fix(middleware): DefaultErrorHandler responds 503 instead of panicking on store error

drivers/middleware/fasthttp/options.go

@@ -1,6 +1,8 @@
 package fasthttp
 
 import (
+	"log"
+
 	"github.com/valyala/fasthttp"
 )
 
@@ -26,8 +28,13 @@ func WithErrorHandler(handler ErrorHandler) Option {
 }
 
 // DefaultErrorHandler is the default ErrorHandler used by a new Middleware.
+// It logs the store error and responds with 503 so that store outages do not
+// crash the request pipeline. Override via WithErrorHandler for custom behavior
+// (e.g. fail-open).
 func DefaultErrorHandler(ctx *fasthttp.RequestCtx, err error) {
-	panic(err)
+	log.Printf("limiter: store error: %v", err)
+	ctx.SetStatusCode(fasthttp.StatusServiceUnavailable)
+	ctx.Response.SetBodyString("Service Unavailable")
 }
 
 // LimitReachedHandler is an handler used to inform when the limit has exceeded.

drivers/middleware/gin/options.go

@@ -1,6 +1,7 @@
 package gin
 
 import (
+	"log"
 	"net/http"
 
 	"github.com/gin-gonic/gin"
@@ -28,8 +29,12 @@ func WithErrorHandler(handler ErrorHandler) Option {
 }
 
 // DefaultErrorHandler is the default ErrorHandler used by a new Middleware.
+// It logs the store error and responds with 503 so that store outages do not
+// crash the request pipeline. Override via WithErrorHandler for custom behavior
+// (e.g. fail-open).
 func DefaultErrorHandler(c *gin.Context, err error) {
-	panic(err)
+	log.Printf("limiter: store error: %v", err)
+	c.String(http.StatusServiceUnavailable, "Service Unavailable")
 }
 
 // LimitReachedHandler is an handler used to inform when the limit has exceeded.

drivers/middleware/stdlib/options.go

@@ -1,6 +1,7 @@
 package stdlib
 
 import (
+	"log"
 	"net/http"
 
 	"github.com/ulule/limiter/v3"
@@ -28,8 +29,12 @@ func WithErrorHandler(handler ErrorHandler) Option {
 }
 
 // DefaultErrorHandler is the default ErrorHandler used by a new Middleware.
+// It logs the store error and responds with 503 so that store outages do not
+// crash the request pipeline. Override via WithErrorHandler for custom behavior
+// (e.g. fail-open).
 func DefaultErrorHandler(w http.ResponseWriter, r *http.Request, err error) {
-	panic(err)
+	log.Printf("limiter: store error: %v", err)
+	http.Error(w, "Service Unavailable", http.StatusServiceUnavailable)
 }
 
 // LimitReachedHandler is an handler used to inform when the limit has exceeded.