gofiber/fiber · error

failed to open: %w

Error message

failed to open: %w

What it means

Returned by the internal readContent helper when os.Open fails to open the named file. readContent is used to load file content into an io.ReaderFrom (e.g. reading a template file for rendering in res.go). The error wraps the underlying os.PathError so the caller sees both the 'failed to open' context and the OS reason.

Source

Thrown at helpers.go:155

	value := reflect.NewAt(field.Type(), unsafe.Pointer(field.UnsafeAddr())).Elem() //nolint:gosec // Access to unexported field is required for listeners that don't expose TLS config methods.
	if !value.IsValid() {
		return nil
	}

	cfg, ok := value.Interface().(*tls.Config)
	if !ok {
		return nil
	}

	return cfg
}

// readContent opens a named file and read content from it
func readContent(rf io.ReaderFrom, name string) (int64, error) {
	// Read file
	f, err := os.Open(filepath.Clean(name))
	if err != nil {
		return 0, fmt.Errorf("failed to open: %w", err)
	}
	defer func() {
		if err = f.Close(); err != nil {
			log.Errorf("Error closing file: %s", err)
		}
	}()
	n, readErr := rf.ReadFrom(f)
	if readErr != nil {
		return n, fmt.Errorf("failed to read: %w", readErr)
	}
	return n, nil
}

// quoteEscapeMask marks the lanes of w holding bytes quoteRawString must
// escape: '\\', '"', any C0 control (including HTAB), or DEL. Lanes >= 0x80
// are never marked; non-ASCII bytes pass through verbatim. This is
// utils.IndexNonQuotable's RFC 9110 set widened by HTAB, which the RFC
// permits as qdtext but this function has always percent-encoded.

View on GitHub (pinned to 9a4c7e57fe)

Solutions

1. Verify the file path exists and is readable by the process (check with ls -l on the path).
2. Use absolute paths or ensure the working directory is set correctly in the deployment.
3. Confirm the template file is included in the Docker image / build artifact.
4. Fix filesystem permissions so the process owner can read the file.

Example fix

// before
c.Render("views/user.tmpl", bind) // file missing

// after
// ensure 'views/user.tmpl' exists at the expected path, or register a template engine
c.Render("views/user.tmpl", bind)

// Ensure a template file is readable before rendering
if _, err := os.Stat(filepath.Clean(name)); err != nil {
    return fmt.Errorf("template not accessible %q: %w", name, err)
}

if err := c.Render(name, bind); err != nil {
    if strings.Contains(err.Error(), "failed to open") {
        return c.Status(fiber.StatusNotFound).SendString("template not found")
    }
    return err
}

When it happens

Trigger: Rendering a template via c.Render() with a template name/path that does not exist on disk, or where the process lacks read permission on the template file. readContent(buf, name) calls os.Open(filepath.Clean(name)) which returns ENOENT or EACCES.

Common situations: Wrong working directory so the relative template path resolves incorrectly, missing template file in the deployment artifact, file permission bits stripping read access, or a typo in the template name passed to c.Render().

Related errors

• failed to read: %w
• fiber: failed to reload views: %w
• file: failed to open file: %q: %w
• failed to render: %w
• logtemplate: unknown tag

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/8ba148d850763c62.json. Report an issue: GitHub.