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