Created
April 10, 2019 19:14
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Extract Exif info from an image
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| package main | |
| import ( | |
| "bufio" | |
| "bytes" | |
| "encoding/binary" | |
| "errors" | |
| "io" | |
| ) | |
| const ( | |
| // JPEG APP1 marker | |
| jpegAPP1 = 0xE1 | |
| ) | |
| var ( | |
| errNoExifHeader = errors.New("exif: exif header not found") | |
| exifHeader = append([]byte("Exif"), 0x00, 0x00) | |
| ) | |
| func extractExif(r io.Reader) ([]byte, error) { | |
| br := bufio.NewReader(r) | |
| for { | |
| // Find APP1 marker | |
| if _, err := br.ReadBytes(0xFF); err != nil { | |
| return nil, err | |
| } | |
| marker, err := br.ReadByte() | |
| if err != nil { | |
| return nil, err | |
| } | |
| if marker != jpegAPP1 { | |
| continue | |
| } | |
| // Extract section length | |
| dataLenBytes := make([]byte, 2) | |
| io.ReadFull(br, dataLenBytes) | |
| dataLen := int64(binary.BigEndian.Uint16(dataLenBytes)) - 2 | |
| if dataLen < int64(len(exifHeader)) { | |
| return nil, errNoExifHeader | |
| } | |
| // Reconstruct APP1 section | |
| var exif bytes.Buffer | |
| exif.WriteByte(0xFF) | |
| exif.WriteByte(jpegAPP1) | |
| exif.Write(dataLenBytes) | |
| _, err = io.CopyN(&exif, br, dataLen) | |
| if err != nil { | |
| return nil, err | |
| } | |
| // Check whether APP1 contains Exif or not | |
| data := exif.Bytes()[4:] // 0xFF + marker + 2 bytes for length | |
| headerBytes := data[:len(exifHeader)] | |
| if !bytes.Equal(headerBytes, exifHeader) { | |
| return nil, errNoExifHeader | |
| } | |
| return exif.Bytes(), nil | |
| } | |
| } |
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