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parser.go
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parser.go
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package frame
import (
"bytes"
"context"
"time"
"github.com/looplab/fsm"
"go.uber.org/zap"
)
// ParseStatus respresents an enum for the status parsing a frame.
type ParseStatus int
const (
// ParseOk means a frame was successfully parsed.
ParseOk ParseStatus = iota
// ParseNotOk means a frame was not successfully parsed.
ParseNotOk
// ParseTimeout means a frame timed out.
ParseTimeout
minFrameSize uint8 = 3
maxFrameSize uint8 = 88
readTimeout = 1500 * time.Millisecond
)
// ParseEvent represents a parsed frame and whether it was successful.
type ParseEvent struct {
status ParseStatus
frame Frame
}
// Parser contains a frame parser.
type Parser struct {
state *fsm.FSM
input <-chan byte
framesReceived chan<- *ParseEvent
acks, naks, cans chan<- bool
sof, length, checksum, readCounter byte
payloadReadBuffer *bytes.Buffer
parseTimeout *time.Timer
l *zap.Logger
ctx context.Context
}
// NewParser will return a new parser
func NewParser(ctx context.Context, input <-chan byte, output chan<- *ParseEvent, acks, naks, cans chan bool, logger *zap.Logger) *Parser {
parser := &Parser{
input: input,
framesReceived: output,
acks: acks,
naks: naks,
cans: cans,
payloadReadBuffer: bytes.NewBuffer([]byte{}),
parseTimeout: time.NewTimer(readTimeout),
l: logger,
ctx: ctx,
}
parser.parseTimeout.Stop()
parser.state = fsm.NewFSM(
"idle",
fsm.Events{
{Name: "PARSE_TIMEOUT", Src: []string{"idle", "length", "data", "checksum"}, Dst: "idle"},
{Name: "RX_SOF", Src: []string{"idle"}, Dst: "length"},
{Name: "RX_ACK", Src: []string{"idle"}, Dst: "idle"},
{Name: "RX_CAN", Src: []string{"idle"}, Dst: "idle"},
{Name: "RX_NAK", Src: []string{"idle"}, Dst: "idle"},
{Name: "RX_LENGTH", Src: []string{"length"}, Dst: "data"},
{Name: "INVALID_LENGTH", Src: []string{"length"}, Dst: "idle"},
{Name: "RX_DATA", Src: []string{"length", "data"}, Dst: "data"},
{Name: "RX_DATA_COMPLETE", Src: []string{"data"}, Dst: "data_complete"},
{Name: "RX_CHECKSUM", Src: []string{"data_complete"}, Dst: "checksum"},
{Name: "CRC_OK", Src: []string{"checksum"}, Dst: "idle"},
{Name: "CRC_NOTOK", Src: []string{"checksum"}, Dst: "idle"},
},
fsm.Callbacks{
"enter_idle": func(e *fsm.Event) {
parser.parseTimeout.Stop()
parser.payloadReadBuffer.Reset()
},
"PARSE_TIMEOUT": func(e *fsm.Event) {
event := &ParseEvent{
status: ParseTimeout,
frame: Frame{},
}
go func() {
parser.framesReceived <- event
}()
},
"RX_ACK": func(e *fsm.Event) {
parser.acks <- true
},
"RX_NAK": func(e *fsm.Event) {
parser.naks <- true
},
"RX_CAN": func(e *fsm.Event) {
parser.cans <- true
},
"RX_SOF": func(e *fsm.Event) {
parser.sof = e.Args[0].(byte)
parser.parseTimeout.Reset(readTimeout)
},
"RX_LENGTH": func(e *fsm.Event) {
parser.length = e.Args[0].(byte)
parser.readCounter = parser.length - 2
},
"RX_DATA": func(e *fsm.Event) {
parser.payloadReadBuffer.WriteByte(e.Args[0].(byte))
parser.readCounter--
},
"checksum": func(e *fsm.Event) {
e.Async()
},
"CRC_OK": func(e *fsm.Event) {
parser.l.Debug("event received, attempting to parse")
event := &ParseEvent{
status: ParseOk,
frame: e.Args[0].(Frame),
}
parser.l.Debug("event parsed", zap.Int("status", int(event.status)))
go func() {
parser.framesReceived <- event
}()
},
"CRC_NOTOK": func(e *fsm.Event) {
parser.l.Debug("event received, attempting to parse")
event := &ParseEvent{
status: ParseNotOk,
frame: e.Args[0].(Frame),
}
parser.l.Debug("event parsed", zap.Int("status", int(event.status)))
go func() {
parser.framesReceived <- event
}()
},
// "before_event": func(e *fsm.Event) {
// if e.Src == "data" && e.Dst == "data" {
// return
// }
// fmt.Printf("%s: %s -> %s\n", e.Event, e.Src, e.Dst)
// },
},
)
go parser.parse()
return parser
}
func (p *Parser) parse() {
for {
select {
case <-p.parseTimeout.C:
p.state.Event("PARSE_TIMEOUT")
case currentByte := <-p.input:
p.processByte(currentByte)
case <-p.ctx.Done():
p.l.Info("closing frame parser")
return
}
}
}
func (p *Parser) processByte(currentByte byte) {
// uncomment to really dig deep. this line is a little verbose
// p.l.Debug("parser processing byte", zap.String("byte", fmt.Sprint(currentByte)), zap.String("current_state", p.state.Current()))
switch {
case p.state.Is("idle"):
switch currentByte {
case HeaderData:
p.state.Event("RX_SOF", currentByte)
case HeaderAck:
p.state.Event("RX_ACK", currentByte)
case HeaderCan:
p.state.Event("RX_CAN", currentByte)
case HeaderNak:
p.state.Event("RX_NAK", currentByte)
}
case p.state.Is("length"):
if currentByte < minFrameSize || currentByte > maxFrameSize {
p.state.Event("INVALID_LENGTH")
} else {
p.state.Event("RX_LENGTH", currentByte)
}
case p.state.Is("data"):
if p.readCounter > 0 {
p.state.Event("RX_DATA", currentByte)
} else {
p.state.Event("RX_DATA", currentByte)
p.state.Event("RX_DATA_COMPLETE")
}
case p.state.Is("data_complete"):
p.state.Event("RX_CHECKSUM", currentByte)
p.state.Transition()
payload := p.payloadReadBuffer.Bytes()
frame := Frame{
Header: p.sof,
Length: p.length,
Type: payload[0],
Payload: payload[1:],
Checksum: currentByte,
}
p.l.Debug("data complete")
if frame.VerifyChecksum() == nil {
p.l.Debug("checksum verified")
p.state.Event("CRC_OK", frame)
} else {
p.l.Debug("checksum invalid")
p.state.Event("CRC_NOTOK", frame)
}
}
}