When HA restarts without a clean DTLS close_notify (crash, host reboot),
the appliance keeps an orphaned DTLS association keyed to the client's
(IP, source port). Reconnecting from a fresh ephemeral port looks like a
new peer, so the device holds the orphan until its own timer reaps it,
which is 5 to 15 min on always-on appliances (fridges), during which the
new session's first reads hang. This is the root cause behind the repeated
"DTLS handshake timeout" reconnect storms on always-on devices (#119).
Bind a deterministic source port per device so every reconnect re-handshakes
over the same 5-tuple, which the device must treat as a rebooted peer and
evict the old association for (RFC 6347 §4.2.8). Recovery drops from a
device-timer wait to a single handshake.
The port must be stable across restarts and unique per device on the HA host
(the library socket is unconnected, so a shared source port would cross-
deliver datagrams). _local_source_port() uses the host's last IPv4 octet as
the offset from DTLS_LOCAL_PORT_BASE (unique on a /24), with a CRC32 fallback
for non-IPv4 hosts.
Requires smartthings-local >= 0.1.1, which adds DtlsCoapSession(local_port=).
The fix is backwards compatible upstream: local_port defaults to None
(previous ephemeral-port behaviour).
Root-caused and verified upstream in QuiteYellow/SmartThings-Local#14
(bench-verified on oven + dryer, field-verified on an always-on fridge
across repeated restarts).
Jack Nagy
0ebcfb00ff