mirror of https://bitbucket.org/ausocean/av.git
217 lines
9.0 KiB
Go
217 lines
9.0 KiB
Go
/*
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NAME
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mpegts.go - provides a data structure intended to encapsulate the properties
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of an MpegTs packet and also functions to allow manipulation of these packets.
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DESCRIPTION
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See Readme.md
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AUTHOR
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Saxon A. Nelson-Milton <saxon.milton@gmail.com>
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LICENSE
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mpegts.go is Copyright (C) 2017 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with revid in gpl.txt. If not, see [GNU licenses](http://www.gnu.org/licenses).
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*/
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package mts
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import (
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"errors"
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)
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const (
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PktSize = 188
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PayloadSize = 176
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)
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/*
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The below data struct encapsulates the fields of an MPEG-TS packet. Below is
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the formatting of an MPEG-TS packet for reference!
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MPEG-TS Packet Formatting
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============================================================================
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| octet no | bit 0 | bit 1 | bit 2 | bit 3 | bit 4 | bit 5 | bit 6 | bit 7 |
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============================================================================
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| octet 0 | sync byte (0x47) |
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----------------------------------------------------------------------------
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| octet 1 | TEI | PUSI | Prior | PID |
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----------------------------------------------------------------------------
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| octet 2 | PID cont. |
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----------------------------------------------------------------------------
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| octet 3 | TSC | AFC | CC |
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----------------------------------------------------------------------------
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| octet 4 | AFL |
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----------------------------------------------------------------------------
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| octet 5 | DI | RAI | ESPI | PCRF | OPCRF | SPF | TPDF | AFEF |
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----------------------------------------------------------------------------
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| optional | PCR (48 bits => 6 bytes) |
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----------------------------------------------------------------------------
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| - | PCR cont. |
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----------------------------------------------------------------------------
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| - | PCR cont. |
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----------------------------------------------------------------------------
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| - | PCR cont. |
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----------------------------------------------------------------------------
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| - | PCR cont. |
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----------------------------------------------------------------------------
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| - | PCR cont. |
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----------------------------------------------------------------------------
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| optional | OPCR (48 bits => 6 bytes) |
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----------------------------------------------------------------------------
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| - | OPCR cont. |
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----------------------------------------------------------------------------
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| - | OPCR cont. |
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----------------------------------------------------------------------------
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| - | OPCR cont. |
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----------------------------------------------------------------------------
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| - | OPCR cont. |
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----------------------------------------------------------------------------
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| - | OPCR cont. |
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----------------------------------------------------------------------------
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| optional | SC |
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----------------------------------------------------------------------------
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| optional | TPDL |
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----------------------------------------------------------------------------
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| optional | TPD (variable length) |
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----------------------------------------------------------------------------
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| - | ... |
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----------------------------------------------------------------------------
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| optional | Extension (variable length) |
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----------------------------------------------------------------------------
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| - | ... |
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----------------------------------------------------------------------------
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| optional | Stuffing (variable length) |
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----------------------------------------------------------------------------
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| - | ... |
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----------------------------------------------------------------------------
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| optional | Payload (variable length) |
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----------------------------------------------------------------------------
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| - | ... |
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----------------------------------------------------------------------------
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*/
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type Packet struct {
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TEI bool // Transport Error Indicator
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PUSI bool // Payload Unit Start Indicator
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Priority bool // Tranposrt priority indicator
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PID uint16 // Packet identifier
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TSC byte // Transport Scrambling Control
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AFC byte // Adaption Field Control
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CC byte // Continuity Counter
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DI bool // Discontinouty indicator
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RAI bool // random access indicator
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ESPI bool // Elementary stream priority indicator
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PCRF bool // PCR flag
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OPCRF bool // OPCR flag
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SPF bool // Splicing point flag
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TPDF bool // Transport private data flag
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AFEF bool // Adaptation field extension flag
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PCR uint64 // Program clock reference
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OPCR uint64 // Original program clock reference
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SC byte // Splice countdown
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TPDL byte // Tranposrt private data length
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TPD []byte // Private data
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Ext []byte // Adaptation field extension
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Payload []byte // Mpeg ts Payload
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}
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// FindPMT will take a clip of mpegts and try to find a PMT table - if one
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// is found, then it is returned, otherwise nil and an error is returned.
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func FindPMT(d []byte) (p []byte, err error) {
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if len(d) < PktSize {
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return nil, errors.New("Mmpegts data not of valid length")
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}
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for i := 0; i < len(d); i += PktSize {
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pid := (uint16(d[i+1]&0x1f) << 8) | uint16(d[i+2])
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if pid == pmtPid {
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p = d[i+4 : i+PktSize]
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return
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}
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}
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return nil, errors.New("Could not find pmt table in mpegts data")
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}
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// FillPayload takes a channel and fills the packets Payload field until the
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// channel is empty or we've the packet reaches capacity
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func (p *Packet) FillPayload(data []byte) int {
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currentPktLen := 6 + asInt(p.PCRF)*6 + asInt(p.OPCRF)*6 +
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asInt(p.SPF)*1 + asInt(p.TPDF)*1 + len(p.TPD)
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p.Payload = make([]byte, PayloadSize-currentPktLen)
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return copy(p.Payload, data)
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}
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func asInt(b bool) int {
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if b {
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return 1
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}
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return 0
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}
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func asByte(b bool) byte {
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if b {
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return 1
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}
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return 0
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}
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// ToByteSlice interprets the fields of the ts packet instance and outputs a
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// corresponding byte slice
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func (p *Packet) Bytes(buf []byte) []byte {
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if buf == nil || cap(buf) != PktSize {
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buf = make([]byte, 0, PktSize)
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}
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buf = buf[:0]
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stuffingLength := 182 - len(p.Payload) - len(p.TPD) - asInt(p.PCRF)*6 -
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asInt(p.OPCRF)*6 - asInt(p.SPF)
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var stuffing []byte
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if stuffingLength > 0 {
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stuffing = make([]byte, stuffingLength)
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}
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for i := range stuffing {
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stuffing[i] = 0xFF
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}
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afl := 1 + asInt(p.PCRF)*6 + asInt(p.OPCRF)*6 + asInt(p.SPF) + asInt(p.TPDF) + len(p.TPD) + len(stuffing)
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buf = append(buf, []byte{
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0x47,
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(asByte(p.TEI)<<7 | asByte(p.PUSI)<<6 | asByte(p.Priority)<<5 | byte((p.PID&0xFF00)>>8)),
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byte(p.PID & 0x00FF),
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(p.TSC<<6 | p.AFC<<4 | p.CC),
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}...)
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if p.AFC == 3 || p.AFC == 2 {
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buf = append(buf, []byte{
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byte(afl), (asByte(p.DI)<<7 | asByte(p.RAI)<<6 | asByte(p.ESPI)<<5 |
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asByte(p.PCRF)<<4 | asByte(p.OPCRF)<<3 | asByte(p.SPF)<<2 |
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asByte(p.TPDF)<<1 | asByte(p.AFEF)),
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}...)
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for i := 40; p.PCRF && i >= 0; i -= 8 {
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buf = append(buf, byte((p.PCR<<15)>>uint(i)))
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}
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for i := 40; p.OPCRF && i >= 0; i -= 8 {
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buf = append(buf, byte(p.OPCR>>uint(i)))
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}
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if p.SPF {
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buf = append(buf, p.SC)
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}
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if p.TPDF {
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buf = append(buf, append([]byte{p.TPDL}, p.TPD...)...)
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}
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buf = append(buf, p.Ext...)
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buf = append(buf, stuffing...)
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}
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buf = append(buf, p.Payload...)
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return buf
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}
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