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|
package png
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"io/ioutil"
"os"
)
const (
pngMagicLen = 8
pngMagic = "\x89PNG\r\n\x1a\n"
)
// Reader is an io.Reader decorator that skips certain PNG chunks known to cause problems.
// If the image stream is not a PNG, it will yield all bytes unchanged to the underlying
// reader.
// See also https://gitlab.com/gitlab-org/gitlab/-/issues/287614
type Reader struct {
underlying io.Reader
chunk io.Reader
bytesRemaining int64
}
func NewReader(r io.Reader) (io.Reader, error) {
magicBytes, err := readMagic(r)
if err != nil {
return nil, err
}
if string(magicBytes) != pngMagic {
debug("Not a PNG - read file unchanged")
return io.MultiReader(bytes.NewReader(magicBytes), r), nil
}
return io.MultiReader(bytes.NewReader(magicBytes), &Reader{underlying: r}), nil
}
func (r *Reader) Read(p []byte) (int, error) {
for r.bytesRemaining == 0 {
const (
headerLen = 8
crcLen = 4
)
var header [headerLen]byte
_, err := io.ReadFull(r.underlying, header[:])
if err != nil {
return 0, err
}
chunkLen := int64(binary.BigEndian.Uint32(header[:4]))
if chunkType := string(header[4:]); chunkType == "iCCP" {
debug("!! iCCP chunk found; skipping")
if _, err := io.CopyN(ioutil.Discard, r.underlying, chunkLen+crcLen); err != nil {
return 0, err
}
continue
}
r.bytesRemaining = headerLen + chunkLen + crcLen
r.chunk = io.MultiReader(bytes.NewReader(header[:]), io.LimitReader(r.underlying, r.bytesRemaining-headerLen))
}
n, err := r.chunk.Read(p)
r.bytesRemaining -= int64(n)
return n, err
}
func debug(args ...interface{}) {
if os.Getenv("DEBUG") == "1" {
fmt.Fprintln(os.Stderr, args...)
}
}
// Consume PNG magic and proceed to reading the IHDR chunk.
func readMagic(r io.Reader) ([]byte, error) {
var magicBytes []byte = make([]byte, pngMagicLen)
_, err := io.ReadFull(r, magicBytes)
if err != nil {
return nil, err
}
return magicBytes, nil
}
|
