gps: add support for GLL sentence type, add original sentence to gps errors

Signed-off-by: deadprogram <ron@hybridgroup.com>

gps/gps.go

@@ -17,22 +17,25 @@ var (
 	errUnknownNMEASentence       = errors.New("unsupported NMEA sentence type")
 	errInvalidGGASentence        = errors.New("invalid GGA NMEA sentence")
 	errInvalidRMCSentence        = errors.New("invalid RMC NMEA sentence")
+	errInvalidGLLSentence        = errors.New("invalid GLL NMEA sentence")
 )
 
 type GPSError struct {
-	Info string
-	Err  error
+	Err      error
+	Info     string
+	Sentence string
 }
 
-func newGPSError(err error, info string) GPSError {
+func newGPSError(err error, sentence string, info string) GPSError {
 	return GPSError{
-		Info: info,
-		Err:  err,
+		Info:     info,
+		Err:      err,
+		Sentence: sentence,
 	}
 }
 
 func (ge GPSError) Error() string {
-	return ge.Err.Error() + " " + ge.Info
+	return ge.Err.Error() + " " + ge.Info + " " + ge.Sentence
 }
 
 // Device wraps a connection to a GPS device.
@@ -156,8 +159,9 @@ func validSentence(sentence string) error {
 	}
 	checksum := strings.ToUpper(hex.EncodeToString([]byte{cs}))
 	if checksum != sentence[len(sentence)-2:len(sentence)] {
-		return newGPSError(errInvalidNMEAChecksum, "expected "+sentence[len(sentence)-2:len(sentence)]+
-			" got "+checksum)
+		return newGPSError(errInvalidNMEAChecksum, sentence,
+			"expected "+sentence[len(sentence)-2:len(sentence)]+
+				" got "+checksum)
 	}
 
 	return nil