From ec4a0ac231e7e081fc7e2255a108ae1ab761885e Mon Sep 17 00:00:00 2001
From: Ankit Patial <ankitpatial@gmail.com>
Date: Sat, 16 Aug 2025 19:25:00 +0530
Subject: [PATCH] middleware stacking bug fix

---
 mux.go      | 25 +++++++++++++++----------
 mux_test.go |  2 +-
 resource.go | 13 ++-----------
 stack.go    |  2 +-
 4 files changed, 19 insertions(+), 23 deletions(-)

diff --git a/mux.go b/mux.go
index 13a9187..1b66beb 100644
--- a/mux.go
+++ b/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
+}
diff --git a/mux_test.go b/mux_test.go
index 78ebb34..14fb071 100644
--- a/mux_test.go
+++ b/mux_test.go
@@ -256,7 +256,7 @@ func TestStack(t *testing.T) {
 	})
 
 	middlewares := []func(http.Handler) http.Handler{middleware1, middleware2}
-	stacked := stack(middlewares, handler)
+	stacked := stack(handler, middlewares)
 
 	w := httptest.NewRecorder()
 	r := httptest.NewRequest(http.MethodGet, "/", nil)
diff --git a/resource.go b/resource.go
index 7b3e655..ae718fa 100644
--- a/resource.go
+++ b/resource.go
@@ -34,19 +34,10 @@ func (m *Mux) Resource(pattern string, fn func(res *Resource), mw ...func(http.H
 		panic("mux: Resource() requires callback")
 	}
 
-	// Copy root middlewares.
-	mws := make([]func(http.Handler) http.Handler, len(m.middlewares)+len(mw))
-	copy(mws, m.middlewares)
-
-	// Append inline middlewares.
-	if len(mw) > 0 {
-		mws = append(mws, mw...)
-	}
-
 	fn(&Resource{
 		mux:         m.mux,
 		pattern:     pattern,
-		middlewares: mws,
+		middlewares: copyMW(m.middlewares, mw),
 		routes:      m.routes,
 	})
 }
@@ -130,7 +121,7 @@ func (res *Resource) handlerFunc(method, pattern string, h http.HandlerFunc) {
 	}
 
 	path := fmt.Sprintf("%s %s", method, pattern)
-	res.mux.Handle(path, stack(res.middlewares, h))
+	res.mux.Handle(path, stack(h, res.middlewares))
 }
 
 // Use will register middleware(s) on Router stack.
diff --git a/stack.go b/stack.go
index 633e78f..9eac189 100644
--- a/stack.go
+++ b/stack.go
@@ -3,7 +3,7 @@ package mux
 import "net/http"
 
 // stack middlewares(http handler) in order they are passed (FIFO)
-func stack(middlewares []func(http.Handler) http.Handler, endpoint http.Handler) http.Handler {
+func stack(endpoint http.Handler, middlewares []func(http.Handler) http.Handler) http.Handler {
 	// Return ahead of time if there aren't any middlewares for the chain
 	if len(middlewares) == 0 {
 		return endpoint