Tencent/WeKnora · error

MCP client config and service are required

Error message

MCP client config and service are required

What it means

NewMCPClient validates its input before doing any work: a nil config or a config whose Service field is nil cannot describe a transport, so construction fails immediately with this sentinel-style error. It is a pure programming/config error, not a runtime failure.

Source

Thrown at internal/mcp/client.go:152

// signal that carries RFC 9728 protected-resource metadata. It returns a
// non-nil *OAuthRequiredError ONLY when the server advertised a metadata URL —
// a bare 401 without metadata is treated as an ordinary auth failure (e.g. a
// wrong/missing API key) so we don't misdirect the user toward OAuth.
func asOAuthRequired(err error) *OAuthRequiredError {
	if err == nil {
		return nil
	}
	var authErr *transport.AuthorizationRequiredError
	if errors.As(err, &authErr) && authErr.ResourceMetadataURL != "" {
		return &OAuthRequiredError{MetadataURL: authErr.ResourceMetadataURL, Err: err}
	}
	return nil
}

// NewMCPClient creates a new MCP client based on the transport type
func NewMCPClient(config *ClientConfig) (MCPClient, error) {
	if config == nil || config.Service == nil {
		return nil, fmt.Errorf("MCP client config and service are required")
	}
	if err := ValidateServiceOutboundURLs(config.Service); err != nil {
		return nil, err
	}

	// Create HTTP client with timeout
	timeout := 30 * time.Second
	if config.Service.AdvancedConfig != nil && config.Service.AdvancedConfig.Timeout > 0 {
		timeout = time.Duration(config.Service.AdvancedConfig.Timeout) * time.Second
	}

	clientCfg := secutils.DefaultSSRFSafeHTTPClientConfig()
	clientCfg.Timeout = timeout
	httpClient := secutils.NewSSRFSafeHTTPClient(clientCfg)

	// Build headers
	headers := make(map[string]string)
	for key, value := range config.Service.Headers {

View on GitHub (pinned to 988cbb0330)

Solutions

1. Ensure the ClientConfig is fully populated — especially the Service field — before calling NewMCPClient
2. Fix config loading so MCP service definitions are parsed and attached
3. Add a nil check with a clear log line at the call site to catch wiring bugs early
4. Validate config at startup rather than at client creation time

Example fix

// before
client, err := NewMCPClient(cfg) // cfg.Service is nil
// after
if cfg == nil || cfg.Service == nil {
    return fmt.Errorf("mcp service %q not configured", serviceID)
}
client, err := NewMCPClient(cfg)

func validateMCPConfig(cfg *ClientConfig) error {
    if cfg == nil || cfg.Service == nil { return errors.New("MCP client config and service are required") }
    return nil
}

func hasMCPService(cfg *ClientConfig) bool { return cfg != nil && cfg.Service != nil }

client, err := NewMCPClient(cfg)
if err != nil {
    if strings.Contains(err.Error(), "required") { return fmt.Errorf("mcp service misconfigured: %w", err) }
    return err
}

When it happens

Trigger: Calling NewMCPClient(nil), or with &ClientConfig{} where Service was never set; GetOrCreateClient passing through an unresolved service record.

Common situations: Config loading skipped or partially failed so the service entry is missing; a map lookup returning a zero-value struct; wiring bugs where the service pointer is dropped between layers.

Understand the failure class

Background: "X is required", "must be set", "cannot be empty": the missing-required-config error family, from Vertex AI project/location to WeChat keys — this error's family across 18 libraries.

Related errors

• URL is required for SSE transport
• URL is required for HTTP Streamable transport
• MCP service is required
• invalid sandbox type
• timeout cannot be negative

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/5c175de0781d4cb0. Report an issue: GitHub.