What causes "no gRPC connection, you must call connect first" in grafana/k6?

Call `client.connect(address, params)` and let it finish before `new grpc.Stream(...)`

no gRPC connection, you must call connect first

Error message

no gRPC connection, you must call connect first

What it means

After a `grpc.Client` is created, its internal `conn` field is nil until `connect()` succeeds (and `close()` resets it to nil). extractClient (internal/js/modules/k6/grpc/grpc.go:179) rejects such a disconnected client with "no gRPC connection, you must call connect first" when it is passed to `new grpc.Stream(client, ...)`. It means you have a valid Client object that has no live connection.

Source

Thrown at internal/js/modules/k6/grpc/grpc.go:180

		common.Throw(rt, err)
	}

	return s.obj
}

// extractClient extracts & validates a grpc.Client from a sobek.Value.
func extractClient(v sobek.Value, rt *sobek.Runtime) (*Client, error) {
	if common.IsNullish(v) {
		return nil, errors.New("empty gRPC client")
	}

	client, ok := v.ToObject(rt).Export().(*Client)
	if !ok {
		return nil, errors.New("not a gRPC client")
	}

	if client.conn == nil {
		return nil, errors.New("no gRPC connection, you must call connect first")
	}

	return client, nil
}

View on GitHub (pinned to 93accf6570)

Solutions

Call `client.connect(address, params)` and let it finish before `new grpc.Stream(...)`
If the client was closed, create a new Client and connect again
Ensure connect() is not inside a try/catch that silently continues on failure

Example fix

// before
const client = new grpc.Client();
const stream = new grpc.Stream(client, '/svc/Method');

// after
const client = new grpc.Client();
client.connect('localhost:8080');
const stream = new grpc.Stream(client, '/svc/Method');

Defensive patterns

Strategy: validation

Validate before calling

const client = new grpc.Client();
client.connect(addr); // throws on failure — do not swallow
// immediately usable; keep a single owner for the client lifecycle

Try / catch

try {
  const stream = new grpc.Stream(client, method);
} catch (e) {
  if (String(e.message).includes('must call connect first')) {
    client.connect(addr); // or re-create the client
    throw e; // next iteration will succeed, or retry here
  }
  throw e;
}

Prevention

Call connect() immediately after `new grpc.Client()` in the same statement block
Do not call client.close() mid-iteration if the client is reused by later iterations — close in teardown or at end-of-life only
Never wrap connect() in a try/catch that continues execution on failure

When it happens

Trigger: Creating `const client = new grpc.Client()` and constructing a Stream without ever calling `client.connect(addr)`; reusing a client after `client.close()` (conn is reset to nil); a connect attempt that failed before the Stream was built.

Common situations: Forgetting connect() when splitting setup across functions; reusing a shared client across iterations after closing it at the end of a previous iteration; connect failure being swallowed earlier in the code.

Related errors

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/66c956fdd3118971. Report an issue: GitHub.