Initial cloud-services repo - gateway service + pkg modules

pkg/utils/vod/crc.go

@@ -0,0 +1,68 @@
+package vod
+
+import (
+	"encoding/binary"
+
+	"github.com/sigurn/crc8"
+)
+
+func NewVODHelper(lengthInCRC bool,
+	crcInLength bool,
+	lengthInLength bool) VODHelper {
+	return VODHelper{
+		table: crc8.MakeTable(crc8.Params{
+			Poly:   0x1D,
+			Init:   0,
+			RefIn:  false,
+			RefOut: false,
+			XorOut: 0,
+			Check:  0,
+			Name:   "CEC-8 VOD",
+		}),
+		lengthInCRC:    lengthInCRC,
+		crcInLength:    crcInLength,
+		lengthInLength: lengthInLength,
+	}
+}
+
+type VODHelper struct {
+	table          *crc8.Table
+	lengthInCRC    bool
+	crcInLength    bool
+	lengthInLength bool
+}
+
+// Given a list of bytes, we calculate our custom CRC-8 on it, then prepend the length and postpend the crc in place of last byte
+// So 0x01 0x02 0x00 -> 0x00 0x05 0x01 0x02 0x00 0xCRC-8(0x01 0x02 0x00)
+// If you have an existing VOD that you are modifying, this function expects you to have removed the length and the crc
+func (v *VODHelper) AddLengthAndCRC(data []byte) []byte {
+	// first 2 bytes are length including length bytes
+	length := make([]byte, 2)
+	lengthPlus := 0
+	if v.crcInLength { // No
+		lengthPlus += 1
+	}
+	if v.lengthInLength { // Yes
+		lengthPlus += 2
+	}
+	binary.BigEndian.PutUint16(length, uint16(len(data)+lengthPlus))
+
+	var crc byte
+	if v.lengthInCRC { // no
+		data = append(length, data...)
+		// calculate crc on data only
+		crc = v.GenerateCRC(data)
+	} else { // yes
+		// calculate crc on data only
+		crc = v.GenerateCRC(data)
+		data = append(length, data...)
+	}
+	data = append(data, crc)
+
+	return data
+}
+
+func (v *VODHelper) GenerateCRC(data []byte) byte {
+	crc := crc8.Checksum(data, v.table)
+	return crc
+}