Fix stability issues (#512)

* Fix stability issues

why:
  Handling malformed messages typically raises `RangeError` exceptions
  when de-serialising RLP, or decoding message data. This is an
  (incomplete) attempt to weed out some out it driven by real live
  tests.

remark:
  Employing the new `snap` protocol there might be different views on what
  the messages really contain (currently specs are more a hint.)

* Update RLP exception handling

* Undo effect-less patch

why:
  problem occurred somewhere above the try/catch handler

* Using `checkedEnumAssign()` for RLP enum

eth/common/eth_types.nim

@@ -3,6 +3,9 @@ import
   stew/[endians2, byteutils], chronicles, stint, nimcrypto/[keccak, hash],
   ../rlp, ../trie/[trie_defs, db]
 
+from stew/objects
+  import checkedEnumAssign
+
 export
   stint, read, append, KeccakHash, rlp, options
 
@@ -454,15 +457,22 @@ proc readTxTyped(rlp: var Rlp, tx: var Transaction) {.inline.} =
   let txType = rlp.getByteValue
   rlp.position += 1
 
-  case TxType(txType):
+  var txVal: TxType
+  if checkedEnumAssign(txVal, txType):
+    case txVal:
     of TxEip2930:
       rlp.readTxEip2930(tx)
+      return
     of TxEip1559:
       rlp.readTxEip1559(tx)
+      return
     else:
+      discard
+
   raise newException(UnsupportedRlpError,
     "TypedTransaction type must be 1 or 2 in this version, got " & $txType)
 
+
 proc read*(rlp: var Rlp, T: type Transaction): T =
   # Individual transactions are encoded and stored as either `RLP([fields..])`
   # for legacy transactions, or `Type || RLP([fields..])`.  Both of these

eth/p2p/rlpx.nim

@@ -62,17 +62,20 @@ proc read(rlp: var Rlp; T: type DisconnectionReasonList): T
     # Be strict here: The expression `rlp.read(DisconnectionReasonList)`
     # accepts lists with at least one item. The array expression wants
     # exactly one item.
+    if rlp.rawData.len < 3:
+      # avoids looping through all items when parsing for an overlarge array
       return DisconnectionReasonList(
         value: rlp.read(array[1,DisconnectionReason])[0])
 
   # Also accepted: a single byte reason code. Is is typically used
   # by variants of the reference implementation `Geth`
-  if rlp.blobLen <= 1:
+  elif rlp.blobLen <= 1:
     return DisconnectionReasonList(
       value: rlp.read(DisconnectionReason))
 
   # Also accepted: a blob of a list (aka object) of reason code. It is
   # used by `bor`, a `geth` fork
+  elif rlp.blobLen < 4:
     var subList = rlp.toBytes.rlpFromBytes
     if subList.isList:
       # Ditto, see above.