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|
package main
import (
"bufio"
"context"
"encoding/json"
"log"
"net"
"sync"
"time"
)
type gpsDevice struct {
Path string `json:"path"`
Driver string `json:"driver"`
Subtype string `json:"subtype"`
BPS int `json:"bps"`
Cycle float64 `json:"cycle"`
}
type gpsTPV struct {
Mode int `json:"mode"`
Status int `json:"status"`
Time string `json:"time"`
Lat *float64 `json:"lat"`
Lon *float64 `json:"lon"`
AltMSL *float64 `json:"altMSL"`
AltHAE *float64 `json:"altHAE"`
GeoidSep *float64 `json:"geoidSep"`
Speed *float64 `json:"speed"`
EPT *float64 `json:"ept"`
EPH *float64 `json:"eph"`
EPV *float64 `json:"epv"`
EPX *float64 `json:"epx"`
EPY *float64 `json:"epy"`
Leap *int `json:"leapseconds"`
}
type gpsSat struct {
PRN int `json:"PRN"`
GnssID *int `json:"gnssid"`
SvID *int `json:"svid"`
Az *float64 `json:"az"`
El *float64 `json:"el"`
SS *float64 `json:"ss"`
Used bool `json:"used"`
}
type gpsDOP struct {
GDOP *float64 `json:"gdop"`
PDOP *float64 `json:"pdop"`
HDOP *float64 `json:"hdop"`
VDOP *float64 `json:"vdop"`
TDOP *float64 `json:"tdop"`
}
type gpsTOFF struct {
// clock - real: how late the serial sentence arrived after the top of second.
Latency float64 `json:"latency"`
}
type GPSSnap struct {
Connected bool `json:"connected"`
Error string `json:"error,omitempty"`
Version string `json:"version,omitempty"`
Device *gpsDevice `json:"device,omitempty"`
TPV *gpsTPV `json:"tpv,omitempty"`
TPVAge *float64 `json:"tpvAge,omitempty"` // seconds since last TPV
DOP gpsDOP `json:"dop"`
NSat *int `json:"nSat,omitempty"`
USat *int `json:"uSat,omitempty"`
Satellites []gpsSat `json:"satellites"`
TOFF *gpsTOFF `json:"toff,omitempty"`
}
type gpsdClient struct {
addr string
mu sync.Mutex
snap GPSSnap
lastTPV time.Time
}
func newGPSD(addr string) *gpsdClient {
return &gpsdClient{addr: addr, snap: GPSSnap{Satellites: []gpsSat{}}}
}
func (g *gpsdClient) Snapshot() GPSSnap {
g.mu.Lock()
defer g.mu.Unlock()
s := g.snap
s.Satellites = append([]gpsSat(nil), g.snap.Satellites...)
if !g.lastTPV.IsZero() {
age := time.Since(g.lastTPV).Seconds()
s.TPVAge = &age
}
return s
}
func (g *gpsdClient) Run(ctx context.Context) {
backoff := time.Second
for ctx.Err() == nil {
err := g.session(ctx)
g.mu.Lock()
g.snap.Connected = false
if err != nil {
g.snap.Error = err.Error()
}
g.mu.Unlock()
if ctx.Err() != nil {
return
}
log.Printf("gpsd: %v (retrying in %s)", err, backoff)
select {
case <-ctx.Done():
return
case <-time.After(backoff):
}
if backoff < 30*time.Second {
backoff *= 2
}
}
}
func (g *gpsdClient) session(ctx context.Context) error {
var d net.Dialer
conn, err := d.DialContext(ctx, "tcp", g.addr)
if err != nil {
return err
}
defer conn.Close()
go func() { <-ctx.Done(); conn.Close() }()
if _, err := conn.Write([]byte(`?WATCH={"enable":true,"json":true,"pps":true};` + "\n")); err != nil {
return err
}
g.mu.Lock()
g.snap.Connected, g.snap.Error = true, ""
g.mu.Unlock()
sc := bufio.NewScanner(conn)
sc.Buffer(make([]byte, 64*1024), 1024*1024) // SKY lines can be large
for {
conn.SetReadDeadline(time.Now().Add(15 * time.Second))
if !sc.Scan() {
if err := sc.Err(); err != nil {
return err
}
return errEOF
}
g.handle(sc.Bytes())
}
}
type eofErr struct{}
func (eofErr) Error() string { return "connection closed by gpsd" }
var errEOF = eofErr{}
func (g *gpsdClient) handle(line []byte) {
var head struct {
Class string `json:"class"`
}
if json.Unmarshal(line, &head) != nil {
return
}
g.mu.Lock()
defer g.mu.Unlock()
switch head.Class {
case "VERSION":
var v struct {
Release string `json:"release"`
}
if json.Unmarshal(line, &v) == nil {
g.snap.Version = v.Release
}
case "DEVICES":
var v struct {
Devices []gpsDevice `json:"devices"`
}
if json.Unmarshal(line, &v) == nil && len(v.Devices) > 0 {
g.snap.Device = &v.Devices[0]
}
case "DEVICE":
var v gpsDevice
if json.Unmarshal(line, &v) == nil {
if g.snap.Device == nil || g.snap.Device.Path == v.Path {
g.snap.Device = &v
}
}
case "TPV":
var v gpsTPV
if json.Unmarshal(line, &v) == nil {
g.snap.TPV = &v
g.lastTPV = time.Now()
}
case "SKY":
var v struct {
gpsDOP
NSat *int `json:"nSat"`
USat *int `json:"uSat"`
Satellites *[]gpsSat `json:"satellites"`
}
if json.Unmarshal(line, &v) != nil {
return
}
g.snap.DOP = v.gpsDOP
if v.USat != nil {
g.snap.USat = v.USat
}
// gpsd sends many partial SKY reports (DOPs only); keep the last full sat list.
if v.Satellites != nil {
g.snap.Satellites = *v.Satellites
n := len(*v.Satellites)
g.snap.NSat = &n
}
case "TOFF":
var v struct {
RealSec int64 `json:"real_sec"`
RealNsec int64 `json:"real_nsec"`
ClockSec int64 `json:"clock_sec"`
ClockNsec int64 `json:"clock_nsec"`
}
if json.Unmarshal(line, &v) == nil {
lat := float64(v.ClockSec-v.RealSec) + float64(v.ClockNsec-v.RealNsec)/1e9
g.snap.TOFF = &gpsTOFF{Latency: lat}
}
}
}
|
