146 lines
3.6 KiB
Go
146 lines
3.6 KiB
Go
/*
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Copyright 2024 Josh Deprez
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package atp
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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)
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const (
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ciFuncMask = 0b11000000
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ciFuncTReq = 0b01000000
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ciFuncTResp = 0b10000000
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ciFuncTRel = 0b11000000
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ciXOBit = 0b00100000
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ciEOMBit = 0b00010000
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ciSTSBit = 0b00001000
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ciTRelTOMask = 0b00000111
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)
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type TReq struct {
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// Control information: 0 1 (XO) 0 0 (Timeout indicator)
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ExactlyOnce bool
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TRelTimeoutIndicator uint8 // only if XO is set
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Bitmap uint8
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TransactionID uint16
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UserBytes [4]byte
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Data []byte
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}
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func (p *TReq) Marshal() ([]byte, error) {
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if p.TRelTimeoutIndicator != 0 && !p.ExactlyOnce {
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return nil, fmt.Errorf("TRel timeout indicator %d only valid for XO TReq", p.TRelTimeoutIndicator)
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}
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if p.TRelTimeoutIndicator > 4 {
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return nil, fmt.Errorf("invalid TRel timeout indicator [%d > 4]", p.TRelTimeoutIndicator)
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}
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b := bytes.NewBuffer(nil)
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ci := byte(ciFuncTReq)
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if p.ExactlyOnce {
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ci |= ciXOBit
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}
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ci |= p.TRelTimeoutIndicator
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b.WriteByte(ci)
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b.WriteByte(p.Bitmap)
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write16(b, p.TransactionID)
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b.Write(p.UserBytes[:])
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b.Write(p.Data)
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return b.Bytes(), nil
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}
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type TResp struct {
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// Control information: 1 0 0 (EOM) (STS) 0 0 0
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EndOfMessage bool
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SendTransactionStatus bool
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Sequence uint8
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TransactionID uint16
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UserBytes [4]byte
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Data []byte
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}
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func (p *TResp) Marshal() ([]byte, error) {
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b := bytes.NewBuffer(nil)
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ci := byte(ciFuncTResp)
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if p.EndOfMessage {
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ci |= ciEOMBit
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}
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if p.SendTransactionStatus {
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ci |= ciSTSBit
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}
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b.WriteByte(ci)
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b.WriteByte(p.Sequence)
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write16(b, p.TransactionID)
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b.Write(p.UserBytes[:])
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b.Write(p.Data)
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return b.Bytes(), nil
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}
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type TRel struct {
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// Control information: 1 1 0 0 0 0 0 0
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TransactionID uint16
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}
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func (p *TRel) Marshal() ([]byte, error) {
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return []byte{
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ciFuncTRel, 0,
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byte(p.TransactionID >> 8),
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byte(p.TransactionID & 0xFF),
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0, 0, 0, 0,
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}, nil
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}
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func UnmarshalPacket(data []byte) (any, error) {
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if len(data) < 8 {
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return nil, fmt.Errorf("insufficient input length %d for ATP packet", len(data))
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}
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switch data[0] & ciFuncMask {
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case ciFuncTReq:
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return &TReq{
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ExactlyOnce: data[0]&ciXOBit != 0,
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TRelTimeoutIndicator: data[0] & ciTRelTOMask,
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Bitmap: data[1],
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TransactionID: binary.BigEndian.Uint16(data[2:4]),
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UserBytes: [4]byte(data[4:8]),
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Data: data[8:],
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}, nil
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case ciFuncTResp:
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return &TResp{
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EndOfMessage: data[0]&ciEOMBit != 0,
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SendTransactionStatus: data[0]&ciSTSBit != 0,
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Sequence: data[1],
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TransactionID: binary.BigEndian.Uint16(data[2:4]),
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UserBytes: [4]byte(data[4:8]),
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Data: data[8:],
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}, nil
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case ciFuncTRel:
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return &TRel{
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TransactionID: binary.BigEndian.Uint16(data[2:4]),
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}, nil
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default:
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return nil, fmt.Errorf("unknown ATP function in control information byte %b", data[0])
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}
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}
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func write16[I ~uint16](b *bytes.Buffer, n I) {
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b.Write([]byte{byte(n >> 8), byte(n & 0xff)})
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}
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