psi: improved commenting in op.go

stream/mts/psi/op.go

@@ -32,29 +32,37 @@ import (
 	"errors"
 )
 
-func TimeBytes(time uint64) (s []byte) {
+// 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) (s []byte) {
 	s = make([]byte, timeDataSize)
-	binary.BigEndian.PutUint64(s[:], time)
+	binary.BigEndian.PutUint64(s[:], t)
 	return s
 }
 
-func chkTime(d []byte) error {
-	if d[timeTagIndx] != timeDescTag {
+// ChkTime takes a psi as a byte slice and checks to see if it has a time descriptor
+// - if so return nil, otherwise return error
+func ChkTime(p []byte) error {
+	if p[timeTagIndx] != timeDescTag {
 		return errors.New("PSI does not contain a time descriptor, cannot update")
 	}
 	return nil
 }
 
-func chkGps(d []byte) error {
-	if d[gpsTagIndx] != gpsDescTag {
+// ChkGps takes a psi as a byte slice and checks to see if it has a gps descriptor
+// - if so return nil, otherwise return error
+func ChkGps(p []byte) error {
+	if p[gpsTagIndx] != gpsDescTag {
 		return errors.New("PSI does not contain a gps descriptor, cannot update")
 	}
 	return nil
 }
 
-// Updatetime
+// UpdateTime takes the byte slice representation of a psi-pmt as well as a time
+// as an integer and attempts to update the time descriptor in the pmt with the
+// given time if the time descriptor exists, otherwise an error is returned
 func UpdateTime(d []byte, t int) error {
-	err := chkTime(d)
+	err := ChkTime(d)
 	if err != nil {
 		return err
 	}
@@ -65,26 +73,35 @@ func UpdateTime(d []byte, t int) error {
 	return nil
 }
 
-func TimeOf(d []byte) (t uint64, err error) {
-	err = chkTime(d)
+// TimeOf takes a byte slice representation of a psi-pmt and extracts it's
+// timestamp, returning as a uint64 if it exists, otherwise returning 0 and nil
+// if it does not exist
+func TimeOf(p []byte) (t uint64, err error) {
+	err = ChkTime(p)
 	if err != nil {
 		return 0, err
 	}
-	for i := range d[timeDataIndx : timeDataIndx+timeDataSize] {
-		t |= uint64(d[i+timeDataIndx]) << uint(56-i*timeDataSize)
+	// TODO: could probably write a byte slice to int func, so that this would
+	// be replaced by extraction of time data slice and then call to conversion func
+	for i := range p[timeDataIndx : timeDataIndx+timeDataSize] {
+		t |= uint64(p[i+timeDataIndx]) << uint(56-i*timeDataSize)
 	}
 	return t, nil
 }
 
+// GpsStrBytes take a string of gps data and converts to a 32 byte slice -
+// easy update of slice representation of a pmt with gps descriptor
 func GpsStrBytes(l string) (out []byte) {
 	out = make([]byte, gpsDataSize)
 	copy(out, []byte(l))
 	return
 }
 
+// UpdateGps takes a byte slice representation of a psi-pmt containing a gps
+// descriptor and attempts to update the gps data value with the passed string.
+// If the psi does not contain a gps descriptor, and error is returned.
 func UpdateGps(d []byte, s string) error {
-	// First check if there is a GPS descriptor
-	err := chkGps(d)
+	err := ChkGps(d)
 	if err != nil {
 		return err
 	}