register function

Middleware register([ CollectorRegistry? registry ])

Register default metrics for the shelf and returns a shelf.Middleware that can be added to the shelf.Pipeline. If no registry is provided, the CollectorRegistry.defaultRegistry is used.

Implementation

shelf.Middleware register([CollectorRegistry? registry]) {
  final histogram = Histogram(
    name: 'http_request_duration_seconds',
    help: 'A histogram of the HTTP request durations.',
    labelNames: ['method', 'code'],
  );

  registry ??= CollectorRegistry.defaultRegistry;
  registry.register(histogram);

  return (innerHandler) {
    return (request) {
      var watch = Stopwatch()..start();

      return Future.sync(() => innerHandler(request)).then((response) {
        histogram.labels([request.method, '${response.statusCode}']).observe(
            watch.elapsedMicroseconds / Duration.microsecondsPerSecond);

        return response;
      }, onError: (error, StackTrace stackTrace) {
        if (error is shelf.HijackException) {
          throw error;
        }

        histogram.labels([request.method, '000']).observe(
            watch.elapsedMicroseconds / Duration.microsecondsPerSecond);

        throw error;
      });
    };
  };
}