middleware stacking bug fix

mux.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"slices"
 	"strings"
 	"sync/atomic"
 )
@@ -102,25 +103,19 @@ func (m *Mux) handle(method, pattern string, h http.HandlerFunc, mw ...func(http
 
 	path := fmt.Sprintf("%s %s", method, pattern)
 	if len(mw) > 0 {
-		mws := make([]func(http.Handler) http.Handler, len(m.middlewares)+len(mw))
-		copy(mws, m.middlewares)
-		mws = append(mws, mw...)
+		m.mux.Handle(path, stack(h, copyMW(m.middlewares, mw)))
 	} else {
-		m.mux.Handle(path, stack(m.middlewares, h))
+		m.mux.Handle(path, stack(h, m.middlewares))
 	}
 
 	m.routes.Add(path)
 }
 
 // With adds inline middlewares for an endpoint handler.
-func (m *Mux) With(middleware ...func(http.Handler) http.Handler) *Mux {
-	mws := make([]func(http.Handler) http.Handler, len(m.middlewares)+len(middleware))
-	copy(mws, m.middlewares)
-	mws = append(mws, middleware...)
-
+func (m *Mux) With(mw ...func(http.Handler) http.Handler) *Mux {
 	im := &Mux{
 		mux:         m.mux,
-		middlewares: mws,
+		middlewares: copyMW(m.middlewares, mw),
 		routes:      m.routes,
 	}
 
@@ -160,3 +155,13 @@ func (m *Mux) PrintRoutes(w io.Writer) {
 func (m *Mux) RouteList() []string {
 	return m.routes.All()
 }
+
+func copyMW(a []func(http.Handler) http.Handler, b []func(http.Handler) http.Handler) []func(http.Handler) http.Handler {
+	if len(b) > 0 {
+		return slices.Concat(a, b)
+	}
+
+	mws := make([]func(http.Handler) http.Handler, len(a))
+	copy(mws, a)
+	return mws
+}