grafana/k6 · error

invalid reflect value: '%#v', it needs to be boolean

Error message

invalid reflect value: '%#v', it needs to be boolean

What it means

The reflect option in client.connect(addr, { reflect: true }) enables fetching proto definitions via gRPC server reflection and must be a JS boolean (params.go:173). Strings like 'true', 1, or other types throw 'invalid reflect value'.

Source

Thrown at internal/js/modules/k6/grpc/params.go:175

		switch k {
		case "plaintext":
			var ok bool
			result.IsPlaintext, ok = v.(bool)
			if !ok {
				return result, fmt.Errorf("invalid plaintext value: '%#v', it needs to be boolean", v)
			}
		case "timeout":
			var err error
			result.Timeout, err = types.GetDurationValue(v)
			if err != nil {
				return result, fmt.Errorf("invalid timeout value: %w", err)
			}
		case "reflect":
			var ok bool
			result.UseReflectionProtocol, ok = v.(bool)
			if !ok {
				return result, fmt.Errorf("invalid reflect value: '%#v', it needs to be boolean", v)
			}
		case "reflectMetadata":
			md, err := newMetadata(params.Get(k))
			if err != nil {
				return result, fmt.Errorf("invalid reflectMetadata param: %w", err)
			}

			result.ReflectionMetadata = md
		case "maxReceiveSize":
			var ok bool
			result.MaxReceiveSize, ok = v.(int64)
			if !ok {
				return result, fmt.Errorf("invalid maxReceiveSize value: '%#v', it needs to be an integer", v)
			}
			if result.MaxReceiveSize < 0 {
				return result, fmt.Errorf("invalid maxReceiveSize value: '%#v, it needs to be a positive integer", v)
			}
		case "maxSendSize":

View on GitHub (pinned to 93accf6570)

Solutions

1. Use true/false literals
2. Coerce env values: __ENV.REFLECT === 'true'
3. Fix config parsing to produce booleans

Example fix

// before
client.connect(addr, { reflect: __ENV.REFLECT });

// after
client.connect(addr, { reflect: __ENV.REFLECT === 'true' });

if (connectParams.reflect !== undefined && typeof connectParams.reflect !== 'boolean') {
  throw new Error(`reflect must be boolean, got ${typeof connectParams.reflect}`);
}
client.connect(addr, connectParams);

function toBool(v) {
  if (typeof v === 'boolean') return v;
  if (typeof v === 'string') return v === 'true';
  throw new Error(`expected boolean, got ${typeof v}`);
}

When it happens

Trigger: connect(addr, { reflect: __ENV.REFLECT }); { reflect: 1 }; { reflect: 'yes' }.

Common situations: Env-driven feature toggles; config systems that serialize booleans as strings or integers.

Related errors

• invalid reflectMetadata param: %w
• invalid plaintext value: '%#v', it needs to be boolean
• invalid maxReceiveSize value: '%#v', it needs to be an integ
• invalid maxSendSize value: '%#v', it needs to be an integer
• invalid authority value: '%#v', it needs to be a string

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/7ca29c9ba4d5b5f7. Report an issue: GitHub.