add encoding utils

utils/encoding.go

@@ -0,0 +1,74 @@
+package utils
+
+// HexToCompact converts a hex path to the compact encoded format
+func HexToCompact(hex []byte) []byte {
+	return hexToCompact(hex)
+}
+
+func hexToCompact(hex []byte) []byte {
+	terminator := byte(0)
+	if hasTerm(hex) {
+		terminator = 1
+		hex = hex[:len(hex)-1]
+	}
+	buf := make([]byte, len(hex)/2+1)
+	buf[0] = terminator << 5 // the flag byte
+	if len(hex)&1 == 1 {
+		buf[0] |= 1 << 4 // odd flag
+		buf[0] |= hex[0] // first nibble is contained in the first byte
+		hex = hex[1:]
+	}
+	decodeNibbles(hex, buf[1:])
+	return buf
+}
+
+// CompactToHex converts a compact encoded path to hex format
+func CompactToHex(compact []byte) []byte {
+	if len(compact) == 0 {
+		return compact
+	}
+	base := KeybytesToHex(compact)
+	// delete terminator flag
+	if base[0] < 2 {
+		base = base[:len(base)-1]
+	}
+	// apply odd flag
+	chop := 2 - base[0]&1
+	return base[chop:]
+}
+
+func KeybytesToHex(str []byte) []byte {
+	l := len(str)*2 + 1
+	var nibbles = make([]byte, l)
+	for i, b := range str {
+		nibbles[i*2] = b / 16
+		nibbles[i*2+1] = b % 16
+	}
+	nibbles[l-1] = 16
+	return nibbles
+}
+
+// HexToKeyBytes turns hex nibbles into key bytes.
+// This can only be used for keys of even length.
+func HexToKeyBytes(hex []byte) []byte {
+	if hasTerm(hex) {
+		hex = hex[:len(hex)-1]
+	}
+	if len(hex)&1 != 0 {
+		panic("can't convert hex key of odd length")
+	}
+	key := make([]byte, len(hex)/2)
+	decodeNibbles(hex, key)
+	return key
+}
+
+func decodeNibbles(nibbles []byte, bytes []byte) {
+	for bi, ni := 0, 0; ni < len(nibbles); bi, ni = bi+1, ni+2 {
+		bytes[bi] = nibbles[ni]<<4 | nibbles[ni+1]
+	}
+}
+
+// hasTerm returns whether a hex key has the terminator flag.
+func hasTerm(s []byte) bool {
+	return len(s) > 0 && s[len(s)-1] == 16
+}