add basic start on artnet decoding

dmx.go

@@ -0,0 +1,49 @@
+package artnet
+
+import (
+	"errors"
+)
+
+type ArtDmx struct {
+	Header   *ArtNetHeader
+	Sequence uint8
+	Physical uint8
+	SubUni   uint8
+	Net      uint8
+	Length   uint16
+	Data     []uint8
+}
+
+func NewArtDmx(header *ArtNetHeader, data []byte) (*ArtDmx, error) {
+	artDmx := ArtDmx{
+		Header: header,
+	}
+
+	if len(data) < 18 {
+		return nil, errors.New("ArtDmx packet must be at least 14 bytes long")
+	}
+	offset := 12
+
+	artDmx.Sequence = data[offset]
+	artDmx.Physical = data[offset+1]
+	artDmx.SubUni = data[offset+2]
+	artDmx.Net = data[offset+3]
+
+	artDmx.Length = uint16(data[offset+4])<<8 + uint16(data[offset+5])
+
+	dmxDataOffset := offset + 6
+
+	if len(data[dmxDataOffset:]) < int(artDmx.Length) {
+		return nil, errors.New("ArtDmx packet length mismatch")
+	}
+
+	artDmx.Data = make([]uint8, artDmx.Length)
+
+	copy(artDmx.Data, data[dmxDataOffset:dmxDataOffset+int(artDmx.Length)])
+
+	return &artDmx, nil
+}
+
+func (ap *ArtDmx) GetOpCode() uint16 {
+	return ap.Header.OpCode
+}