What causes "packet header type does not match device" in OpenNHP/opennhp?

Verify the sender's target address/port actually belongs to this device type

packet header type does not match device

Error message

packet header type does not match device

What it means

Device.RecvPrecheck checks the packet's header type against the receiving device's allowed incoming types via CheckRecvHeaderType. If this device should never receive a packet of that type (e.g. an AC getting a DHP message it does not handle), the packet is rejected.

Solutions

Verify the sender's target address/port actually belongs to this device type
Check d.deviceType — the recv header allowlist is derived from it
Ensure relay/forward paths tag packets with the correct header type
Confirm both peers run the same protocol version and packet-type table

Example fix

// before
dev, _ := nhpcore.NewDevice(nhpcore.NHP_AGENT) // but receives AOP packets
// after
dev, _ := nhpcore.NewDevice(nhpcore.NHP_SERVER) // AOP is a server-received type

Defensive patterns

Strategy: validation

Validate before calling

t, _ := pkt.HeaderTypeAndSize()
if !dev.CheckRecvHeaderType(t) {
    return fmt.Errorf("type %d not accepted by this device", t)
}

Type guard

func accepts(dev *nhpcore.Device, pkt *nhpcore.Packet) bool {
    t, _ := pkt.HeaderTypeAndSize()
    return dev.CheckRecvHeaderType(t)
}

Try / catch

if _, _, err := dev.RecvPrecheck(pkt); err != nil && strings.Contains(err.Error(), "header type does not match") {
    log.Warnf("misrouted packet dropped")
    return
}

Prevention

Double-check target host:port belongs to the intended device type
Configure deviceType correctly at startup
Log and alert on repeated type mismatches (possible misrouting)

When it happens

Trigger: recvPacketRoutine, HandleRelayForward, or PacketToMsg delivers a packet whose header type t is not in the receiving device's CheckRecvHeaderType allowlist — typically packets sent to the wrong device/endpoint or misrouted UDP traffic.

Common situations: Pointing an agent at the wrong endpoint (e.g. AC address instead of server); configuring a device with the wrong deviceType so its recv filter excludes expected types; port reuse by another process.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

AI-assisted analysis of OpenNHP/opennhp@6e04ca5ff0 (2026-09-07). Data as JSON: /api/errors/6b3a078680d126b4. Report an issue: GitHub.

Appendix: source

Thrown at nhp/core/packet.go:253

	}
	log.Info("Device type: %d, recv header type %d not allowed", d.deviceType, t)
	return false
}

func (d *Device) RecvPrecheck(pkt *Packet) (int, int, error) {
	headerSize := pkt.Header().Size()

	// check type and payload size
	t, s := pkt.HeaderTypeAndSize()
	if t == NHP_KPL {
		if s == 0 {
			return t, s, nil
		} else {
			return t, s, fmt.Errorf("keepalive packet size is incorrect")
		}
	}
	if !d.CheckRecvHeaderType(t) {
		return t, s, fmt.Errorf("packet header type does not match device")
	}

	totalLen := len(pkt.Content)
	if totalLen != headerSize+s {
		return t, s, fmt.Errorf("packet total size is incorrect")
	}

	return t, s, nil
}

func (d *Device) AllocatePoolPacket() *Packet {
	buf := d.pool.Get()
	return &Packet{Buf: buf, Content: buf[:], PoolAllocated: true}
}

func (d *Device) ReleasePoolPacket(pkt *Packet) {
	if pkt != nil && pkt.Buf != nil && pkt.PoolAllocated {
		d.pool.Put(pkt.Buf)

View on GitHub (pinned to 6e04ca5ff0)