 'big')
-                more = (bv >> 3) & 1
-                server_szx = bv & 0x07
-                if server_szx != szx:
-                    szx = server_szx
+            if not b2:
+                break
+            _, more, server_szx = block_fields(b2[0])
             if not more:
                 break
-            num += 1
+            if server_szx != szx:
+                # Server negotiated the block size down. Block numbers
+                # are indices into the new size, so the next one has to
+                # come off the byte offset we have actually accumulated,
+                # not off num + 1.
+                szx = server_szx
+                num = len(blob) >> (szx + 4)
+            else:
+                num += 1
             if num > self.MAX_BLOCKS:
                 raise BlockwiseError()
-        return last_code, blob
+        return last_code, blob, blocks, tok
+
+    def _exchange_block(self, tok, path_segs, query, num, szx, deadline):
+        """Send one block request under `tok` and return its response
+        container, retransmitting up to _BLOCK_MAX_ATTEMPTS times.
+
+        A response whose Block2 NUM is not the one we asked for is a
+        retransmit of an earlier block, not the next one. Concatenating
+        it would corrupt the buffer, so keep waiting on the same
+        attempt budget instead."""
+        for attempt in range(_BLOCK_MAX_ATTEMPTS):
+            ev = threading.Event()
+            container = {}
+            with self._state_lock:
+                self._pending[tok] = (ev, container)
+            try:
+                mid = self._next_mid()
+                opts = [(URI_PATH, s.encode()) for s in path_segs]
+                for q in query:
+                    opts.append((URI_QUERY, q.encode()))
+                opts.append((ACCEPT, CF_CBOR))
+                if num > 0:
+                    opts.append((BLOCK2, block_value(num, 0, szx)))
+                self._send_dgram(
+                    build_coap(TYPE_CON, METHOD_GET, mid, tok, opts))
+                while True:
+                    per_wait = min(_BLOCK_ACK_TIMEOUT,
+                                   max(0.1, deadline - time.time()))
+                    if not self._wait_for_block(ev, per_wait):
+                        break  # attempt timed out
+                    if 'err' in container or self._block_num_matches(
+                            container, num):
+                        return container
+                    logger.debug(
+                        "GET %s /%s block %d: stale block, still waiting",
+                        self.host, '/'.join(path_segs), num)
+                    ev.clear()
+                    container.clear()
+                    if deadline - time.time() <= 0:
+                        break
+                remaining = deadline - time.time()
+                if remaining <= 0 or attempt == _BLOCK_MAX_ATTEMPTS - 1:
+                    logger.debug(
+                        "GET %s /%s block %d: timed out after %d attempt(s)",
+                        self.host, '/'.join(path_segs), num, attempt + 1,
+                    )
+                    raise SessionTimeoutError()
+                logger.debug(
+                    "GET %s /%s block %d: attempt %d/%d timeout, retrying",
+                    self.host, '/'.join(path_segs), num,
+                    attempt + 1, _BLOCK_MAX_ATTEMPTS,
+                )
+            finally:
+                with self._state_lock:
+                    self._pending.pop(tok, None)
+        raise SessionTimeoutError()
+
+    def _wait_for_block(self, ev, per_wait):
+        """Wait for one block response, giving up early if the reader
+        dies underneath us.
+
+        Only the reader thread can resolve a token, so once it is gone
+        the wait can never succeed. Polling in slices turns what would
+        be a full per-block timeout into an immediate SessionClosedError,
+        which is the same fail-fast contract get() gets from _check_live()
+        at entry — it just has to hold for every block, not only the
+        first."""
+        deadline = time.time() + per_wait
+        while True:
+            slice_s = min(_BLOCK_LIVENESS_POLL_S, deadline - time.time())
+            if slice_s <= 0:
+                return False
+            if ev.wait(slice_s):
+                return True
+            self._check_live()
+
+    @staticmethod
+    def _block_num_matches(container, num):
+        """True if this response carries the block we asked for. A
+        response with no Block2 option is the whole representation, so
+        it only answers block 0."""
+        if container.get('code', 0) >> 5 != 2:
+            return True     # error responses end the transfer either way
+        b2 = [v for n, v in container.get('options', ()) if n == BLOCK2]
+        if not b2:
+            return num == 0
+        return block_fields(b2[0])[0] == num
 
     def post(self, path_segs, body_cbor, timeout=8.0):
         """Single-frame POST with a CBOR-encoded body. Returns
@@ -738,8 +1023,11 @@ class DtlsCoapSession:
                               body_cbor)
         ev = threading.Event()
         container = {}
-        self._pending[tok] = (ev, container)
+        with self._state_lock:
+            self._pending[tok] = (ev, container)
         try:
+            self.pace()
+            self._check_live()
             self._send_dgram(datagram)
             if not ev.wait(timeout):
                 raise SessionTimeoutError()
@@ -747,7 +1035,8 @@ class DtlsCoapSession:
                 raise container['err']
             return container['code'], container['payload']
         finally:
-            self._pending.pop(tok, None)
+            with self._state_lock:
+                self._pending.pop(tok, None)
 
     def ping(self):
         """RFC 7252 §4.4 CoAP Ping — empty CON, no token, no payload.
@@ -802,6 +1091,8 @@ class DtlsCoapSession:
         Returns the token used (in case the caller wants to deregister
         later)."""
         self._check_live()
+        self.pace()
+        self._check_live()
         tok = self._next_observe_tok()
         href = '/' + '/'.join(path_segs)
         # Register the token BEFORE sending — otherwise the device

smartthings_local/protocol/ocf_multicast.py

@@ -0,0 +1,322 @@
+"""Bounded discovery of a known host's plaintext OCF response port.
+
+Some OCF devices receive multicast discovery on UDP 5683 but reply from an
+ephemeral port. This module records only token-correlated response ports from
+the caller's expected IPv4 address. The results are candidates: callers still
+need directory parsing, a DTLS probe, and authenticated identity validation.
+"""
+
+from __future__ import annotations
+
+import ipaddress
+import math
+import secrets
+import selectors
+import socket
+import time
+from dataclasses import dataclass
+
+from ..errors import MalformedMessageError
+from .coap import (
+    ACCEPT,
+    CF_CBOR,
+    METHOD_GET,
+    TYPE_ACK,
+    TYPE_CON,
+    TYPE_NON,
+    URI_PATH,
+    URI_QUERY,
+    build_coap,
+    parse_coap,
+)
+
+__all__ = [
+    "OcfResponderPortDiscoveryResult",
+    "discover_ocf_responder_ports",
+]
+
+_OCF_MULTICAST_GROUP = socket.inet_ntoa(bytes((224, 0, 1, 187)))
+_OCF_DISCOVERY_PORT = 5683
+_OCF_CBOR = (10_000).to_bytes(2, "big")
+_OCF_CONTENT_FORMAT_VERSION = 2049
+_OCF_VERSION_1_0 = (2048).to_bytes(2, "big")
+_CONTENT = 0x45
+_MAX_DATAGRAM_BYTES = 8192
+_MAX_DATAGRAMS_PER_ROUND = 64
+_MAX_PORTS = 8
+
+
+@dataclass(frozen=True, slots=True, repr=False)
+class OcfResponderPortDiscoveryResult:
+    """Redacted result of one known-host multicast discovery operation."""
+
+    ports: tuple[int, ...]
+    attempts: int
+    responses: int
+    error_code: str | None = None
+
+    @property
+    def found(self) -> bool:
+        """Return whether at least one response port was discovered."""
+        return bool(self.ports)
+
+    def __repr__(self) -> str:
+        return (
+            "OcfResponderPortDiscoveryResult("
+            f"found={self.found!r}, port_count={len(self.ports)}, "
+            f"attempts={self.attempts}, responses={self.responses}, "
+            f"error_code={self.error_code!r})"
+        )
+
+
+def _validate_address(value: object, name: str) -> tuple[str, bytes]:
+    if not isinstance(value, str):
+        raise TypeError(f"{name} must be an IPv4 address string")
+    try:
+        address = ipaddress.IPv4Address(value)
+    except ipaddress.AddressValueError as exc:
+        raise ValueError(f"{name} must be a valid IPv4 address") from exc
+    if address.is_multicast or address.is_unspecified or address.is_reserved:
+        raise ValueError(f"{name} must be a unicast IPv4 address")
+    return str(address), address.packed
+
+
+def _validate_options(
+    *,
+    discovery_port: object,
+    timeout: object,
+    rounds: object,
+) -> tuple[int, float, int]:
+    if isinstance(discovery_port, bool) or not isinstance(discovery_port, int):
+        raise TypeError("discovery_port must be an integer")
+    if not 1 <= discovery_port <= 65535:
+        raise ValueError("discovery_port must be between 1 and 65535")
+    if isinstance(timeout, bool) or not isinstance(timeout, (int, float)):
+        raise TypeError("timeout must be a number")
+    timeout_value = float(timeout)
+    if not math.isfinite(timeout_value) or not 0 < timeout_value <= 30:
+        raise ValueError("timeout must be greater than zero and at most 30")
+    if isinstance(rounds, bool) or not isinstance(rounds, int):
+        raise TypeError("rounds must be an integer")
+    if not 1 <= rounds <= 4:
+        raise ValueError("rounds must be between one and four")
+    return discovery_port, timeout_value, rounds
+
+
+def _request(
+    token: bytes,
+    message_id: int,
+    *,
+    versioned: bool,
+    filtered: bool,
+) -> bytes:
+    options = [
+        (URI_PATH, b"oic"),
+        (URI_PATH, b"res"),
+        (ACCEPT, _OCF_CBOR if versioned else CF_CBOR),
+    ]
+    if filtered:
+        options.append((URI_QUERY, b"rt=oic.r.doxm"))
+    if versioned:
+        options.append((_OCF_CONTENT_FORMAT_VERSION, _OCF_VERSION_1_0))
+    return build_coap(TYPE_NON, METHOD_GET, message_id, token, options)
+
+
+def _result(
+    ports: tuple[int, ...],
+    attempts: int,
+    responses: int,
+    error_code: str | None = None,
+) -> OcfResponderPortDiscoveryResult:
+    return OcfResponderPortDiscoveryResult(
+        ports=ports,
+        attempts=attempts,
+        responses=responses,
+        error_code=error_code,
+    )
+
+
+def discover_ocf_responder_ports(
+    target_address: str,
+    *,
+    interface_address: str,
+    discovery_port: int = _OCF_DISCOVERY_PORT,
+    timeout: float = 3.0,
+    rounds: int = 2,
+) -> OcfResponderPortDiscoveryResult:
+    """Find plaintext OCF response ports for one known IPv4 host.
+
+    Each round sends modern OCF and legacy IoTivity NON requests to the
+    link-local multicast group. Only a 2.05 response with a request token and
+    the exact target source address contributes a candidate. One monotonic
+    deadline bounds all rounds, and every socket is closed before return.
+    """
+
+    _target_address, target_key = _validate_address(target_address, "target_address")
+    interface_address, interface_key = _validate_address(
+        interface_address, "interface_address"
+    )
+    discovery_port, timeout, rounds = _validate_options(
+        discovery_port=discovery_port,
+        timeout=timeout,
+        rounds=rounds,
+    )
+
+    try:
+        selector = selectors.DefaultSelector()
+    except (OSError, ValueError):
+        return _result((), 0, 0, "interface_unavailable")
+    active = None
+    try:
+        active = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
+        active.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_IF, interface_key)
+        active.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 1)
+        active.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_LOOP, 0)
+        active.bind((interface_address, 0))
+        active.setblocking(False)
+        selector.register(active, selectors.EVENT_READ)
+    except (OSError, ValueError):
+        if active is not None:
+            try:
+                active.close()
+            except OSError:
+                pass
+        selector.close()
+        return _result((), 0, 0, "interface_unavailable")
+
+    started = time.monotonic()
+    deadline = started + timeout
+    accepted_tokens: set[bytes] = set()
+    observations: set[tuple[bytes, int]] = set()
+    ports: list[int] = []
+    seen_ports: set[int] = set()
+    attempts = 0
+    responses = 0
+    too_many_ports = False
+
+    try:
+        for round_number in range(rounds):
+            if time.monotonic() >= deadline:
+                break
+            # Preserve the unfiltered modern and legacy requests used by the
+            # installed appliance generations. Older media firmware can omit
+            # usable endpoint policy from its large unfiltered directory but
+            # answer the smaller legacy DOXM-filtered lookup, so send that as
+            # a third bounded fallback rather than narrowing every request.
+            for versioned, filtered in (
+                (True, False),
+                (False, False),
+                (False, True),
+            ):
+                token = secrets.token_bytes(8)
+                while token in accepted_tokens:
+                    token = secrets.token_bytes(8)
+                accepted_tokens.add(token)
+                request = _request(
+                    token,
+                    secrets.randbits(16),
+                    versioned=versioned,
+                    filtered=filtered,
+                )
+                try:
+                    sent = active.sendto(
+                        request,
+                        (_OCF_MULTICAST_GROUP, discovery_port),
+                    )
+                except OSError:
+                    continue
+                attempts += 1
+                if sent != len(request):
+                    continue
+
+            round_deadline = started + timeout * (round_number + 1) / rounds
+            datagrams = 0
+            while datagrams < _MAX_DATAGRAMS_PER_ROUND:
+                remaining = min(deadline, round_deadline) - time.monotonic()
+                if remaining <= 0:
+                    break
+                try:
+                    events = selector.select(remaining)
+                except (OSError, ValueError):
+                    break
+                if not events:
+                    break
+                try:
+                    datagram, source = active.recvfrom(_MAX_DATAGRAM_BYTES + 1)
+                except (BlockingIOError, OSError):
+                    continue
+                datagrams += 1
+                if len(datagram) > _MAX_DATAGRAM_BYTES:
+                    continue
+                if (
+                    len(datagram) < 4
+                    or datagram[0] >> 6 != 1
+                    or datagram[0] & 0x0F > 8
+                    or 4 + (datagram[0] & 0x0F) > len(datagram)
+                ):
+                    continue
+                if not isinstance(source, tuple) or len(source) != 2:
+                    continue
+                source_host, source_port = source
+                if not isinstance(source_host, str):
+                    continue
+                try:
+                    source_key = socket.inet_pton(socket.AF_INET, source_host)
+                except OSError:
+                    continue
+                if source_key != target_key:
+                    continue
+                if (
+                    isinstance(source_port, bool)
+                    or not isinstance(source_port, int)
+                    or not 1 <= source_port <= 65535
+                ):
+                    continue
+                try:
+                    message_type, code, mid, token, _options, payload = parse_coap(
+                        datagram
+                    )
+                except (IndexError, ValueError, MalformedMessageError):
+                    continue
+                if (
+                    token not in accepted_tokens
+                    or code != _CONTENT
+                    or message_type not in (TYPE_NON, TYPE_CON)
+                    or not payload
+                ):
+                    continue
+                if message_type == TYPE_CON:
+                    try:
+                        active.sendto(build_coap(TYPE_ACK, 0, mid, b"", []), source)
+                    except OSError:
+                        pass
+                observation = (token, source_port)
+                if observation in observations:
+                    continue
+                observations.add(observation)
+                responses += 1
+                if source_port in seen_ports:
+                    continue
+                if len(ports) >= _MAX_PORTS:
+                    too_many_ports = True
+                    continue
+                seen_ports.add(source_port)
+                ports.append(source_port)
+
+        if too_many_ports:
+            return _result((), attempts, responses, "ambiguous_response")
+        if ports:
+            return _result(tuple(ports), attempts, responses)
+        if attempts == 0:
+            return _result((), attempts, responses, "interface_unavailable")
+        return _result((), attempts, responses, "no_response")
+    finally:
+        try:
+            selector.unregister(active)
+        except (KeyError, OSError, ValueError):
+            pass
+        try:
+            active.close()
+        except OSError:
+            pass
+        selector.close()

smartthings_local/protocol/owner_psk.py

@@ -0,0 +1,128 @@
+"""Pure IoTivity manufacturer-certificate OwnerPSK derivation."""
+
+from __future__ import annotations
+
+from collections.abc import Mapping
+import hashlib
+import hmac
+from types import MappingProxyType
+from typing import Final
+
+
+CONFIRMED_MFG_CERTIFICATE_OXM_LABEL: Final = b"x.org.iotivity.conmfgcert"
+STANDARD_MFG_CERTIFICATE_OXM_LABEL: Final = b"oic.sec.doxm.mfgcert"
+
+# OpenSSL cipher names mapped to the key-block lengths used by IoTivity's
+# CAGenerateOwnerPSK implementation.
+MFG_CERTIFICATE_KEY_BLOCK_LENGTHS: Final[Mapping[str, int]] = MappingProxyType(
+    {
+        "ECDHE-ECDSA-AES128-SHA256": 96,
+        "ECDHE-ECDSA-AES128-CCM": 40,
+        "ECDHE-ECDSA-AES128-CCM8": 40,
+        "ECDHE-ECDSA-AES128-GCM-SHA256": 120,
+        "AES256-SHA256": 128,
+        "ECDHE-ECDSA-AES256-SHA384": 160,
+        "ECDHE-ECDSA-AES256-GCM-SHA384": 184,
+        "AES128-GCM-SHA256": 120,
+    }
+)
+
+_TLS_MASTER_SECRET_BYTES: Final = 48
+_TLS_RANDOM_BYTES: Final = 32
+_OCF_UUID_BYTES: Final = 16
+_OWNER_PSK_BYTES: Final = 16
+
+
+def _require_bytes(name: str, value: bytes, length: int) -> bytes:
+    if not isinstance(value, bytes):
+        raise TypeError(f"{name} must be bytes")
+    if len(value) != length:
+        raise ValueError(f"{name} must be exactly {length} bytes")
+    return value
+
+
+def _require_uuid(name: str, value: bytes) -> bytes:
+    value = _require_bytes(name, value, _OCF_UUID_BYTES)
+    if not any(value):
+        raise ValueError(f"{name} must not be the nil UUID")
+    return value
+
+
+def _tls12_p_hash_sha256(
+    key: bytes,
+    label: bytes,
+    random1: bytes,
+    random2: bytes,
+    length: int,
+) -> bytes:
+    seed = label + random1 + random2
+    a_value = hmac.new(key, seed, hashlib.sha256).digest()
+    output = bytearray()
+    while len(output) < length:
+        output.extend(hmac.new(key, a_value + seed, hashlib.sha256).digest())
+        a_value = hmac.new(key, a_value, hashlib.sha256).digest()
+    return bytes(output[:length])
+
+
+def derive_mfg_certificate_owner_psk(
+    *,
+    master_secret: bytes,
+    client_random: bytes,
+    server_random: bytes,
+    owner_uuid: bytes,
+    device_uuid: bytes,
+    cipher_name: str,
+    oxm_label: bytes,
+) -> bytes:
+    """Derive a 128-bit OwnerPSK from caller-supplied DTLS state.
+
+    This implements IoTivity's two-stage TLS 1.2 SHA-256 P_hash operation.
+    It performs no session access, network I/O, ownership writes, or storage.
+    The caller must supply state from an authenticated manufacturer-certificate
+    session and explicitly select the OXM label used by that transaction.
+    IoTivity's other 96-byte ECDH_ANON, ECDHE_PSK, and ECDHE_RSA mappings are
+    intentionally outside this helper's manufacturer-certificate allowlist.
+    """
+
+    if not isinstance(cipher_name, str):
+        raise TypeError("cipher_name must be a string")
+    key_block_bytes = MFG_CERTIFICATE_KEY_BLOCK_LENGTHS.get(cipher_name)
+    if key_block_bytes is None:
+        raise ValueError("unexpected manufacturer-certificate DTLS cipher")
+
+    master_secret = _require_bytes(
+        "master_secret", master_secret, _TLS_MASTER_SECRET_BYTES
+    )
+    client_random = _require_bytes(
+        "client_random", client_random, _TLS_RANDOM_BYTES
+    )
+    server_random = _require_bytes(
+        "server_random", server_random, _TLS_RANDOM_BYTES
+    )
+    owner_uuid = _require_uuid("owner_uuid", owner_uuid)
+    device_uuid = _require_uuid("device_uuid", device_uuid)
+    if not isinstance(oxm_label, bytes):
+        raise TypeError("oxm_label must be bytes")
+    if oxm_label not in {
+        CONFIRMED_MFG_CERTIFICATE_OXM_LABEL,
+        STANDARD_MFG_CERTIFICATE_OXM_LABEL,
+    }:
+        raise ValueError("unexpected manufacturer-certificate OXM label")
+
+    key_block = _tls12_p_hash_sha256(
+        master_secret,
+        b"key expansion",
+        server_random,
+        client_random,
+        key_block_bytes,
+    )
+    # IoTivity's OTM callers pass the owner UUID first and the target device
+    # UUID second. The lower adapter's historical rsrc/prov parameter names
+    # describe those arguments inconsistently, so preserve the caller order.
+    return _tls12_p_hash_sha256(
+        key_block,
+        oxm_label,
+        owner_uuid,
+        device_uuid,
+        _OWNER_PSK_BYTES,
+    )

tests/test_coap_wire.py

@@ -2,7 +2,8 @@ import pytest
 
 from smartthings_local.errors import MalformedMessageError
 from smartthings_local.protocol.coap import (
-    build_coap, parse_coap, encode_options, block_value, fmt_code,
+    build_coap, parse_coap, encode_options, block_value, block_fields,
+    fmt_code,
     TYPE_CON, METHOD_GET, URI_PATH, ACCEPT, CF_CBOR, BLOCK2,
 )
 
@@ -43,6 +44,23 @@ def test_block_value_promotes_to_two_bytes_when_num_is_large():
     assert len(v) == 2
 
 
+@pytest.mark.parametrize('num, more, szx', [
+    (0, 0, 0),
+    (0, 1, 6),
+    (2, 1, 6),
+    (1, 0, 4),
+    (0xFFF, 0, 0),
+    (0xFFFFF, 1, 7),
+])
+def test_block_fields_inverts_block_value(num, more, szx):
+    assert block_fields(block_value(num, more, szx)) == (num, more, szx)
+
+
+def test_block_fields_treats_empty_value_as_block_zero():
+    # RFC 7959 §2.2: a zero-length Block option means num=0, m=0, szx=0.
+    assert block_fields(b'') == (0, 0, 0)
+
+
 def test_fmt_code_formats_class_dot_detail():
     assert fmt_code(0x45) == '2.05'
     assert fmt_code(0x84) == '4.04'

tests/test_import_isolation.py

@@ -17,6 +17,7 @@ def test_smartthings_local_imports_without_mqtt_demo_present(tmp_path):
 
     import_lines = [
         "import smartthings_local.protocol.coap",
+        "import smartthings_local.protocol.ocf_multicast",
         "import smartthings_local.protocol.dtls_session",
         "import smartthings_local.ocf.state_cache",
         "import smartthings_local.ocf.poll_scheduler",

tests/test_observe_block2.py

@@ -0,0 +1,508 @@
+"""Blockwise OBSERVE notifications (QuiteYellow/SmartThings-Local#39).
+
+A notification carries only the first block of the representation
+(RFC 7959 §2.6). Before this, _dispatch_coap handed that first block
+straight to on_notification and the consumer decoded a truncated CBOR
+buffer. These tests pin the replacement: a truncated notification is
+withheld, the resource is re-read from block 0 under a fresh one-shot
+token, and only the reassembled representation reaches the callback.
+
+The re-read starts at block 0 rather than continuing at NUM=1 for two
+reasons, both recorded on #39: RFC 7959 §3.4 forbids continuing on the
+observation's token, and Samsung's RT-OCF drops a transfer that opens
+at NUM>0 under a token it has not seen.
+"""
+import logging
+import socket
+import threading
+import time
+
+import pytest
+from OpenSSL import SSL
+
+from smartthings_local.errors import BlockwiseError
+from smartthings_local.protocol import dtls_session
+from smartthings_local.protocol.coap import (
+    BLOCK2, ETAG, METHOD_GET, OBSERVE, TYPE_ACK, TYPE_NON,
+    block_fields, block_value, build_coap, parse_coap,
+)
+from smartthings_local.protocol.dtls_session import DtlsCoapSession
+
+SZX = 6  # 1024-byte blocks, the only size these appliances honour
+_LOGGER_NAME = "smartthings_local.protocol.dtls_session"
+
+
+class _NullAuth:
+    """Structural AuthenticationProvider — never configured, we skip connect()."""
+
+    def configure_context(self, _context):
+        return None
+
+
+class _LoopbackConn:
+    """SSL.Connection stand-in that answers requests from a script.
+
+    `responder` is called with each parsed request and returns a list of
+    CoAP datagrams to hand back (possibly empty, to model a silent
+    device). Responses surface on recv() the way decrypted records do.
+    """
+
+    def __init__(self, responder):
+        self._responder = responder
+        self._inbox = []
+        self._lock = threading.Lock()
+        self.sent = []
+
+    # -- client -> device
+    def send(self, datagram):
+        self.sent.append(parse_coap(datagram))
+        for reply in self._responder(parse_coap(datagram)):
+            with self._lock:
+                self._inbox.append(reply)
+        return len(datagram)
+
+    def bio_read(self, _n):
+        return b""
+
+    # -- device -> client
+    def inject(self, datagram):
+        """Push a device-initiated frame (an OBSERVE notification)."""
+        with self._lock:
+            self._inbox.append(datagram)
+
+    def bio_write(self, _datagram):
+        return None
+
+    def recv(self, _n):
+        with self._lock:
+            if self._inbox:
+                return self._inbox.pop(0)
+        raise SSL.WantReadError()
+
+    def shutdown(self):
+        return None
+
+    def pending(self):
+        with self._lock:
+            return len(self._inbox)
+
+
+class _PumpSock:
+    """UDP socket stand-in. recv() returns a dummy datagram whenever the
+    connection has something decrypted waiting, so the reader loop keeps
+    pumping; otherwise it times out like a real socket."""
+
+    def __init__(self, conn):
+        self._conn = conn
+        self.closed = False
+
+    def settimeout(self, _value):
+        return None
+
+    def recv(self, _n):
+        for _ in range(20):
+            if self.closed:
+                raise OSError("closed")
+            if self._conn.pending():
+                return b"\x00"
+            time.sleep(0.005)
+        raise socket.timeout()
+
+    def send(self, data):
+        return len(data)
+
+    def close(self):
+        self.closed = True
+
+
+def _make_session(responder, **kwargs):
+    calls = []
+    sess = DtlsCoapSession(
+        "host", 1234, auth=_NullAuth(),
+        on_notification=lambda href, payload: calls.append((href, payload)),
+        **kwargs)
+    sess.conn = _LoopbackConn(responder)
+    sess.sock = _PumpSock(sess.conn)
+    sess.start_reader()
+    return sess, calls
+
+
+def _notification(tok, payload, *, block2=None, mtype=TYPE_NON, obs=1):
+    opts = [(OBSERVE, bytes([obs]))]
+    if block2 is not None:
+        opts.append((BLOCK2, block2))
+    return build_coap(mtype, 0x45, 0x1234, tok, opts, payload)
+
+
+def _content(tok, mid, payload, *, block2=None, etag=None):
+    opts = []
+    if etag is not None:
+        opts.append((ETAG, etag))
+    if block2 is not None:
+        opts.append((BLOCK2, block2))
+    return build_coap(TYPE_ACK, 0x45, mid, tok, opts, payload)
+
+
+def _requested_block(request):
+    """(num, szx) the request asked for, or (0, None) with no Block2."""
+    _, _, _, _, opts, _ = request
+    b2 = [v for n, v in opts if n == BLOCK2]
+    if not b2:
+        return 0, None
+    num, _, szx = block_fields(b2[0])
+    return num, szx
+
+
+def _wait_for(predicate, timeout=3.0):
+    deadline = time.time() + timeout
+    while time.time() < deadline:
+        if predicate():
+            return True
+        time.sleep(0.01)
+    return False
+
+
+def _close(sess):
+    sess.close()
+    sess.join()
+
+
+# --------------------------------------------------------------------
+# The no-regression case
+
+
+def test_single_block_notification_is_delivered_inline():
+    sess, calls = _make_session(lambda request: [])
+    try:
+        tok = sess.subscribe(["oven", "vs", "0"])
+        sess.conn.inject(_notification(tok, b"\xa1\x01\x02"))
+
+        assert _wait_for(lambda: calls)
+        assert calls == [("/oven/vs/0", b"\xa1\x01\x02")]
+        # The subscribe GET is the only thing we sent — no refetch.
+        assert len(sess.conn.sent) == 1
+    finally:
+        _close(sess)
+
+
+def test_complete_block_zero_notification_is_delivered_inline():
+    """Block2 present but M=0 and NUM=0 means the whole representation
+    fit in one block. Nothing to fetch back."""
+    sess, calls = _make_session(lambda request: [])
+    try:
+        tok = sess.subscribe(["oven", "vs", "0"])
+        sess.conn.inject(
+            _notification(tok, b"\xa1\x01\x02",
+                          block2=block_value(0, 0, SZX)))
+
+        assert _wait_for(lambda: calls)
+        assert calls == [("/oven/vs/0", b"\xa1\x01\x02")]
+        assert len(sess.conn.sent) == 1
+    finally:
+        _close(sess)
+
+
+# --------------------------------------------------------------------
+# The fix
+
+
+def test_truncated_notification_is_refetched_and_reassembled():
+    blocks = [b"A" * 1024, b"B" * 40]
+
+    def responder(request):
+        _mtype, code, mid, tok, opts, _ = request
+        if code != METHOD_GET or any(n == OBSERVE for n, _ in opts):
+            return []           # the subscribe registration itself
+        num, _ = _requested_block(request)
+        more = 1 if num + 1 < len(blocks) else 0
+        return [_content(tok, mid, blocks[num],
+                         block2=block_value(num, more, SZX))]
+
+    sess, calls = _make_session(responder)
+    try:
+        tok = sess.subscribe(["mode", "vs", "0"])
+        sess.conn.inject(
+            _notification(tok, blocks[0],
+                          block2=block_value(0, 1, SZX)))
+
+        assert _wait_for(lambda: calls), "callback never fired"
+        assert calls == [("/mode/vs/0", b"".join(blocks))]
+    finally:
+        _close(sess)
+
+
+def test_refetch_uses_a_fresh_one_shot_token_not_the_observe_token():
+    """RFC 7959 §3.4: the requests for additional blocks cannot use the
+    token of the observation relationship."""
+    blocks = [b"A" * 1024, b"B" * 40]
+
+    def responder(request):
+        _mtype, _code, mid, tok, opts, _ = request
+        if any(n == OBSERVE for n, _ in opts):
+            return []
+        num, _ = _requested_block(request)
+        more = 1 if num + 1 < len(blocks) else 0
+        return [_content(tok, mid, blocks[num],
+                         block2=block_value(num, more, SZX))]
+
+    sess, calls = _make_session(responder)
+    try:
+        observe_tok = sess.subscribe(["mode", "vs", "0"])
+        assert len(observe_tok) == 1, "OBSERVE registrations use 1-byte tokens"
+        sess.conn.inject(
+            _notification(observe_tok, blocks[0],
+                          block2=block_value(0, 1, SZX)))
+        assert _wait_for(lambda: calls)
+
+        refetch = [r for r in sess.conn.sent
+                   if not any(n == OBSERVE for n, _ in r[4])]
+        assert refetch, "no refetch request was sent"
+        tokens = {r[3] for r in refetch}
+        assert observe_tok not in tokens
+        assert all(len(t) == 4 for t in tokens), "one-shot tokens are 4-byte"
+        assert len(tokens) == 1, "the transfer must hold one token throughout"
+
+        # And the transfer restarts at block 0 rather than continuing at 1.
+        assert _requested_block(refetch[0])[0] == 0
+        assert [_requested_block(r)[0] for r in refetch] == [0, 1]
+        # No Observe option on a continuation request.
+        assert not any(n == OBSERVE for r in refetch for n, _ in r[4])
+    finally:
+        _close(sess)
+
+
+def test_silent_device_drops_the_notification_without_delivering_a_partial():
+    sess, calls = _make_session(lambda request: [])
+    try:
+        tok = sess.subscribe(["mode", "vs", "0"])
+        sess.conn.inject(
+            _notification(tok, b"A" * 1024,
+                          block2=block_value(0, 1, SZX)))
+        # Give the worker a chance to try and fail. _BLOCK_ACK_TIMEOUT is
+        # 4s per attempt, so we only need to see that nothing partial got
+        # through in the meantime.
+        assert not _wait_for(lambda: calls, timeout=0.6)
+        assert sess._reader_thread.is_alive(), "reader must survive"
+    finally:
+        _close(sess)
+
+
+def test_non_2xx_refetch_is_dropped_rather_than_delivered():
+    def responder(request):
+        _mtype, _code, mid, tok, opts, _ = request
+        if any(n == OBSERVE for n, _ in opts):
+            return []
+        return [build_coap(TYPE_ACK, 0x84, mid, tok, [], b"")]
+
+    sess, calls = _make_session(responder)
+    try:
+        tok = sess.subscribe(["mode", "vs", "0"])
+        sess.conn.inject(
+            _notification(tok, b"A" * 1024,
+                          block2=block_value(0, 1, SZX)))
+        assert not _wait_for(lambda: calls, timeout=0.6)
+    finally:
+        _close(sess)
+
+
+def test_notification_burst_collapses_to_one_refetch_per_resource():
+    blocks = [b"A" * 1024, b"B" * 40]
+    gate = threading.Event()
+
+    def responder(request):
+        _mtype, _code, mid, tok, opts, _ = request
+        if any(n == OBSERVE for n, _ in opts):
+            return []
+        gate.wait(2.0)          # hold the first transfer open
+        num, _ = _requested_block(request)
+        more = 1 if num + 1 < len(blocks) else 0
+        return [_content(tok, mid, blocks[num],
+                         block2=block_value(num, more, SZX))]
+
+    sess, calls = _make_session(responder)
+    try:
+        tok = sess.subscribe(["mode", "vs", "0"])
+        for seq in range(5):
+            sess.conn.inject(
+                _notification(tok, blocks[0], obs=seq + 1,
+                              block2=block_value(0, 1, SZX)))
+        # Five notifications, one queue entry: latest wins per href.
+        assert _wait_for(lambda: sess._refetch_pending or sess.conn.sent[1:])
+        assert len(sess._refetch_pending) <= 1
+        gate.set()
+
+        assert _wait_for(lambda: calls)
+        assert _wait_for(
+            lambda: not sess._refetch_pending and len(calls) >= 1)
+        time.sleep(0.2)
+        # Two transfers at most: the one in flight when the burst landed,
+        # plus one for the final state.
+        starts = [r for r in sess.conn.sent
+                  if not any(n == OBSERVE for n, _ in r[4])
+                  and _requested_block(r)[0] == 0]
+        assert len(starts) <= 2, f"{len(starts)} refetches for one burst"
+        assert calls[-1] == ("/mode/vs/0", b"".join(blocks))
+    finally:
+        gate.set()
+        _close(sess)
+
+
+def test_close_during_a_queued_refetch_stops_the_worker():
+    sess, _calls = _make_session(lambda request: [])
+    tok = sess.subscribe(["mode", "vs", "0"])
+    sess.conn.inject(
+        _notification(tok, b"A" * 1024, block2=block_value(0, 1, SZX)))
+    assert _wait_for(lambda: sess._refetch_thread is not None)
+
+    sess.close()
+    sess.join()     # hangs if the worker outlives the session
+    assert not sess._refetch_thread.is_alive()
+
+
+def test_refetch_worker_exits_when_the_reader_dies():
+    sess, _calls = _make_session(lambda request: [])
+    tok = sess.subscribe(["mode", "vs", "0"])
+    sess.conn.inject(
+        _notification(tok, b"A" * 1024, block2=block_value(0, 1, SZX)))
+    assert _wait_for(lambda: sess._refetch_thread is not None)
+
+    # Kill the reader the way a socket error does, without close().
+    sess.sock.closed = True
+    assert _wait_for(lambda: not sess._reader_running.is_set(), timeout=5.0)
+    sess._refetch_thread.join(6.0)
+    assert not sess._refetch_thread.is_alive()
+    sess.close()
+
+
+def test_debug_bridge_promotes_the_refetch_outcome_to_info(monkeypatch, caplog):
+    """The hardware validation for #39 reads this line to confirm which
+    token the re-read used, so it has to survive the bridge's INFO
+    default. Without DEBUG_BRIDGE it stays at debug."""
+    monkeypatch.setattr(dtls_session, "DEBUG_BRIDGE", True)
+    blocks = [b"A" * 1024, b"B" * 40]
+
+    def responder(request):
+        _mtype, _code, mid, tok, opts, _ = request
+        if any(n == OBSERVE for n, _ in opts):
+            return []
+        num, _ = _requested_block(request)
+        more = 1 if num + 1 < len(blocks) else 0
+        return [_content(tok, mid, blocks[num],
+                         block2=block_value(num, more, SZX))]
+
+    sess, calls = _make_session(responder)
+    try:
+        with caplog.at_level(logging.INFO, logger=_LOGGER_NAME):
+            tok = sess.subscribe(["mode", "vs", "0"])
+            sess.conn.inject(
+                _notification(tok, blocks[0], block2=block_value(0, 1, SZX)))
+            assert _wait_for(lambda: calls)
+
+        line = next((r.getMessage() for r in caplog.records
+                     if r.getMessage().startswith("refetch /mode/vs/0")), None)
+        assert line is not None, "no refetch line at INFO"
+        assert "blocks=2" in line
+        assert f"bytes={sum(len(b) for b in blocks)}" in line
+        assert line.endswith("ok")
+        # The token in the line is the one-shot token, not the observe one.
+        assert f"tok={tok.hex()} " not in line
+    finally:
+        _close(sess)
+
+
+# --------------------------------------------------------------------
+# Shared Block2 loop hardening
+
+
+def test_stale_block_number_is_not_concatenated():
+    """A retransmit of block 0 arriving while we wait for block 1 must
+    not be appended as if it were block 1."""
+    served = []
+
+    def responder(request):
+        _mtype, _code, mid, tok, _opts, _ = request
+        num, _ = _requested_block(request)
+        served.append(num)
+        if num == 0:
+            return [_content(tok, mid, b"A" * 1024,
+                             block2=block_value(0, 1, SZX))]
+        # Answer the block-1 request with a duplicate of block 0 first.
+        return [
+            _content(tok, mid, b"A" * 1024, block2=block_value(0, 1, SZX)),
+            _content(tok, mid, b"B" * 40, block2=block_value(1, 0, SZX)),
+        ]
+
+    sess, _calls = _make_session(responder)
+    try:
+        code, payload = sess.get(["mode", "vs", "0"], timeout=5.0)
+        assert code == 0x45
+        assert payload == b"A" * 1024 + b"B" * 40
+    finally:
+        _close(sess)
+
+
+def test_etag_change_mid_transfer_restarts_then_fails():
+    etags = [b"\x01", b"\x02", b"\x03", b"\x04"]
+
+    def responder(request):
+        _mtype, _code, mid, tok, _opts, _ = request
+        num, _ = _requested_block(request)
+        # A different ETag on every single response: the representation
+        # never settles, so reassembly can never be consistent.
+        etag = etags.pop(0) if etags else b"\xff"
+        payload = b"A" * 1024 if num == 0 else b"B" * 40
+        more = 1 if num == 0 else 0
+        return [_content(tok, mid, payload, etag=etag,
+                         block2=block_value(num, more, SZX))]
+
+    sess, _calls = _make_session(responder)
+    try:
+        with pytest.raises(BlockwiseError):
+            sess.get(["mode", "vs", "0"], timeout=5.0)
+    finally:
+        _close(sess)
+
+
+def test_stable_etag_across_blocks_reassembles():
+    def responder(request):
+        _mtype, _code, mid, tok, _opts, _ = request
+        num, _ = _requested_block(request)
+        payload = b"A" * 1024 if num == 0 else b"B" * 40
+        more = 1 if num == 0 else 0
+        return [_content(tok, mid, payload, etag=b"\x77",
+                         block2=block_value(num, more, SZX))]
+
+    sess, _calls = _make_session(responder)
+    try:
+        code, payload = sess.get(["mode", "vs", "0"], timeout=5.0)
+        assert code == 0x45
+        assert payload == b"A" * 1024 + b"B" * 40
+    finally:
+        _close(sess)
+
+
+def test_szx_downshift_asks_for_the_block_after_what_we_have():
+    """Server answers block 0 at SZX=6 (1024B) then drops to SZX=4
+    (256B). Block numbers index the new size, so the next request is
+    block 4, not block 1."""
+    requested = []
+
+    def responder(request):
+        _mtype, _code, mid, tok, _opts, _ = request
+        num, szx = _requested_block(request)
+        requested.append((num, szx))
+        if num == 0:
+            return [_content(tok, mid, b"A" * 1024,
+                             block2=block_value(0, 1, 4))]
+        return [_content(tok, mid, b"B" * 100,
+                         block2=block_value(num, 0, 4))]
+
+    sess, _calls = _make_session(responder)
+    try:
+        code, payload = sess.get(["mode", "vs", "0"], timeout=5.0)
+        assert code == 0x45
+        assert payload == b"A" * 1024 + b"B" * 100
+        # 1024 bytes in hand at 256B blocks = blocks 0..3 done, ask for 4.
+        assert requested[1] == (4, 4)
+    finally:
+        _close(sess)

tests/test_ocf_multicast.py

@@ -0,0 +1,392 @@
+"""Known-host OCF multicast responder-port discovery tests."""
+
+from __future__ import annotations
+
+from types import SimpleNamespace
+
+import pytest
+
+from smartthings_local.protocol.coap import (
+    ACCEPT,
+    TYPE_CON,
+    TYPE_NON,
+    URI_PATH,
+    URI_QUERY,
+    build_coap,
+    parse_coap,
+)
+from smartthings_local.protocol.ocf_multicast import (
+    _OCF_MULTICAST_GROUP,
+    OcfResponderPortDiscoveryResult,
+    discover_ocf_responder_ports,
+)
+
+_TARGET = "192.0.2.20"
+_OTHER = "192.0.2.21"
+_INTERFACE = "192.0.2.10"
+
+
+class _FakeSocket:
+    def __init__(self, responder=None):
+        self.responder = responder
+        self.incoming = []
+        self.sent = []
+        self.options = []
+        self.bound = None
+        self.blocking = None
+        self.closed = False
+
+    def setsockopt(self, level, option, value):
+        self.options.append((level, option, value))
+
+    def bind(self, address):
+        self.bound = address
+
+    def setblocking(self, enabled):
+        self.blocking = enabled
+
+    def sendto(self, datagram, destination):
+        self.sent.append((datagram, destination))
+        if self.responder is not None:
+            self.incoming.extend(self.responder(datagram, destination))
+        return len(datagram)
+
+    def recvfrom(self, _size):
+        return self.incoming.pop(0)
+
+    def close(self):
+        self.closed = True
+
+
+class _FakeSelector:
+    def __init__(self, active):
+        self.active = active
+        self.closed = False
+
+    def register(self, *_args):
+        return None
+
+    def unregister(self, *_args):
+        return None
+
+    def select(self, _timeout):
+        if not self.active.incoming:
+            return []
+        return [(SimpleNamespace(fileobj=self.active), selectors_event_read())]
+
+    def close(self):
+        self.closed = True
+
+
+def selectors_event_read():
+    return 1
+
+
+def _response(
+    datagram, _destination=None, *, host=_TARGET, port=43123, message_type=TYPE_NON
+):
+    _mtype, _code, mid, token, _options, _payload = parse_coap(datagram)
+    response_mid = mid if message_type != TYPE_CON else (mid + 1) & 0xFFFF
+    return [
+        (
+            build_coap(message_type, 0x45, response_mid, token, [], b"directory"),
+            (host, port),
+        )
+    ]
+
+
+@pytest.fixture
+def patch_socket(monkeypatch):
+    created = []
+
+    def install(responder=None):
+        active = _FakeSocket(responder)
+        selector = _FakeSelector(active)
+        created.append((active, selector))
+        monkeypatch.setattr(
+            "smartthings_local.protocol.ocf_multicast.socket.socket",
+            lambda *_args: active,
+        )
+        monkeypatch.setattr(
+            "smartthings_local.protocol.ocf_multicast.selectors.DefaultSelector",
+            lambda: selector,
+        )
+        return active, selector
+
+    return install
+
+
+def test_sends_proven_directory_requests_and_filtered_fallback_on_interface(
+    patch_socket,
+):
+    active, selector = patch_socket(_response)
+
+    result = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+        rounds=1,
+    )
+
+    assert result.ports == (43123,)
+    assert result.attempts == 3
+    assert result.responses == 3
+    assert active.bound == (_INTERFACE, 0)
+    assert active.blocking is False
+    assert active.closed
+    assert selector.closed
+    assert all(
+        destination == (_OCF_MULTICAST_GROUP, 5683) for _, destination in active.sent
+    )
+
+    requests = [parse_coap(datagram) for datagram, _ in active.sent]
+    assert all(
+        [value for number, value in item[4] if number == URI_PATH] == [b"oic", b"res"]
+        for item in requests
+    )
+    queries = [
+        [value for number, value in item[4] if number == URI_QUERY] for item in requests
+    ]
+    assert queries == [[], [], [b"rt=oic.r.doxm"]]
+    accepts = [
+        [value for number, value in item[4] if number == ACCEPT] for item in requests
+    ]
+    assert accepts == [[b"\x27\x10"], [b"\x3c"], [b"\x3c"]]
+    assert [value for number, value in requests[0][4] if number == 2049] == [
+        b"\x08\x00"
+    ]
+    assert [value for number, value in requests[1][4] if number == 2049] == []
+    assert [value for number, value in requests[2][4] if number == 2049] == []
+
+
+@pytest.mark.parametrize(
+    ("accepted_accept", "accepted_query"),
+    (
+        (b"\x27\x10", ()),
+        (b"\x3c", ()),
+        (b"\x3c", (b"rt=oic.r.doxm",)),
+    ),
+)
+def test_each_directory_request_profile_can_find_the_responder(
+    patch_socket, accepted_accept, accepted_query
+):
+    def responder(datagram, destination):
+        _mtype, _code, _mid, _token, options, _payload = parse_coap(datagram)
+        accept = next(value for number, value in options if number == ACCEPT)
+        query = tuple(value for number, value in options if number == URI_QUERY)
+        if (accept, query) != (accepted_accept, accepted_query):
+            return []
+        return _response(datagram, destination)
+
+    patch_socket(responder)
+    result = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+        rounds=1,
+    )
+
+    assert result.ports == (43123,)
+    assert result.responses == 1
+
+
+def test_accepts_only_token_correlated_content_from_the_target(patch_socket):
+    def responder(datagram, _destination):
+        responses = _response(datagram)
+        _mtype, _code, mid, token, _options, _payload = parse_coap(datagram)
+        responses.extend(
+            [
+                (build_coap(TYPE_NON, 0x45, mid, b"wrong", [], b"x"), (_TARGET, 49999)),
+                (build_coap(TYPE_NON, 0x44, mid, token, [], b"x"), (_TARGET, 49998)),
+                (build_coap(TYPE_NON, 0x45, mid, token, [], b"x"), (_OTHER, 49997)),
+                (build_coap(TYPE_NON, 0x45, mid, token, [], b""), (_TARGET, 49996)),
+            ]
+        )
+        return responses
+
+    patch_socket(responder)
+    result = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+        rounds=1,
+    )
+
+    assert result.ports == (43123,)
+    assert result.responses == 3
+
+
+def test_ignores_malformed_and_oversized_datagrams(patch_socket):
+    def responder(datagram, _destination):
+        valid = _response(datagram)
+        invalid_version = bytes([valid[0][0][0] & 0x3F]) + valid[0][0][1:]
+        invalid_token_length = bytes([0x49]) + valid[0][0][1:]
+        return [
+            (b"\x40", (_TARGET, 49999)),
+            (invalid_version, (_TARGET, 49998)),
+            (invalid_token_length, (_TARGET, 49997)),
+            (b"x" * 8193, (_TARGET, 49996)),
+            *valid,
+        ]
+
+    patch_socket(responder)
+    result = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+        rounds=1,
+    )
+
+    assert result.ports == (43123,)
+    assert result.responses == 3
+
+
+def test_acknowledges_confirmable_responses(patch_socket):
+    active, _selector = patch_socket(
+        lambda datagram, _destination: _response(datagram, message_type=TYPE_CON)
+    )
+
+    result = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+        rounds=1,
+    )
+
+    assert result.found
+    acknowledgements = [
+        (parse_coap(datagram), destination)
+        for datagram, destination in active.sent
+        if parse_coap(datagram)[0] == 2
+    ]
+    assert len(acknowledgements) == 3
+    assert all(item[0][1] == 0 and item[0][3] == b"" for item in acknowledgements)
+    assert all(
+        destination == (_TARGET, 43123) for _item, destination in acknowledgements
+    )
+
+
+def test_collects_a_small_bounded_candidate_set(patch_socket):
+    response_number = 0
+
+    def responder(datagram, _destination):
+        nonlocal response_number
+        port = 40000 + response_number % 8
+        response_number += 1
+        return _response(datagram, port=port)
+
+    patch_socket(responder)
+    result = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+        rounds=4,
+    )
+
+    assert result.ports == tuple(range(40000, 40008))
+    assert result.error_code is None
+
+
+def test_fails_closed_when_too_many_distinct_ports_answer(patch_socket):
+    next_port = 40000
+
+    def responder(datagram, _destination):
+        nonlocal next_port
+        responses = [
+            *_response(datagram, port=next_port),
+            *_response(datagram, port=next_port + 1),
+        ]
+        next_port += 2
+        return responses
+
+    patch_socket(responder)
+    result = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+        rounds=4,
+    )
+
+    assert result.ports == ()
+    assert result.responses == 24
+    assert result.error_code == "ambiguous_response"
+
+
+def test_no_response_and_interface_failures_are_fixed_results(
+    patch_socket, monkeypatch
+):
+    active, _selector = patch_socket()
+    no_response = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+        rounds=1,
+    )
+    assert no_response == OcfResponderPortDiscoveryResult(
+        ports=(),
+        attempts=3,
+        responses=0,
+        error_code="no_response",
+    )
+    assert active.closed
+
+    class BrokenSocket:
+        def setsockopt(self, *_args):
+            raise OSError("synthetic")
+
+        def close(self):
+            return None
+
+    monkeypatch.setattr(
+        "smartthings_local.protocol.ocf_multicast.socket.socket",
+        lambda *_args: BrokenSocket(),
+    )
+    unavailable = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+    )
+    assert unavailable.error_code == "interface_unavailable"
+    assert unavailable.attempts == 0
+
+    monkeypatch.setattr(
+        "smartthings_local.protocol.ocf_multicast.selectors.DefaultSelector",
+        lambda: (_ for _ in ()).throw(OSError("synthetic")),
+    )
+    unavailable = discover_ocf_responder_ports(
+        _TARGET,
+        interface_address=_INTERFACE,
+    )
+    assert unavailable.error_code == "interface_unavailable"
+    assert unavailable.attempts == 0
+
+
+@pytest.mark.parametrize(
+    ("kwargs", "exception"),
+    [
+        ({"target_address": 123}, TypeError),
+        ({"target_address": "not-an-address"}, ValueError),
+        ({"target_address": _OCF_MULTICAST_GROUP}, ValueError),
+        ({"interface_address": "0.0.0.0"}, ValueError),
+        ({"discovery_port": True}, TypeError),
+        ({"discovery_port": 0}, ValueError),
+        ({"timeout": float("nan")}, ValueError),
+        ({"rounds": 0}, ValueError),
+        ({"rounds": 5}, ValueError),
+    ],
+)
+def test_rejects_invalid_options_without_opening_a_socket(
+    monkeypatch, kwargs, exception
+):
+    values = {
+        "target_address": _TARGET,
+        "interface_address": _INTERFACE,
+        **kwargs,
+    }
+    socket_factory = pytest.fail
+    monkeypatch.setattr(
+        "smartthings_local.protocol.ocf_multicast.socket.socket",
+        socket_factory,
+    )
+    with pytest.raises(exception):
+        discover_ocf_responder_ports(**values)
+
+
+def test_result_repr_omits_ports_and_addresses():
+    result = OcfResponderPortDiscoveryResult(ports=(43123,), attempts=2, responses=1)
+
+    rendered = repr(result)
+    assert "43123" not in rendered
+    assert _TARGET not in rendered
+    assert "port_count=1" in rendered

tests/test_oven_flatten.py

@@ -0,0 +1,86 @@
+"""Oven descriptor flatten() contracts for the HA Number entity's range.
+
+The oven reports ``x.com.samsung.da.desired = 0`` whenever no cycle is
+set. That is "no setpoint", not a 0 °C target, and publishing it as one
+makes Home Assistant reject every state message against the Number
+entity's declared 30-270 range.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from mqtt_demo.samples import oven
+
+
+def _links(desired, current=180):
+    """A /temperatures/vs/0 link tree carrying one desired/current pair."""
+    return {
+        '/temperatures/vs/0': {
+            'x.com.samsung.da.items': [{
+                'x.com.samsung.da.current': str(current),
+                'x.com.samsung.da.desired': str(desired),
+            }],
+        },
+    }
+
+
+@pytest.mark.parametrize('desired', [
+    oven.SETPOINT_MIN_C,
+    oven.SETPOINT_MIN_C + oven.SETPOINT_STEP_C,
+    180,
+    oven.SETPOINT_MAX_C,
+])
+def test_settable_setpoints_are_published_unchanged(desired):
+    assert oven.flatten(_links(desired))['target_temp_c'] == desired
+
+
+@pytest.mark.parametrize('desired', [
+    0,                              # the idle oven; see module docstring
+    oven.SETPOINT_MIN_C - 1,
+    oven.SETPOINT_MAX_C + 1,
+])
+def test_unsettable_setpoints_are_published_as_absent(desired):
+    assert oven.flatten(_links(desired))['target_temp_c'] is None
+
+
+def test_out_of_range_setpoint_does_not_suppress_current_temperature():
+    """The guard applies to the setpoint alone. A cooling oven still
+    reports its cavity temperature after the cycle ends."""
+    sensors = oven.flatten(_links(0, current=210))
+
+    assert sensors['target_temp_c'] is None
+    assert sensors['current_temp_c'] == 210
+
+
+def test_missing_temperature_resource_leaves_both_absent():
+    sensors = oven.flatten({})
+
+    assert sensors['target_temp_c'] is None
+    assert sensors['current_temp_c'] is None
+
+
+def test_every_committed_write_is_a_value_flatten_will_publish():
+    """The write path snaps to the step grid *before* bounds-checking, so
+    it accepts more than flatten() publishes: 29 commits as 30, and 271 as
+    270. That is fine for a slider, but it means the two range checks are
+    not symmetric. What has to hold is the weaker invariant: any setpoint
+    the oven is actually told to adopt is one flatten() will show back,
+    otherwise a write appears to succeed and then reads as unknown."""
+    handler = oven.command_handlers()[oven.CMD_SETPOINT]
+
+    for requested in range(-20, oven.SETPOINT_MAX_C + 40):
+        write = handler(str(requested), _links(180))
+        if write is None:
+            continue
+        _path, body = write
+        committed = int(body['x.com.samsung.da.items'][0][
+            'x.com.samsung.da.desired'])
+        assert oven.flatten(_links(committed))['target_temp_c'] == committed
+
+
+def test_zero_is_rejected_on_the_write_path_too():
+    """0 is the one value that neither snaps into range nor publishes."""
+    handler = oven.command_handlers()[oven.CMD_SETPOINT]
+
+    assert handler('0', _links(180)) is None

tests/test_owner_psk.py

@@ -0,0 +1,144 @@
+"""IoTivity manufacturer-certificate OwnerPSK derivation contracts."""
+
+from __future__ import annotations
+
+import pytest
+
+from smartthings_local.protocol.owner_psk import (
+    CONFIRMED_MFG_CERTIFICATE_OXM_LABEL,
+    MFG_CERTIFICATE_KEY_BLOCK_LENGTHS,
+    STANDARD_MFG_CERTIFICATE_OXM_LABEL,
+    derive_mfg_certificate_owner_psk,
+)
+
+
+_VALID_INPUTS = {
+    "master_secret": bytes(range(48)),
+    "client_random": bytes(range(32)),
+    "server_random": bytes(range(32, 64)),
+    "owner_uuid": bytes.fromhex("00112233445566778899aabbccddeeff"),
+    "device_uuid": bytes.fromhex("ffeeddccbbaa99887766554433221100"),
+    "cipher_name": "ECDHE-ECDSA-AES128-GCM-SHA256",
+    "oxm_label": CONFIRMED_MFG_CERTIFICATE_OXM_LABEL,
+}
+
+
+# These synthetic expected values were generated from the fixed inputs above;
+# they were not captured from IoTivity or a device. They lock deterministic
+# output for the selected mappings, while the table test below states the
+# key-block-length contract explicitly.
+def test_fixed_synthetic_gcm_regression_vector():
+    assert derive_mfg_certificate_owner_psk(**_VALID_INPUTS).hex() == (
+        "ccd6c618a91290dee8c106544ed79a33"
+    )
+
+
+def test_owner_then_device_uuid_order_matches_iotivity_callers():
+    reversed_context = derive_mfg_certificate_owner_psk(
+        **{
+            **_VALID_INPUTS,
+            "owner_uuid": _VALID_INPUTS["device_uuid"],
+            "device_uuid": _VALID_INPUTS["owner_uuid"],
+        }
+    )
+
+    assert reversed_context.hex() == "8f0f2416c483546dc1806db769b21b68"
+    assert reversed_context != derive_mfg_certificate_owner_psk(**_VALID_INPUTS)
+
+
+def test_fixed_synthetic_ccm8_regression_vector():
+    inputs = {
+        **_VALID_INPUTS,
+        "cipher_name": "ECDHE-ECDSA-AES128-CCM8",
+    }
+    assert derive_mfg_certificate_owner_psk(**inputs).hex() == (
+        "ddd3d945e266ee3dc27ff3a2c4321d32"
+    )
+
+
+def test_standard_and_confirmed_labels_derive_distinct_keys():
+    confirmed = derive_mfg_certificate_owner_psk(**_VALID_INPUTS)
+    standard = derive_mfg_certificate_owner_psk(
+        **{**_VALID_INPUTS, "oxm_label": STANDARD_MFG_CERTIFICATE_OXM_LABEL}
+    )
+
+    assert standard.hex() == "26ee1fe4c3e74509a2f5db5ab41b1e47"
+    assert standard != confirmed
+
+
+def test_iotivity_cipher_key_block_lengths_are_immutable():
+    assert dict(MFG_CERTIFICATE_KEY_BLOCK_LENGTHS) == {
+        "ECDHE-ECDSA-AES128-SHA256": 96,
+        "ECDHE-ECDSA-AES128-CCM": 40,
+        "ECDHE-ECDSA-AES128-CCM8": 40,
+        "ECDHE-ECDSA-AES128-GCM-SHA256": 120,
+        "AES256-SHA256": 128,
+        "ECDHE-ECDSA-AES256-SHA384": 160,
+        "ECDHE-ECDSA-AES256-GCM-SHA384": 184,
+        "AES128-GCM-SHA256": 120,
+    }
+    with pytest.raises(TypeError):
+        MFG_CERTIFICATE_KEY_BLOCK_LENGTHS["new-cipher"] = 1
+
+
+@pytest.mark.parametrize(
+    ("field", "length"),
+    [
+        ("master_secret", 48),
+        ("client_random", 32),
+        ("server_random", 32),
+        ("owner_uuid", 16),
+        ("device_uuid", 16),
+    ],
+)
+def test_binary_inputs_require_exact_bytes_and_lengths(field, length):
+    with pytest.raises(TypeError, match=f"{field} must be bytes"):
+        derive_mfg_certificate_owner_psk(
+            **{**_VALID_INPUTS, field: bytearray(length)}
+        )
+    for invalid_length in (length - 1, length + 1):
+        with pytest.raises(ValueError, match=f"exactly {length} bytes"):
+            derive_mfg_certificate_owner_psk(
+                **{**_VALID_INPUTS, field: b"x" * invalid_length}
+            )
+
+
+@pytest.mark.parametrize("field", ["owner_uuid", "device_uuid"])
+def test_nil_uuid_is_rejected(field):
+    with pytest.raises(ValueError, match="must not be the nil UUID"):
+        derive_mfg_certificate_owner_psk(
+            **{**_VALID_INPUTS, field: bytes(16)}
+        )
+
+
+def test_cipher_and_label_must_be_explicit_supported_values():
+    with pytest.raises(TypeError, match="cipher_name must be a string"):
+        derive_mfg_certificate_owner_psk(
+            **{**_VALID_INPUTS, "cipher_name": b"cipher"}
+        )
+    with pytest.raises(ValueError, match="unexpected.*cipher"):
+        derive_mfg_certificate_owner_psk(
+            **{**_VALID_INPUTS, "cipher_name": "ECDHE-RSA-AES128-GCM-SHA256"}
+        )
+    with pytest.raises(TypeError, match="oxm_label must be bytes"):
+        derive_mfg_certificate_owner_psk(
+            **{**_VALID_INPUTS, "oxm_label": "oic.sec.doxm.mfgcert"}
+        )
+    with pytest.raises(ValueError, match="unexpected.*label"):
+        derive_mfg_certificate_owner_psk(
+            **{**_VALID_INPUTS, "oxm_label": b"unsupported"}
+        )
+
+
+def test_failures_do_not_include_key_material():
+    key_material = b"private-master-secret"
+    with pytest.raises(ValueError) as raised:
+        derive_mfg_certificate_owner_psk(
+            **{
+                **_VALID_INPUTS,
+                "master_secret": key_material,
+                "cipher_name": "unsupported",
+            }
+        )
+    assert key_material.hex() not in str(raised.value)
+    assert "private-master-secret" not in str(raised.value)

tests/test_public_api_contract.py

@@ -18,6 +18,11 @@ from smartthings_local.protocol.dtls_session import (
     ConnectCancellation,
     DtlsCoapSession,
 )
+from smartthings_local.protocol.ocf_multicast import (
+    OcfResponderPortDiscoveryResult,
+    discover_ocf_responder_ports,
+)
+from smartthings_local.protocol.owner_psk import derive_mfg_certificate_owner_psk
 
 
 def _assert_compatible_signature(callable_object, expected: list[str]) -> None:
@@ -56,6 +61,32 @@ def test_dtls_session_constructor_keeps_file_memory_and_local_port_inputs():
     assert auth_parameter.default is None
 
 
+def test_known_host_multicast_discovery_has_a_bounded_explicit_interface_api():
+    parameters = inspect.signature(discover_ocf_responder_ports).parameters
+    assert list(parameters) == [
+        "target_address",
+        "interface_address",
+        "discovery_port",
+        "timeout",
+        "rounds",
+    ]
+    assert parameters["target_address"].default is inspect.Parameter.empty
+    for name in ("interface_address", "discovery_port", "timeout", "rounds"):
+        assert parameters[name].kind is inspect.Parameter.KEYWORD_ONLY
+    assert parameters["interface_address"].default is inspect.Parameter.empty
+    assert parameters["discovery_port"].default == 5683
+    assert parameters["timeout"].default == 3.0
+    assert parameters["rounds"].default == 2
+
+    result = OcfResponderPortDiscoveryResult(
+        ports=(43123,),
+        attempts=2,
+        responses=1,
+    )
+    assert result.found is True
+    assert result.ports == (43123,)
+
+
 def test_certificate_auth_is_a_public_authentication_provider():
     provider = CertificateAuth.from_files("/synthetic/cert.pem", "/synthetic/key")
     assert isinstance(provider, AuthenticationProvider)
@@ -114,6 +145,26 @@ def test_psk_auth_is_a_public_authentication_provider():
     )
 
 
+def test_owner_psk_derivation_keeps_every_security_input_explicit():
+    parameters = inspect.signature(
+        derive_mfg_certificate_owner_psk
+    ).parameters
+    assert list(parameters) == [
+        "master_secret",
+        "client_random",
+        "server_random",
+        "owner_uuid",
+        "device_uuid",
+        "cipher_name",
+        "oxm_label",
+    ]
+    assert all(
+        parameter.kind is inspect.Parameter.KEYWORD_ONLY
+        and parameter.default is inspect.Parameter.empty
+        for parameter in parameters.values()
+    )
+
+
 def test_dtls_session_keeps_current_consumer_methods():
     expected = {
         "close",

tests/test_request_pacing.py

@@ -0,0 +1,169 @@
+"""Session-owned pacing for request sends."""
+
+from __future__ import annotations
+
+from unittest.mock import Mock
+
+import pytest
+
+from smartthings_local.errors import SessionClosedError
+from smartthings_local.protocol import dtls_session
+from smartthings_local.protocol.coap import (
+    METHOD_GET,
+    METHOD_POST,
+    OBSERVE,
+    TYPE_ACK,
+    TYPE_CON,
+    build_coap,
+    parse_coap,
+)
+from smartthings_local.protocol.dtls_session import DtlsCoapSession
+
+
+class _NullAuth:
+    def configure_context(self, _context):
+        return None
+
+
+def _session():
+    session = DtlsCoapSession(
+        "device.example",
+        5684,
+        auth=_NullAuth(),
+        rate_limit_rps=1_000_000,
+    )
+    session.conn = object()
+    return session
+
+
+def test_first_get_post_and_subscribe_are_paced_before_send():
+    session = _session()
+    order = []
+    requests = []
+
+    def pace():
+        order.append("pace")
+
+    def send(datagram):
+        order.append("send")
+        request = parse_coap(datagram)
+        requests.append(request)
+        _mtype, _code, mid, token, options, _payload = request
+        if any(number == OBSERVE for number, _value in options):
+            assert session._observe_tokens[token] == "/mode/vs/0"
+            return
+        session._dispatch_coap(
+            build_coap(TYPE_ACK, 0x45, mid, token, [], b"ok")
+        )
+
+    session.pace = pace
+    session._send_dgram = send
+
+    assert session.get(["device", "0"]) == (0x45, b"ok")
+    assert session.post(["mode", "vs", "0"], b"payload") == (0x45, b"ok")
+    observe_token = session.subscribe(["mode", "vs", "0"])
+
+    assert session._observe_tokens[observe_token] == "/mode/vs/0"
+    assert order == ["pace", "send", "pace", "send", "pace", "send"]
+    assert [request[1] for request in requests] == [
+        METHOD_GET,
+        METHOD_POST,
+        METHOD_GET,
+    ]
+
+
+def test_every_subscribe_in_registration_burst_honors_rate_limit(monkeypatch):
+    session = _session()
+    now = [100.0]
+    waits = []
+    sends = []
+
+    class StopEvent:
+        def wait(self, delay):
+            waits.append(delay)
+            now[0] += delay
+
+    def send(datagram):
+        sends.append(datagram)
+        session._last_send_ts = now[0]
+
+    monkeypatch.setattr(dtls_session.time, "monotonic", lambda: now[0])
+    session._stop = StopEvent()
+    session._min_req_interval = 0.2
+    session._last_send_ts = 0.0
+    session._send_dgram = send
+
+    for index in range(11):
+        session.subscribe(["resource", "vs", str(index)])
+
+    assert len(sends) == 11
+    assert waits == [pytest.approx(0.2)] * 10
+
+
+def test_existing_caller_pacing_before_subscribe_does_not_wait_twice(
+    monkeypatch,
+):
+    session = _session()
+    now = [100.05]
+    waits = []
+
+    class StopEvent:
+        def wait(self, delay):
+            waits.append(delay)
+            now[0] += delay
+
+    monkeypatch.setattr(dtls_session.time, "monotonic", lambda: now[0])
+    session._stop = StopEvent()
+    session._min_req_interval = 0.2
+    session._last_send_ts = 100.0
+    session._send_dgram = Mock()
+
+    session.pace()
+    session.subscribe(["mode", "vs", "0"])
+
+    assert waits == [pytest.approx(0.15)]
+    session._send_dgram.assert_called_once()
+
+
+def test_subscribe_rechecks_liveness_after_pacing_before_registering():
+    session = _session()
+    session._send_dgram = Mock()
+
+    def close_during_pacing():
+        session.conn = None
+
+    session.pace = close_during_pacing
+
+    with pytest.raises(SessionClosedError):
+        session.subscribe(["mode", "vs", "0"])
+
+    assert session._observe_tokens == {}
+    session._send_dgram.assert_not_called()
+
+
+def test_ack_ping_and_observe_deregister_are_not_paced():
+    session = _session()
+    session.pace = Mock(side_effect=AssertionError("control send was paced"))
+
+    class Connection:
+        def __init__(self):
+            self.sent = []
+
+        def send(self, datagram):
+            self.sent.append(datagram)
+
+        def bio_read(self, _size):
+            return b""
+
+    connection = Connection()
+    session.conn = connection
+
+    session.ping()
+    session._send_observe_dereg(b"\x40", ["mode", "vs", "0"])
+    session._dispatch_coap(
+        build_coap(TYPE_CON, 0x45, 0x1234, b"unknown", [], b"state")
+    )
+
+    session.pace.assert_not_called()
+    assert len(connection.sent) == 3
+    assert parse_coap(connection.sent[-1])[:4] == (TYPE_ACK, 0, 0x1234, b"")

tests/test_session_connect_deadline.py

@@ -323,12 +323,12 @@ def test_connect_services_openssl_retransmit_timer(monkeypatch):
 
 
 @pytest.mark.parametrize("success_delay", (0.1, 0.2))
-def test_handshake_success_at_or_after_deadline_is_rejected(
+def test_handshake_success_at_or_after_deadline_is_retained(
     monkeypatch,
     success_delay,
 ):
     clock = _Clock()
-    connection, sock, _endpoint, _open_calls = _install_handshake(
+    connection, sock, endpoint, _open_calls = _install_handshake(
         monkeypatch,
         clock,
     )
@@ -338,7 +338,11 @@ def test_handshake_success_at_or_after_deadline_is_rejected(
 
     connection.do_handshake = late_success
 
-    with pytest.raises(SessionTimeoutError):
-        _session().connect(timeout=0.1)
+    session = _session()
+    session.connect(timeout=0.1)
 
-    assert sock.closed
+    assert session.conn is connection
+    assert session.sock is sock
+    assert session.endpoint is endpoint
+    assert session.dest == endpoint.sockaddr
+    assert not sock.closed

tests/test_session_interruption.py

@@ -220,9 +220,44 @@ def test_cancel_wakes_blocked_connect_without_poll_latency(monkeypatch):
         peer.close()
 
 
-def test_cancel_wins_race_with_reported_handshake_success(monkeypatch):
+def test_reported_handshake_success_wins_cancel_during_unsubscribe(
+    monkeypatch,
+):
+    class CancelDuringUnsubscribe(ConnectCancellation):
+        def _unsubscribe(self, reader, writer):
+            self.set()
+            return super()._unsubscribe(reader, writer)
+
+    cancel = CancelDuringUnsubscribe()
+    connection = _Connection(succeed=True)
+    data_socket, peer = socket.socketpair()
+    endpoint = _install_connection(monkeypatch, connection, data_socket)
+    session = _session()
+
+    try:
+        session.connect(cancel=cancel)
+        assert cancel.is_set()
+        assert session.sock is data_socket
+        assert session.conn is connection
+        assert session.endpoint is endpoint
+        assert session.dest == endpoint.sockaddr
+        assert not cancel._writers
+    finally:
+        session.close()
+        peer.close()
+
+
+def test_cancel_during_backend_failure_does_not_read_unset_completion(
+    monkeypatch,
+):
     cancel = ConnectCancellation()
-    connection = _Connection(on_success=cancel.set, succeed=True)
+    connection = _Connection()
+
+    def fail_after_cancel():
+        cancel.set()
+        raise SSL.Error("synthetic backend failure")
+
+    connection.do_handshake = fail_after_cancel
     data_socket, peer = socket.socketpair()
     _install_connection(monkeypatch, connection, data_socket)
     session = _session()
@@ -233,6 +268,7 @@ def test_cancel_wins_race_with_reported_handshake_success(monkeypatch):
         assert data_socket.fileno() == -1
         assert session.sock is None
         assert session.conn is None
+        assert not cancel._writers
     finally:
         peer.close()
 

tests/test_worker_cleanup.py

@@ -3,7 +3,12 @@
 from __future__ import annotations
 
 import threading
+from types import SimpleNamespace
 
+import pytest
+
+from mqtt_demo import bridge as bridge_module
+from mqtt_demo.bridge import PushBridge
 from smartthings_local.ocf.keepalive import KeepaliveTask
 from smartthings_local.ocf.observe_refresh import ObserveRefreshTask
 from smartthings_local.ocf.poll_scheduler import PollScheduler, PollTier
@@ -73,3 +78,238 @@ def test_poll_scheduler_worker_stops_without_leaking_thread():
         [PollTier("idle", interval_s=3600.0, paths=())],
     )
     _assert_worker_stops(scheduler.run_forever, "test-poll-scheduler")
+
+
+class _SessionWorker:
+    def __init__(self, *args, **kwargs):
+        self.stop = None
+        self.started = threading.Event()
+        self.exited = threading.Event()
+        self.on_reachable = kwargs.get("on_reachable")
+        self.on_unreachable = kwargs.get("on_unreachable")
+        self.last_success_ts = 0.0
+
+    def run_forever(self, stop):
+        self.stop = stop
+        self.started.set()
+        stop.wait()
+        self.exited.set()
+
+
+class _JoinedSession:
+    def __init__(self, workers, start_index, error=None):
+        self.workers = workers
+        self.start_index = start_index
+        self.error = error
+
+    def join(self):
+        assert all(
+            worker.started.wait(_THREAD_DEADLINE_S)
+            for worker in self.workers[self.start_index:]
+        )
+        if self.error is not None:
+            raise self.error
+
+
+class _BlockingJoinedSession(_JoinedSession):
+    def __init__(self, workers):
+        super().__init__(workers, 0)
+        self.joined = threading.Event()
+        self.release = threading.Event()
+
+    def join(self):
+        super().join()
+        self.joined.set()
+        assert self.release.wait(_THREAD_DEADLINE_S)
+
+
+def _bridge():
+    bridge = object.__new__(PushBridge)
+    bridge.descriptor = SimpleNamespace(
+        observe_paths=(),
+        poll_tiers=[],
+        is_active=lambda _state: False,
+    )
+    bridge.shared = SimpleNamespace(PING_INTERVAL_S=3600.0)
+    bridge.app = SimpleNamespace(klass="test")
+    bridge.log = SimpleNamespace(info=lambda *args: None, warning=lambda *args: None)
+    bridge.cache = SimpleNamespace(links={})
+    bridge.stop = threading.Event()
+    bridge._session_stop_lock = threading.Lock()
+    bridge._session_stop = None
+    bridge.scheduler = None
+    bridge.keepalive = None
+    bridge.observe_refresh = None
+    bridge._seed_from_device0 = lambda _session: None
+    bridge._retag_logger_with_serial = lambda: None
+    bridge.maybe_publish_state = lambda **kwargs: None
+    bridge.set_availability = lambda _online: None
+    return bridge
+
+
+@pytest.mark.parametrize(
+    ("session_count", "join_error"),
+    [
+        pytest.param(2, None, id="reconnect"),
+        pytest.param(1, RuntimeError("reader failed"), id="reader-error"),
+    ],
+)
+def test_bridge_retires_session_workers_before_returning(
+    monkeypatch, session_count, join_error
+):
+    workers = []
+
+    def worker_factory(*args, **kwargs):
+        worker = _SessionWorker(*args, **kwargs)
+        workers.append(worker)
+        return worker
+
+    monkeypatch.setattr(bridge_module, "PollScheduler", worker_factory)
+    monkeypatch.setattr(bridge_module, "KeepaliveTask", worker_factory)
+    monkeypatch.setattr(bridge_module, "ObserveRefreshTask", worker_factory)
+
+    bridge = _bridge()
+
+    session_stops = []
+    for session_index in range(session_count):
+        start_index = len(workers)
+        session = _JoinedSession(
+            workers,
+            start_index,
+            error=join_error if session_index == session_count - 1 else None,
+        )
+        if session.error is None:
+            bridge._run_session_inner(session)
+        else:
+            with pytest.raises(RuntimeError, match="reader failed"):
+                bridge._run_session_inner(session)
+
+        session_workers = workers[start_index:]
+        assert len(session_workers) == 3
+        assert len({id(worker.stop) for worker in session_workers}) == 1
+        session_stops.append(session_workers[0].stop)
+
+    assert len(workers) == session_count * 3
+    assert len({id(stop) for stop in session_stops}) == session_count
+    assert all(stop is not bridge.stop for stop in session_stops)
+    assert all(stop.is_set() for stop in session_stops)
+    assert not bridge.stop.is_set()
+    assert all(worker.exited.is_set() for worker in workers)
+    keepalive_workers = tuple(
+        workers[index] for index in range(1, len(workers), 3)
+    )
+    assert all(worker.on_reachable is None for worker in keepalive_workers)
+    assert all(worker.on_unreachable is None for worker in keepalive_workers)
+    assert bridge.scheduler is None
+    assert bridge.keepalive is None
+    assert bridge.observe_refresh is None
+    assert bridge._session_stop is None
+
+
+def test_bridge_retires_started_worker_when_later_thread_fails_to_start(
+    monkeypatch,
+):
+    workers = []
+
+    def worker_factory(*args, **kwargs):
+        worker = _SessionWorker(*args, **kwargs)
+        workers.append(worker)
+        return worker
+
+    monkeypatch.setattr(bridge_module, "PollScheduler", worker_factory)
+    monkeypatch.setattr(bridge_module, "KeepaliveTask", worker_factory)
+    monkeypatch.setattr(bridge_module, "ObserveRefreshTask", worker_factory)
+
+    bridge = _bridge()
+
+    original_start = threading.Thread.start
+    start_count = 0
+
+    def fail_second_start(thread):
+        nonlocal start_count
+        start_count += 1
+        if start_count == 2:
+            raise RuntimeError("synthetic thread start failure")
+        original_start(thread)
+
+    monkeypatch.setattr(threading.Thread, "start", fail_second_start)
+
+    with pytest.raises(RuntimeError, match="synthetic thread start failure"):
+        bridge._run_session_inner(SimpleNamespace(join=lambda: None))
+
+    assert len(workers) == 3
+    assert workers[0].started.wait(_THREAD_DEADLINE_S)
+    assert workers[0].exited.wait(_THREAD_DEADLINE_S)
+    assert workers[0].stop is not bridge.stop
+    assert workers[0].stop.is_set()
+    assert workers[1].stop is None
+    assert workers[2].stop is None
+    assert bridge.scheduler is None
+    assert bridge.keepalive is None
+    assert bridge.observe_refresh is None
+    assert bridge._session_stop is None
+
+
+def test_request_stop_wakes_current_session_workers(monkeypatch):
+    workers = []
+
+    def worker_factory(*args, **kwargs):
+        worker = _SessionWorker(*args, **kwargs)
+        workers.append(worker)
+        return worker
+
+    monkeypatch.setattr(bridge_module, "PollScheduler", worker_factory)
+    monkeypatch.setattr(bridge_module, "KeepaliveTask", worker_factory)
+    monkeypatch.setattr(bridge_module, "ObserveRefreshTask", worker_factory)
+
+    bridge = _bridge()
+    session = _BlockingJoinedSession(workers)
+    session_thread = threading.Thread(
+        target=bridge._run_session_inner,
+        args=(session,),
+        daemon=True,
+    )
+    session_thread.start()
+
+    try:
+        assert session.joined.wait(_THREAD_DEADLINE_S)
+        session_stop = bridge._session_stop
+        assert session_stop is not None
+        assert not session_stop.is_set()
+
+        bridge.request_stop()
+
+        assert bridge.stop.is_set()
+        assert session_stop.is_set()
+        assert all(
+            worker.exited.wait(_THREAD_DEADLINE_S) for worker in workers
+        )
+        assert session_thread.is_alive()
+    finally:
+        session.release.set()
+        session_thread.join(_THREAD_DEADLINE_S)
+
+    assert not session_thread.is_alive()
+    assert bridge._session_stop is None
+
+
+def test_session_workers_observe_stop_requested_before_handoff(monkeypatch):
+    workers = []
+
+    def worker_factory(*args, **kwargs):
+        worker = _SessionWorker(*args, **kwargs)
+        workers.append(worker)
+        return worker
+
+    monkeypatch.setattr(bridge_module, "PollScheduler", worker_factory)
+    monkeypatch.setattr(bridge_module, "KeepaliveTask", worker_factory)
+    monkeypatch.setattr(bridge_module, "ObserveRefreshTask", worker_factory)
+
+    bridge = _bridge()
+    bridge.request_stop()
+    bridge._run_session_inner(_JoinedSession(workers, 0))
+
+    assert len(workers) == 3
+    assert all(worker.stop.is_set() for worker in workers)
+    assert all(worker.exited.wait(_THREAD_DEADLINE_S) for worker in workers)
+    assert bridge._session_stop is None