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"

	"drjosh.dev/jrouter/atalk"
	"drjosh.dev/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(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:
		return port.Router.handleNBPFwdReq(ctx, ddpkt, nbpkt)

	case nbp.FunctionBrRq:
		return port.handleNBPBrRq(ctx, ddpkt, nbpkt)

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

func (port *EtherTalkPort) handleNBPBrRq(ctx context.Context, ddpkt *ddp.ExtPacket, nbpkt *nbp.Packet) error {
	// A BrRq was addressed to us. The sender (on a local network) is aware that
	// the network is extended and routed, and instead of broadcasting a LkUp
	// itself, is asking us to do it.

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

	// This logic would be required on a non-extended network:
	// if tuple.Zone == "" || tuple.Zone == "*" {
	// 	tuple.Zone = port.DefaultZoneName
	// }

	routes := port.Router.RouteTable.RoutesForZone(tuple.Zone)

	for _, route := range routes {
		if outPort := route.EtherTalkDirect; 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:    port.MyAddr.Network,
					SrcNode:   port.MyAddr.Node,
					SrcSocket: 2,
					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
			// This uses the *input* port information.
			outDDP2, err := port.helloWorldThisIsMe(nbpkt.NBPID, tuple)
			if err != nil {
				return err
			}
			if outDDP2 == nil {
				continue
			}
			log.Print("NBP: Replying to BrRq directly with LkUp-Reply for myself")
			// Can reply to this BrRq on the same port we got it, because it
			// wasn't routed
			if err := port.Send(ctx, outDDP2); err != nil {
				return err
			}

			continue
		}

		// The zone table row is *not* for a local network.
		// Translate it into a FwdReq and route that to the routers that do have
		// that zone as a local network.
		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:    route.NetStart,
				DstNode:   0x00, // Any router for the dest network
				DstSocket: 2,
				Proto:     ddp.ProtoNBP,
			},
			Data: nbpRaw,
		}

		if err := port.Router.Output(ctx, outDDP); err != nil {
			return err
		}
	}
	return nil
}

func (rtr *Router) handleNBPFwdReq(ctx context.Context, ddpkt *ddp.ExtPacket, nbpkt *nbp.Packet) error {
	// A FwdReq was addressed to us. That means a remote router thinks the
	// zone is available on one or more of our local networks.

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

	for _, outPort := range rtr.Ports {
		if !outPort.AvailableZones.Contains(tuple.Zone) {
			continue
		}
		log.Printf("NBP: Converting FwdReq to LkUp (%v)", tuple)

		// Convert it to a LkUp and broadcast on the corresponding port
		nbpkt.Function = nbp.FunctionLkUp
		nbpRaw, err := nbpkt.Marshal()
		if err != nil {
			return fmt.Errorf("couldn't marshal LkUp: %v", err)
		}

		// Inside AppleTalk SE, pp 8-20:
		// "If the destination network is extended, however, the router must also
		// change the destination network number to $0000, so that the packet is
		// received by all nodes on the network (within the correct zone multicast
		// address)."
		ddpkt.DstNet = 0x0000
		ddpkt.DstNode = 0xFF // Broadcast node address within the dest network
		ddpkt.Data = nbpRaw

		if err := outPort.ZoneMulticast(tuple.Zone, ddpkt); err != nil {
			return err
		}

		// But also... if it matches us, reply directly with a LkUp-Reply of our own
		outDDP, err := outPort.helloWorldThisIsMe(nbpkt.NBPID, tuple)
		if err != nil || outDDP == nil {
			return err
		}
		if err := rtr.Output(ctx, outDDP); err != nil {
			return err
		}
	}
	return nil
}

// Returns an NBP LkUp-Reply for the router itself, with the address from this port.
func (port *EtherTalkPort) helloWorldThisIsMe(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)
	}

	// Inside AppleTalk SE, pp 7-16:
	// "In BrRq, FwdReq, and LkUp packets, which carry only a single tuple, the
	// address field contains the internet address of the requester, allowing
	// the responder to address the LkUp-Reply datagram."
	// Inside AppleTalk SE, pp 8-20:
	// "Note: NBP is defined so that the router's NBP process does not
	// participate in the NBP response process; the response is sent directly to
	// the original requester through DDP. It is important that the original
	// requester's field be obtained from the address field of the NBP tuple."
	return &ddp.ExtPacket{
		ExtHeader: ddp.ExtHeader{
			Size:      uint16(len(respRaw)) + atalk.DDPExtHeaderSize,
			Cksum:     0,
			DstNet:    tuple.Network,
			DstNode:   tuple.Node,
			DstSocket: tuple.Socket,
			SrcNet:    port.MyAddr.Network,
			SrcNode:   port.MyAddr.Node,
			SrcSocket: 2,
			Proto:     ddp.ProtoNBP,
		},
		Data: respRaw,
	}, nil
}