Tencent/WeKnora · error

failed to list resources: %w

Error message

failed to list resources: %w

What it means

ListResources wraps errors from c.client.ListResources after initialize. The resources/list RPC failed — dropped session, JSON-RPC error (most often 'method not supported' because the server doesn't implement resources), timeout, or transport failure. The client may have been marked disconnected by checkErrorAndDisconnectIfNeeded before returning.

Source

Thrown at internal/mcp/client.go:455

		}
	}

	return tools, nil
}

// ListResources retrieves the list of available resources
func (c *mcpGoClient) ListResources(ctx context.Context) ([]*types.MCPResource, error) {
	if !c.initialized {
		return nil, ErrNotConnected
	}

	req := mcp.ListResourcesRequest{}
	result, err := oauthCall(ctx, c, func() (*mcp.ListResourcesResult, error) {
		return c.client.ListResources(ctx, req)
	})
	if err != nil {
		c.checkErrorAndDisconnectIfNeeded(err)
		return nil, fmt.Errorf("failed to list resources: %w", err)
	}

	// Convert to our types
	resources := make([]*types.MCPResource, len(result.Resources))
	for i, resource := range result.Resources {
		resources[i] = &types.MCPResource{
			URI:         resource.URI,
			Name:        resource.Name,
			Description: resource.Description,
			MimeType:    resource.MIMEType,
		}
	}

	return resources, nil
}

// CallTool calls a tool on the MCP service
func (c *mcpGoClient) CallTool(ctx context.Context, name string, args map[string]interface{}) (*CallToolResult, error) {

View on GitHub (pinned to 988cbb0330)

Solutions

1. Check the server's initialize capabilities include resources before calling; treat 'not supported' as an empty result rather than an error
2. Reconnect (Connect + Initialize) and retry if the session was lost
3. Raise the timeout if the resource listing is slow
4. Verify proxy/LB idle-timeout settings for long-lived connections

Example fix

// before
resources, err := c.ListResources(ctx)
if err != nil { return nil, err }
// after
if !c.serverSupportsResources() { // check InitializeResult capabilities
    return []*types.MCPResource{}, nil
}
resources, err := c.ListResources(ctx)
if err != nil { return nil, fmt.Errorf("list resources: %w", err) }

func listResourcesIfSupported(ctx context.Context, c MCPClient) ([]*types.MCPResource, error) {
    resources, err := c.ListResources(ctx)
    if err != nil && (errors.Is(err, ErrNotConnected) || strings.Contains(err.Error(), "failed to list resources")) {
        // treat unsupported/failed resource listing as empty rather than fatal
        return []*types.MCPResource{}, nil
    }
    return resources, err
}

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

resources, err := c.ListResources(ctx)
if err != nil {
    if isListResourcesFailure(err) && !c.capabilities.Resources {
        log.Info("server does not support resources; skipping")
        return nil, nil
    }
    return reconnectAndListResources(ctx, c)
}

When it happens

Trigger: ListResources called on an initialized client where the server does not support the resources capability, the session/connection was lost, or the context timed out during the RPC.

Common situations: Calling ListResources against a tools-only MCP server (very common — many servers implement tools but not resources); expired session on a reused long-lived client; proxy cutting idle streamable connections.

Related errors

• failed to list resources: %w
• failed to list tools: %w
• failed to create SSE client: %w
• URL is required for HTTP Streamable transport
• failed to create HTTP streamable client: %w

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/1dd64e1354d06f80. Report an issue: GitHub.