⚡ perf: reduce avoidable work in the request hot path

app.go

@@ -1548,6 +1548,11 @@ func (app *App) init() *App {
 // error handler. Otherwise, it uses the configured error handler for
 // the app, which if not set is the DefaultErrorHandler.
 func (app *App) ErrorHandler(ctx Ctx, err error) error {
+	// Fast path: no mounted sub-apps, so no prefix lookup is needed
+	if len(app.mountFields.appListKeys) == 0 {
+		return app.config.ErrorHandler(ctx, err)
+	}
+
 	var (
 		mountedErrHandler  ErrorHandler
 		mountedPrefixParts int

ctx.go

@@ -365,11 +365,12 @@ func (c *DefaultCtx) ViewBind(vars Map) error {
 // Route returns the matched Route struct.
 func (c *DefaultCtx) Route() *Route {
 	if c.route == nil {
-		// Fallback for fasthttp error handler
+		// Fallback for fasthttp error handler; equals c.Method() without
+		// the variadic call so Route stays within the inlining budget
 		return &Route{
 			path:     c.pathOriginal,
 			Path:     c.pathOriginal,
-			Method:   c.Method(),
+			Method:   c.app.method(c.methodInt),
 			Handlers: emptyRouteHandlers[:],
 			Params:   emptyRouteParams[:],
 		}

path.go

@@ -520,9 +520,10 @@ func (parser *routeParser) getMatch(detectionPath, path string, params *[maxPara
 			i = segment.Length
 			// is optional part or the const part must match with the given string
 			// check if the end of the segment is an optional slash
+			// the unsigned compare proves 0 <= i <= len(detectionPath), keeping detectionPath[:i] bounds-check free
 			if segment.HasOptionalSlash && partLen == i-1 && detectionPath == segment.Const[:i-1] {
 				i--
-			} else if i > partLen || detectionPath[:i] != segment.Const {
+			} else if uint(i) > uint(len(detectionPath)) || detectionPath[:i] != segment.Const {
 				return false
 			}
 		} else {

router.go

@@ -232,15 +232,11 @@ func (app *App) next(c *DefaultCtx) (bool, error) {
 	if !ok {
 		tree = app.treeStack[methodInt][0]
 	}
-	lenr := len(tree) - 1
-
-	indexRoute := c.indexRoute
-
-	// Loop over the route stack starting from previous index
-	for indexRoute < lenr {
-		// Increment route index
-		indexRoute++
+	indexRoute := max(c.indexRoute+1, 0)
 
+	// Loop over the route stack starting from previous index;
+	// the clamp above plus the len(tree) guard keep tree[indexRoute] bounds-check free
+	for ; indexRoute < len(tree); indexRoute++ {
 		// Get *Route
 		route := tree[indexRoute]
 
@@ -337,15 +333,11 @@ func (app *App) nextCustom(c CustomCtx) (bool, error) {
 	if !ok {
 		tree = app.treeStack[methodInt][0]
 	}
-	lenr := len(tree) - 1
-
-	indexRoute := c.getIndexRoute()
-
-	// Loop over the route stack starting from previous index
-	for indexRoute < lenr {
-		// Increment route index
-		indexRoute++
+	indexRoute := max(c.getIndexRoute()+1, 0)
 
+	// Loop over the route stack starting from previous index;
+	// the clamp above plus the len(tree) guard keep tree[indexRoute] bounds-check free
+	for ; indexRoute < len(tree); indexRoute++ {
 		// Get *Route
 		route := tree[indexRoute]