googleapis/mcp-toolbox · error

destination_dir is invalid for tool %q: %w

Error message

destination_dir is invalid for tool %q: %w

What it means

The configured destination_dir failed cloudstoragecommon.ValidateLocalPath, which requires an absolute local path and rejects paths containing '..'. The underlying validation error is wrapped with %w and surfaced in this message.

Source

Thrown at internal/tools/cloudstorage/cloudstoragedownloadobject/cloudstoragedownloadobject.go:86

var _ tools.ToolConfig = Config{}

func (cfg Config) ToolConfigType() string {
	return resourceType
}

func (cfg Config) Initialize(context.Context) (tools.Tool, error) {
	if cfg.Description == "" {
		return nil, fmt.Errorf("description is required for tool %q", cfg.Name)
	}
	if cfg.Bucket != nil && *cfg.Bucket == "" {
		return nil, fmt.Errorf("bucket cannot be empty for tool %q", cfg.Name)
	}
	if cfg.DestinationDir != nil {
		if *cfg.DestinationDir == "" {
			return nil, fmt.Errorf("destination_dir cannot be empty for tool %q", cfg.Name)
		}
		if _, err := cloudstoragecommon.ValidateLocalPath(*cfg.DestinationDir); err != nil {
			return nil, fmt.Errorf("destination_dir is invalid for tool %q: %w", cfg.Name, err)
		}
	}

	objectParam := parameters.NewStringParameter(objectKey, "Full object name (path) within the bucket, e.g. 'path/to/file.txt'.")
	destinationDesc := "Absolute local filesystem path where the object will be written. Relative paths and paths containing '..' are rejected."
	if cfg.DestinationDir != nil {
		destinationDesc = "Relative path under the configured destination_dir where the object will be written. Absolute paths and paths that escape destination_dir are rejected."
	}
	allParameters := parameters.Parameters{}
	if cfg.Bucket == nil {
		allParameters = append(allParameters, parameters.NewStringParameter(bucketKey, "Name of the Cloud Storage bucket containing the object."))
	}
	allParameters = append(allParameters, objectParam)
	allParameters = append(allParameters, parameters.NewStringParameter(destinationKey, destinationDesc))
	if cfg.Overwrite == nil {
		allParameters = append(allParameters, parameters.NewBooleanParameter(overwriteKey, "If true, overwrite the destination when it already exists. If false (default), the tool returns an error when the destination exists.", parameters.WithBooleanDefault(false)))
	}

View on GitHub (pinned to 8cc6e09de2)

Solutions

  1. Use an absolute path without '..' for destination_dir
  2. Resolve the base directory at config time (e.g. use an absolute mounted volume path)
  3. Run cloudstoragecommon.ValidateLocalPath on your value before deploying to see the wrapped cause

Example fix

// before
destination_dir: ./downloads
// after
destination_dir: /var/lib/toolbox/downloads
Defensive patterns

Strategy: validation

Validate before calling

if _, err := cloudstoragecommon.ValidateLocalPath(dest); err != nil {
    return fmt.Errorf("invalid destination_dir: %w", err)
}

Try / catch

if err := startToolbox(); err != nil {
    var pathErr *fmt.wrapError
    if errors.As(err, &pathErr) && strings.Contains(err.Error(), "destination_dir is invalid") {
        // use absolute path without '..'
    }
    log.Fatal(err)
}

Prevention

When it happens

Trigger: destination_dir is relative (e.g. 'downloads' or './out') or contains a '..' traversal component (e.g. '/data/../etc') when initializing cloudstorage-download-object.

Common situations: Users entering relative paths in configs; attempting path traversal to write outside the sandbox; containers where the intended mount path differs from the configured one.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/716de00bc4f26448. Report an issue: GitHub.