[ETCM-921] Clean magic number and add unit test for PrefixedRLPEncodable

Author: strauss-m

rlp/src/main/scala/io/iohk/ethereum/rlp/package.scala

@@ -58,7 +58,7 @@ package object rlp {
     * @param prefixedRLPEncodeable the RLPEncodable to prefix with
     */
   case class PrefixedRLPEncodable(prefix: Byte, prefixedRLPEncodeable: RLPEncodeable) extends RLPEncodeable {
-    require(prefix <= 0x07f, "prefix should be lower than 0x7f")
+    require(prefix >= 0, "prefix should be in the range [0; 0x7f]")
   }
 
   trait RLPEncoder[T] {

src/main/scala/io/iohk/ethereum/domain/Transaction.scala

@@ -23,13 +23,25 @@ sealed trait Transaction extends Product with Serializable {
 
 object Transaction {
   val Type01: Byte = 1.toByte
+
+  val MinAllowedType: Byte = 0
+  val MaxAllowedType: Byte = 0x7f
+
   val LegacyThresholdLowerBound: Int = 0xc0
   val LegacyThresholdUpperBound: Int = 0xfe
 
   def withGasLimit(gl: BigInt): Transaction => Transaction = {
     case tx: LegacyTransaction         => tx.copy(gasLimit = gl)
     case tx: TransactionWithAccessList => tx.copy(gasLimit = gl)
   }
+
+  implicit class TransactionTypeValidator(val transactionType: Byte) extends AnyVal {
+    def isValidTransactionType: Boolean = transactionType >= MinAllowedType && transactionType <= MaxAllowedType
+  }
+
+  implicit class ByteArrayTransactionTypeValidator(val binaryData: Array[Byte]) extends AnyVal {
+    def isValidTransactionType: Boolean = binaryData.length == 1 && binaryData.head.isValidTransactionType
+  }
 }
 
 sealed trait TypedTransaction extends Transaction

src/main/scala/io/iohk/ethereum/network/p2p/messages/BaseETH6XMessages.scala

@@ -161,6 +161,8 @@ object BaseETH6XMessages {
   object TypedTransaction {
     implicit class TypedTransactionsRLPAggregator(val encodables: Seq[RLPEncodeable]) extends AnyVal {
 
+      import Transaction.ByteArrayTransactionTypeValidator
+
       /** Convert a Seq of RLPEncodable containing TypedTransaction informations into a Seq of
         * Prefixed RLPEncodable.
         *
@@ -181,7 +183,7 @@ object BaseETH6XMessages {
       def toTypedRLPEncodables: Seq[RLPEncodeable] =
         encodables match {
           case Seq() => Seq()
-          case Seq(RLPValue(v), rlpList: RLPList, tail @ _*) if v.length == 1 && v.head < 0x7f =>
+          case Seq(RLPValue(v), rlpList: RLPList, tail @ _*) if v.isValidTransactionType =>
             PrefixedRLPEncodable(v.head, rlpList) +: tail.toTypedRLPEncodables
           case Seq(head, tail @ _*) => head +: tail.toTypedRLPEncodables
         }