gofiber/fiber · error · ErrFileOpen

file: failed to open file: %q: %w

Error message

file: failed to open file: %q: %w

What it means

Returned by Ctx.SaveFileToStorage when multipart.FileHeader.Open() fails while trying to read an uploaded file. It wraps the sentinel ErrFileOpen along with the offending filename and the underlying error. This happens before any bytes are read, indicating the multipart part's file descriptor could not be opened.

Source

Thrown at ctx.go:572

}

// SaveFile saves any multipart file to disk.
func (*DefaultCtx) SaveFile(fileheader *multipart.FileHeader, path string) error {
	if fileheader == nil {
		return ErrFileHeaderNil
	}
	return fasthttp.SaveMultipartFile(fileheader, path)
}

// SaveFileToStorage saves any multipart file to an external storage system.
func (c *DefaultCtx) SaveFileToStorage(fileheader *multipart.FileHeader, path string, storage Storage) error {
	if fileheader == nil {
		return ErrFileHeaderNil
	}

	file, err := fileheader.Open()
	if err != nil {
		return fmt.Errorf("%w: %q: %w", ErrFileOpen, fileheader.Filename, err)
	}
	defer file.Close() //nolint:errcheck // not needed

	maxUploadSize := c.app.config.BodyLimit
	if maxUploadSize <= 0 {
		maxUploadSize = DefaultBodyLimit
	}

	if fileheader.Size > 0 && fileheader.Size > int64(maxUploadSize) {
		return fmt.Errorf("%w: %q: %w", ErrFileRead, fileheader.Filename, fasthttp.ErrBodyTooLarge)
	}

	buf := bytebufferpool.Get()
	defer bytebufferpool.Put(buf)

	limitedReader := io.LimitReader(file, int64(maxUploadSize)+1)
	if _, err = buf.ReadFrom(limitedReader); err != nil {
		return fmt.Errorf("%w: %q: %w", ErrFileRead, fileheader.Filename, err)

View on GitHub (pinned to 9a4c7e57fe)

Solutions

1. Check the wrapped underlying error to distinguish OS-level (permission/disk) from protocol-level causes.
2. Ensure the OS temp directory (TMPDIR) is writable and has adequate free space.
3. Increase or verify Server.BodyLimit so the full multipart body is buffered before SaveFileToStorage runs.
4. Handle the error and respond to the client with a 4xx rather than crashing the handler.

Example fix

// before
err := c.SaveFileToStorage(fh, "/uploads/"+fh.Filename, storage)
if err != nil {
    panic(err)
}

// after
err := c.SaveFileToStorage(fh, "/uploads/"+fh.Filename, storage)
if err != nil {
    if errors.Is(err, fiber.ErrFileOpen) {
        return c.Status(fiber.StatusBadRequest).SendString("could not open upload")
    }
    return err
}

// Validate the file header before storing
if fileHeader == nil {
    return fiber.ErrFileHeaderNil
}
if fileHeader.Size <= 0 {
    return fmt.Errorf("empty upload: %q", fileHeader.Filename)
}

if err := c.SaveFileToStorage(fh, path, storage); err != nil {
    if errors.Is(err, fiber.ErrFileOpen) {
        return c.Status(fiber.StatusBadRequest).SendString("cannot open upload")
    }
    return err
}

When it happens

Trigger: Calling c.SaveFileToStorage(fileHeader, path, storage) where fileHeader.Open() returns an error. Common when the multipart form is malformed, the temporary file backing the upload was already cleaned up, or the OS denies access to the spool file.

Common situations: Exceeding the OS temp disk quota, a reverse proxy truncating the multipart body mid-upload, client disconnect after the body is parsed but before storage, or a corrupted multipart boundary.

Related errors

• file: failed to read file: %q: %w
• file: failed to store file: %q to %q: %w
• file: file header is nil
• file: failed to read file
• file: failed to store file

AI-assisted analysis of gofiber/fiber@9a4c7e57fe (2026-08-04). Data as JSON: /data/errors/f60281be58ee122f.json. Report an issue: GitHub.