matchedPathOf function
The route pattern that matched request, or null when none did.
The pattern, not the path: /todos/{id} rather than /todos/7. That
is what a span name, a metric label, or a log line should carry — naming
them after the path makes every id its own operation, and a dashboard of a
million one-request operations says nothing.
null for a request that reached the fallback, or one built in a test
without a router, because no route matched it.
Implementation
String? matchedPathOf(Request request) {
final raw = request.context[matchedPathKey];
return raw is String ? raw : null;
}