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