add basic start on artnet decoding

poll.go

@@ -0,0 +1,40 @@
+package artnet
+
+import (
+	"errors"
+)
+
+type ArtPoll struct {
+	Header          *ArtNetHeader
+	Flags           uint8
+	DiagPriority    uint8
+	AddressTopHi    uint8
+	AddressTopLo    uint8
+	AddressBottomHi uint8
+	AddressBottomLo uint8
+	EstaManHi       uint8
+	EstaManLo       uint8
+	OemHi           uint8
+	OemLo           uint8
+}
+
+func NewArtPoll(header *ArtNetHeader, data []byte) (*ArtPoll, error) {
+	artPoll := ArtPoll{
+		Header: header,
+	}
+
+	if len(data) < 14 {
+		return nil, errors.New("ArtPoll packet must be at least 14 bytes long")
+	}
+	offset := 12
+	artPoll.Flags = data[offset]
+	artPoll.DiagPriority = data[offset+1]
+
+	//TODO(jwetzell): unpack extended poll fields
+
+	return &artPoll, nil
+}
+
+func (ap *ArtPoll) GetOpCode() uint16 {
+	return ap.Header.OpCode
+}