jrouter/atalk/atp/atp.go

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2024-04-14 17:01:04 +10:00
/*
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 atp
import (
"bytes"
"encoding/binary"
"fmt"
)
const (
ciFuncMask = 0b11000000
ciFuncTReq = 0b01000000
ciFuncTResp = 0b10000000
ciFuncTRel = 0b11000000
ciXOBit = 0b00100000
ciEOMBit = 0b00010000
ciSTSBit = 0b00001000
ciTRelTOMask = 0b00000111
)
type TReq struct {
// Control information: 0 1 (XO) 0 0 (Timeout indicator)
ExactlyOnce bool
TRelTimeoutIndicator uint8 // only if XO is set
Bitmap uint8
TransactionID uint16
UserBytes [4]byte
Data []byte
}
func (p *TReq) Marshal() ([]byte, error) {
if p.TRelTimeoutIndicator != 0 && !p.ExactlyOnce {
return nil, fmt.Errorf("TRel timeout indicator %d only valid for XO TReq", p.TRelTimeoutIndicator)
}
if p.TRelTimeoutIndicator > 4 {
return nil, fmt.Errorf("invalid TRel timeout indicator [%d > 4]", p.TRelTimeoutIndicator)
}
b := bytes.NewBuffer(nil)
ci := byte(ciFuncTReq)
if p.ExactlyOnce {
ci |= ciXOBit
}
ci |= p.TRelTimeoutIndicator
b.WriteByte(ci)
b.WriteByte(p.Bitmap)
write16(b, p.TransactionID)
b.Write(p.UserBytes[:])
b.Write(p.Data)
return b.Bytes(), nil
}
type TResp struct {
// Control information: 1 0 0 (EOM) (STS) 0 0 0
EndOfMessage bool
SendTransactionStatus bool
Sequence uint8
TransactionID uint16
UserBytes [4]byte
Data []byte
}
func (p *TResp) Marshal() ([]byte, error) {
b := bytes.NewBuffer(nil)
ci := byte(ciFuncTResp)
if p.EndOfMessage {
ci |= ciEOMBit
}
if p.SendTransactionStatus {
ci |= ciSTSBit
}
b.WriteByte(ci)
b.WriteByte(p.Sequence)
write16(b, p.TransactionID)
b.Write(p.UserBytes[:])
b.Write(p.Data)
return b.Bytes(), nil
}
type TRel struct {
// Control information: 1 1 0 0 0 0 0 0
TransactionID uint16
}
func (p *TRel) Marshal() ([]byte, error) {
return []byte{
ciFuncTRel, 0,
byte(p.TransactionID >> 8),
byte(p.TransactionID & 0xFF),
0, 0, 0, 0,
}, nil
}
func UnmarshalPacket(data []byte) (any, error) {
if len(data) < 8 {
return nil, fmt.Errorf("insufficient input length %d for ATP packet", len(data))
}
switch data[0] & ciFuncMask {
case ciFuncTReq:
return &TReq{
ExactlyOnce: data[0]&ciXOBit != 0,
TRelTimeoutIndicator: data[0] & ciTRelTOMask,
Bitmap: data[1],
TransactionID: binary.BigEndian.Uint16(data[2:4]),
UserBytes: [4]byte(data[4:8]),
Data: data[8:],
}, nil
case ciFuncTResp:
return &TResp{
EndOfMessage: data[0]&ciEOMBit != 0,
SendTransactionStatus: data[0]&ciSTSBit != 0,
Sequence: data[1],
TransactionID: binary.BigEndian.Uint16(data[2:4]),
UserBytes: [4]byte(data[4:8]),
Data: data[8:],
}, nil
case ciFuncTRel:
return &TRel{
TransactionID: binary.BigEndian.Uint16(data[2:4]),
}, nil
default:
return nil, fmt.Errorf("unknown ATP function in control information byte %b", data[0])
}
}
func write16[I ~uint16](b *bytes.Buffer, n I) {
b.Write([]byte{byte(n >> 8), byte(n & 0xff)})
}