jrouter/router/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 router

import (
	"context"
	"fmt"
	"log"

	"gitea.drjosh.dev/josh/jrouter/atalk"
	"gitea.drjosh.dev/josh/jrouter/atalk/nbp"
	"github.com/sfiera/multitalk/pkg/ddp"
)

func (port *EtherTalkPort) HandleNBP(ctx context.Context, 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...
		outDDP, err := port.helloWorldThisIsMe(ddpkt, nbpkt.NBPID, &nbpkt.Tuples[0])
		if err != nil || outDDP == nil {
			return err
		}
		log.Print("NBP: Replying to LkUp with LkUp-Reply for myself")
		// Note: AARP can block
		return port.Send(ctx, outDDP)

	case nbp.FunctionFwdReq:
		// TODO: handle FwdReq in

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

		zones := port.Router.ZoneTable.LookupName(tuple.Zone)

		for _, z := range zones {
			if outPort := z.LocalPort; outPort != nil {
				// If it's for a local zone, translate it to a LkUp and broadcast
				// out the corresponding 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."
				nbpkt.Function = nbp.FunctionLkUp
				nbpRaw, err := nbpkt.Marshal()
				if err != nil {
					return fmt.Errorf("couldn't marshal LkUp: %v", err)
				}

				outDDP := ddp.ExtPacket{
					ExtHeader: ddp.ExtHeader{
						Size:      atalk.DDPExtHeaderSize + uint16(len(nbpRaw)),
						Cksum:     0,
						SrcNet:    ddpkt.SrcNet,
						SrcNode:   ddpkt.SrcNode,
						SrcSocket: ddpkt.SrcSocket,
						DstNet:    0x0000, // Local network broadcast
						DstNode:   0xFF,   // Broadcast node address within the dest network
						DstSocket: 2,
						Proto:     ddp.ProtoNBP,
					},
					Data: nbpRaw,
				}

				log.Printf("NBP: zone multicasting LkUp for tuple %v", tuple)
				if err := outPort.ZoneMulticast(tuple.Zone, &outDDP); err != nil {
					return err
				}

				// But also...if we match the query, reply as though it was a LkUp
				outDDP2, err := outPort.helloWorldThisIsMe(ddpkt, nbpkt.NBPID, tuple)
				if err != nil {
					return err
				}
				if outDDP2 == nil {
					continue
				}
				log.Print("NBP: Replying to BrRq directly with LkUp-Reply for myself")
				if err := port.Router.Forward(ctx, outDDP2); err != nil {
					return err
				}

				continue
			}

			// Translate it into a FwdReq and route it to the
			// routers with the appropriate zone(s).
			nbpkt.Function = nbp.FunctionFwdReq
			nbpRaw, err := nbpkt.Marshal()
			if err != nil {
				return fmt.Errorf("couldn't marshal FwdReq: %v", err)
			}

			outDDP := &ddp.ExtPacket{
				ExtHeader: ddp.ExtHeader{
					Size:      atalk.DDPExtHeaderSize + uint16(len(nbpRaw)),
					Cksum:     0,
					SrcNet:    ddpkt.SrcNet,
					SrcNode:   ddpkt.SrcNode,
					SrcSocket: ddpkt.SrcSocket,
					DstNet:    z.Network,
					DstNode:   0x00, // Any router for the dest network
					DstSocket: 2,
					Proto:     ddp.ProtoNBP,
				},
				Data: nbpRaw,
			}

			return port.Router.Forward(ctx, outDDP)
		}

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

	return nil
}

// Returns an NBP LkUp-Reply for the router itself, with the address from this port.
func (port *EtherTalkPort) helloWorldThisIsMe(ddpkt *ddp.ExtPacket, nbpID uint8, tuple *nbp.Tuple) (*ddp.ExtPacket, error) {
	if tuple.Object != "jrouter" && tuple.Object != "=" {
		return nil, nil
	}
	if tuple.Type != "AppleRouter" && tuple.Type != "=" {
		return nil, nil
	}
	if tuple.Zone != port.DefaultZoneName && tuple.Zone != "*" && tuple.Zone != "" {
		return nil, nil
	}
	respPkt := &nbp.Packet{
		Function: nbp.FunctionLkUpReply,
		NBPID:    nbpID,
		Tuples: []nbp.Tuple{
			{
				Network:    port.MyAddr.Network,
				Node:       port.MyAddr.Node,
				Socket:     253,
				Enumerator: 0,
				Object:     "jrouter",
				Type:       "AppleRouter",
				Zone:       port.DefaultZoneName,
			},
		},
	}
	respRaw, err := respPkt.Marshal()
	if err != nil {
		return nil, fmt.Errorf("couldn't marshal LkUp-Reply: %v", err)
	}
	return &ddp.ExtPacket{
		ExtHeader: ddp.ExtHeader{
			Size:      uint16(len(respRaw)) + atalk.DDPExtHeaderSize,
			Cksum:     0,
			DstNet:    ddpkt.SrcNet,
			DstNode:   ddpkt.SrcNode,
			DstSocket: ddpkt.SrcSocket,
			SrcNet:    port.MyAddr.Network,
			SrcNode:   port.MyAddr.Node,
			SrcSocket: 2,
			Proto:     ddp.ProtoNBP,
		},
		Data: respRaw,
	}, nil
}