gps: revamp validSentence() to avoid heap allocation for errors. This error can occur too frequently to allow for such allocations

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

gps/gps.go

@@ -20,30 +20,9 @@ var (
 	errInvalidGLLSentence        = errors.New("invalid GLL NMEA sentence")
 	errGPSCommandRejected        = errors.New("GPS command rejected (NAK)")
 	errNoACKToGPSCommand         = errors.New("no ACK to GPS command")
+	errInvalidNMEASentanceFormat = errors.New("invalid NMEA sentence format")
 )
 
-type GPSError struct {
-	Err      error
-	Info     string
-	Sentence string
-}
-
-func newGPSError(err error, sentence string, info string) GPSError {
-	return GPSError{
-		Info:     info,
-		Err:      err,
-		Sentence: sentence,
-	}
-}
-
-func (ge GPSError) Error() string {
-	return ge.Err.Error() + " " + ge.Info + " " + ge.Sentence
-}
-
-func (ge GPSError) Unwrap() error {
-	return ge.Err
-}
-
 const (
 	minimumNMEALength = 7
 	startingDelimiter = '$'
@@ -182,9 +161,7 @@ func validSentence(sentence string) error {
 	}
 	checksum := strings.ToUpper(hex.EncodeToString([]byte{cs}))
 	if checksum != sentence[len(sentence)-2:len(sentence)] {
-		return newGPSError(errInvalidNMEAChecksum, sentence,
+		return errInvalidNMEASentanceFormat
-			"expected "+sentence[len(sentence)-2:len(sentence)]+
-				" got "+checksum)
 	}
 
 	return nil

gps/gpsparser.go

@@ -104,7 +104,7 @@ func (parser *Parser) Parse(sentence string) (Fix, error) {
 		return fix, nil
 	}
 
-	return fix, newGPSError(errUnknownNMEASentence, sentence, typ)
+	return fix, errInvalidNMEASentanceFormat
 }
 
 // findTime returns the time from an NMEA sentence:

gps/gpsparser_test.go

@@ -8,13 +8,13 @@ import (
 )
 
 func TestParseUnknownSentence(t *testing.T) {
-	c := qt.New(t)
-
 	p := NewParser()
 
 	val := "$GPGSV,3,1,09,07,14,317,22,08,31,284,25,10,32,133,39,16,85,232,29*7F"
 	_, err := p.Parse(val)
-	c.Assert(err.Error(), qt.Contains, "unsupported NMEA sentence type")
+	if err == nil {
+		t.Error("should have unknown sentence err")
+	}
 }
 
 func TestParseGGA(t *testing.T) {