Add MTU discovery with typed ProtocolError enum#200
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okhsunrog merged 6 commits intojamesmunns:mainfrom Mar 28, 2026
Merged
Add MTU discovery with typed ProtocolError enum#200okhsunrog merged 6 commits intojamesmunns:mainfrom
okhsunrog merged 6 commits intojamesmunns:mainfrom
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Cherry-picked from feature/mtu-discovery and adapted for unified Router: - Add mtu() to InterfaceSink trait (cobs_stream, framed_stream, multi_interface) - Add ISE_PACKET_TOO_BIG protocol error (18) and PacketTooBig payload struct - Add MTU check in EdgePort::send_raw before forwarding - Send PROTOCOL_ERROR back to source when forwarded frame exceeds outgoing MTU - Add ErgotPathMtuEndpoint well-known endpoint with PathMtuQuery/PathMtuResult
Replace ProtocolError(u16) with a proper enum where each variant can
carry its own data. This allows IsePacketTooBig { mtu: u16 } to
natively encode the bottleneck MTU in the wire frame, eliminating the
need for a separate query round-trip.
Remove the now-unnecessary PacketTooBig struct and
encode_frame_err_with_payload helper. Add e2e tests for wire format
round-trip and router MTU enforcement.
Add PacketReceiver/PacketSender traits and a combined RX/TX worker that handles the frame processing loop, optional liveness timeout, and interface state management. New transports (BLE, CAN FD, ESP-NOW, SPI) only need to implement the two traits (~10 lines each) instead of duplicating the full worker loop.
The std feature was unconditionally enabling embassy-time via "embassy-time/std", which pulls in embassy-executor-timer-queue and its unresolved __embassy_time_queue_item_from_waker symbol. This caused MSVC linker failures on Windows for tokio-based demos that don't provide an embassy executor. Changed to "embassy-time?/std" so the std sub-feature only activates if embassy-time is already enabled by another feature.
run() already sets InterfaceState::Down on exit. The Drop impl now checks whether the interface is already Down before setting it again.
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Add MTU discovery so routers can detect and report oversized frames.
InterfaceSinkgains anmtu()method,EdgePort::send_rawchecks frame size before sending, and the router replies with aPacketTooBigerror carrying the bottleneck MTU value. To make this work cleanly on the wire,ProtocolErroris changed from astruct(u16)newtype to a proper enum — each variant can now carry its own typed payload (e.g.IsePacketTooBig { mtu: u16 }), serialized natively by postcard.mtu()toInterfaceSinktrait; implement incobs_stream::Sink,framed_stream::Sink, andmulti_interface!macroInterfaceSendError::PacketTooBig { mtu }variant with MTU check inEdgePort::send_rawprocess_framecatchesPacketTooBigand sends error back to source with the MTU valueProtocolError(u16)+ associated constants withenum ProtocolError— variants carry typed dataPacketTooBigstruct andencode_frame_err_with_payload(enum handles this natively)ErgotPathMtuEndpointwell-known endpoint (types only, no server yet)Breaking changes:
ProtocolErroris now an enum — all code matching onProtocolError::SSE_NO_SPACEetc. must useProtocolError::SseNoSpacestyle variantsInterfaceSinkimplementations must addfn mtu(&self) -> u16