Feat: add support to custom registry.

collector.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 var (
@@ -34,6 +35,10 @@ type CollectorOpts struct {
 	// Skip is an optional predicate function that determines whether to skip recording metrics for a given request.
 	// If nil, all requests are recorded. If provided, requests where Skip returns true will not be recorded.
 	Skip func(r *http.Request) bool
+
+	// Registry specifies the Prometheus registry to which the metrics will be registered.
+	// If nil, the default Prometheus registry is used.
+	Registry prometheus.Registerer
 }
 
 // requestLabels defines labels for the counter of total incoming HTTP requests.
@@ -63,6 +68,9 @@ type inflightLabels struct {
 // - http_requests_inflight: Number of incoming HTTP requests currently in flight
 // - http_request_duration_seconds: Response latency in seconds for completed requests
 func Collector(opts CollectorOpts) func(next http.Handler) http.Handler {
+
+	registerMetrics(opts.Registry)
+
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			if opts.Skip != nil && opts.Skip(r) {

counter.go

@@ -8,7 +8,6 @@ func Counter(name string, help string) CounterMetric {
 		Name: mustValidMetricName(name),
 		Help: help,
 	}, []string{})
-	prometheus.MustRegister(vec)
 	return CounterMetric{vec: vec}
 }
 
@@ -18,7 +17,6 @@ func CounterWith[T any](name string, help string) CounterMetricLabeled[T] {
 		Name: mustValidMetricName(name),
 		Help: help,
 	}, getLabelKeys[T]())
-	prometheus.MustRegister(vec)
 	return CounterMetricLabeled[T]{vec: vec}
 }
 

gauge.go

@@ -8,7 +8,6 @@ func Gauge(name, help string) GaugeMetric {
 		Name: mustValidMetricName(name),
 		Help: help,
 	}, []string{})
-	prometheus.MustRegister(vec)
 	return GaugeMetric{vec: vec}
 }
 
@@ -18,7 +17,6 @@ func GaugeWith[T any](name, help string) GaugeMetricLabeled[T] {
 		Name: mustValidMetricName(name),
 		Help: help,
 	}, getLabelKeys[T]())
-	prometheus.MustRegister(vec)
 	return GaugeMetricLabeled[T]{vec: vec}
 }
 

handler.go

@@ -15,3 +15,12 @@ import (
 func Handler() http.Handler {
 	return promhttp.HandlerFor(prometheus.DefaultGatherer, promhttp.HandlerOpts{})
 }
+
+// HandlerFor returns an HTTP handler that serves Prometheus metrics from the provided registry
+// in the OpenMetrics exposition format.
+//
+// This handler should typically be mounted at "/metrics" and protected from public access,
+// e.g. via middleware.BasicAuth or exposed only on a private port.
+func HandlerFor(registry *prometheus.Registry) http.Handler {
+	return promhttp.HandlerFor(registry, promhttp.HandlerOpts{})
+}

histogram.go

@@ -9,7 +9,6 @@ func Histogram(name, help string, buckets []float64) HistogramMetric {
 		Help:    help,
 		Buckets: buckets,
 	}, []string{})
-	prometheus.MustRegister(vec)
 	return HistogramMetric{vec: vec}
 }
 
@@ -20,7 +19,6 @@ func HistogramWith[T any](name, help string, buckets []float64) HistogramMetricL
 		Help:    help,
 		Buckets: buckets,
 	}, getLabelKeys[T]())
-	prometheus.MustRegister(vec)
 	return HistogramMetricLabeled[T]{vec: vec}
 }
 

registry.go

@@ -0,0 +1,13 @@
+package metrics
+
+import "github.com/prometheus/client_golang/prometheus"
+
+// registerMetrics registers all metrics with the provided Prometheus registry.
+func registerMetrics(registry prometheus.Registerer) {
+	if registry == nil {
+		registry = prometheus.DefaultRegisterer.(*prometheus.Registry)
+	}
+	registry.MustRegister(requestsCounter.vec)
+	registry.MustRegister(inflightGauge.vec)
+	registry.MustRegister(requestsHistogram.vec)
+}