114 lines
3.1 KiB
Go
114 lines
3.1 KiB
Go
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package mp3
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import (
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"bytes"
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"encoding/binary"
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"errors"
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"hash/crc32"
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"html"
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"io"
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"net/http"
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"strconv"
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"strings"
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)
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var (
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ErrNoMetaint = errors.New("mp3: key 'icy-metaint' not found in HTTP header")
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ErrCorruptedMetadata = errors.New("mp3: corrupted metadata")
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ErrNoStreamTitle = errors.New("mp3: no 'StreamTitle' tag in metadata")
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)
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type Extractor struct {
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metaint int64 // Distance between two metadata chunks
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hasStreamTitle bool
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streamTitle string // Metadata tag determining the filename
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}
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func NewExtractor(respHdr http.Header) (*Extractor, error) {
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mi := respHdr.Get("icy-metaint")
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if mi == "" {
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return nil, ErrNoMetaint
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}
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miNum, _ := strconv.ParseInt(mi, 10, 64)
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return &Extractor{
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metaint: miNum,
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}, nil
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}
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func (d *Extractor) ReadBlock(r io.Reader, w io.Writer) (isFirst bool, err error) {
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var musicData bytes.Buffer
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// We want to write everything to the output, as well as musicData for
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// calculating the checksum.
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multi := io.MultiWriter(w, &musicData)
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// Read until the metadata chunk. The part that is read here is also what
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// contains the actual mp3 music data.
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io.CopyN(multi, r, d.metaint)
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// Read number of metadata blocks (blocks within this function are not what
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// is meant with `ReadBlock()`).
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var numBlocks uint8
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err = binary.Read(r, binary.LittleEndian, &numBlocks)
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// Whether this block is the beginning of a new track.
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var isBOF bool
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// Read metadata blocks.
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if numBlocks > 0 {
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// Metadata is only actually stored in the first metadata chunk
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// of a given file. Therefore, every metadata chunk with more than 1
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// block always marks the beginning of a file.
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isBOF = true
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// Each block is 16 bytes in size. Any excess bytes in the last block
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// are set to '\0', which is great because the `string()` conversion
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// function ignores null bytes. The whole string is escaped via HTML.
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// Metadata format: k0='v0';k1='v1';
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raw := make([]byte, numBlocks*16)
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if _, err := r.Read(raw); err != nil {
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return false, err
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}
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rawString := html.UnescapeString(string(raw))
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for _, data := range strings.Split(rawString, ";") {
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s := strings.Split(data, "=")
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if len(s) == 2 {
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if s[0] == "StreamTitle" {
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d.hasStreamTitle = true
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// Strip stream title's first and last character (single
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// quotes).
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t := s[1]
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if len(t) < 2 {
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return false, ErrCorruptedMetadata
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}
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t = t[1 : len(t)-1]
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if t == "Unknown" {
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// If there is no stream title, use format:
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// Unknown_<crc32 checksum>
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// Where the checksum is only that of the first block.
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sumStr := strconv.FormatInt(int64(crc32.ChecksumIEEE(musicData.Bytes())), 10)
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d.streamTitle = "Unknown_" + sumStr
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} else {
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d.streamTitle = t
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}
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}
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} else if len(s) != 1 {
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return false, ErrCorruptedMetadata
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}
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}
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if !d.hasStreamTitle {
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return false, ErrNoStreamTitle
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}
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}
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return isBOF, nil
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}
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func (d *Extractor) TryGetFilename() (filename string, hasFilename bool) {
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if !d.hasStreamTitle {
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return "", false
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}
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base := strings.ReplaceAll(d.streamTitle, "/", "_") // Replace invalid characters.
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return base + ".mp3", true
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}
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