kataras/iris · error

makeHandler: function is nil

Error message

makeHandler: function is nil

What it means

makeHandler requires a non-nil function/value to convert into an Iris request handler. A nil fn produces an unusable handler, so it panics immediately.

Source

Thrown at hero/handler.go:98

			_, _ = ctx.WriteString(err.Error())
		}

		ctx.StopExecution()
	})
)

var (
	irisHandlerType     = reflect.TypeOf((*context.Handler)(nil)).Elem()
	irisHandlerFuncType = reflect.TypeOf(func(*context.Context) {})
)

func isIrisHandlerType(typ reflect.Type) bool {
	return typ == irisHandlerType || typ == irisHandlerFuncType
}

func makeHandler(fn any, c *Container, paramsCount int) context.Handler {
	if fn == nil {
		panic("makeHandler: function is nil")
	}

	// 0. A normal handler.
	if handler, ok := isHandler(fn); ok {
		return handler
	}

	// 1. A handler which returns just an error, handle it faster.
	if handlerWithErr, ok := isHandlerWithError(fn); ok {
		return func(ctx *context.Context) {
			if err := handlerWithErr(ctx); err != nil {
				c.GetErrorHandler(ctx).HandleError(ctx, err)
			}
		}
	}

	v := valueOf(fn)
	typ := v.Type()

View on GitHub (pinned to 7bedaf55a0)

Solutions

1. Verify the function is assigned before registering: if h == nil { panic } before c.Handler(h).
2. Check controller initialization order so method values are non-nil.
3. For interface methods, ensure the concrete controller is initialized.

Example fix

// before
var handler context.Handler // nil
app.Handle("GET", "/", handler)
// after
handler := myController.Index
if handler == nil { panic("handler not set") }
app.Handle("GET", "/", handler)

if handlerFn == nil { panic("handler function not initialized") }
app.Handle("GET", "/", handlerFn)

func nonNilHandler(fn any) bool { return fn != nil && !reflect.ValueOf(fn).IsNil() }

When it happens

Trigger: Calling c.Handler(nil), HandlerWithParams(nil, ...), or MethodHandler with a nil method value (e.g. an interface method on a nil struct pointer).

Common situations: A controller field/method that is nil because initialization failed; conditional assignment left the handler unset; a typed-nil func variable var h func(ctx iris.Context) passed directly.

Related errors

• makeHandler: func(...<T>) iris.Handler: expected %d function
• toml: %w
• toml :%w
• unexpected "fsOrDir" argument type of %T (string or fs.FS or
• Passed handler cannot be converted directly: - http.H

AI-assisted analysis of kataras/iris@7bedaf55a0 (2026-08-30). Data as JSON: /api/errors/d46fc297cdd4a69b. Report an issue: GitHub.