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

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package pngstructure
import (
"bytes"
"errors"
"fmt"
"io"
"encoding/binary"
"hash/crc32"
"github.com/dsoprea/go-exif/v3"
exifcommon "github.com/dsoprea/go-exif/v3/common"
riimage "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, error) {
if len(chunks) == 0 {
err := errors.New("ChunkSlice must be initialized with at least one chunk (IHDR)")
return nil, err
} else if chunks[0].Type != IHDRChunkType {
err := errors.New("first chunk in any ChunkSlice must be an IHDR")
return nil, err
}
return &ChunkSlice{chunks}, nil
}
func NewPngChunkSlice() (*ChunkSlice, error) {
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) error {
if _, err := w.Write(PngSignature[:]); err != nil {
return err
}
// TODO(dustin): !! This should respect
// the safe-to-copy characteristic.
for _, c := range cs.chunks {
if _, err := c.WriteTo(w); err != nil {
return 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 {
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) {
index := cs.Index()
if chunks, found := index[EXifChunkType]; found {
return chunks[0], nil
}
return nil, exif.ErrNoExif
}
// Exif returns an `exif.Ifd` instance with the existing tags.
func (cs *ChunkSlice) Exif() (*exif.Ifd, []byte, error) {
chunk, err := cs.FindExif()
if err != nil {
return nil, nil, err
}
im, err := exifcommon.NewIfdMappingWithStandard()
if err != nil {
return nil, nil, err
}
ti := exif.NewTagIndex()
_, index, err := exif.Collect(im, ti, chunk.Data)
if err != nil {
return nil, nil, 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() (*exif.IfdBuilder, error) {
rootIfd, _, err := cs.Exif()
if err != nil {
return nil, err
}
return exif.NewIfdBuilderFromExistingChain(rootIfd), nil
}
// SetExif encodes and sets EXIF data into this segment.
func (cs *ChunkSlice) SetExif(ib *exif.IfdBuilder) error {
// Encode.
ibe := exif.NewIfdByteEncoder()
exifData, err := ibe.EncodeToExif(ib)
if err != nil {
return err
}
// Set.
exifChunk, err := cs.FindExif()
switch {
case err == nil:
// EXIF chunk already exists.
exifChunk.Data = exifData
exifChunk.Length = uint32(len(exifData))
case errors.Is(err, exif.ErrNoExif):
// Add a EXIF chunk for the first time.
exifChunk = &Chunk{
Type: EXifChunkType,
Data: exifData,
Length: uint32(len(exifData)),
}
// Insert exif 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:]...,
)...,
)
default:
return err
}
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, error) {
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, error) {
if len(c.Data) != int(c.Length) {
return nil, errors.New("length of data not correct")
}
b := make([]byte, 0, 4+4+c.Length+4)
b = binary.BigEndian.AppendUint32(b, c.Length)
b = append(b, c.Type...)
b = append(b, c.Data...)
b = binary.BigEndian.AppendUint32(b, c.Crc)
return b, nil
}
// Write encodes and writes the bytes for this chunk.
func (c *Chunk) WriteTo(w io.Writer) (int, error) {
if len(c.Data) != int(c.Length) {
return 0, errors.New("length of data not correct")
}
var n int
b := make([]byte, 4) // uint32 buf
binary.BigEndian.PutUint32(b, c.Length)
if nn, err := w.Write(b); err != nil {
return n + nn, err
}
n += len(b)
if nn, err := io.WriteString(w, c.Type); err != nil {
return n + nn, err
}
n += len(c.Type)
if nn, err := w.Write(c.Data); err != nil {
return n + nn, err
}
n += len(c.Data)
binary.BigEndian.PutUint32(b, c.Crc)
if nn, err := w.Write(b); err != nil {
return n + nn, err
}
n += len(b)
return n, nil
}
// readHeader verifies that the PNG header bytes appear next.
func (ps *PngSplitter) readHeader(r io.Reader) error {
var (
sigLen = len(PngSignature)
header = make([]byte, sigLen)
)
if _, err := r.Read(header); err != nil {
return err
}
ps.currentOffset += sigLen
if !bytes.Equal(header, PngSignature[:]) {
return 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,
) {
// 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 for the
// chunks we've already completely read. Then, we'll
// be called again from the end 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() {
ps.crcErrors = append(ps.crcErrors, type_)
if ps.doCheckCrc {
err = ErrCrcFailure
return
}
}
advance += chunkSize
ps.currentOffset += chunkSize
data = data[chunkSize:]
}
}
var (
// Enforce interface conformance.
_ riimage.MediaContext = new(ChunkSlice)
)