micro/go-micro · error

flow: Verify requires a body step

Error message

flow: Verify requires a body step

What it means

flow.Verify wraps a body step with a retry-and-grade loop; this error is returned at run time when the wrapped body step is nil. Verify cannot retry a step that does not exist, so the returned State is passed through unchanged with this error. It indicates a programming mistake in how Verify was called, not a runtime failure of the body itself.

Source

Thrown at flow/verify.go:69

// JSON field named "feedback" (or VerifyFeedbackField). When all attempts fail,
// it returns the last output without error, annotated with verification fields so
// the run can keep the bounded failure outcome in its state:
// "verification_passed": false, "verification_feedback", and
// "verification_attempts".
func Verify(body StepFunc, grader Grader, opts ...VerifyOption) StepFunc {
	o := VerifyOptions{MaxAttempts: 2, FeedbackField: "feedback"}
	for _, op := range opts {
		op(&o)
	}
	if o.MaxAttempts <= 0 {
		o.MaxAttempts = 2
	}
	if o.FeedbackField == "" {
		o.FeedbackField = "feedback"
	}
	return func(ctx context.Context, in State) (State, error) {
		if body == nil {
			return in, fmt.Errorf("flow: Verify requires a body step")
		}
		if grader == nil {
			return in, fmt.Errorf("flow: Verify requires a grader")
		}
		cur := in
		last := in
		feedback := ""
		for attempt := 1; attempt <= o.MaxAttempts; attempt++ {
			if err := ctx.Err(); err != nil {
				return last, err
			}
			if feedback != "" {
				var err error
				cur, err = stateWithField(cur, o.FeedbackField, feedback)
				if err != nil {
					return last, err
				}
			}

View on GitHub (pinned to 24529f1404)

Solutions

1. Pass a non-nil Step function as the body argument to flow.Verify.
2. Guard the call site: only wrap with Verify when the body was successfully constructed.
3. Fail fast at construction time by checking body != nil before calling Verify instead of at run time.

Example fix

// before
var body flow.StepFunc // nil
return flow.Verify(body, grader)
// after
if body == nil {
    return nil, fmt.Errorf("body step not configured")
}
return flow.Verify(body, grader)

if body == nil {
    return nil, errors.New("verify: body step must be configured")
}
return flow.Verify(body, grader), nil

func bodyConfigured(f flow.StepFunc) bool { return f != nil }

out, err := verifiedStep(ctx, in)
if err != nil && strings.Contains(err.Error(), "Verify requires a body step") {
    // configuration bug: fix flow wiring, not a runtime condition
}

When it happens

Trigger: Calling flow.Verify(nil, grader) or Verify with a body variable that was declared but never assigned, so the returned step function returns "flow: Verify requires a body step" on first execution.

Common situations: Conditionally assigning the body step and a branch leaving it nil; passing the result of a factory that can return nil; refactoring that removed the body but kept the Verify wrapper.

Related errors

• flow: Verify requires a grader
• verify attempt %d: %w
• verify grade attempt %d: %w
• flow: LLMGrader requires a flow model (set Provider/APIKey)
• LLM step requires a flow model (set Provider/APIKey)

AI-assisted analysis of micro/go-micro@24529f1404 (2026-09-01). Data as JSON: /api/errors/7702dfe48ed99419. Report an issue: GitHub.