psi: modified error messages for updateTime and updateLocation to make clearer

stream/mts/psi/helpers.go

@@ -33,12 +33,6 @@ import (
 	"errors"
 )
 
-// error message
-var (
-	ErrNoLocation = errors.New("psi does not have location descriptor")
-	ErrNoTime     = errors.New("psi does not have time descriptor")
-)
-
 // TimeBytes takes a timestamp as an uint64 and converts to an 8 byte slice -
 // allows for updating of timestamp in pmt time descriptor.
 func TimeBytes(t uint64) []byte {
@@ -70,7 +64,7 @@ func HasLocation(p []byte) bool {
 // given time if the time descriptor exists, otherwise an error is returned
 func UpdateTime(dst []byte, t uint64) error {
 	if !HasTime(dst) {
-		return ErrNoTime
+		return errors.New("pmt does not have time descriptor, cannot update")
 	}
 	ts := TimeBytes(uint64(t))
 	for i := range dst[timeDataIndx : timeDataIndx+timeDataSize] {
@@ -85,7 +79,7 @@ func UpdateTime(dst []byte, t uint64) error {
 // if it does not exist
 func TimeFrom(p []byte) (t uint64, err error) {
 	if !HasTime(p) {
-		return 0, ErrNoTime
+		return 0, errors.New("pmt does not have a time descriptor")
 	}
 	t = binary.BigEndian.Uint64(p[timeDataIndx : timeDataIndx+timeDataSize])
 	return t, nil
@@ -96,7 +90,7 @@ func TimeFrom(p []byte) (t uint64, err error) {
 // if it does not exist
 func LocationFrom(p []byte) (g string, err error) {
 	if !HasLocation(p) {
-		return "", ErrNoLocation
+		return "", errors.New("pmt does not have location descriptor")
 	}
 	gBytes := p[locationDataIndx : locationDataIndx+locationDataSize]
 	gBytes = bytes.Trim(gBytes, "\x00")
@@ -117,7 +111,7 @@ func LocationStrBytes(s string) []byte {
 // If the psi does not contain a location descriptor, and error is returned.
 func UpdateLocation(d []byte, s string) error {
 	if !HasLocation(d) {
-		return ErrNoLocation
+		return errors.New("pmt does not location descriptor, cannot update")
 	}
 	gb := LocationStrBytes(s)
 	for i := range d[locationDataIndx : locationDataIndx+locationDataSize] {