feature: add track decoder

TODO.txt

@@ -1,4 +1,3 @@
 - pause state should be reset on a play command
 - match node balancing against lavalink-client's
     https://github.com/FredBoat/Lavalink-Client/blob/master/src/main/java/lavalink/client/io/LavalinkLoadBalancer.java#L121-L146
-- track decoder

decoder.go

@@ -0,0 +1,128 @@
+package gavalink
+
+import (
+	"bytes"
+	"encoding/base64"
+	"encoding/binary"
+	"io"
+)
+
+const trackInfoVersioned int32 = 1
+
+// DecodeString decodes a base64 Lavaplayer string to a TrackInfo
+func DecodeString(data string) (*TrackInfo, error) {
+	b, err := base64.StdEncoding.DecodeString(data)
+	if err != nil {
+		return nil, err
+	}
+	r := bytes.NewReader(b)
+	return Decode(r)
+}
+
+// Decode decodes a reader into a TrackInfo
+func Decode(r io.Reader) (*TrackInfo, error) {
+	// https://github.com/serenity-rs/lavalink.rs/blob/master/src/decoder.rs
+
+	var value uint8
+	if err := binary.Read(r, binary.LittleEndian, &value); err != nil {
+		return nil, err
+	}
+
+	flags := int32(int64(value) & 0xC00000000)
+
+	// irrelevant data?
+	var ignore [2]byte
+	if err := binary.Read(r, binary.LittleEndian, &ignore); err != nil {
+		return nil, err
+	}
+
+	var version uint8
+	if flags&trackInfoVersioned == 0 {
+		version = 1
+	} else {
+		if err := binary.Read(r, binary.LittleEndian, &version); err != nil {
+			return nil, err
+		}
+	}
+
+	if err := binary.Read(r, binary.LittleEndian, &ignore); err != nil {
+		return nil, err
+	}
+
+	title, err := readString(r)
+	if err != nil {
+		return nil, err
+	}
+
+	author, err := readString(r)
+	if err != nil {
+		return nil, err
+	}
+
+	var length uint64
+	if err := binary.Read(r, binary.BigEndian, &length); err != nil {
+		return nil, err
+	}
+
+	identifier, err := readString(r)
+	if err != nil {
+		return nil, err
+	}
+
+	var stream uint8
+	if err := binary.Read(r, binary.LittleEndian, &stream); err != nil {
+		return nil, err
+	}
+
+	var hasURL uint8
+	if err := binary.Read(r, binary.LittleEndian, &hasURL); err != nil {
+		return nil, err
+	}
+
+	var url string
+	if hasURL == 1 {
+		url, err = readString(r)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		var size uint8
+		if err := binary.Read(r, binary.LittleEndian, &size); err != nil {
+			return nil, err
+		}
+
+		ignore := make([]byte, size)
+		if err := binary.Read(r, binary.LittleEndian, &ignore); err != nil {
+			return nil, err
+		}
+	}
+
+	/*source, err := readString(r)
+	if err != nil {
+		return nil, err
+	}*/
+
+	track := &TrackInfo{
+		Identifier: identifier,
+		Title:      title,
+		Author:     author,
+		URI:        url,
+		Stream:     stream == 1,
+		Length:     int(length),
+	}
+
+	return track, nil
+}
+
+func readString(r io.Reader) (string, error) {
+	var size uint16
+	if err := binary.Read(r, binary.BigEndian, &size); err != nil {
+		return "", err
+	}
+	buf := make([]byte, size)
+	if err := binary.Read(r, binary.BigEndian, &buf); err != nil {
+		return "", err
+	}
+
+	return string(buf), nil
+}

decoder_test.go

@@ -0,0 +1,17 @@
+package gavalink_test
+
+import (
+	"testing"
+
+	"github.com/foxbot/gavalink"
+)
+
+func TestDecoder(t *testing.T) {
+	data := "QAAAkAIALGxvZmkgaGlwIGhvcCByYWRpbyAtIGJlYXRzIHRvIHJlbGF4L3N0dWR5IHRvAApDaGlsbGVkQ293f/////////8AC2hIVzFvWTI2a3hRAQEAK2h0dHBzOi8vd3d3LnlvdXR1YmUuY29tL3dhdGNoP3Y9aEhXMW9ZMjZreFEAB3lvdXR1YmUAAAAAAAAAAA=="
+	track, err := gavalink.DecodeString(data)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	t.Log(track)
+}