kataras/iris · error

at least one context response handler function is required

Error message

at least one context response handler function is required

What it means

joinContextResponseFuncs composes a list of ContextResponseFunc handlers and panics when the list is empty or the first handler is nil, since composing zero response handlers is meaningless.

Source

Thrown at x/errors/handlers.go:335

// Example Code:
//
//	app.Post("/", errors.Intercept(func(ctx iris.Context, req *CreateRequest, resp *CreateResponse) error{ ... }), errors.CreateHandler(service.Create))
func Intercept[T, R any](responseHandlers ...ContextResponseFunc[T, R]) context.Handler {
	if len(responseHandlers) == 0 {
		return nil
	}

	responseHandler := joinContextResponseFuncs(responseHandlers)

	return func(ctx *context.Context) {
		ctx.Values().Set(contextResponseHandlerFuncKey, responseHandler)
		ctx.Next()
	}
}

func joinContextResponseFuncs[T, R any](responseHandlerFuncs []ContextResponseFunc[T, R]) ContextResponseFunc[T, R] {
	if len(responseHandlerFuncs) == 0 || responseHandlerFuncs[0] == nil {
		panic("at least one context response handler function is required")
	}

	if len(responseHandlerFuncs) == 1 {
		return responseHandlerFuncs[0]
	}

	return func(ctx *context.Context, req T, resp *R) error {
		for _, handler := range responseHandlerFuncs {
			if handler == nil {
				continue
			}

			if err := handler(ctx, req, resp); err != nil {
				return err
			}
		}

		return nil

View on GitHub (pinned to 7bedaf55a0)

Solutions

1. Provide at least one non-nil ContextResponseFunc to Intercept
2. Sanitize the slice (drop nils) before calling Intercept
3. Return a default/no-op handler when the list would be empty

Example fix

// before
resp := xerrors.Intercept(nilHandlers...)
// after
if len(handlers) > 0 && handlers[0] != nil {
    resp = xerrors.Intercept(handlers...)
}

func canJoinResponseFuncs[T, R any](fs []ContextResponseFunc[T, R]) bool {
    return len(fs) > 0 && fs[0] != nil
}

defer func() { if r := recover(); r != nil { log.Printf("response chain panic: %v", r) } }()
h := joinContextResponseFuncs(handlers)

When it happens

Trigger: Calling x/errors Intercept(...) (which calls joinContextResponseFuncs) with no response handlers or with a nil first element.

Common situations: Same as the request-side twin: dynamically built handler slices left empty, or nil entries from map lookups.

Related errors

• at least one context request handler function is required
• iris: switch: hosts: invalid target type: %T
• panic(err)
• panic(err)
• default configuration file '" + filename + "' does not exist

AI-assisted analysis of kataras/iris@7bedaf55a0 (2026-08-30). Data as JSON: /api/errors/8a061958e22e5e73. Report an issue: GitHub.