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104 lines
2.5 KiB
104 lines
2.5 KiB
package util |
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import ( |
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"strings" |
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euni "golang.org/x/text/encoding/unicode" |
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) |
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// got the logic from: https://github.com/bogem/id3v2 , thank you very much. |
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const first7BitsMask = uint32(254) << 24 // shifting 11111110 to the end of uint32 |
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// Converts given bytes into integer |
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func BytesToInt(gBytes []byte) uint32 { |
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var integer uint32 = 0 |
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for _, b := range gBytes { |
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integer = integer << 8 |
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integer = integer | uint32(b) |
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} |
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return integer |
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} |
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// Decodes given integer bytes into integer, ignores the first bit |
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// of every given byte in binary form |
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func BytesToIntSynchsafe(gBytes []byte) uint32 { |
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var integer uint32 = 0 |
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for _, b := range gBytes { |
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integer = integer << 7 |
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integer = integer | uint32(b) |
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} |
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return integer |
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} |
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// The exact opposite of what `BytesToIntIgnoreFirstBit` does |
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func SynchsafeIntToBytes(gInt uint32) []byte { |
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bytes := make([]byte, 32) |
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// looping 4 times (32 bits / 8 bits (4 bytes in int32)) |
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for i := 0; i < 32; i += 8 { |
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gIntCopy := gInt //11010101 11001011 00100000 10111111 |
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first7 := gIntCopy & first7BitsMask //11010100 00000000 00000000 00000000 |
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shifted := first7 >> 25 //00000000 00000000 00000000 01101010 |
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bytes = append(bytes, byte(shifted)) |
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} |
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return bytes |
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} |
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// Converts given bytes into string, ignoring the first 31 non-printable ASCII characters. |
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// (LOSSY, if given bytes contain some nasty ones) |
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func ToStringLossy(gBytes []byte) string { |
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var runes []rune |
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for _, b := range gBytes { |
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if b <= 31 { |
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continue |
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} |
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runes = append(runes, rune(b)) |
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} |
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return strings.ToValidUTF8(string(runes), "") |
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} |
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// Decodes the given frame`s contents |
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func DecodeText(fContents []byte) string { |
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textEncoding := fContents[0] // the first byte is the encoding |
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switch textEncoding { |
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case 0: |
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// ISO-8859-1 |
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return ToStringLossy(fContents[1:]) |
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case 1: |
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// UTF-16 with BOM |
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encoding := euni.UTF16(euni.BigEndian, euni.ExpectBOM) |
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decoder := encoding.NewDecoder() |
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decodedBytes := make([]byte, len(fContents)*2) |
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_, _, err := decoder.Transform(decodedBytes, fContents[1:], true) |
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if err != nil { |
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return "" |
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} |
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return string(decodedBytes) |
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case 2: |
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// UTF-16 |
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encoding := euni.UTF16(euni.BigEndian, euni.IgnoreBOM) |
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decoder := encoding.NewDecoder() |
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decodedBytes := make([]byte, len(fContents)*2) |
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_, _, err := decoder.Transform(decodedBytes, fContents[1:], true) |
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if err != nil { |
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return "" |
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} |
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return string(decodedBytes) |
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case 3: |
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// UTF-8 |
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return ToStringLossy(fContents[1:]) |
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} |
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return "" |
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}
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