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100 lines
2.0 KiB
100 lines
2.0 KiB
package id3ed |
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////////////////////////////////////// |
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//(ᗜˬᗜ)~⭐//Under construction//(ᗜ‸ᗜ)// |
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////////////////////////////////////// |
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import ( |
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"bytes" |
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"fmt" |
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"io" |
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"strconv" |
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) |
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// ID3v2.x header structure |
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type Header struct { |
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Identifier string |
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Version string |
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Unsynchronisated bool |
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Compressed bool |
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Size int64 |
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} |
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// Reads and structuralises ID3v2 header |
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func GetHeader(rs io.ReadSeeker) (*Header, error) { |
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var header Header |
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rs.Seek(0, io.SeekStart) |
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identifier, err := read(rs, 3) |
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if err != nil { |
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return nil, err |
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} |
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// check if ID3v2 is used |
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if !bytes.Equal([]byte(ID3v2IDENTIFIER), identifier) { |
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return nil, fmt.Errorf("no ID3v2 identifier found") |
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} |
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header.Identifier = string(identifier) |
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// version |
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majorVersionByte, err := read(rs, 1) |
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if err != nil { |
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return nil, err |
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} |
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revisionNumberByte, err := read(rs, 1) |
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if err != nil { |
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return nil, err |
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} |
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majorVersion, err := bytesToInt(majorVersionByte) |
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if err != nil { |
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return nil, err |
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} |
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revisionNumber, err := bytesToInt(revisionNumberByte) |
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if err != nil { |
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return nil, err |
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} |
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header.Version = fmt.Sprintf("%d%d", -majorVersion, revisionNumber) |
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// flags |
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flags, err := read(rs, 1) |
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if err != nil { |
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return nil, err |
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} |
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bits := fmt.Sprintf("%08b", flags) // 1 byte is 8 bits |
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if bits[0] == 1 { |
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header.Unsynchronisated = true |
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} else { |
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header.Unsynchronisated = false |
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} |
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if bits[1] == 1 { |
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header.Compressed = true |
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} else { |
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header.Compressed = false |
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} |
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// size |
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sizeBytes, err := read(rs, 4) |
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if err != nil { |
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return nil, err |
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} |
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// represent each byte in size as binary and get rid from the first useless bit, |
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// then concatenate filtered parts |
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var filteredSizeStr string |
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for _, b := range sizeBytes { |
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// the first bit is always 0, so filter it out |
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filteredPart := fmt.Sprintf("%08b", b)[1:] // byte is 8 bits |
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filteredSizeStr += filteredPart |
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} |
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// converting filtered binary size into usable int64 |
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size, err := strconv.ParseInt(filteredSizeStr, 2, 64) |
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if err != nil { |
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return nil, err |
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} |
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header.Size = int64(size) |
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return &header, nil |
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}
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