stream/mts/psi: modified how update crc works so that we're only giving it data that's included in crc calc as well as the crc field itself. Added some consts to allow working with SyntaxSectionLen. Added trimPadding func so that we can easily get rid of any padding. Fixed createDescriptor func which was found to be broken from TestCreateDescriptor

stream/mts/psi/crc.go

@@ -37,13 +37,13 @@ import (
 func addCrc(out []byte) []byte {
 	t := make([]byte, len(out)+4)
 	copy(t, out)
-	updateCrc(t)
+	updateCrc(t[1:])
 	return t
 }
 
 // updateCrc updates the crc of bytes slice, writing the checksum into the last four bytes.
 func updateCrc(b []byte) {
-	crc32 := crc32_Update(0xffffffff, crc32_MakeTable(bits.Reverse32(crc32.IEEE)), b[1:len(b)-4])
+	crc32 := crc32_Update(0xffffffff, crc32_MakeTable(bits.Reverse32(crc32.IEEE)), b[:len(b)-4])
 	binary.BigEndian.PutUint32(b[len(b)-4:], crc32)
 }
 

stream/mts/psi/helpers.go

@@ -64,15 +64,14 @@ func UpdateTime(dst []byte, t uint64) error {
 	for i := range dst[TimeDataIndx : TimeDataIndx+TimeDataSize] {
 		dst[i+TimeDataIndx] = ts[i]
 	}
-	updateCrc(dst)
+	updateCrc(dst[1:])
 	return nil
 }
 
 // SyntaxSecLenFrom takes a byte slice representation of a psi and extracts
 // it's syntax section length
-func SyntaxSecLenFrom(p []byte) (l uint8) {
-	l = uint8(p[syntaxSecLenIndx]) - crcSize
-	return
+func SyntaxSecLenFrom(p []byte) int {
+	return int(((p[SyntaxSecLenIdx1] & SyntaxSecLenMask1) << 8) | p[SyntaxSecLenIdx2])
 }
 
 // TimeFrom takes a byte slice representation of a psi-pmt and extracts it's
@@ -112,7 +111,7 @@ func UpdateLocation(d []byte, s string) error {
 	for i := range loc {
 		loc[i] = 0
 	}
-	updateCrc(d)
+	updateCrc(d[1:])
 	return nil
 }
 

stream/mts/psi/psi.go

@@ -70,8 +70,10 @@ const (
 
 // Other misc consts
 const (
-	syntaxSecLenIndx = 3
-	crcSize          = 4
+	SyntaxSecLenIdx1  = 2
+	SyntaxSecLenIdx2  = 3
+	SyntaxSecLenMask1 = 0x03
+	crcSize           = 4
 )
 
 const (
@@ -275,24 +277,40 @@ func (p *PSIBytes) descriptors() []byte {
 
 func (p *PSIBytes) createDescriptor(tag int, data []byte) {
 	curProgLen := p.ProgramInfoLen()
+	oldSyntaxSectionLen := SyntaxSecLenFrom(*p)
 	dataLen := len(data)
 
 	// Calculate the new descriptors index and length.
 	newDescIdx := DescriptorsIdx + curProgLen
 	newDescLen := dataLen + 2
-
 	// Copy data down from newDescIdx to create room for the new descriptor.
-	copy((*p)[newDescIdx+newDescLen:], (*p)[newDescIdx:dataLen-newDescLen])
-
+	copy((*p)[newDescIdx+newDescLen:], (*p)[newDescIdx:newDescIdx+newDescLen])
 	// Set the tag, data len and data of the new desriptor.
 	(*p)[newDescIdx] = byte(tag)
 	(*p)[newDescIdx+1] = byte(dataLen)
 	copy((*p)[newDescIdx+2:newDescIdx+2+dataLen], data)
 
 	// Update the program info length to account for the new descriptor.
-	newProgInfoLen := curProgLen + dataLen
-	(*p)[ProgramInfoLenIdx1] = byte(newProgInfoLen >> 8)
+	// TODO: put this in function set program info length
+	addedLen := dataLen + 2
+	newProgInfoLen := curProgLen + addedLen
+	(*p)[ProgramInfoLenIdx1] &= 0xff ^ ProgramInfoLenMask1
+	(*p)[ProgramInfoLenIdx1] |= byte(newProgInfoLen>>8) & ProgramInfoLenMask1
 	(*p)[ProgramInfoLenIdx2] = byte(newProgInfoLen)
+
+	// set section length
+	// TODO: put this in func set program info length
+	newSyntaxSectionLen := int(oldSyntaxSectionLen) + addedLen
+	(*p)[SyntaxSecLenIdx1] &= 0xff ^ SyntaxSecLenMask1
+	(*p)[SyntaxSecLenIdx1] |= byte(newSyntaxSectionLen>>8) & SyntaxSecLenMask1
+	(*p)[SyntaxSecLenIdx2] = byte(newSyntaxSectionLen)
+}
+
+func (p *PSIBytes) trimPadding() []byte {
+	sectionLength := SyntaxSecLenFrom(*p)
+	paddingIdx := (4 + sectionLength)
+	o := (*p)[:paddingIdx]
+	return o
 }
 
 func (d *Descriptor) update(data []byte) {