psi: re-wrote bytes for desc and essd to make less bug prone, though at a cost for performance - but optimisation can happen later

stream/mts/psi/psi.go

@@ -10,7 +10,7 @@ type PSI struct {
 	pf  byte   // Point field
 	pfb []byte // Pointer filler bytes
 	tid byte   // Table ID
-	ssi bool   // Sectiopn syntax indicator (1 for PAT, PMT, CAT)
+	ssi bool   // Section syntax indicator (1 for PAT, PMT, CAT)
 	pb  bool   // Private bit (0 for PAT, PMT, CAT)
 	sl  uint16 // Section length
 	tss *TSS   // Table syntax section (length defined by SL) if length 0 then nil
@@ -69,38 +69,33 @@ func (p *PSI) Bytes() (out []byte) {
 	return nil
 }
 
-func (t *TSS) Fill(space []byte) error {
+func (t *TSS) Fill(s []byte) {
+}
+
+func (p *PAT) Fill(s []byte) {
+}
+
+func (p *PMT) Bytes() (out []byte) {
 	return nil
 }
 
-func (p *PAT) Fill(space []byte) error {
-	return nil
+func (d *Desc) Bytes() (out []byte) {
+	out = make([]byte, DescHeadLen)
+	out[0] = d.dt
+	out[1] = d.dl
+	out = append(out, d.dd...)
+	return
 }
 
-func (p *PMT) Fill(space []byte) error {
-	checkSpace(space)
-	return nil
-}
-
-func (d *Desc) Fill(space []byte) error {
-	checkSpace(space, DescHeadLen+int(d.dl))
-	space[0] = d.dt
-	space[1] = d.dl
-	copy(space[2:], d.dd)
-	return out
-}
-
-func (e *ESSD) Fill(space []byte) error {
-	checkSpace(space, ESSDHeadLen+e.esil)
-	return nil
-}
-
-func checkSpace(s []byte, c uint) {
-	if s == nil {
-		panic("Slice provided is nil")
-	} else if len(s) != 0 {
-		panic("Slice provided already has something in it")
-	} else if cap(s) != c {
-		panic("Slice provided has wrong capacity")
+func (e *ESSD) Bytes() (out []byte) {
+	out = make([]byte, ESSDHeadLen)
+	out[0] = e.st
+	out[1] = 0xe0 | e.epid>>3
+	out[2] = e.epid
+	out[3] = 0xf0 | byte(e.esil>>6)
+	out[4] = byte(e.esil)
+	for _, d := range e.esd {
+		out = append(out, d.Bytes()...)
 	}
+	return
 }