juanfont/headscale · error

leading 0 not permitted in protocol number

Error message

leading 0 not permitted in protocol number

What it means

Returned by Protocol.validate (hscontrol/policy/v2/types.go:1770) when a numeric "proto" value starts with a zero — including the bare string "0" — mirroring Tailscale's strict parsing. Leading-zero forms like "006" or "017" are rejected even though they'd be numerically valid, to keep canonical representation.

Source

Thrown at hscontrol/policy/v2/types.go:132

	ErrHostResolve                 = errors.New("error resolving host")
	ErrInvalidPrefix               = errors.New("invalid prefix")
	ErrInvalidAutogroup            = errors.New("invalid autogroup")
	ErrUnknownAutogroup            = errors.New("unknown autogroup")
	ErrHostportMissingColon        = errors.New("hostport must contain a colon")
	ErrTypeNotSupported            = errors.New("type not supported")
	ErrInvalidAlias                = errors.New("invalid alias format")
	ErrInvalidAutoApprover         = errors.New("invalid auto approver format")
	ErrInvalidOwner                = errors.New("invalid owner format")
	ErrGroupNotDefined             = errors.New("group not defined in policy")
	ErrInvalidGroupMember          = errors.New("invalid group member type")
	ErrGroupValueNotArray          = errors.New("group value must be an array of users")
	ErrInvalidHostIP               = errors.New("hostname contains invalid IP address")
	ErrTagNotDefined               = errors.New("tag not found")
	ErrAutoApproverNotAlias        = errors.New("auto approver is not an alias")
	ErrInvalidACLAction            = errors.New("invalid ACL action")
	ErrInvalidSSHAction            = errors.New("invalid SSH action")
	ErrInvalidProtocolNumber       = errors.New("invalid protocol number")
	ErrProtocolLeadingZero         = errors.New("leading 0 not permitted in protocol number")
	ErrProtocolOutOfRange          = errors.New("protocol number out of range (0-255)")
	ErrAutogroupNotSupported       = errors.New("autogroup not supported in headscale")
	ErrAutogroupInternetSrc        = errors.New("autogroup:internet can only be used in ACL destinations")
	ErrAutogroupSelfSrc            = errors.New("\"autogroup:self\" not valid on the src side of a rule")
	ErrAutogroupNotSupportedACLSrc = errors.New("autogroup not supported for ACL sources")
	ErrAutogroupNotSupportedACLDst = errors.New("autogroup not supported for ACL destinations")
	ErrAutogroupDangerAllDst       = errors.New("cannot use autogroup:danger-all as a dst")
	ErrAutogroupNotSupportedSSHSrc = errors.New("autogroup not supported for SSH sources")
	ErrAutogroupNotSupportedSSHDst = errors.New("autogroup not supported for SSH destinations")
	ErrHostNotDefined              = errors.New("host not defined in policy")
	ErrSSHSourceAliasNotSupported  = errors.New("alias not supported for SSH source")
	ErrSSHDestAliasNotSupported    = errors.New("alias not supported for SSH destination")
	ErrUnknownField                = errors.New("unknown field")
	ErrProtocolNoSpecificPorts     = errors.New("protocol does not support specific ports")
	ErrTestEmptyAssertions         = errors.New("test entry must have at least one of \"accept\" or \"deny\"")
	ErrTestProtocolNotAllowed      = errors.New("test protocol must be tcp, udp, sctp, or empty")
	ErrTestDestinationMultiPort    = errors.New("test destination port must be a single port")
	ErrTestDestinationCIDR         = errors.New("test destination must be a single host, not a CIDR range")

View on GitHub (pinned to 565fd254d0)

Solutions

1. Strip leading zeros: "06" → "6", "017" → "17"
2. Prefer the protocol name (tcp, udp, ...) where one exists
3. For protocol 0, omit "proto" from the rule instead of writing "0"

Example fix

// before
{"action": "accept", "proto": "017", "src": ["*"], "dst": ["tag:dns:53"]}

// after
{"action": "accept", "proto": "udp", "src": ["*"], "dst": ["tag:dns:53"]}

func canonicalProto(s string) bool {
	if len(s) > 1 && s[0] == '0' {
		return false // leading zero
	}
	return s != "0"
}

func isProtocolLeadingZero(err error) bool {
	return errors.Is(err, policy.ErrProtocolLeadingZero)
}

if err := json.Unmarshal(b, &acl); err != nil {
	if errors.Is(err, policy.ErrProtocolLeadingZero) {
		return fmt.Errorf("strip leading zeros from proto (and never write \"0\"; omit proto instead): %w", err)
	}
	return err
}

When it happens

Trigger: Policy with "proto": "006", "proto": "017", or "proto": "0". Note that the bare "0" also triggers this even though 0 is in the valid numeric range; there is no way to write protocol 0 numerically.

Common situations: Zero-padding protocol numbers for alignment, copying fixed-width tables, or scripts generating policies with %03d formatting.

Related errors

• invalid protocol number
• protocol number out of range (0-255)
• protocol does not support specific ports
• proto name "*" not known; use protocol number 0-255 or proto
• test(s) failed

AI-assisted analysis of juanfont/headscale@565fd254d0 (2026-08-15). Data as JSON: /api/errors/a5c0bdb067c48d14. Report an issue: GitHub.