mirror of
https://github.com/onyx-and-iris/vbantxt.git
synced 2026-02-15 00:47:51 +00:00
onyx-and-iris
0d0dbedbcd
factory method now validates streamname size.
framecounter now stored as uint32. it's written to a byte buffer on each call to {Packet}.header()
add comment regarding framecounter wraparound.
95 lines
2.3 KiB
Go
95 lines
2.3 KiB
Go
package vbantxt
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"github.com/charmbracelet/log"
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)
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const (
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vbanProtocolTxt = 0x40
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streamNameSz = 16
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headerSz = 4 + 1 + 1 + 1 + 1 + 16 + 4
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)
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// BpsOpts defines the available baud rate options.
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var BpsOpts = []int{
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0, 110, 150, 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 31250,
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38400, 57600, 115200, 128000, 230400, 250000, 256000, 460800, 921600,
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1000000, 1500000, 2000000, 3000000,
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}
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type packet struct {
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streamname [streamNameSz]byte
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bpsIndex uint8
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channel uint8
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framecounter uint32
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hbuf *bytes.Buffer
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}
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// newPacket creates a new packet with the given stream name and default values for other fields.
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// It validates the stream name length and ensures the default baud rate is present in BpsOpts.
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func newPacket(streamname string) (packet, error) {
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if len(streamname) > streamNameSz {
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return packet{}, fmt.Errorf(
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"streamname too long: %d chars, max %d",
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len(streamname),
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streamNameSz,
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)
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}
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var streamnameBuf [streamNameSz]byte
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copy(streamnameBuf[:], streamname)
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bpsIndex := indexOf(BpsOpts, 256000)
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if bpsIndex == -1 {
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return packet{}, fmt.Errorf("default baud rate 256000 not found in BpsOpts")
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}
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return packet{
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streamname: streamnameBuf,
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bpsIndex: uint8(bpsIndex),
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channel: 0,
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framecounter: 0,
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hbuf: bytes.NewBuffer(make([]byte, 0, headerSz)),
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}, nil
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}
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// sr defines the samplerate for the request.
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func (p *packet) sr() byte {
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return byte(vbanProtocolTxt + p.bpsIndex)
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}
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// nbc defines the channel of the request.
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func (p *packet) nbc() byte {
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return byte(p.channel)
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}
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// header returns a fully formed packet header.
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func (p *packet) header() []byte {
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p.hbuf.Reset()
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p.hbuf.WriteString("VBAN")
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p.hbuf.WriteByte(p.sr())
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p.hbuf.WriteByte(byte(0))
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p.hbuf.WriteByte(p.nbc())
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p.hbuf.WriteByte(byte(0x10))
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p.hbuf.Write(p.streamname[:])
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var frameBytes [4]byte
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binary.LittleEndian.PutUint32(frameBytes[:], p.framecounter)
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p.hbuf.Write(frameBytes[:])
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return p.hbuf.Bytes()
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}
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// bumpFrameCounter increments the frame counter by 1.
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// The uint32 will safely wrap to 0 after reaching max value (4,294,967,295),
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// which is expected behaviour for network protocol sequence numbers.
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func (p *packet) bumpFrameCounter() {
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p.framecounter++
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log.Debugf("framecounter: %d", p.framecounter)
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}
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