reorganise some of the internals of the package.

functional options added.

client.go

@@ -0,0 +1,48 @@
+package vbantxt
+
+import (
+	"fmt"
+	"net"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// client represents the UDP client
+type client struct {
+	conn *net.UDPConn
+}
+
+// NewClient returns a UDP client
+func newClient(host string, port int) (client, error) {
+	udpAddr, err := net.ResolveUDPAddr("udp4", fmt.Sprintf("%s:%d", host, port))
+	if err != nil {
+		return client{}, err
+	}
+	conn, err := net.DialUDP("udp4", nil, udpAddr)
+	if err != nil {
+		return client{}, err
+	}
+	log.Infof("Outgoing address %s", conn.RemoteAddr())
+
+	return client{conn: conn}, nil
+}
+
+// Write implements the io.WriteCloser interface
+func (c client) Write(buf []byte) (int, error) {
+	n, err := c.conn.Write(buf)
+	if err != nil {
+		return 0, err
+	}
+	log.Debugf("Sending '%s' to: %s", string(buf), c.conn.RemoteAddr())
+
+	return n, nil
+}
+
+// Close implements the io.WriteCloser interface
+func (c client) Close() error {
+	err := c.conn.Close()
+	if err != nil {
+		return err
+	}
+	return nil
+}

errors.go

@@ -0,0 +1,9 @@
+package vbantxt
+
+// Error is used to define sentinel errors.
+type Error string
+
+// Error implements the error interface.
+func (r Error) Error() string {
+	return string(r)
+}

option.go

@@ -0,0 +1,35 @@
+package vbantxt
+
+import (
+	"time"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// Option is a functional option type that allows us to configure the VbanTxt.
+type Option func(*VbanTxt)
+
+// WithRateLimit is a functional option to set the ratelimit for requests
+func WithRateLimit(ratelimit time.Duration) Option {
+	return func(vt *VbanTxt) {
+		vt.ratelimit = ratelimit
+	}
+}
+
+// WithBPSOpt is a functional option to set the bps index for {VbanTx}.{Packet}.bpsIndex
+func WithBPSOpt(bpsIndex int) Option {
+	return func(vt *VbanTxt) {
+		if bpsIndex < 0 || bpsIndex >= len(BpsOpts) {
+			log.Warnf("invalid bpsIndex %d, defaulting to 0", bpsIndex)
+			return
+		}
+		vt.packet.bpsIndex = bpsIndex
+	}
+}
+
+// WithChannel is a functional option to set the bps index for {VbanTx}.{Packet}.channel
+func WithChannel(channel int) Option {
+	return func(vt *VbanTxt) {
+		vt.packet.channel = channel
+	}
+}

packet.go

@@ -1,50 +1,72 @@
-package main
+package vbantxt
 
-var r *requestHeader
+import (
+	"encoding/binary"
 
-const VBAN_PROTOCOL_TXT = 0x40
+	log "github.com/sirupsen/logrus"
+)
 
-// requestHeader represents a single request header
-type requestHeader struct {
+const (
+	vbanProtocolTxt = 0x40
+	streamNameSz    = 16
+	headerSz        = 4 + 1 + 1 + 1 + 1 + 16 + 4
+)
+
+var BpsOpts = []int{0, 110, 150, 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 31250,
+	38400, 57600, 115200, 128000, 230400, 250000, 256000, 460800, 921600,
+	1000000, 1500000, 2000000, 3000000}
+
+type packet struct {
 	name         string
 	bpsIndex     int
 	channel      int
 	framecounter []byte
 }
 
-// newRequestHeader returns a pointer to a requestHeader struct as a singleton
-func newRequestHeader(streamname string, bpsI, channel int) *requestHeader {
-	if r != nil {
-		return r
+// newPacket returns a packet struct with default values, framecounter at 0.
+func newPacket(streamname string) packet {
+	return packet{
+		name:         streamname,
+		bpsIndex:     0,
+		channel:      0,
+		framecounter: make([]byte, 4),
 	}
-	return &requestHeader{streamname, bpsI, channel, make([]byte, 4)}
 }
 
 // sr defines the samplerate for the request
-func (r *requestHeader) sr() byte {
-	return byte(VBAN_PROTOCOL_TXT + r.bpsIndex)
+func (p *packet) sr() byte {
+	return byte(vbanProtocolTxt + p.bpsIndex)
 }
 
 // nbc defines the channel of the request
-func (r *requestHeader) nbc() byte {
-	return byte(r.channel)
+func (p *packet) nbc() byte {
+	return byte(p.channel)
 }
 
 // streamname defines the stream name of the text request
-func (r *requestHeader) streamname() []byte {
-	b := make([]byte, 16)
-	copy(b, r.name)
+func (p *packet) streamname() []byte {
+	b := make([]byte, streamNameSz)
+	copy(b, p.name)
 	return b
 }
 
-// header returns a fully formed text request packet header
-func (t *requestHeader) header() []byte {
-	h := []byte("VBAN")
-	h = append(h, t.sr())
+// header returns a fully formed packet header
+func (p *packet) header() []byte {
+	h := make([]byte, 0, headerSz)
+	h = append(h, []byte("VBAN")...)
+	h = append(h, p.sr())
 	h = append(h, byte(0))
-	h = append(h, t.nbc())
+	h = append(h, p.nbc())
 	h = append(h, byte(0x10))
-	h = append(h, t.streamname()...)
-	h = append(h, t.framecounter...)
+	h = append(h, p.streamname()...)
+	h = append(h, p.framecounter...)
 	return h
 }
+
+// bumpFrameCounter increments the frame counter by 1
+func (p *packet) bumpFrameCounter() {
+	x := binary.LittleEndian.Uint32(p.framecounter)
+	binary.LittleEndian.PutUint32(p.framecounter, x+1)
+
+	log.Tracef("framecounter: %d", x)
+}

vbantxt.go

@@ -0,0 +1,59 @@
+package vbantxt
+
+import (
+	"fmt"
+	"io"
+	"time"
+)
+
+// VbanTxt is used to send VBAN-TXT requests to a distant Voicemeeter/Matrix.
+type VbanTxt struct {
+	client    io.WriteCloser
+	packet    packet
+	ratelimit time.Duration
+}
+
+// New constructs a fully formed VbanTxt instance. This is the package's entry point.
+// It sets default values for it's fields and then runs the option functions.
+func New(host string, port int, streamname string, options ...Option) (*VbanTxt, error) {
+	client, err := newClient(host, port)
+	if err != nil {
+		return nil, fmt.Errorf("error creating UDP client for (%s:%d): %w", host, port, err)
+	}
+
+	vt := &VbanTxt{
+		client:    client,
+		packet:    newPacket(streamname),
+		ratelimit: time.Duration(20) * time.Millisecond,
+	}
+
+	for _, o := range options {
+		o(vt)
+	}
+
+	return vt, nil
+}
+
+// Send is resonsible for firing each VBAN-TXT request.
+// It waits for {vt.ratelimit} time before returning.
+func (vt VbanTxt) Send(cmd string) error {
+	_, err := vt.client.Write(append(vt.packet.header(), []byte(cmd)...))
+	if err != nil {
+		return fmt.Errorf("error sending command (%s): %w", cmd, err)
+	}
+
+	vt.packet.bumpFrameCounter()
+
+	time.Sleep(vt.ratelimit)
+
+	return nil
+}
+
+// Close is responsible for closing the UDP Client connection
+func (vt VbanTxt) Close() error {
+	err := vt.client.Close()
+	if err != nil {
+		return fmt.Errorf("error attempting to close UDP Client: %w", err)
+	}
+	return nil
+}