grafana/k6 · error

invalid GRPC Stream's method: %w

Error message

invalid GRPC Stream's method: %w

What it means

The method name passed to new grpc.Stream() must resolve to a protobuf MethodDescriptor known by that client. client.getMethodDescriptor() only knows services loaded in init via client.load(importPaths, protoFiles) or discovered through server reflection (client.connect(addr, { reflect: true })). An unknown service/method name, a missing or unloaded proto, or a reflection lookup failure produces this error.

Source

Thrown at internal/js/modules/k6/grpc/grpc.go:123

func (mi *ModuleInstance) Exports() modules.Exports {
	return modules.Exports{
		Named: mi.exports,
	}
}

// stream returns a new stream object
func (mi *ModuleInstance) stream(c sobek.ConstructorCall) *sobek.Object {
	rt := mi.vu.Runtime()

	client, err := extractClient(c.Argument(0), rt)
	if err != nil {
		common.Throw(rt, fmt.Errorf("invalid GRPC Stream's client: %w", err))
	}

	methodName := sanitizeMethodName(c.Argument(1).String())
	methodDescriptor, err := client.getMethodDescriptor(methodName)
	if err != nil {
		common.Throw(rt, fmt.Errorf("invalid GRPC Stream's method: %w", err))
	}

	p, err := newCallParams(mi.vu, c.Argument(2))
	if err != nil {
		common.Throw(rt, fmt.Errorf("invalid GRPC Stream's parameters: %w", err))
	}

	p.SetSystemTags(mi.vu.State(), client.addr, methodName)

	logger := mi.vu.State().Logger.WithField("streamMethod", methodName)

	s := &stream{
		vu:               mi.vu,
		client:           client,
		methodDescriptor: methodDescriptor,
		method:           methodName,
		logger:           logger,

View on GitHub (pinned to 93accf6570)

Solutions

1. Open the .proto and copy the method path exactly as package.Service/Method; ensure client.load() runs in init code and its import path resolves the proto's package declaration
2. If using server reflection, connect with { reflect: true } and confirm the server actually implements the reflection service
3. Check the results of client.load() and the connect() call for earlier failures before constructing the Stream

Example fix

// before
client.connect('localhost:8080');
const stream = new grpc.Stream(client, '/testing.TestService/ServerStream');

// after
client.load(['protobufs'], 'service.proto'); // defines package testing
client.connect('localhost:8080');
const stream = new grpc.Stream(client, '/testing.TestService/ServerStream');

// No public JS API lists loaded methods; at minimum assert the proto loaded
const loaded = client.load(['protobufs'], 'service.proto');
if (!loaded || loaded.length === 0) {
  throw new Error('service.proto failed to load; refusing to build a stream');
}

let stream;
try {
  stream = new grpc.Stream(client, METHOD);
} catch (err) {
  if (String(err.message).includes("invalid GRPC Stream's method")) {
    console.error(`method ${METHOD} unknown: check client.load() paths or enable server reflection with reflect: true`);
  }
  throw err;
}

When it happens

Trigger: client.load() not called (or called with a wrong import path / proto file) before new grpc.Stream; a typo in the fully qualified name like '/grpc.testing.TestService/StreamingOutputCall'; relying on reflection while the server does not implement the gRPC reflection service or reflect:true was not passed to connect().

Common situations: Method renamed or moved in a new .proto revision; scripts copied from another service with a different package name; reflection enabled in dev but disabled in the load-test environment; missing leading slash or wrong package qualification.

Related errors

• can't convert method info: %w
• invalid GRPC Stream's client: %w
• invalid GRPC Stream's parameters: %w
• unknown GRPC stream's event type: %s
• invalid reflect value: '%#v', it needs to be boolean

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/4edefc3508d71683. Report an issue: GitHub.