/
meta.go
289 lines (244 loc) · 6 KB
/
meta.go
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package pngx
import (
"bufio"
"bytes"
"compress/zlib"
"encoding/binary"
"github.com/mocukie/webpdeep/pkg/imagex"
"hash"
"hash/crc32"
"image/png"
"io"
"io/ioutil"
"math"
"unsafe"
)
const pngMagic = "\x89PNG\r\n\x1a\n"
type iTXtChunk struct {
key string
languageTag string
translatedKeyword string
text []byte
}
type MetaReader struct {
in io.Reader
reaming int
tmp *bytes.Buffer
crc hash.Hash32
tags map[string][]byte
}
func NewMetaReader(reader io.Reader) (imagex.MetaChunksReader, error) {
magick := make([]byte, len(pngMagic))
if _, err := io.ReadFull(reader, magick); err != nil {
return nil, err
}
if string(magick) != pngMagic {
return nil, png.FormatError("not a PNG file")
}
return &MetaReader{
in: reader,
tmp: bytes.NewBuffer(magick),
crc: crc32.NewIEEE(),
reaming: len(pngMagic),
tags: map[string][]byte{},
}, nil
}
func (mr *MetaReader) Get(tag string) []byte {
return mr.tags[tag]
}
func (mr *MetaReader) Empty() bool {
return len(mr.tags) == 0
}
func (mr *MetaReader) Read(p []byte) (int, error) {
reader := io.MultiReader(mr.tmp, mr.in)
var err error
read := 0
for read < len(p) {
var r int
r, err = reader.Read(p[read:])
read += r
if err == io.EOF {
break
} else if err != nil {
return read, err
}
}
mr.reaming -= read
if mr.reaming >= 0 {
return read, err
}
mr.reaming *= -1
if chkErr := mr.parseChunk(p[read-mr.reaming : read]); chkErr != nil {
err = chkErr
}
return read, err
}
func (mr *MetaReader) parseChunk(read []byte) (err error) {
mr.tmp.Reset()
for pos := 0; mr.reaming > 0; {
var dataLen uint32
var fourcc []byte
if mr.reaming < 8 {
r := io.MultiReader(bytes.NewBuffer(read[pos:]), io.TeeReader(mr.in, mr.tmp))
buf := make([]byte, 8)
if _, err = io.ReadFull(r, buf); err != nil {
return
}
dataLen = binary.BigEndian.Uint32(buf[:4])
fourcc = buf[4:]
} else {
dataLen = binary.BigEndian.Uint32(read[pos : pos+4])
fourcc = read[pos+4 : pos+8]
}
delta := int(dataLen + 8 + 4)
mr.reaming -= delta
var tagName string
var bodyParse func(io.Reader) ([]byte, error)
if string(fourcc) == "iCCP" && mr.tags["ICCP"] == nil {
tagName = "ICCP"
bodyParse = func(body io.Reader) ([]byte, error) {
_, icc, err := mr.parseZTXt(body.(*bufio.Reader))
return icc, err
}
} else if string(fourcc) == "eXIf" && mr.tags["EXIF"] == nil {
tagName = "EXIF"
bodyParse = ioutil.ReadAll
} else if string(fourcc) == "iTXt" {
tagName = "XMP"
bodyParse = func(body io.Reader) ([]byte, error) {
iTXt, err := mr.parseITXt(body.(*bufio.Reader))
if err != nil || iTXt.key != "XML:com.adobe.xmp" {
return nil, err
}
return iTXt.text, nil
}
} else {
pos += delta
continue
}
chunk, body := mr.prepareChunkReader(pos, dataLen, read)
//skip chunk fourcc
if _, err = body.Discard(4); err != nil {
return err
}
var tagData []byte
tagData, err = bodyParse(body)
if err != nil {
break
}
var ok bool
if ok, err = mr.verifyChecksum(chunk); err != nil {
break
} else if !ok {
err = png.FormatError("invalid checksum")
break
}
if len(tagData) != 0 {
mr.tags[tagName] = tagData
}
pos += delta
}
mr.reaming *= -1
return
}
func (mr *MetaReader) prepareChunkReader(pos int, dataLen uint32, read []byte) (io.Reader, *bufio.Reader) {
var chunk io.Reader //fourcc + data + crc
if mr.reaming < 0 {
chunk = io.MultiReader(bytes.NewBuffer(read[pos+4:]), io.TeeReader(mr.in, mr.tmp))
} else {
chunk = bytes.NewBuffer(read[pos+4 : pos+int(dataLen+8+4)])
}
mr.crc.Reset()
body := bufio.NewReader(io.TeeReader(io.LimitReader(chunk, int64(dataLen+4)), mr.crc)) //fourcc + data
return chunk, body
}
func (mr *MetaReader) verifyChecksum(r io.Reader) (bool, error) {
var checksum uint32
if err := binary.Read(r, binary.BigEndian, &checksum); err != nil {
return false, err
}
return checksum == mr.crc.Sum32(), nil
}
func (mr *MetaReader) parseZTXt(body *bufio.Reader) (string, []byte, error) {
key, err := readCStr(body, 79)
if err != nil {
return "", nil, err
}
if b, err := body.ReadByte(); err != nil {
return "", nil, err
} else if b != 0 {
//The only presently legitimate value for Compression method is 0 (deflate/inflate compression)
return "", nil, png.FormatError("unknown compression method")
}
zr, err := zlib.NewReader(body)
if err != nil {
return "", nil, err
}
defer zr.Close()
value := bytes.NewBuffer(make([]byte, 0, bytes.MinRead))
if _, err := value.ReadFrom(zr); err != nil {
return "", nil, err
}
return key, value.Bytes(), nil
}
func (mr *MetaReader) parseITXt(body *bufio.Reader) (*iTXtChunk, error) {
var err error
var iTXt = new(iTXtChunk)
iTXt.key, err = readCStr(body, 79)
if err != nil {
return nil, err
}
com, err := body.ReadByte()
if err != nil {
return nil, err
}
if com == 1 {
if b, err := body.ReadByte(); err != nil {
return nil, err
} else if b != 0 {
//The only presently legitimate value for Compression method is 0 (deflate/inflate compression)
return nil, png.FormatError("unknown compression method")
}
}
iTXt.languageTag, err = readCStr(body, -1)
if err != nil {
return nil, err
}
iTXt.translatedKeyword, err = readCStr(body, -1)
if err != nil {
return nil, err
}
var r io.Reader = body
if com == 1 {
r, err = zlib.NewReader(body)
if err != nil {
return nil, err
}
defer r.(io.ReadCloser).Close()
}
value := bytes.NewBuffer(make([]byte, 0, bytes.MinRead))
if _, err = value.ReadFrom(r); err != nil {
return nil, err
}
iTXt.text = value.Bytes()
return iTXt, nil
}
func readCStr(r *bufio.Reader, lim int) (string, error) {
var str = make([]byte, 0, 32)
if lim <= 0 {
lim = math.MinInt32
}
for n := 0; n < lim; n++ {
if b, err := r.ReadByte(); err != nil {
return "", err
} else if b == 0 {
break
} else {
str = append(str, b)
}
}
return *(*string)(unsafe.Pointer(&str)), nil
}
func init() {
imagex.RegisterFormat("png", pngMagic, NewMetaReader, png.Decode)
}