txthinking/brook · error

data too small

Error message

data too small

What it means

Length validation in PacketServerConnFactory.Handle: the first UDP packet from a client is shorter than the 12+4+16 byte minimum needed for the protocol header (salt/nonce plus encrypted fixed fields plus GCM tag), so it cannot be a legitimate brook packet and is discarded. Typically caused by stray traffic, port scans, or a non-brook client hitting the packet server port.

Source

Thrown at packetserverconn.go:48

	"github.com/txthinking/x"
	"golang.org/x/crypto/hkdf"
)

type PacketServerConnFactory struct {
	Conns map[string]*PacketConn
	Lock  *sync.Mutex
}

func NewPacketServerConnFactory() *PacketServerConnFactory {
	return &PacketServerConnFactory{
		Conns: make(map[string]*PacketConn),
		Lock:  &sync.Mutex{},
	}
}

func (f *PacketServerConnFactory) Handle(addr *net.UDPAddr, b, p []byte, w func([]byte) (int, error), timeout int) (net.Conn, []byte, error) {
	if len(b) < 12+4+16 {
		return nil, nil, errors.New("data too small")
	}
	ck := x.BP32.Get().([]byte)
	if _, err := io.ReadFull(hkdf.New(sha256.New, p, b[:12], ClientHKDFInfo), ck); err != nil {
		x.BP32.Put(ck)
		return nil, nil, err
	}

	cb, err := aes.NewCipher(ck)
	if err != nil {
		x.BP32.Put(ck)
		return nil, nil, err
	}
	x.BP32.Put(ck)
	ca, err := cipher.NewGCM(cb)
	if err != nil {
		return nil, nil, err
	}
	if _, err := ca.Open(b[:12], b[:12], b[12:], nil); err != nil {

View on GitHub (pinned to 5cd13ef3b1)

Solutions

1. Ensure the client is a compatible brook version speaking the packet protocol
2. Confirm the traffic is actually addressed to the brook UDP port (scans/noise also trigger this)
3. If legitimate packets are truncated, check for middleboxes fragmenting or clipping UDP payloads

When it happens

Trigger: Thrown at packetserverconn.go:48 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of txthinking/brook@5cd13ef3b1 (2026-09-06). Data as JSON: /api/errors/c429d09a3dfb65ac. Report an issue: GitHub.