Tencent/WeKnora · error

failed to list resources: %w

Error message

failed to list resources: %w

What it means

An MCP client was obtained successfully, but the ListResources RPC against the MCP server failed. This is a remote-side failure (server rejected the call, timed out, or returned an MCP protocol error), wrapped with %w for cause inspection.

Source

Thrown at internal/application/service/mcp_service.go:611

	// Get service
	service, err := s.mcpServiceRepo.GetByID(ctx, tenantID, id)
	if err != nil {
		return nil, fmt.Errorf("failed to get MCP service: %w", err)
	}
	if service == nil {
		return nil, fmt.Errorf("MCP service not found")
	}

	// Get or create client
	client, err := s.mcpManager.GetOrCreateClient(ctx, service)
	if err != nil {
		return nil, fmt.Errorf("failed to get MCP client: %w", err)
	}

	// List resources
	resources, err := client.ListResources(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to list resources: %w", err)
	}

	return resources, nil
}

View on GitHub (pinned to 988cbb0330)

Solutions

1. Verify the MCP server advertises the resources capability in its initialize response
2. Increase the context timeout for the ListResources call if the server is slow
3. Inspect the wrapped error to distinguish protocol errors from transport errors
4. Upgrade the MCP server if its version predates resources/list support

Example fix

// before
ctx := context.Background()
resources, err := svc.GetMCPServiceResources(ctx, tenantID, serviceID)
// after
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()
resources, err := svc.GetMCPServiceResources(ctx, tenantID, serviceID)

// confirm the server advertises resources support before listing
caps, err := client.ServerCapabilities(ctx)
if err != nil || caps.Resources == nil {
	return errors.New("MCP server does not support resources")
}

func isListResourcesErr(err error) bool {
	return err != nil && strings.Contains(err.Error(), "failed to list resources")
}

ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
defer cancel()
resources, err := svc.GetMCPServiceResources(ctx, tenantID, serviceID)
if isListResourcesErr(err) {
	return retryWithBackoff(ctx, 2, call) // transient RPC failures
}

When it happens

Trigger: GetMCPServiceResources called on a service with a live client, but client.ListResources(ctx) returns an error: server timeout, unsupported resources capability, or protocol/permission error from the MCP server.

Common situations: MCP server does not implement the resources capability (resources/list unsupported); server-side timeout under load; auth token expired mid-session; server version mismatch with client capabilities.

Related errors

• failed to list resources: %w
• failed to list tools: %w
• failed to call tool: %w
• failed to read resource: %w
• failed to get MCP client: %w

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/427fa53df2fcdb87. Report an issue: GitHub.