107 lines
2.6 KiB
Go
107 lines
2.6 KiB
Go
package sniff
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import (
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"bytes"
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"encoding/binary"
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"golang.org/x/exp/slices"
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)
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type Sniffer interface {
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Sniff(header []byte) bool
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}
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var audioExtensions = map[string]Sniffer{
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// ref: https://mimesniff.spec.whatwg.org
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".mp3": prefixSniffer("ID3"),
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".ogg": prefixSniffer("OggS"),
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".wav": prefixSniffer("RIFF"),
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// ref: https://www.loc.gov/preservation/digital/formats/fdd/fdd000027.shtml
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".wma": prefixSniffer{
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0x30, 0x26, 0xb2, 0x75, 0x8e, 0x66, 0xcf, 0x11,
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0xa6, 0xd9, 0x00, 0xaa, 0x00, 0x62, 0xce, 0x6c,
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},
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// ref: https://www.garykessler.net/library/file_sigs.html
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".m4a": m4aSniffer{}, // MPEG-4 container, Apple Lossless Audio Codec
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".mp4": &mpeg4Sniffer{}, // MPEG-4 container, other fallback
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".flac": prefixSniffer("fLaC"), // ref: https://xiph.org/flac/format.html
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".dff": prefixSniffer("FRM8"), // DSDIFF, ref: https://www.sonicstudio.com/pdf/dsd/DSDIFF_1.5_Spec.pdf
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}
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// AudioExtension sniffs the known audio types, and returns the file extension.
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// header is recommended to at least 16 bytes.
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func AudioExtension(header []byte) (string, bool) {
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for ext, sniffer := range audioExtensions {
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if sniffer.Sniff(header) {
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return ext, true
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}
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}
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return "", false
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}
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// AudioExtensionWithFallback is equivalent to AudioExtension, but returns fallback
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// most likely to use .mp3 as fallback, because mp3 files may not have ID3v2 tag.
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func AudioExtensionWithFallback(header []byte, fallback string) string {
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ext, ok := AudioExtension(header)
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if !ok {
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return fallback
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}
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return ext
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}
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type prefixSniffer []byte
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func (s prefixSniffer) Sniff(header []byte) bool {
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return bytes.HasPrefix(header, s)
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}
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type m4aSniffer struct{}
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func (m4aSniffer) Sniff(header []byte) bool {
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box := readMpeg4FtypBox(header)
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if box == nil {
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return false
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}
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return box.majorBrand == "M4A " || slices.Contains(box.compatibleBrands, "M4A ")
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}
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type mpeg4Sniffer struct{}
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func (s *mpeg4Sniffer) Sniff(header []byte) bool {
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return readMpeg4FtypBox(header) != nil
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}
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type mpeg4FtpyBox struct {
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majorBrand string
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minorVersion uint32
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compatibleBrands []string
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}
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func readMpeg4FtypBox(header []byte) *mpeg4FtpyBox {
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if (len(header) < 8) || !bytes.Equal([]byte("ftyp"), header[4:8]) {
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return nil // not a valid ftyp box
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}
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size := binary.BigEndian.Uint32(header[0:4]) // size
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if size < 16 || size%4 != 0 {
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return nil // invalid ftyp box
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}
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box := mpeg4FtpyBox{
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majorBrand: string(header[8:12]),
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minorVersion: binary.BigEndian.Uint32(header[12:16]),
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}
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// compatible brands
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for i := 16; i < int(size) && i+4 < len(header); i += 4 {
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box.compatibleBrands = append(box.compatibleBrands, string(header[i:i+4]))
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}
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return &box
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}
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