Add SszError to message decoding result (#1660)

This allows for improved error messages. Required changing the PortalResult from cstring to string for the error.

fluffy/network/wire/messages.nim

@@ -142,16 +142,16 @@ func encodeMessage*[T: SomeMessage](m: T): seq[byte] =
   elif T is OfferMessage: SSZ.encode(Message(kind: offer, offer: m))
   elif T is AcceptMessage: SSZ.encode(Message(kind: accept, accept: m))
 
-func decodeMessage*(body: openArray[byte]): Result[Message, cstring] =
+func decodeMessage*(body: openArray[byte]): Result[Message, string] =
   try:
     if body.len < 1: # TODO: This check should probably move a layer down
       return err("No message data, peer might not support this talk protocol")
     ok(SSZ.decode(body, Message))
-  except SszError:
-    err("Invalid message encoding")
+  except SszError as e:
+    err("Invalid message encoding: " & e.msg)
 
 template innerMessage[T: SomeMessage](
-    message: Message, expected: MessageKind): Result[T, cstring] =
+    message: Message, expected: MessageKind): Result[T, string] =
   if (message.kind == expected):
     ok(message.expected)
   else:
@@ -160,7 +160,7 @@ template innerMessage[T: SomeMessage](
 # Each `Message` variants corresponds to an MessageKind. Therefore, the inner
 # message can be extracted when providing the expected message type T.
 # If the message does not hold the expacted variant, return error.
-func getInnerMessage*[T: SomeMessage](m: Message): Result[T, cstring] =
+func getInnerMessage*[T: SomeMessage](m: Message): Result[T, string] =
   innerMessage[T](m, messageKind(T))
 
 func getTalkReqOverhead*(protocolIdLen: int): int =

fluffy/network/wire/portal_protocol.nim

@@ -171,7 +171,7 @@ type
     offerQueue: AsyncQueue[OfferRequest]
     offerWorkers: seq[Future[void]]
 
-  PortalResult*[T] = Result[T, cstring]
+  PortalResult*[T] = Result[T, string]
 
   FoundContentKind* = enum
     Nodes,
@@ -495,9 +495,10 @@ proc reqResponse[Request: SomeMessage, Response: SomeMessage](
   # not supporting the specific talk protocol, as according to specification
   # an empty response needs to be send in that case.
   # See: https://github.com/ethereum/devp2p/blob/master/discv5/discv5-wire.md#talkreq-request-0x05
-  let messageResponse = talkresp
-    .flatMap(proc (x: seq[byte]): Result[Message, cstring] = decodeMessage(x))
-    .flatMap(proc (m: Message): Result[Response, cstring] =
+
+  let messageResponse = talkresp.mapErr(proc (x: cstring): string = $x)
+    .flatMap(proc (x: seq[byte]): Result[Message, string] = decodeMessage(x))
+    .flatMap(proc (m: Message): Result[Response, string] =
       getInnerMessage[Response](m))
 
   if messageResponse.isOk():