map_wire

Overview

A road-graph segment on the wire, derived once for everyone who publishes one. It is the same argument as map_rules one layer down: map_server (map/nearest, map/route) and nodes/map_match (the horizon) both answer “what road is this”, and each had its own copy of the enum mapping, an identical thirty-line wireClassOf() in two files plus the same four speed setters written out three times. map_common.capnp exists so the two nodes name a road class the same way; this library exists so they derive it the same way.

There is no zenoh here, only the generated capnp types, so it stays testable without a bus. It links map_rules, road_graph and schemas publicly, because those are the types it maps between.

Public headers

Header	Declares
map_wire/segment.h	classOf() from map_rules::RouteClass or the raw byte a SegmentRecord stores, speedSourceOf() likewise, fillSpeed() from a road_graph::SegmentRecord into a MapSpeed::Builder, and osmWayIdOf() for the schema’s unsigned way id.

Using it

Link the map_wire target. Both nodes call it the same way when they fill a candidate or a horizon profile; this is nodes/map_server/services.cpp.

const road_graph::SegmentRecord& segment = graph.segments()[match.segment];
auto out = list[i];
out.setName(std::string(graph.nameOf(segment)));
out.setRef(std::string(graph.refOf(segment)));
out.setRoadClass(map_wire::classOf(segment.routeClass));
map_wire::fillSpeed(out.initSpeed(), segment);

Behaviour worth knowing

The mappings are written out as exhaustive switches rather than casts, even though the two enumerations are parallel to their wire counterparts today. A static_cast keeps compiling after someone inserts a value into either side, and the result is every road on the dash reporting the class of its neighbour. Spelled out, -Wswitch-enum makes that insertion a build failure here. speedSourceOf() was a static_cast at both call sites before this library existed, and “sign” versus “guessed from the road class” is the difference between a limit a dash may show a driver and one it must not.

fillSpeed() takes hasPosted from the segment’s flag, never from postedKph being non-zero: zero is a legal limit in exactly the places where getting it wrong matters.

Tests

Target	Labels	Proves
map_wire_test_segment	map_wire unit	Every RouteClass and every SpeedSource maps to its own wire value, checked value by value rather than for a couple of classes; a speed without the posted flag says so on the wire; a way id past 2^31 reaches the wire unchanged.

The switch makes adding a value a build failure; this test makes reordering one a test failure.