Add NBP packet format

atalk/nbp/nbp.go

@@ -0,0 +1,158 @@
+/*
+   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 nbp
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+
+	"github.com/sfiera/multitalk/pkg/ddp"
+)
+
+// Function represents the NBP packet Function field.
+type Function uint8
+
+// Various functions.
+const (
+	FunctionBrRq      Function = 1
+	FunctionLkUp      Function = 2
+	FunctionLkUpReply Function = 3 // can have more than 1 tuple
+	FunctionFwdReq    Function = 4
+)
+
+// Packet represents an NBP packet.
+type Packet struct {
+	Function Function // top 4 bits of first byte
+	// TupleCount uint4 // bottom 4 bits of first byte
+	NBPID  uint8
+	Tuples []Tuple
+}
+
+func (p *Packet) Marshal() ([]byte, error) {
+	b := bytes.NewBuffer(nil)
+	if p.Function < 1 || p.Function > 4 {
+		return nil, fmt.Errorf("invalid NBP function %d", p.Function)
+	}
+	if len(p.Tuples) > 15 {
+		return nil, fmt.Errorf("too many NBP tuples (%d > 15)", len(p.Tuples))
+	}
+	b.WriteByte(byte(p.Function<<4) | byte(len(p.Tuples)))
+	b.WriteByte(p.NBPID)
+	for i, t := range p.Tuples {
+		if err := t.writeTo(b); err != nil {
+			return nil, fmt.Errorf("marshaling NBP tuple %d: %w", i, err)
+		}
+	}
+	return b.Bytes(), nil
+}
+
+func Unmarshal(data []byte) (*Packet, error) {
+	if len(data) < 2 {
+		return nil, fmt.Errorf("insufficient input length %d for NBP packet", len(data))
+	}
+	p := &Packet{
+		Function: Function(data[0] >> 4),
+		NBPID:    data[1],
+	}
+	tupleCount := data[0] & 0x0F
+	data = data[2:]
+	for range tupleCount {
+		if len(data) < 8 {
+			return nil, fmt.Errorf("insufficient remaining input length %d for NBP tuple", len(data))
+		}
+		t := Tuple{
+			Network:    ddp.Network(binary.BigEndian.Uint16(data[:2])),
+			Node:       ddp.Node(data[2]),
+			Socket:     data[3],
+			Enumerator: data[4],
+		}
+		data = data[5:]
+
+		var err error
+		t.Object, data, err = readLV(data)
+		if err != nil {
+			return nil, fmt.Errorf("reading NBP tuple Object: %w", err)
+		}
+		t.Type, data, err = readLV(data)
+		if err != nil {
+			return nil, fmt.Errorf("reading NBP tuple Type: %w", err)
+		}
+		t.Zone, data, err = readLV(data)
+		if err != nil {
+			return nil, fmt.Errorf("reading NBP tuple Zone: %w", err)
+		}
+		p.Tuples = append(p.Tuples, t)
+	}
+	return p, nil
+}
+
+// Tuple represents an NBP tuple.
+type Tuple struct {
+	Network    ddp.Network
+	Node       ddp.Node
+	Socket     uint8
+	Enumerator uint8
+	Object     string // length-prefixed
+	Type       string // length-prefixed
+	Zone       string // length-prefixed; "" interpreted as "*"
+}
+
+func (t *Tuple) writeTo(b *bytes.Buffer) error {
+	if len(t.Object) > 32 {
+		return fmt.Errorf("object field too long (%d > 32)", len(t.Object))
+	}
+	if len(t.Type) > 32 {
+		return fmt.Errorf("type field too long (%d > 32)", len(t.Type))
+	}
+	if len(t.Zone) > 32 {
+		return fmt.Errorf("zone field too long (%d > 32)", len(t.Zone))
+	}
+	write16(b, t.Network)
+	b.WriteByte(byte(t.Node))
+	b.WriteByte(t.Socket)
+	b.WriteByte(t.Enumerator)
+	b.WriteByte(byte(len(t.Object)))
+	b.WriteString(t.Object)
+	b.WriteByte(byte(len(t.Type)))
+	b.WriteString(t.Type)
+	b.WriteByte(byte(len(t.Zone)))
+	b.WriteString(t.Zone)
+	return nil
+}
+
+func (t *Tuple) String() string {
+	return fmt.Sprintf("%d.%d.%d (enum %d) <-> %s:%s@%s",
+		t.Network, t.Node, t.Socket, t.Enumerator, t.Object, t.Type, t.Zone,
+	)
+}
+
+func write16[I ~uint16](b *bytes.Buffer, n I) {
+	b.Write([]byte{byte(n >> 8), byte(n & 0xff)})
+}
+
+func readLV(data []byte) (string, []byte, error) {
+	if len(data) < 1 {
+		return "", data, fmt.Errorf("insufficient input length %d for length-prefixed string", len(data))
+	}
+	slen := int(data[0])
+	data = data[1:]
+	if len(data) < slen {
+		return "", data, fmt.Errorf("insufficient remaining input length %d for length-prefixed string of length %d", len(data), slen)
+	}
+	return string(data[:slen]), data[slen:], nil
+}