av/container/mts/psi/psi.go

/*
NAME
  psi.go

DESCRIPTION
  See Readme.md

AUTHOR
  Saxon Milton <saxon@ausocean.org>

LICENSE
  psi.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 for more details.

  You should have received a copy of the GNU General Public License
  along with revid in gpl.txt.  If not, see http://www.gnu.org/licenses.
*/

// Package psi provides encoding of MPEG-TS program specific information.
package psi

import (
	"errors"

	"github.com/Comcast/gots/psi"
)

// PacketSize of psi (without MPEG-TS header)
const PacketSize = 184

// Lengths of section definitions.
const (
	ESSDDefLen = 5
	DescDefLen = 2
	PMTDefLen  = 4
	PATLen     = 4
	TSSDefLen  = 5
	PSIDefLen  = 3
)

// Table Type IDs.
const (
	patID = 0x00
	pmtID = 0x02
)

// Consts relating to time description
// TODO: remove this, we don't do metadata like this anymore.
const (
	TimeDescTag  = 234
	TimeTagIndx  = 13
	TimeDataIndx = 15
	TimeDataSize = 8 // bytes, because time is stored in uint64
)

// Consts relating to location description
// TODO: remove this, we don't do metadata like this anymore.
const (
	LocationDescTag  = 235
	LocationTagIndx  = 23
	LocationDataIndx = 25
	LocationDataSize = 32 // bytes
)

// crc hassh Size
const crcSize = 4

// Consts relating to syntax section.
const (
	TotalSyntaxSecLen = 180
	SyntaxSecLenIdx1  = 2
	SyntaxSecLenIdx2  = 3
	SyntaxSecLenMask1 = 0x03
	SectionLenMask1   = 0x03
)

// Consts relating to program info len.
const (
	ProgramInfoLenIdx1  = 11
	ProgramInfoLenIdx2  = 12
	ProgramInfoLenMask1 = 0x03
)

// DescriptorsIdx is the index that the descriptors start at.
const DescriptorsIdx = ProgramInfoLenIdx2 + 1

// MetadataTag is the descriptor tag used for metadata.
const MetadataTag = 0x26

// TODO: get rid of these - not a good idea.
type (
	PSIBytes   []byte
	Descriptor []byte
)

// Program specific information
type PSI struct {
	Pf  byte   // Point field
	Pfb []byte // Pointer filler bytes
	Tid byte   // Table ID
	Ssi bool   // Section syntax indicator (1 for PAT, PMT, CAT)
	Pb  bool   // Private bit (0 for PAT, PMT, CAT)
	Sl  uint16 // Section length
	Tss *TSS   // Table syntax section (length defined by SL) if length 0 then nil
	Crc uint32 // crc32 of entire table excluding pointer field, pointer filler bytes and the trailing CRC32
}

// Table syntax section
type TSS struct {
	Tide uint16       // Table ID extension
	V    byte         // Version number
	Cni  bool         // Current/next indicator
	Sn   byte         // Section number
	Lsn  byte         // Last section number
	Sd   SpecificData // Specific data PAT/PMT
}

// Specific Data, (could be PAT or PMT)
type SpecificData interface {
	Bytes() []byte
}

// Program association table, implements SpecificData
type PAT struct {
	Pn    uint16 // Program Number
	Pmpid uint16 // Program map PID
}

// Program mapping table, implements SpecificData
type PMT struct {
	Pcrpid uint16 // Program clock reference pid
	Pil    uint16 // Program info length
	Pd     []Desc // Program descriptors
	Essd   *ESSD  // Elementary stream specific data
}

// Elementary stream specific data
type ESSD struct {
	St   byte   // Stream type
	Epid uint16 // Elementary pid
	Esil uint16 // Elementary stream
	Esd  []Desc // Elementary stream desriptors
}

// Descriptor
type Desc struct {
	Dt byte   // Descriptor tag
	Dl byte   // Descriptor length
	Dd []byte // Descriptor data
}

// Bytes outputs a byte slice representation of the PSI
func (p *PSI) Bytes() []byte {
	out := make([]byte, 4)
	out[0] = p.Pf
	if p.Pf != 0 {
		panic("No support for pointer filler bytes")
	}
	out[1] = p.Tid
	out[2] = 0x80 | 0x30 | (0x03 & byte(p.Sl>>8))
	out[3] = byte(p.Sl)
	out = append(out, p.Tss.Bytes()...)
	out = AddCrc(out)
	return out
}

// Bytes outputs a byte slice representation of the TSS
func (t *TSS) Bytes() []byte {
	out := make([]byte, TSSDefLen)
	out[0] = byte(t.Tide >> 8)
	out[1] = byte(t.Tide)
	out[2] = 0xc0 | (0x3e & (t.V << 1)) | (0x01 & asByte(t.Cni))
	out[3] = t.Sn
	out[4] = t.Lsn
	out = append(out, t.Sd.Bytes()...)
	return out
}

// Bytes outputs a byte slice representation of the PAT
func (p *PAT) Bytes() []byte {
	out := make([]byte, PATLen)
	out[0] = byte(p.Pn >> 8)
	out[1] = byte(p.Pn)
	out[2] = 0xe0 | (0x1f & byte(p.Pmpid>>8))
	out[3] = byte(p.Pmpid)
	return out
}

// Bytes outputs a byte slice representation of the PMT
func (p *PMT) Bytes() []byte {
	out := make([]byte, PMTDefLen)
	out[0] = 0xe0 | (0x1f & byte(p.Pcrpid>>8)) // byte 10
	out[1] = byte(p.Pcrpid)
	out[2] = 0xf0 | (0x03 & byte(p.Pil>>8))
	out[3] = byte(p.Pil)
	for _, d := range p.Pd {
		out = append(out, d.Bytes()...)
	}
	out = append(out, p.Essd.Bytes()...)
	return out
}

// Bytes outputs a byte slice representation of the Desc
func (d *Desc) Bytes() []byte {
	out := make([]byte, DescDefLen)
	out[0] = d.Dt
	out[1] = d.Dl
	out = append(out, d.Dd...)
	return out
}

// Bytes outputs a byte slice representation of the ESSD
func (e *ESSD) Bytes() []byte {
	out := make([]byte, ESSDDefLen)
	out[0] = e.St
	out[1] = 0xe0 | (0x1f & byte(e.Epid>>8))
	out[2] = byte(e.Epid)
	out[3] = 0xf0 | (0x03 & byte(e.Esil>>8))
	out[4] = byte(e.Esil)
	for _, d := range e.Esd {
		out = append(out, d.Bytes()...)
	}
	return out
}

func asByte(b bool) byte {
	if b {
		return 0x01
	}
	return 0x00
}

// AddDescriptor adds or updates a descriptor in a PSI given a descriptor tag
// and data. If the psi is not a pmt, then an error is returned. If a descriptor
// with the given tag is not found in the psi, room is made and a descriptor with
// given tag and data is created. If a descriptor with the tag is found, the
// descriptor is resized as required and the new data is copied in.
func (p *PSIBytes) AddDescriptor(tag int, data []byte) error {
	if psi.TableID(*p) != pmtID {
		return errors.New("trying to add descriptor, but not pmt")
	}

	i, desc := p.HasDescriptor(tag)
	if desc == nil {
		err := p.createDescriptor(tag, data)
		return err
	}

	oldDescLen := desc.len()
	oldDataLen := int(desc[1])
	newDataLen := len(data)
	newDescLen := 2 + newDataLen
	delta := newDescLen - oldDescLen

	// If the old data length is more than the new data length, we need shift data
	// after descriptor up, and then trim the psi. If the oldDataLen is less than
	// new data then we need reseize psi and shift data down. If same do nothing.
	switch {
	case oldDataLen > newDataLen:
		copy((*p)[i+newDescLen:], (*p)[i+oldDescLen:])
		*p = (*p)[:len(*p)+delta]
	case oldDataLen < newDataLen:
		tmp := make([]byte, len(*p)+delta)
		copy(tmp, *p)
		*p = tmp
		copy((*p)[i+newDescLen:], (*p)[i+oldDescLen:])
	}

	// Copy in new data
	(*p)[i+1] = byte(newDataLen)
	copy((*p)[i+2:], data)

	newProgInfoLen := p.ProgramInfoLen() + delta
	p.setProgInfoLen(newProgInfoLen)
	newSectionLen := int(psi.SectionLength(*p)) + delta
	p.setSectionLen(newSectionLen)
	UpdateCrc((*p)[1:])
	return nil
}

// HasDescriptor checks if a descriptor of the given tag exists in a PSI. If the descriptor
// of the given tag exists, an index of this descriptor, as well as the Descriptor is returned.
// If the descriptor of the given tag cannot be found, -1 and a nil slice is returned.
//
// TODO: check if pmt, return error if not ?
func (p *PSIBytes) HasDescriptor(tag int) (int, Descriptor) {
	descs := p.descriptors()
	if descs == nil {
		return -1, nil
	}
	for i := 0; i < len(descs); i += 2 + int(descs[i+1]) {
		if int(descs[i]) == tag {
			return i + DescriptorsIdx, descs[i : i+2+int(descs[i+1])]
		}
	}
	return -1, nil
}

// createDescriptor creates a descriptor in a psi given a tag and data. It does so
// by resizing the psi, shifting existing data down and copying in new descriptor
// in new space.
func (p *PSIBytes) createDescriptor(tag int, data []byte) error {
	curProgLen := p.ProgramInfoLen()
	oldSyntaxSectionLen := SyntaxSecLenFrom(*p)
	if TotalSyntaxSecLen-(oldSyntaxSectionLen+2+len(data)) <= 0 {
		return errors.New("Not enough space in psi to create descriptor.")
	}
	dataLen := len(data)
	newDescIdx := DescriptorsIdx + curProgLen
	newDescLen := dataLen + 2

	// Increase size of psi and copy data down to make room for new descriptor.
	tmp := make([]byte, len(*p)+newDescLen)
	copy(tmp, *p)
	*p = tmp
	copy((*p)[newDescIdx+newDescLen:], (*p)[newDescIdx:newDescIdx+newDescLen])
	// Set the tag, data len and data of the new desriptor.
	(*p)[newDescIdx] = byte(tag)
	(*p)[newDescIdx+1] = byte(dataLen)
	copy((*p)[newDescIdx+2:newDescIdx+2+dataLen], data)

	// Set length fields and update the psi crc.
	addedLen := dataLen + 2
	newProgInfoLen := curProgLen + addedLen
	p.setProgInfoLen(newProgInfoLen)
	newSyntaxSectionLen := int(oldSyntaxSectionLen) + addedLen
	p.setSectionLen(newSyntaxSectionLen)
	UpdateCrc((*p)[1:])

	return nil
}

// setProgInfoLen sets the program information length in a psi with a pmt.
func (p *PSIBytes) setProgInfoLen(l int) {
	(*p)[ProgramInfoLenIdx1] &= 0xff ^ ProgramInfoLenMask1
	(*p)[ProgramInfoLenIdx1] |= byte(l>>8) & ProgramInfoLenMask1
	(*p)[ProgramInfoLenIdx2] = byte(l)
}

// setSectionLen sets section length in a psi.
func (p *PSIBytes) setSectionLen(l int) {
	(*p)[SyntaxSecLenIdx1] &= 0xff ^ SyntaxSecLenMask1
	(*p)[SyntaxSecLenIdx1] |= byte(l>>8) & SyntaxSecLenMask1
	(*p)[SyntaxSecLenIdx2] = byte(l)
}

// descriptors returns the descriptors in a psi if they exist, otherwise
// a nil slice is returned.
func (p *PSIBytes) descriptors() []byte {
	return (*p)[DescriptorsIdx : DescriptorsIdx+p.ProgramInfoLen()]
}

// len returns the length of a descriptor in bytes.
func (d *Descriptor) len() int {
	return int(2 + (*d)[1])
}

// ProgramInfoLen returns the program info length of a PSI.
//
// TODO: check if pmt - if not return 0 ? or -1 ?
func (p *PSIBytes) ProgramInfoLen() int {
	return int((((*p)[ProgramInfoLenIdx1] & ProgramInfoLenMask1) << 8) | (*p)[ProgramInfoLenIdx2])
}