fix(subrouter): stop aliasing route.params via Context.paramsKeys

Author: tigerwill90

context.go

@@ -96,6 +96,7 @@ func (c *Context) reset(w http.ResponseWriter, r *http.Request) {
 	c.cachedQueries = nil
 	c.scope = RouteHandler
 	*c.params = (*c.params)[:0]
+	*c.paramsKeys = (*c.paramsKeys)[:0]
 	*c.subPatterns = (*c.subPatterns)[:0]
 }
 
@@ -105,6 +106,7 @@ func (c *Context) resetNil() {
 	c.cachedQueries = nil
 	c.route = nil
 	*c.params = (*c.params)[:0]
+	*c.paramsKeys = (*c.paramsKeys)[:0]
 	*c.subPatterns = (*c.subPatterns)[:0]
 }
 
@@ -126,6 +128,7 @@ func (c *Context) resetWithWriter(w ResponseWriter, r *http.Request) {
 	c.cachedQueries = nil
 	c.scope = RouteHandler
 	*c.params = (*c.params)[:0]
+	*c.paramsKeys = (*c.paramsKeys)[:0]
 	*c.subPatterns = (*c.subPatterns)[:0]
 }
 
@@ -188,8 +191,9 @@ func (c *Context) ClientIP() (*net.IPAddr, error) {
 // Params returns an iterator over the matched wildcard parameters for the current route.
 func (c *Context) Params() iter.Seq[Param] {
 	return func(yield func(Param) bool) {
+		keys := c.keys()
 		for i, p := range *c.params {
-			if !yield(Param{Key: (*c.paramsKeys)[i], Value: p}) {
+			if !yield(Param{Key: keys[i], Value: p}) {
 				return
 			}
 		}
@@ -198,15 +202,25 @@ func (c *Context) Params() iter.Seq[Param] {
 
 // Param retrieve a matching wildcard segment by name.
 func (c *Context) Param(name string) string {
-	for i := range *c.params {
-		key := (*c.paramsKeys)[i]
-		if key == name {
-			return (*c.params)[i]
+	keys := c.keys()
+	for i, p := range *c.params {
+		if keys[i] == name {
+			return p
 		}
 	}
 	return ""
 }
 
+func (c *Context) keys() []string {
+	if len(*c.paramsKeys) > 0 {
+		return *c.paramsKeys
+	}
+	if c.route != nil {
+		return c.route.params
+	}
+	return nil
+}
+
 // Method returns the request method.
 func (c *Context) Method() string {
 	return c.req.Method

fox.go

@@ -398,7 +398,6 @@ func (fox *Router) Lookup(w ResponseWriter, r *http.Request) (route *Route, cc *
 	if n != nil {
 		c.route = n.routes[idx]
 		c.pattern = c.route.pattern.str
-		*c.paramsKeys = c.route.params
 		return c.route, c, tsr
 	}
 
@@ -611,7 +610,6 @@ func (fox *Router) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if !tsr && n != nil {
 		c.route = n.routes[idx]
 		c.pattern = c.route.pattern.str
-		*c.paramsKeys = c.route.params
 		c.route.hall(c)
 		return
 	}
@@ -622,7 +620,6 @@ func (fox *Router) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 			if route.handleSlash == RelaxedSlash {
 				c.route = route
 				c.pattern = c.route.pattern.str
-				*c.paramsKeys = c.route.params
 				route.hall(c)
 				return
 			}
@@ -643,7 +640,6 @@ func (fox *Router) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 			if idx, n, tsr := tree.lookup(r.Method, r.Host, CleanPath(path), c, false); n != nil && (!tsr || n.routes[idx].handleSlash == RelaxedSlash) {
 				c.route = n.routes[idx]
 				c.pattern = c.route.pattern.str
-				*c.paramsKeys = c.route.params
 				c.route.hall(c)
 				return
 			}
@@ -977,18 +973,25 @@ func Sub(router *Router) HandlerFunc {
 		*subCtx.subPatterns = append(*subCtx.subPatterns, *c.subPatterns...)
 
 		lastTk := route.pattern.tokens[len(route.pattern.tokens)-1]
+		// For a top-level parent c.paramsKeys is empty, so we
+		// read the last key directly from c.route.params. For nested
+		// sub-routers, c.paramsKeys holds the composed chain.
+		keys := *c.paramsKeys
+		if len(keys) == 0 {
+			keys = c.route.params
+		}
 		var p string
 		switch lastTk.typ {
 		case nodeWildcard:
-			key := (*c.paramsKeys)[len(*c.paramsKeys)-1]
+			key := keys[len(keys)-1]
 			extra := len(key) + wildcardExtraChar
 			if lastTk.regexp != nil {
 				// +1 for the ':' separator between name and regex source.
 				extra += 1 + len(rawExpr(lastTk.regexp))
 			}
 			p = strings.TrimSuffix(c.pattern[:len(c.pattern)-extra], "/")
 		case nodeParam:
-			key := (*c.paramsKeys)[len(*c.paramsKeys)-1]
+			key := keys[len(keys)-1]
 			extra := len(key) + paramExtraChar
 			if lastTk.regexp != nil {
 				extra += 1 + len(rawExpr(lastTk.regexp))
@@ -1029,7 +1032,7 @@ func Sub(router *Router) HandlerFunc {
 		// Subrouters are never evaluated in lazy lookup mode, so params are always
 		// captured. If parent has no params beyond the catch-all, this is a no-op.
 		*subCtx.params = append(*subCtx.params, (*c.params)[:len(*c.params)-1]...)
-		*subCtx.paramsKeys = append((*subCtx.paramsKeys)[:0], (*c.paramsKeys)[:len(*c.paramsKeys)-1]...)
+		*subCtx.paramsKeys = append((*subCtx.paramsKeys)[:0], keys[:len(keys)-1]...)
 
 		// Serve the sub router
 		router.serveSubRouter(subCtx, suffix)

fox_test.go

@@ -1506,6 +1506,26 @@ func TestRouter_ServeHTTP_HandleSubRouter(t *testing.T) {
 		assert.Equal(t, "/api/users", w.Body.String())
 	})
 
+	t.Run("sub-router used directly then via Sub preserves route.params", func(t *testing.T) {
+		sub := MustRouter()
+		subRoute, err := sub.Add(MethodGet, "/users/{id}", emptyHandler)
+		require.NoError(t, err)
+		originalParams := slices.Clone(subRoute.params)
+
+		req := httptest.NewRequest(http.MethodGet, "/users/42", nil)
+		w := httptest.NewRecorder()
+		sub.ServeHTTP(w, req)
+
+		fx := MustRouter()
+		require.NoError(t, onlyError(fx.Add(MethodGet, "/api/{tenant}/+{rest}", Sub(sub))))
+
+		req = httptest.NewRequest(http.MethodGet, "/api/acme/users/42", nil)
+		w = httptest.NewRecorder()
+		fx.ServeHTTP(w, req)
+
+		assert.Equal(t, originalParams, subRoute.params)
+	})
+
 	t.Run("sub-router no route handler sees clean context", func(t *testing.T) {
 		var pat, tenant string
 		var route *Route

txn.go

@@ -327,7 +327,6 @@ func (txn *Txn) Lookup(w ResponseWriter, r *http.Request) (route *Route, cc *Con
 	if n != nil {
 		c.route = n.routes[idx]
 		c.pattern = c.route.pattern.str
-		*c.paramsKeys = c.route.params
 		return c.route, c, tsr
 	}