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40 lines
741 B
Go
40 lines
741 B
Go
package imagemeta
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import (
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"bytes"
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"encoding/binary"
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"io"
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)
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var pngMagick = []byte("\x89PNG\r\n\x1a\n")
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type PngFormatError string
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func (e PngFormatError) Error() string { return "invalid PNG format: " + string(e) }
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func DecodePngMeta(r io.Reader) (Meta, error) {
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var tmp [16]byte
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if _, err := io.ReadFull(r, tmp[:8]); err != nil {
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return nil, err
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}
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if !bytes.Equal(pngMagick, tmp[:8]) {
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return nil, PngFormatError("not a PNG image")
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}
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if _, err := io.ReadFull(r, tmp[:]); err != nil {
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return nil, err
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}
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return &meta{
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format: "png",
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width: int(binary.BigEndian.Uint32(tmp[8:12])),
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height: int(binary.BigEndian.Uint32(tmp[12:16])),
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}, nil
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}
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func init() {
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RegisterFormat(string(pngMagick), DecodePngMeta)
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}
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