jrouter/atalk/nbp/nbp.go

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/*
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
)
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func (f Function) String() string {
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switch f {
case FunctionBrRq:
return "BrRq"
case FunctionLkUp:
return "LkUp"
case FunctionLkUpReply:
return "LkUp-Reply"
case FunctionFwdReq:
return "FwdReq"
default:
return "unknown"
}
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}
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// 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
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if tupleCount == 0 {
return nil, fmt.Errorf("no tuples")
}
// Only LkUp-Reply can have more than 1 tuple
if tupleCount > 1 && p.Function != FunctionLkUpReply {
return nil, fmt.Errorf("wrong number of tuples %d for function %s", tupleCount, p.Function)
}
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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]),
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Socket: ddp.Socket(data[3]),
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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
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Socket ddp.Socket
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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))
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b.WriteByte(byte(t.Socket))
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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
}
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func (t Tuple) String() string {
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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
}