What causes "invalid port (type %T): %v" in slackhq/nebula?

Set port as a plain integer: port: 4242

invalid port (type %T): %v

Error message

invalid port (type %T): %v

What it means

This error is returned by newCalculatedRemotesEntryFromConfig when the 'port' value in a calculated_remotes entry is neither an int nor a string (the Go dynamic type is reported via %T). Config values of unsupported types such as bool, float, lists, or nested maps cannot be interpreted as a port.

Source

Thrown at calculated_remote.go:159

	if err != nil {
		return nil, fmt.Errorf("invalid mask: %s", rawMask)
	}

	var port int
	rawValue = rawMap["port"]
	if rawValue == nil {
		return nil, fmt.Errorf("missing port: %v", rawMap)
	}
	switch v := rawValue.(type) {
	case int:
		port = v
	case string:
		port, err = strconv.Atoi(v)
		if err != nil {
			return nil, fmt.Errorf("invalid port: %s: %w", v, err)
		}
	default:
		return nil, fmt.Errorf("invalid port (type %T): %v", rawValue, rawValue)
	}

	return newCalculatedRemote(cidr, maskCidr, port)
}

View on GitHub (pinned to dd8f660c0a)

Solutions

Set port as a plain integer: port: 4242
Quote the value to force string type if your YAML tooling mangles it: port: "4242"
Check indentation so the port value is a scalar, not a nested structure

Example fix

// before
calculated_remotes:
  - mask: 10.0.0.0/8
    port:
      main: 4242
// after
calculated_remotes:
  - mask: 10.0.0.0/8
    port: 4242

Defensive patterns

Strategy: type-guard

Validate before calling

func isScalarPort(v any) bool {
    switch t := v.(type) {
    case int:
        return t > 0 && t <= 65535
    case string:
        return validPortString(t)
    default:
        return false
    }
}

Type guard

func isIntLike(raw any) bool {
    switch raw.(type) {
    case int, string:
        return true
    default:
        return false
    }
}

Try / catch

if err != nil {
    if strings.Contains(err.Error(), "invalid port (type") {
        log.Fatalf("calculated_remotes port has unsupported YAML type: %v", err)
    }
    return err
}

Prevention

Ensure the port value is a YAML scalar; watch indentation that creates maps
Avoid YAML booleans (yes/no/on) and floats as port values
Validate types with a config schema (e.g. JSON Schema over the YAML) before load

When it happens

Trigger: Setting port in a calculated_remotes entry to a non-scalar type, e.g. port: true, port: 4242.5 (parsed as float), or a list/map value in the YAML.

Common situations: YAML misconfiguration where the port line is accidentally structured (extra indentation making it a map), boolean-ish values like yes/no, or float-looking numbers.

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

AI-assisted analysis of slackhq/nebula@dd8f660c0a (2026-09-03). Data as JSON: /api/errors/888a5aa2c022b289. Report an issue: GitHub.