thanos-io/thanos · error

empty alertState

Error message

empty alertState

What it means

Raised in AlertState.UnmarshalJSON as a guard: the unquoted alert-state string is empty, meaning the JSON payload contained "" (or an escaped empty string) for the rule state, which maps to no valid AlertState value.

Solutions

1. Provide a non-empty state string such as "firing", "pending", or "inactive"
2. Fix the producer that emits empty state fields
3. Add client-side validation to reject empty state before decoding

When it happens

Trigger: Thrown at pkg/rules/rulespb/custom.go:279 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/94eb0468b2abcd06. Report an issue: GitHub.

Appendix: source

Thrown at pkg/rules/rulespb/custom.go:279

}

func (r *RuleGroup) MarshalJSON() ([]byte, error) {
	if r.Rules == nil {
		// Ensure that empty slices are marshaled as '[]' and not 'null'.
		r.Rules = make([]*Rule, 0)
	}
	type plain RuleGroup
	return json.Marshal((*plain)(r))
}

func (x *AlertState) UnmarshalJSON(entry []byte) error {
	fieldStr, err := strconv.Unquote(string(entry))
	if err != nil {
		return errors.Wrapf(err, "alertState: unquote %v", string(entry))
	}

	if fieldStr == "" {
		return errors.New("empty alertState")
	}

	state, ok := AlertState_value[strings.ToUpper(fieldStr)]
	if !ok {
		return errors.Errorf("unknown alertState: %v", string(entry))
	}
	*x = AlertState(state)
	return nil
}

func (x *AlertState) MarshalJSON() ([]byte, error) {
	return []byte(strconv.Quote(strings.ToLower(x.String()))), nil
}

// Compare compares alert state x and y and returns:
//
//	< 0 if x < y  (alert state x is more critical than alert state y)
//	  0 if x == y

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