Method handleRelay

endpoints/relay/relay.go:853–1010

handleRelay is the main relay endpoint. Expected request: POST /relay/{clusterId} Content-Type: application/octet-stream Body: raw inner NHP packet bytes (KNK / RKN / etc., encrypted by agent) Response: 200 OK — body contains raw NHP ACK / COK packet bytes (encrypted to agent) 400 Bad Requ

(w http.ResponseWriter, r *http.Request)

//	504 Gateway Timeout  — NHP Server did not respond in time
//	502 Bad Gateway  — internal error
func (rs *RelayServer) handleRelay(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}

	cr, status, errMsg := rs.resolveCluster(r)
	if cr == nil {
		http.Error(w, errMsg, status)
		return
	}

	// Read inner NHP packet from request body. Cap at maxPacketSize+1 so we
	// can reject oversize bodies without pulling an unbounded amount into
	// memory. A single r.Body.Read() is not guaranteed to return the full
	// payload; io.ReadAll drains until EOF.
	innerPacket, err := io.ReadAll(io.LimitReader(r.Body, int64(maxPacketSize)+1))
	if err != nil {
		http.Error(w, "failed to read body", http.StatusBadRequest)
		return
	}
	if len(innerPacket) == 0 {
		http.Error(w, "empty packet", http.StatusBadRequest)
		return
	}
	if len(innerPacket) > maxPacketSize {
		http.Error(w, "packet too large", http.StatusBadRequest)
		return
	}
	n := len(innerPacket)

	// Extract the counter from the inner packet header (bytes [16:24], big-endian uint64).
	// The NHP server echoes this counter in its ACK/COK response, so we use it
	// to match the response back to this HTTP request.
	if n < 24 {
		http.Error(w, "inner packet too short", http.StatusBadRequest)
		return
	}
	innerCounter := binary.BigEndian.Uint64(innerPacket[16:24])

	// Body is valid; pick a target instance. normalize() blocks an empty
	// instance list in phase 1, but phase 2's health checks can legitimately
	// empty the healthy pool, so surface that as a 503 instead of panicking
	// on a nil dereference downstream.
	inst := cr.pickInstance()
	if inst == nil {
		http.Error(w, "cluster has no usable instance", http.StatusServiceUnavailable)
		return
	}

	realAddr, err := realClientAddr(r)
	if err != nil {
		log.Error("[Relay] %v", err)
		http.Error(w, "relay misconfigured: missing X-Real-IP header from local reverse proxy", http.StatusBadGateway)
		return
	}
	realAddrKey := realAddr.String()
	log.Info("[Relay] forwarding %d-byte inner packet (counter=%d, cluster=%s) from client %s to %s",