jrouter/nbp.go

/*
   Copyright 2024 Josh Deprez

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package main

import (
	"errors"
	"fmt"
	"log"

	"gitea.drjosh.dev/josh/jrouter/atalk/nbp"
	"github.com/google/gopacket/pcap"
	"github.com/sfiera/multitalk/pkg/aarp"
	"github.com/sfiera/multitalk/pkg/ddp"
	"github.com/sfiera/multitalk/pkg/ethernet"
	"github.com/sfiera/multitalk/pkg/ethertalk"
)

func handleNBP(pcapHandle *pcap.Handle, myHWAddr, srcHWAddr ethernet.Addr, myAddr aarp.AddrPair, cfg *config, ddpkt *ddp.ExtPacket) error {
	if ddpkt.Proto != ddp.ProtoNBP {
		return fmt.Errorf("invalid DDP type %d on socket 2", ddpkt.Proto)
	}

	nbpkt, err := nbp.Unmarshal(ddpkt.Data)
	if err != nil {
		return fmt.Errorf("invalid packet: %w", err)
	}

	log.Printf("NBP: Got %v id %d with tuples %v", nbpkt.Function, nbpkt.NBPID, nbpkt.Tuples)

	switch nbpkt.Function {
	case nbp.FunctionLkUp:
		// when in AppleTalk, do as Apple Internet Router does...
		tuple := nbpkt.Tuples[0]
		if tuple.Object != "jrouter" && tuple.Object != "=" {
			return nil
		}
		if tuple.Type != "AppleRouter" && tuple.Type != "=" {
			return nil
		}
		if tuple.Zone != cfg.EtherTalk.ZoneName && tuple.Zone != "*" && tuple.Zone != "" {
			return nil
		}
		respPkt := &nbp.Packet{
			Function: nbp.FunctionLkUpReply,
			NBPID:    nbpkt.NBPID,
			Tuples: []nbp.Tuple{
				{
					Network:    myAddr.Proto.Network,
					Node:       myAddr.Proto.Node,
					Socket:     253,
					Enumerator: 0,
					Object:     "jrouter",
					Type:       "AppleRouter",
					Zone:       cfg.EtherTalk.ZoneName,
				},
			},
		}
		respRaw, err := respPkt.Marshal()
		if err != nil {
			return fmt.Errorf("couldn't marshal LkUp-Reply: %v", err)
		}
		ddpkt.DstNet = ddpkt.SrcNet
		ddpkt.DstNode = ddpkt.SrcNode
		ddpkt.DstSocket = ddpkt.SrcSocket
		ddpkt.SrcNet = myAddr.Proto.Network
		ddpkt.SrcNode = myAddr.Proto.Node
		ddpkt.SrcSocket = 2
		ddpkt.Data = respRaw
		outFrame, err := ethertalk.AppleTalk(myHWAddr, *ddpkt)
		if err != nil {
			return err
		}
		outFrame.Dst = srcHWAddr
		outFrameRaw, err := ethertalk.Marshal(*outFrame)
		if err != nil {
			return err
		}
		return pcapHandle.WritePacketData(outFrameRaw)

	case nbp.FunctionBrRq:
		// There must be 1!
		tuple := nbpkt.Tuples[0]

		if tuple.Zone != cfg.EtherTalk.ZoneName {
			// TODO: Translate it into a FwdReq and route it to the
			// routers with the appropriate zone(s).
			return errors.New("TODO: BrRq-FwdReq translation")
		}

		// If it's for the local zone, translate it to a LkUp and broadcast it back
		// out the EtherTalk port.
		// "Note: On an internet, nodes on extended networks performing lookups in
		// their own zone must replace a zone name of asterisk (*) with their actual
		// zone name before sending the packet to A-ROUTER. All nodes performing
		// lookups in their own zone will receive LkUp packets from themselves
		// (actually sent by a router). The node's NBP process should expect to
		// receive these packets and must reply to them."
		// TODO: use zone-specific multicast
		nbpkt.Function = nbp.FunctionLkUp
		nbpRaw, err := nbpkt.Marshal()
		if err != nil {
			return fmt.Errorf("couldn't marshal LkUp: %v", err)
		}

		ddpkt.DstNode = 0xFF // Broadcast node address within the dest network
		ddpkt.Data = nbpRaw

		outFrame, err := ethertalk.AppleTalk(myHWAddr, *ddpkt)
		if err != nil {
			return err
		}
		outFrameRaw, err := ethertalk.Marshal(*outFrame)
		if err != nil {
			return err
		}
		return pcapHandle.WritePacketData(outFrameRaw)

	default:
		return fmt.Errorf("TODO: handle function %v", nbpkt.Function)
	}
}