gotosocial/vendor/github.com/dsoprea/go-png-image-structure/v2/png.go

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package pngstructure
import (
"bytes"
"errors"
"fmt"
"io"
"encoding/binary"
"hash/crc32"
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"github.com/dsoprea/go-exif/v3"
"github.com/dsoprea/go-exif/v3/common"
"github.com/dsoprea/go-logging"
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"github.com/dsoprea/go-utility/v2/image"
)
var (
PngSignature = [8]byte{137, 'P', 'N', 'G', '\r', '\n', 26, '\n'}
EXifChunkType = "eXIf"
IHDRChunkType = "IHDR"
)
var (
ErrNotPng = errors.New("not png data")
ErrCrcFailure = errors.New("crc failure")
)
// ChunkSlice encapsulates a slice of chunks.
type ChunkSlice struct {
chunks []*Chunk
}
func NewChunkSlice(chunks []*Chunk) *ChunkSlice {
if len(chunks) == 0 {
log.Panicf("ChunkSlice must be initialized with at least one chunk (IHDR)")
} else if chunks[0].Type != IHDRChunkType {
log.Panicf("first chunk in any ChunkSlice must be an IHDR")
}
return &ChunkSlice{
chunks: chunks,
}
}
func NewPngChunkSlice() *ChunkSlice {
ihdrChunk := &Chunk{
Type: IHDRChunkType,
}
ihdrChunk.UpdateCrc32()
return NewChunkSlice([]*Chunk{ihdrChunk})
}
func (cs *ChunkSlice) String() string {
return fmt.Sprintf("ChunkSlize<LEN=(%d)>", len(cs.chunks))
}
// Chunks exposes the actual slice.
func (cs *ChunkSlice) Chunks() []*Chunk {
return cs.chunks
}
// Write encodes and writes all chunks.
func (cs *ChunkSlice) WriteTo(w io.Writer) (err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
_, err = w.Write(PngSignature[:])
log.PanicIf(err)
// TODO(dustin): !! This should respect the safe-to-copy characteristic.
for _, c := range cs.chunks {
_, err := c.WriteTo(w)
log.PanicIf(err)
}
return nil
}
// Index returns a map of chunk types to chunk slices, grouping all like chunks.
func (cs *ChunkSlice) Index() (index map[string][]*Chunk) {
index = make(map[string][]*Chunk)
for _, c := range cs.chunks {
if grouped, found := index[c.Type]; found == true {
index[c.Type] = append(grouped, c)
} else {
index[c.Type] = []*Chunk{c}
}
}
return index
}
// FindExif returns the the segment that hosts the EXIF data.
func (cs *ChunkSlice) FindExif() (chunk *Chunk, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
index := cs.Index()
if chunks, found := index[EXifChunkType]; found == true {
return chunks[0], nil
}
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log.Panic(exif.ErrNoExif)
// Never called.
return nil, nil
}
// Exif returns an `exif.Ifd` instance with the existing tags.
func (cs *ChunkSlice) Exif() (rootIfd *exif.Ifd, data []byte, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
chunk, err := cs.FindExif()
log.PanicIf(err)
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im, err := exifcommon.NewIfdMappingWithStandard()
log.PanicIf(err)
ti := exif.NewTagIndex()
// TODO(dustin): Refactor and support `exif.GetExifData()`.
_, index, err := exif.Collect(im, ti, chunk.Data)
log.PanicIf(err)
return index.RootIfd, chunk.Data, nil
}
// ConstructExifBuilder returns an `exif.IfdBuilder` instance (needed for
// modifying) preloaded with all existing tags.
func (cs *ChunkSlice) ConstructExifBuilder() (rootIb *exif.IfdBuilder, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
rootIfd, _, err := cs.Exif()
log.PanicIf(err)
ib := exif.NewIfdBuilderFromExistingChain(rootIfd)
return ib, nil
}
// SetExif encodes and sets EXIF data into this segment.
func (cs *ChunkSlice) SetExif(ib *exif.IfdBuilder) (err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
// Encode.
ibe := exif.NewIfdByteEncoder()
exifData, err := ibe.EncodeToExif(ib)
log.PanicIf(err)
// Set.
exifChunk, err := cs.FindExif()
if err == nil {
// EXIF chunk already exists.
exifChunk.Data = exifData
exifChunk.Length = uint32(len(exifData))
} else {
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if log.Is(err, exif.ErrNoExif) != true {
log.Panic(err)
}
// Add a EXIF chunk for the first time.
exifChunk = &Chunk{
Type: EXifChunkType,
Data: exifData,
Length: uint32(len(exifData)),
}
// Insert it after the IHDR chunk (it's a reliably appropriate place to
// put it).
cs.chunks = append(cs.chunks[:1], append([]*Chunk{exifChunk}, cs.chunks[1:]...)...)
}
exifChunk.UpdateCrc32()
return nil
}
// PngSplitter hosts the princpal `Split()` method uses by `bufio.Scanner`.
type PngSplitter struct {
chunks []*Chunk
currentOffset int
doCheckCrc bool
crcErrors []string
}
func (ps *PngSplitter) Chunks() *ChunkSlice {
return NewChunkSlice(ps.chunks)
}
func (ps *PngSplitter) DoCheckCrc(doCheck bool) {
ps.doCheckCrc = doCheck
}
func (ps *PngSplitter) CrcErrors() []string {
return ps.crcErrors
}
func NewPngSplitter() *PngSplitter {
return &PngSplitter{
chunks: make([]*Chunk, 0),
doCheckCrc: true,
crcErrors: make([]string, 0),
}
}
// Chunk describes a single chunk.
type Chunk struct {
Offset int
Length uint32
Type string
Data []byte
Crc uint32
}
func (c *Chunk) String() string {
return fmt.Sprintf("Chunk<OFFSET=(%d) LENGTH=(%d) TYPE=[%s] CRC=(%d)>", c.Offset, c.Length, c.Type, c.Crc)
}
func calculateCrc32(chunk *Chunk) uint32 {
c := crc32.NewIEEE()
c.Write([]byte(chunk.Type))
c.Write(chunk.Data)
return c.Sum32()
}
func (c *Chunk) UpdateCrc32() {
c.Crc = calculateCrc32(c)
}
func (c *Chunk) CheckCrc32() bool {
expected := calculateCrc32(c)
return c.Crc == expected
}
// Bytes encodes and returns the bytes for this chunk.
func (c *Chunk) Bytes() []byte {
defer func() {
if state := recover(); state != nil {
err := log.Wrap(state.(error))
log.Panic(err)
}
}()
if len(c.Data) != int(c.Length) {
log.Panicf("length of data not correct")
}
preallocated := make([]byte, 0, 4+4+c.Length+4)
b := bytes.NewBuffer(preallocated)
err := binary.Write(b, binary.BigEndian, c.Length)
log.PanicIf(err)
_, err = b.Write([]byte(c.Type))
log.PanicIf(err)
if c.Data != nil {
_, err = b.Write(c.Data)
log.PanicIf(err)
}
err = binary.Write(b, binary.BigEndian, c.Crc)
log.PanicIf(err)
return b.Bytes()
}
// Write encodes and writes the bytes for this chunk.
func (c *Chunk) WriteTo(w io.Writer) (count int, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
if len(c.Data) != int(c.Length) {
log.Panicf("length of data not correct")
}
err = binary.Write(w, binary.BigEndian, c.Length)
log.PanicIf(err)
_, err = w.Write([]byte(c.Type))
log.PanicIf(err)
_, err = w.Write(c.Data)
log.PanicIf(err)
err = binary.Write(w, binary.BigEndian, c.Crc)
log.PanicIf(err)
return 4 + len(c.Type) + len(c.Data) + 4, nil
}
// readHeader verifies that the PNG header bytes appear next.
func (ps *PngSplitter) readHeader(r io.Reader) (err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
len_ := len(PngSignature)
header := make([]byte, len_)
_, err = r.Read(header)
log.PanicIf(err)
ps.currentOffset += len_
if bytes.Compare(header, PngSignature[:]) != 0 {
log.Panic(ErrNotPng)
}
return nil
}
// Split fulfills the `bufio.SplitFunc` function definition for
// `bufio.Scanner`.
func (ps *PngSplitter) Split(data []byte, atEOF bool) (advance int, token []byte, err error) {
defer func() {
if state := recover(); state != nil {
err = log.Wrap(state.(error))
}
}()
// We might have more than one chunk's worth, and, if `atEOF` is true, we
// won't be called again. We'll repeatedly try to read additional chunks,
// but, when we run out of the data we were given then we'll return the
// number of bytes fo rthe chunks we've already completely read. Then,
// we'll be called again from theend ofthose bytes, at which point we'll
// indicate that we don't yet have enough for another chunk, and we should
// be then called with more.
for {
len_ := len(data)
if len_ < 8 {
return advance, nil, nil
}
length := binary.BigEndian.Uint32(data[:4])
type_ := string(data[4:8])
chunkSize := (8 + int(length) + 4)
if len_ < chunkSize {
return advance, nil, nil
}
crcIndex := 8 + length
crc := binary.BigEndian.Uint32(data[crcIndex : crcIndex+4])
content := make([]byte, length)
copy(content, data[8:8+length])
c := &Chunk{
Length: length,
Type: type_,
Data: content,
Crc: crc,
Offset: ps.currentOffset,
}
ps.chunks = append(ps.chunks, c)
if c.CheckCrc32() == false {
ps.crcErrors = append(ps.crcErrors, type_)
if ps.doCheckCrc == true {
log.Panic(ErrCrcFailure)
}
}
advance += chunkSize
ps.currentOffset += chunkSize
data = data[chunkSize:]
}
return advance, nil, nil
}
var (
// Enforce interface conformance.
_ riimage.MediaContext = new(ChunkSlice)
)