charmbracelet/crush · error

failed to enable docker MCP: %w

Error message

failed to enable docker MCP: %w

What it means

This error is returned by Client.EnableDockerMCP when the HTTP POST to /workspaces/{id}/mcp/docker/enable fails at the transport level. The request never produced an HTTP response, and the original cause (connection failure, timeout, cancellation) is preserved via %w. It is a connectivity/request-execution problem, not a server-side rejection.

Source

Thrown at internal/client/config.go:267

	if err := json.NewDecoder(rsp.Body).Decode(&result); err != nil {
		return nil, fmt.Errorf("failed to decode skill response: %w", err)
	}
	return &result, nil
}

// MCPResourceContents holds the contents of an MCP resource.
type MCPResourceContents struct {
	URI      string `json:"uri"`
	MIMEType string `json:"mime_type,omitempty"`
	Text     string `json:"text,omitempty"`
	Blob     []byte `json:"blob,omitempty"`
}

// EnableDockerMCP enables the Docker MCP server on the workspace.
func (c *Client) EnableDockerMCP(ctx context.Context, id string) error {
	rsp, err := c.post(ctx, fmt.Sprintf("/workspaces/%s/mcp/docker/enable", id), nil, nil, nil)
	if err != nil {
		return fmt.Errorf("failed to enable docker MCP: %w", err)
	}
	defer rsp.Body.Close()
	if rsp.StatusCode != http.StatusOK {
		return fmt.Errorf("failed to enable docker MCP: status code %d", rsp.StatusCode)
	}
	return nil
}

// DisableDockerMCP disables the Docker MCP server on the workspace.
func (c *Client) DisableDockerMCP(ctx context.Context, id string) error {
	rsp, err := c.post(ctx, fmt.Sprintf("/workspaces/%s/mcp/docker/disable", id), nil, nil, nil)
	if err != nil {
		return fmt.Errorf("failed to disable docker MCP: %w", err)
	}
	defer rsp.Body.Close()
	if rsp.StatusCode != http.StatusOK {
		return fmt.Errorf("failed to disable docker MCP: status code %d", rsp.StatusCode)
	}

View on GitHub (pinned to 7944b8e522)

Solutions

1. Check server reachability and the configured base URL.
2. Inspect the wrapped cause (errors.Is/As) to classify: timeout vs refused vs cancelled.
3. Retry with backoff for transient failures.
4. Confirm the server version supports the docker MCP enable endpoint.
5. Verify no proxy/firewall strips or blocks the POST.

Example fix

// before
err := client.EnableDockerMCP(ctx, wsID)
if err != nil { return err }
// after
err := client.EnableDockerMCP(ctx, wsID)
if err != nil {
    // transient network issues are common; retry once
    if retryable(err) {
        time.Sleep(2 * time.Second)
        err = client.EnableDockerMCP(ctx, wsID)
    }
    if err != nil { return err }
}

// Pre-check reachability before toggling MCP
func canReach(baseURL string) bool {
    resp, err := http.Get(baseURL + "/health")
    if err != nil { return false }
    resp.Body.Close()
    return resp.StatusCode == http.StatusOK
}

func isRetryable(err error) bool {
    var ne net.Error
    if errors.As(err, &ne) { return true }
    return errors.Is(err, context.DeadlineExceeded) || errors.Is(err, syscall.ECONNRESET)
}

err := client.EnableDockerMCP(ctx, wsID)
for i := 0; err != nil && isRetryable(err) && i < 3; i++ {
    time.Sleep(time.Duration(1<<i) * time.Second)
    err = client.EnableDockerMCP(ctx, wsID)
}
if err != nil { return err }

When it happens

Trigger: Calling EnableDockerMCP(ctx, workspaceID) while the server is unreachable, the connection drops mid-request, the context expires, or c.post fails to build the request.

Common situations: Control-plane server not running; Docker MCP feature requires a newer server that doesn't yet expose the route at that host; network policy blocks POSTs; transient network blip in CI.

Related errors

• failed to disable docker MCP: %w
• failed to list skills: %w
• failed to read skill: %w
• failed to enable docker MCP: status code %d
• failed to disable docker MCP: status code %d

AI-assisted analysis of charmbracelet/crush@7944b8e522 (2026-08-29). Data as JSON: /api/errors/d6abb595e9e91ffa. Report an issue: GitHub.