cayleygraph/cayley · error

could not open file %q: %v

Error message

could not open file %q: %v

What it means

QuadReaderFor resolves a data path, which may be a local file path or a URL. For local paths, it opens the file with os.Open; if the open fails for a reason other than not-exist (e.g. permission denied, is a directory), the error is wrapped as this message with the path and cause.

Source

Thrown at internal/load.go:60

func QuadReaderFor(path, typ string) (quad.ReadCloser, error) {
	var (
		r io.Reader
		c io.Closer
	)
	if path == "-" {
		r = os.Stdin
	} else if u, err := url.Parse(path); err != nil || u.Scheme == "file" || u.Scheme == "" {
		// Don't alter relative URL path or non-URL path parameter.
		if u.Scheme != "" && err == nil {
			// Recovery heuristic for mistyping "file://path/to/file".
			path = filepath.Join(u.Host, u.Path)
		}
		f, err := os.Open(path)
		if os.IsNotExist(err) {
			return nil, err
		} else if err != nil {
			return nil, fmt.Errorf("could not open file %q: %v", path, err)
		}
		r, c = f, f
	} else {
		res, err := http.Get(path)
		if err != nil {
			return nil, fmt.Errorf("could not get resource <%s>: %v", u, err)
		}
		// TODO(dennwc): save content type for format auto-detection
		r, c = res.Body, res.Body
	}

	r, err := decompressor.New(r)
	if err != nil {
		if c != nil {
			c.Close()
		}
		if err == io.EOF {
			return nopCloser{quad.NewReader(nil)}, nil

View on GitHub (pinned to 81dcd7d73e)

Solutions

1. Check the wrapped cause to distinguish permission-denied vs is-a-directory
2. Verify the path points to a readable regular file (ls -l)
3. Run the process as a user with read permission or fix file permissions (chmod/chown)
4. If the file truly doesn't exist, expect the raw os.ErrNotExist instead of this wrapper

Example fix

// before
./cayley load --data /etc/cayley # directory, not a file
// after
./cayley load --data /etc/cayley/quads.nq

info, err := os.Stat(path)
if err != nil { return err }
if info.IsDir() { return fmt.Errorf("%s is a directory", path) }
if info.Mode().Perm()&0o400 == 0 { return fmt.Errorf("%s not readable", path) }

r, err := internal.QuadReaderFor(ctx, path)
if err != nil && strings.Contains(err.Error(), "could not open file") {
    // fix permissions/path and retry
}

When it happens

Trigger: Loading a quad file via a file:// URL or plain path where os.Open returns a non-NotExist error: unreadable permissions, path is a directory, I/O error.

Common situations: Running Cayley as a user without read access to the data file; pointing --data at a directory instead of a file; SELinux/app restrictions on file access.

Understand the failure class

Background: "open() failed", "failed to open file", "cannot create file" — what a file open error means and how to fix it — this error's family across 42 libraries.

Related errors

• could not open config file %q: %v
• could not write history to %q: %v

AI-assisted analysis of cayleygraph/cayley@81dcd7d73e (2026-09-06). Data as JSON: /api/errors/bdf0f65432088a4f. Report an issue: GitHub.