What causes "discovery timeout" in AlexxIT/go2rtc?

Verify the device UID/identifier is correct

discovery timeout

Error message

discovery timeout

What it means

discovery waits for the camera's discovery response (cmdDiscoRes) on the LAN/broadcast channel; if it never arrives, DialDTLS fails with this error. It means the host could not discover the camera before giving up, so no session address was learned.

Solutions

Verify the device UID/identifier is correct
Ensure host and camera are on the same L2 network or that UDP discovery relays are available
Power-cycle the camera and retry DialDTLS
Check for client/AP isolation or firewall rules blocking the discovery packets

Defensive patterns

Strategy: retry

Validate before calling

// precondition checks before DialDTLS
if deviceUID == "" || !sameSubnet(hostIP, camSubnet) {
	return fmt.Errorf("discovery cannot reach camera network")
}

Try / catch

conn, err := dtls.DialDTLS(ctx, uid, psk)
if err != nil {
	if strings.Contains(err.Error(), "discovery timeout") {
		// power-cycle/ping camera, then retry once
	}
	return err
}

Prevention

Verify the UID and that host and camera share the L2 network
Disable AP/client isolation on the wireless network
Retry discovery after power-cycling the camera
Warn users when camera is offline before dialing

When it happens

Trigger: DialDTLS -> discovery when no UDP packet with cmdDiscoRes at offset 8 is received within the discovery window — camera offline, wrong network/broadcast, or discovery response dropped.

Common situations: Camera on a different subnet/VLAN than the host; camera asleep or just powered on; mDNS/UDP broadcast blocked by AP isolation; wrong device UID leading to no responder.

Understand the failure class

Background: Request timed out: what client-side request timeouts mean across libraries (Request timed out, TIMED_OUT, APITimeoutError) — this error's family across 39 libraries.

Timeouts: ETIMEDOUT, deadlines, and hung requests — what actually expires when a request times out.

Related errors

AI-assisted analysis of AlexxIT/go2rtc@c245815e75 (2026-09-07). Data as JSON: /api/errors/95600bd5a3c4dfcc. Report an issue: GitHub.

Appendix: source

Thrown at pkg/tutk/dtls/conn_dtls.go:541

			if binary.LittleEndian.Uint16(buf[4:]) == cmdDiscoCC51 {
				c.addr, c.isCC51, c.ticket = addr, true, binary.LittleEndian.Uint16(buf[14:])
				if n >= 24 {
					copy(c.sid, buf[16:24])
				}
				return c.discoDoneCC51()
			}
			continue
		}

		// IOTC Protocol (Basis)
		data := tutk.ReverseTransCodeBlob(buf[:n])
		if len(data) >= 16 && binary.LittleEndian.Uint16(data[8:]) == cmdDiscoRes {
			c.addr, c.isCC51 = addr, false
			return c.discoDone()
		}
	}

	return fmt.Errorf("discovery timeout")
}

func (c *DTLSConn) discoDone() error {
	c.Write(c.msgDisco(2))
	time.Sleep(100 * time.Millisecond)
	_, err := c.WriteAndWait(c.msgSession(), func(res []byte) bool {
		return len(res) >= 16 && binary.LittleEndian.Uint16(res[8:]) == cmdSessionRes
	})
	return err
}

func (c *DTLSConn) discoDoneCC51() error {
	_, err := c.WriteAndWait(c.msgDiscoCC51(2, c.ticket, false), func(res []byte) bool {
		if len(res) < packetSizeCC51 || string(res[:2]) != magicCC51 {
			return false
		}
		cmd := binary.LittleEndian.Uint16(res[4:])
		dir := binary.LittleEndian.Uint16(res[8:])

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