76 lines
1.6 KiB
Go
76 lines
1.6 KiB
Go
package main
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import (
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"bufio"
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"errors"
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"fmt"
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"io"
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"log"
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"os"
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)
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const fname = "/home/rob/home-office/example.mp3"
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const (
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maskSync = 0b11111111111000000000000000000000
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maskVersion = 0b00000000000110000000000000000000
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maskLayer = 0b00000000000001100000000000000000
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maskProtection = 0b00000000000000010000000000000000
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maskBitrate = 0b00000000000000001111000000000000
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maskSamplerate = 0b00000000000000000000110000000000
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maskPadding = 0b00000000000000000000001000000000
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maskPrivate = 0b00000000000000000000000100000000
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maskChannelMode = 0b00000000000000000000000011000000
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maskExtension = 0b00000000000000000000000000110000
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maskCopyright = 0b00000000000000000000000000001000
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maskOriginal = 0b00000000000000000000000000000100
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maskEmphasis = 0b00000000000000000000000000000011
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)
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type header uint32
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func main() {
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f, err := os.Open(fname)
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if err != nil {
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log.Fatal(err)
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}
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bufreader := bufio.NewReader(f)
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buf := make([]byte, 4)
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var i int
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for {
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_, err := io.ReadFull(bufreader, buf)
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if err != nil {
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if err == io.EOF {
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break
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}
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log.Fatal(err)
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}
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header, err := newHeader(buf)
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if err == nil {
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fmt.Printf("Got header: %08X\n", header)
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}
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i++
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bufreader.Discard(3)
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}
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}
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// TODO use unsafe here? https://codereview.stackexchange.com/a/60161
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func newHeader(buf []byte) (header, error) {
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if len(buf) < 4 {
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return 0, errors.New("insufficient bytes")
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}
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if buf[0] != 0xFF || buf[1]&0xE0 != 0xE0 {
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return 0, errors.New("no header")
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}
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// always little-endian for now
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n := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
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return header(n), nil
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}
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