lora/lorawan: implement minimal Join() function, and supporting functions

Signed-off-by: deadprogram <ron@hybridgroup.com>

lora/lorawan/bytes.go

@@ -1,37 +1,23 @@
 package lorawan
 
-// revertByteArray inverts de order of a given byte slice
-func revertByteArray(s []byte) []byte {
+import "crypto/rand"
+
+// reverseBytes reverses order of a given byte slice
+func reverseBytes(s []byte) []byte {
+	result := make([]byte, len(s))
 	for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
-		s[i], s[j] = s[j], s[i]
+		result[i], result[j] = s[j], s[i]
 	}
-	return s
+	return result
 }
 
-// byteToHex return string hex representation of byte
-func byteToHex(b byte) string {
-	bb := (b >> 4) & 0x0F
-	ret := ""
-	if bb < 10 {
-		ret += string(rune('0' + bb))
-	} else {
-		ret += string(rune('A' + (bb - 10)))
+// GetRand16 returns 2 random bytes
+func GetRand16() ([2]uint8, error) {
+	randomBytes := make([]byte, 2)
+	_, err := rand.Read(randomBytes)
+	if err != nil {
+		return [2]uint8{}, err
 	}
 
-	bb = (b) & 0xF
-	if bb < 10 {
-		ret += string(rune('0' + bb))
-	} else {
-		ret += string(rune('A' + (bb - 10)))
-	}
-	return ret
-}
-
-// BytesToHexString converts byte slice to hex string representation
-func bytesToHexString(data []byte) string {
-	s := ""
-	for i := 0; i < len(data); i++ {
-		s += byteToHex(data[i])
-	}
-	return s
+	return [2]uint8{randomBytes[0], randomBytes[1]}, nil
 }