nats-io/nats-server · error

no responders requires headers support

Error message

no responders requires headers support

What it means

The client expects no-responders behavior but did not negotiate header support, so the server cannot deliver the 503 no-responders status message on the reply subject. Detected in the publish path; the server sends -ERR and closes the connection with NoRespondersRequiresHeaders.

Source

Thrown at server/errors.go:189

	// ErrRevocation is returned when a credential has been revoked.
	ErrRevocation = errors.New("credentials have been revoked")

	// ErrServerNotRunning is used to signal an error that a server is not running.
	ErrServerNotRunning = errors.New("server is not running")

	// ErrServerNameHasSpaces signals that the server name contains spaces, which is not allowed.
	ErrServerNameHasSpaces = errors.New("server name cannot contain spaces")

	// ErrBadMsgHeader signals the parser detected a bad message header
	ErrBadMsgHeader = errors.New("bad message header detected")

	// ErrMsgHeadersNotSupported signals the parser detected a message header
	// but they are not supported on this server.
	ErrMsgHeadersNotSupported = errors.New("message headers not supported")

	// ErrNoRespondersRequiresHeaders signals that a client needs to have headers
	// on if they want no responders behavior.
	ErrNoRespondersRequiresHeaders = errors.New("no responders requires headers support")

	// ErrClusterNameConfigConflict signals that the options for cluster name in cluster and gateway are in conflict.
	ErrClusterNameConfigConflict = errors.New("cluster name conflicts between cluster and gateway definitions")

	// ErrClusterNameRemoteConflict signals that a remote server has a different cluster name.
	ErrClusterNameRemoteConflict = errors.New("cluster name from remote server conflicts")

	// ErrClusterNameHasSpaces signals that the cluster name contains spaces, which is not allowed.
	ErrClusterNameHasSpaces = errors.New("cluster name cannot contain spaces")

	// ErrClusterNameReserved signals that the cluster name is reserved for internal protocol use.
	ErrClusterNameReserved = errors.New("cluster name is reserved")

	// ErrMalformedSubject is returned when a subscription is made with a subject that does not conform to subject rules.
	ErrMalformedSubject = errors.New("malformed subject")

	// ErrSubscribePermissionViolation is returned when processing of a subscription fails due to permissions.
	ErrSubscribePermissionViolation = errors.New("subscribe permission violation")

View on GitHub (pinned to 3a66a489d2)

Solutions

  1. Enable headers in the client connection options before requesting no-responders
  2. Disable no-responders detection in the client if headers cannot be used
  3. Upgrade the client library to one that negotiates headers automatically
Defensive patterns

Strategy: validation

When it happens

Trigger: Thrown at server/errors.go:189 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/9733a23f2e34026d. Report an issue: GitHub.