func NewHandlerFactory()

in metrics/handler.go [29:116]
77 lines of code
1 McCabe index (conditional complexity)

func NewHandlerFactory(opts ...HandlerFactoryOption) HandlerFactory {
	factoryConfig := applyHandlerFactoryOptions(opts)

	var (
		httpInFlightRequests = prometheus.NewGauge(prometheus.GaugeOpts{
			Namespace: factoryConfig.namespace,
			Subsystem: factoryConfig.subsystem,
			Name:      httpInFlightRequestsMetricName,
			Help:      "A gauge of requests currently being served by the http server.",
		})

		httpRequestsTotal = prometheus.NewCounterVec(
			prometheus.CounterOpts{
				Namespace: factoryConfig.namespace,
				Subsystem: factoryConfig.subsystem,
				Name:      httpRequestsTotalMetricName,
				Help:      "A counter for requests to the http server.",
			},
			factoryConfig.labels,
		)

		httpRequestDurationSeconds = prometheus.NewHistogramVec(
			prometheus.HistogramOpts{
				Namespace: factoryConfig.namespace,
				Subsystem: factoryConfig.subsystem,
				Name:      httpRequestDurationSecondsMetricName,
				Help:      "A histogram of latencies for requests to the http server.",
				Buckets:   factoryConfig.requestDurationBuckets,
			},
			factoryConfig.labels,
		)

		httpRequestSizeBytes = prometheus.NewHistogramVec(
			prometheus.HistogramOpts{
				Namespace: factoryConfig.namespace,
				Subsystem: factoryConfig.subsystem,
				Name:      httpRequestSizeBytesMetricName,
				Help:      "A histogram of sizes of requests to the http server.",
				Buckets:   factoryConfig.byteSizeBuckets,
			},
			factoryConfig.labels,
		)

		httpResponseSizeBytes = prometheus.NewHistogramVec(
			prometheus.HistogramOpts{
				Namespace: factoryConfig.namespace,
				Subsystem: factoryConfig.subsystem,
				Name:      httpResponseSizeBytesMetricName,
				Help:      "A histogram of response sizes for requests to the http server.",
				Buckets:   factoryConfig.byteSizeBuckets,
			},
			factoryConfig.labels,
		)

		httpTimeToWriteHeaderSeconds = prometheus.NewHistogramVec(
			prometheus.HistogramOpts{
				Namespace: factoryConfig.namespace,
				Subsystem: factoryConfig.subsystem,
				Name:      httpTimeToWriteHeaderSecondsMetricName,
				Help:      "A histogram of request durations until the response headers are written.",
				Buckets:   factoryConfig.timeToWriteHeaderDurationBuckets,
			},
			factoryConfig.labels,
		)
	)

	prometheus.MustRegister(httpInFlightRequests)
	prometheus.MustRegister(httpRequestsTotal)
	prometheus.MustRegister(httpRequestDurationSeconds)
	prometheus.MustRegister(httpRequestSizeBytes)
	prometheus.MustRegister(httpResponseSizeBytes)
	prometheus.MustRegister(httpTimeToWriteHeaderSeconds)

	return func(next http.Handler, handlerOpts ...HandlerOption) http.Handler {
		handlerConfig, promOpts := applyHandlerOptions(handlerOpts)

		handler := next

		handler = promhttp.InstrumentHandlerCounter(handlerConfig.applyOptionsToCounterVec(httpRequestsTotal), handler, promOpts...)
		handler = promhttp.InstrumentHandlerDuration(handlerConfig.applyOptionsToObserverVec(httpRequestDurationSeconds), handler, promOpts...)
		handler = promhttp.InstrumentHandlerInFlight(httpInFlightRequests, handler)
		handler = promhttp.InstrumentHandlerRequestSize(handlerConfig.applyOptionsToObserverVec(httpRequestSizeBytes), handler, promOpts...)
		handler = promhttp.InstrumentHandlerResponseSize(handlerConfig.applyOptionsToObserverVec(httpResponseSizeBytes), handler, promOpts...)
		handler = promhttp.InstrumentHandlerTimeToWriteHeader(handlerConfig.applyOptionsToObserverVec(httpTimeToWriteHeaderSeconds), handler, promOpts...)

		return handler
	}
}