grpc/grpc-go · error

/ must come in between service and method, only one /

Error message

/ must come in between service and method, only one /

What it means

Returned by validateMethodString (gcp/observability/config.go:65) when strings.Split(method, "/") does not yield exactly two parts. This means there is either no '/' at all, or more than one '/' (e.g. 'foo', 'a/b/c'). The observability config requires exactly one '/' separating the fully-qualified service name from the method name.

Source

Thrown at gcp/observability/config.go:65

		return ""
	}
	if credentials.ProjectID == "" {
		logger.Infof("Failed to find project ID in default credential: %v", err)
		return ""
	}
	logger.Infof("Found project ID from Google Default Credential: %v", credentials.ProjectID)
	return credentials.ProjectID
}

// validateMethodString validates whether the string passed in is a valid
// pattern.
func validateMethodString(method string) error {
	if strings.HasPrefix(method, "/") {
		return errors.New("cannot have a leading slash")
	}
	serviceMethod := strings.Split(method, "/")
	if len(serviceMethod) != 2 {
		return errors.New("/ must come in between service and method, only one /")
	}
	if serviceMethod[1] == "" {
		return errors.New("method name must be non empty")
	}
	if serviceMethod[0] == "*" {
		return errors.New("cannot have service wildcard * i.e. (*/m)")
	}
	return nil
}

func validateLogEventMethod(methods []string, exclude bool) error {
	for _, method := range methods {
		if method == "*" {
			if exclude {
				return errors.New("cannot have exclude and a '*' wildcard")
			}
			continue
		}

View on GitHub (pinned to 03255a9237)

Solutions

1. Ensure each method entry has exactly one '/' between service and method: <package>.<Service>/<Method>.
2. Strip accidental trailing slashes and avoid extra path segments.
3. Lint the methods list before deploying the config.

Example fix

// before
{"methods":["foo.Bar"]}        // no '/'
{"methods":["foo.Bar/Baz/extra"]} // too many '/'

// after
{"methods":["foo.Bar/Baz"]}

parts := strings.Split(method, "/")
if len(parts) != 2 || parts[0] == "" {
    return fmt.Errorf("method %q must be <service>/<method> with exactly one '/'", method)
}

if _, err := unmarshalAndVerifyConfig(raw); err != nil { log.Fatalf("config: %v", err) }

When it happens

Trigger: A methods entry that is a bare service name with no method (foo.Bar), a bare method (Bar), an empty string, or contains multiple slashes (a/b/c, foo.Bar/Baz/extra). Reached while parsing the observability config.

Common situations: Typing only the service name; using a path-like method string; concatenating package + service + method with extra slashes; trailing slash (foo.Bar/Baz/).

Related errors

• cannot have a leading slash
• method name must be non empty
• cannot have exclude and a '*' wildcard
• empty token_exchange_service_uri in options
• required field SubjectTokenPath is not specified

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/0f8e94d1202a05b4. Report an issue: GitHub.