fix(router): tree bug where loop index is not decremented. (#3460)

fixes https://github.com/gin-gonic/gin/issues/3459

routes_test.go

@@ -670,3 +670,22 @@ func TestRouteContextHoldsFullPath(t *testing.T) {
 	w := PerformRequest(router, http.MethodGet, "/not-found")
 	assert.Equal(t, http.StatusNotFound, w.Code)
 }
+
+func TestEngineHandleMethodNotAllowedCornerCase(t *testing.T) {
+	r := New()
+	r.HandleMethodNotAllowed = true
+
+	base := r.Group("base")
+	base.GET("/metrics", handlerTest1)
+
+	v1 := base.Group("v1")
+
+	v1.GET("/:id/devices", handlerTest1)
+	v1.GET("/user/:id/groups", handlerTest1)
+
+	v1.GET("/orgs/:id", handlerTest1)
+	v1.DELETE("/orgs/:id", handlerTest1)
+
+	w := PerformRequest(r, "GET", "/base/v1/user/groups")
+	assert.Equal(t, http.StatusNotFound, w.Code)
+}

tree.go

@@ -459,9 +459,9 @@ walk: // Outer loop for walking the tree
 					// If the path at the end of the loop is not equal to '/' and the current node has no child nodes
 					// the current node needs to roll back to last valid skippedNode
 					if path != "/" {
-						for l := len(*skippedNodes); l > 0; {
-							skippedNode := (*skippedNodes)[l-1]
-							*skippedNodes = (*skippedNodes)[:l-1]
+						for length := len(*skippedNodes); length > 0; length-- {
+							skippedNode := (*skippedNodes)[length-1]
+							*skippedNodes = (*skippedNodes)[:length-1]
 							if strings.HasSuffix(skippedNode.path, path) {
 								path = skippedNode.path
 								n = skippedNode.node
@@ -576,9 +576,9 @@ walk: // Outer loop for walking the tree
 			// If the current path does not equal '/' and the node does not have a registered handle and the most recently matched node has a child node
 			// the current node needs to roll back to last valid skippedNode
 			if n.handlers == nil && path != "/" {
-				for l := len(*skippedNodes); l > 0; {
-					skippedNode := (*skippedNodes)[l-1]
-					*skippedNodes = (*skippedNodes)[:l-1]
+				for length := len(*skippedNodes); length > 0; length-- {
+					skippedNode := (*skippedNodes)[length-1]
+					*skippedNodes = (*skippedNodes)[:length-1]
 					if strings.HasSuffix(skippedNode.path, path) {
 						path = skippedNode.path
 						n = skippedNode.node
@@ -633,9 +633,9 @@ walk: // Outer loop for walking the tree
 
 		// roll back to last valid skippedNode
 		if !value.tsr && path != "/" {
-			for l := len(*skippedNodes); l > 0; {
-				skippedNode := (*skippedNodes)[l-1]
-				*skippedNodes = (*skippedNodes)[:l-1]
+			for length := len(*skippedNodes); length > 0; length-- {
+				skippedNode := (*skippedNodes)[length-1]
+				*skippedNodes = (*skippedNodes)[:length-1]
 				if strings.HasSuffix(skippedNode.path, path) {
 					path = skippedNode.path
 					n = skippedNode.node