Lands the broadcast layer of F15. Session::connect_nmx now starts a
local CallbackExporter on an OS-assigned ephemeral port, builds a
callback OBJREF advertising it (using local_hostname() with a
127.0.0.1 fallback), and registers that OBJREF with NmxClient::register_engine_2
(was register_engine_2_without_callback). A router task drains the
exporter's CallbackEvent stream, decodes each CallbackInvoked body as
NmxSubscriptionMessage, and broadcasts parsed messages on a
tokio::sync::broadcast channel.
Per-subscription correlation routing — turning these raw messages
into per-Subscription DataChange streams — is the next iteration's
work. F15 stays open until that lands.
New Session API
- Session::callbacks() -> broadcast::Receiver<Arc<NmxSubscriptionMessage>>:
raw observable of every parsed callback message. Test seam +
escape hatch for consumers that need raw access today.
- Session::callback_exporter_addr() -> Option<SocketAddr>: returns the
exporter's local addr (Some until shutdown_nmx, None after).
SessionInner additions
- callback_exporter: Mutex<Option<CallbackExporter>> — taken in shutdown.
- callback_tx: broadcast::Sender<Arc<NmxSubscriptionMessage>>.
- router_handle: std::sync::Mutex<Option<JoinHandle<()>>>.
shutdown_nmx now performs the full cleanup chain:
1. UnregisterEngine over the live NMX transport.
2. CallbackExporter::shutdown (cancels accept loop).
3. Wait for router task — exits naturally once exporter's mpsc
sender side closes. Std::sync::Mutex guard taken-out-then-dropped
before await to avoid clippy::await_holding_lock.
Routing rationale (callback_router fn)
- CallbackEvent::CallbackInvoked → parse via
NmxSubscriptionMessage::parse_inner → broadcast Arc<msg>.
- Other event variants (Bind / Auth3Ignored / ProtocolError / etc.)
silently dropped at this layer; consumers needing them can listen
to a future diagnostic-channel hook (no followup yet).
- Parse failures silent — the .NET reference fires a separate
UnparsedCallbackReceived event we don't model yet.
Cargo.toml: added mxaccess-callback as a direct dep on mxaccess.
Tests (5 new in mxaccess; total 35)
- callbacks receiver observes injected NmxSubscriptionMessage.
- multi-subscriber broadcast hands out the same Arc to each receiver.
- callback_exporter_addr is Some before shutdown, None after.
- router_task end-to-end: feed a hand-built CallbackInvoked event
with a 39-byte 0x32 SubscriptionStatus body, observe the parsed
message on the broadcast.
- router silently drops non-CallbackInvoked events (e.g. Bind).
Test count delta: 506 -> 511 (+5). All four DoD gates green.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Joseph Doherty
2b849aed7a