at least one context request handler function is required

Error message

at least one context request handler function is required

What it means

joinContextRequestFuncs combines a variadic list of ContextRequestFunc handlers; it panics when the list is empty or its first element is nil, because there must be at least one handler to compose and return.

Source

Thrown at x/errors/handlers.go:233

//			validation.Slice("hobbies", r.Hobbies).Length(1, 10),
//		)
//	}
func Validation[T any](validators ...ContextRequestFunc[T]) context.Handler {
	if len(validators) == 0 {
		return nil
	}

	validator := joinContextRequestFuncs(validators)

	return func(ctx *context.Context) {
		ctx.Values().Set(contextRequestHandlerFuncKey, validator)
		ctx.Next()
	}
}

func joinContextRequestFuncs[T any](requestHandlerFuncs []ContextRequestFunc[T]) ContextRequestFunc[T] {
	if len(requestHandlerFuncs) == 0 || requestHandlerFuncs[0] == nil {
		panic("at least one context request handler function is required")
	}

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

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

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

		return nil

View on GitHub (pinned to 7bedaf55a0)

Solutions

Pass at least one non-nil ContextRequestFunc to Validation
Filter nil handlers before building the chain
Guard the call site: only call Validation when len(handlers) > 0

Example fix

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

Defensive patterns

Strategy: validation

Validate before calling

func canJoinRequestFuncs[T any](fs []ContextRequestFunc[T]) bool {
    return len(fs) > 0 && fs[0] != nil
}

Try / catch

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

Prevention

Never append nil handlers to handler slices
Check slice length before composing chains
Use builder helpers that reject nil entries early

When it happens

Trigger: Calling x/errors Validation(...) (which calls joinContextRequestFuncs) with zero handler functions or with handlers[0] == nil.

Common situations: Building a validation chain dynamically by appending handlers in a loop that appends nothing; accidentally appending a nil handler from an uninitialized variable.

Related errors

AI-assisted analysis of kataras/iris@7bedaf55a0 (2026-08-30). Data as JSON: /api/errors/1c5ed81185ca66f8. Report an issue: GitHub.