From 7d65b328f0fc62bf35c5ad4387b6b6564da28d42 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?K=C3=A9vin=20Dunglas?= <kevin@dunglas.fr>
Date: Wed, 19 Feb 2025 01:02:22 +0100
Subject: [PATCH] fix: duplicate metrics collector registration attempted panic

---
 caddy/caddy_test.go | 14 +++++++++++++-
 metrics.go          | 17 ++++++++++++++---
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/caddy/caddy_test.go b/caddy/caddy_test.go
index 33ae50df..d352ce5e 100644
--- a/caddy/caddy_test.go
+++ b/caddy/caddy_test.go
@@ -52,7 +52,19 @@ localhost:9080 {
 		mercure {
 			anonymous
 			publisher_jwt !ChangeMe!
-			%s
+			%[1]s
+		}
+
+		respond 404
+	}
+}
+
+example.com:9080 {
+	route {
+		mercure {
+			anonymous
+			publisher_jwt !ChangeMe!
+			%[1]s
 		}
 
 		respond 404
diff --git a/metrics.go b/metrics.go
index e5398bfe..70a695d5 100644
--- a/metrics.go
+++ b/metrics.go
@@ -1,6 +1,7 @@
 package mercure
 
 import (
+	"errors"
 	"net/http"
 
 	"github.com/dunglas/mercure/common"
@@ -62,9 +63,19 @@ func NewPrometheusMetrics(registry prometheus.Registerer) *PrometheusMetrics {
 		),
 	}
 
-	m.registry.MustRegister(m.subscribers)
-	m.registry.MustRegister(m.subscribersTotal)
-	m.registry.MustRegister(m.updatesTotal)
+	// https://github.com/caddyserver/caddy/pull/6820
+	if err := m.registry.Register(m.subscribers); err != nil &&
+		!errors.As(err, &prometheus.AlreadyRegisteredError{}) {
+		panic(err)
+	}
+	if err := m.registry.Register(m.subscribersTotal); err != nil &&
+		!errors.As(err, &prometheus.AlreadyRegisteredError{}) {
+		panic(err)
+	}
+	if err := m.registry.Register(m.updatesTotal); err != nil &&
+		!errors.As(err, &prometheus.AlreadyRegisteredError{}) {
+		panic(err)
+	}
 
 	return m
 }