Make msgId fixed int32

eth/p2p/rlpx.nim

@@ -429,8 +429,9 @@ proc recvMsg*(peer: Peer): Future[tuple[msgId: int, msgData: Rlp]] {.async.} =
   var rlp = rlpFromBytes(decryptedBytes.toRange)
 
   try:
-    let msgid = rlp.read(int)
-    return (msgId, rlp)
+    # int32 as this seems more than big enough for the amount of msgIds
+    let msgId = rlp.read(int32)
+    return (msgId.int, rlp)
   except RlpError:
     await peer.disconnectAndRaise(BreachOfProtocol,
                                   "Cannot read RLPx message id")

tests/p2p/p2p_test_helper.nim

@@ -46,5 +46,5 @@ template sourceDir*: string = currentSourcePath.rsplit(DirSep, 1)[0]
 proc recvMsgMock*(msg: openArray[byte]): tuple[msgId: int, msgData: Rlp] =
   var rlp = rlpFromBytes(@msg.toRange)
 
-  let msgid = rlp.read(int)
-  return (msgId, rlp)
+  let msgId = rlp.read(int32)
+  return (msgId.int, rlp)

tests/p2p/test_rlpx_thunk.json

@@ -9,8 +9,13 @@
     "error": "UnsupportedMessageError",
     "description": "This is a message id not used by devp2p, eth or whisper"
   },
-  "Message id that is negative": {
+  "Message id that is bigger than int32": {
     "payload": "888888888888888888",
+    "error": "RlpTypeMismatch",
+    "description": "This payload will result in too large int for a message id"
+  },
+  "Message id that is negative": {
+    "payload": "8488888888",
     "error": "UnsupportedMessageError",
     "description": "This payload will result in a negative number as message id"
   },