gofiber/fiber · error

open file error

Error message

open file error: %w

What it means

addFormFile opens the file at f.path with os.Open when no reader was supplied. This wraps the os.Open error: the path does not exist, is not readable, is a directory, or permissions deny access.

Solutions

1. Verify the file exists and is readable (os.Stat / os.Open) before queuing the upload.
2. Use absolute paths, or SetReader with an already-open handle to control lifetime.
3. Ensure the process has read permission on the file and its parent directory.

Example fix

// before
f := &client.File{}
f.SetPath(userPath)

// after
if _, err := os.Stat(userPath); err != nil {
    return fmt.Errorf("upload file missing: %w", err)
}
f := &client.File{}
f.SetPath(userPath)

if info, err := os.Stat(path); err != nil {
    return fmt.Errorf("upload file unavailable: %w", err)
} else if info.IsDir() {
    return errors.New("upload path is a directory")
}

if _, err := os.Open(path); err != nil {
    return fmt.Errorf("cannot read upload %q: %w", path, err)
}

When it happens

Trigger: Calling File.SetPath with a nonexistent or unreadable path; pointing at a directory; file deleted between scheduling and sending; permission denied under the process's UID.

Common situations: Hard-coded paths that don't exist in the deployment; temp files cleaned up before the request fires; container path-permission mismatches; relative paths resolved from an unexpected working directory.

Related errors

• create file error
• failed to check directory
• failed to copy file data
• failed to create directory
• boundary generation

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/f722538c35e2f63e. Report an issue: GitHub.

Appendix: source

Thrown at client/hooks.go:308

		if f.fieldName == "" {
			f.fieldName = "file" + strconv.Itoa(i+1)
		}

		if err := addFormFile(mw, f, fileBuf); err != nil {
			return err
		}
	}

	return nil
}

func addFormFile(mw *multipart.Writer, f *File, fileBuf *[]byte) error {
	// If reader is not set, open the file.
	if f.reader == nil {
		var err error
		f.reader, err = os.Open(f.path)
		if err != nil {
			return fmt.Errorf("open file error: %w", err)
		}
	}

	// Ensure the file reader is always closed after copying.
	defer f.reader.Close() //nolint:errcheck // not needed

	// Create form file and copy the content.
	w, err := mw.CreateFormFile(f.fieldName, f.name)
	if err != nil {
		return fmt.Errorf("create file error: %w", err)
	}

	if _, err := io.CopyBuffer(w, f.reader, *fileBuf); err != nil {
		return fmt.Errorf("failed to copy file data: %w", err)
	}

	return nil
}

View on GitHub (pinned to a105acad6c)