nats-io/nats-server · error

expected 'cert_match' to be a valid non-empty string

Error message

expected 'cert_match' to be a valid non-empty string

What it means

ErrBadCertMatchField is a config-validation error raised when the cert_match option is not a string or is empty. cert_match holds the actual value (thumbprint, subject, etc.) used to find the certificate in the store, so it must be present and non-empty.

Source

Thrown at server/certstore/errors.go:69

	ErrFailedX509Extract = errors.New("unable to extract x509 from certificate")

	// ErrBadMatchByType represents unknown CERT_MATCH_BY passed
	ErrBadMatchByType = errors.New("cert match by type not implemented")

	// ErrBadCertStore represents unknown CERT_STORE passed
	ErrBadCertStore = errors.New("cert store type not implemented")

	// ErrConflictCertFileAndStore represents ambiguous configuration of both file and store
	ErrConflictCertFileAndStore = errors.New("'cert_file' and 'cert_store' may not both be configured")

	// ErrBadCertStoreField represents malformed cert_store option
	ErrBadCertStoreField = errors.New("expected 'cert_store' to be a valid non-empty string")

	// ErrBadCertMatchByField represents malformed cert_match_by option
	ErrBadCertMatchByField = errors.New("expected 'cert_match_by' to be a valid non-empty string")

	// ErrBadCertMatchField represents malformed cert_match option
	ErrBadCertMatchField = errors.New("expected 'cert_match' to be a valid non-empty string")

	// ErrBadCaCertMatchField represents malformed cert_match option
	ErrBadCaCertMatchField = errors.New("expected 'ca_certs_match' to be a valid non-empty string array")

	// ErrBadCertMatchSkipInvalidField represents malformed cert_match_skip_invalid option
	ErrBadCertMatchSkipInvalidField = errors.New("expected 'cert_match_skip_invalid' to be a boolean")

	// ErrOSNotCompatCertStore represents cert_store passed that exists but is not valid on current OS
	ErrOSNotCompatCertStore = errors.New("cert_store not compatible with current operating system")
)

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Provide the actual match value, e.g. cert_match: "AB12CD34..." (thumbprint without spaces, correct case per the matcher).
2. Verify any env substitution ($CERT_MATCH) resolves to a non-empty value in the server environment.
3. Quote the value in YAML/JSON to keep it a string.
4. Cross-check the value against `certutil -store My` output so it exactly matches an existing certificate.

Example fix

// before
cert_match: ${CERT_MATCH}   # unset
// after
cert_match: "AB12CD34EF56..."

if s, ok := cfg.TLS.CertMatch.(string); !ok || s == "" {
    return errors.New("cert_match must be a non-empty string")
}

func isBadCertMatchField(err error) bool { return errors.Is(err, certstore.ErrBadCertMatchField) }

if ce, ok := err.(*server.configErr); ok && strings.Contains(ce.Error(), "cert_match") {
    // supply the thumbprint/subject value
}

When it happens

Trigger: server/opts.go:5294 — TLS config parsing: the cert_match value fails the string/non-empty check, returning &configErr{tk, certstore.ErrBadCertMatchField.Error()}; tc.CertMatch is only set once validation passes.

Common situations: Thumbprint pasted with surrounding whitespace removed wrongly, env var not set leaving an empty value, or config template rendering dropping the field.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• expected 'cert_store' to be a valid non-empty string
• expected 'cert_match_by' to be a valid non-empty string
• 'cert_file' and 'cert_store' may not both be configured
• invalid chain link
• ErrBadCryptoStoreProvider

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/a4d9ecbe4bd1bdfe. Report an issue: GitHub.