gofiber/fiber · error

file: failed to read file

Error message

file: failed to read file

What it means

ErrFileRead is returned by DefaultCtx.SaveFileToStorage at three sites (ctx.go:582, 590, 594) when the upload exceeds the configured BodyLimit, when LimitReader.ReadFrom fails mid-stream, or when the buffered length crosses the cap. Each return wraps the filename and (where relevant) fasthttp.ErrBodyTooLarge via fmt.Errorf("%w: %q: %w", ErrFileRead, fileheader.Filename, err).

Solutions

1. Raise BodyLimit on the app or route: fiber.New(fiber.Config{BodyLimit: 50 * 1024 * 1024}).
2. Inspect the wrapped error with errors.Is(err, fasthttp.ErrBodyTooLarge) to distinguish size violations from genuine read failures.
3. Validate Content-Length at the handler boundary and reject oversized uploads with 413 before reading.

Example fix

// before
app := fiber.New() // default BodyLimit ~4MiB
// after
app := fiber.New(fiber.Config{BodyLimit: 100 * 1024 * 1024})

// Reject oversized uploads at the handler boundary before reading.
const maxUpload = 50 << 20
if c.Get(fiber.HeaderContentLength) != "" {
    if n, _ := strconv.ParseInt(c.Get(fiber.HeaderContentLength), 10, 64); n > maxUpload {
        return c.Status(fiber.StatusRequestEntityTooLarge).SendString("too large")
    }
}
// Also size the app correctly:
// fiber.New(fiber.Config{BodyLimit: maxUpload})

if err := c.SaveFileToStorage(fh, key, storage); err != nil {
    if errors.Is(err, fiber.ErrFileRead) {
        if errors.Is(err, fasthttp.ErrBodyTooLarge) {
            return c.Status(fiber.StatusRequestEntityTooLarge).SendString("upload too large")
        }
        return c.Status(fiber.StatusInternalServerError).SendString("upload read failed")
    }
    return err
}

When it happens

Trigger: Calling c.SaveFileToStorage(fh, path, storage) when fileheader.Size already exceeds app.config.BodyLimit (ctx.go:580-583), or when the limited read returns an error (ctx.go:588-590), or when buf.Len() crosses maxUploadSize after a successful read (ctx.go:592-594). DefaultBodyLimit is used when BodyLimit is non-positive.

Common situations: Uploading files larger than the server's BodyLimit; clients that lie about Content-Length so the declared size is small but the stream is large; forgetting to raise BodyLimit on upload routes; reverse proxies that buffer the whole upload before forwarding.

Related errors

• file: failed to open file
• failed to close multipart writer
• file: file header is nil
• Request Entity Too Large
• write formdata error

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/cb359d977d9a268c. Report an issue: GitHub.

Appendix: source

Thrown at error.go:104

	SyntaxError = json.SyntaxError

	// UnmarshalTypeError describes a JSON value that was
	// not appropriate for a value of a specific Go type.
	UnmarshalTypeError = json.UnmarshalTypeError

	// UnsupportedTypeError is returned by Marshal when attempting
	// to encode an unsupported value type.
	UnsupportedTypeError = json.UnsupportedTypeError

	// UnsupportedValueError exposes json.UnsupportedValueError to describe unsupported values encountered during encoding.
	UnsupportedValueError = json.UnsupportedValueError
)

// File errors
var (
	ErrFileHeaderNil = errors.New("file: file header is nil")
	ErrFileOpen      = errors.New("file: failed to open file")
	ErrFileRead      = errors.New("file: failed to read file")
	ErrFileStore     = errors.New("file: failed to store file")
)

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