Adapt portal_*Offer method to the latest specification (#2689)

fluffy/network/wire/portal_protocol.nim

@@ -984,6 +984,8 @@ proc offer*(
 ): Future[PortalResult[ContentKeysBitList]] {.async: (raises: [CancelledError]).} =
   if len(content) > contentKeysLimit:
     return err("Cannot offer more than 64 content items")
+  if len(content) == 0:
+    return err("Cannot offer empty content list")
 
   let contentList = List[ContentKV, contentKeysLimit].init(content)
   let req = OfferRequest(dst: dst, kind: Direct, contentList: contentList)

fluffy/rpc/rpc_portal_api.nim

@@ -161,19 +161,24 @@ proc installPortalApiHandlers*(
         return ("{\"enrs\":" & jsonEnrs & "}").JsonString
 
   rpcServer.rpc("portal_" & network & "Offer") do(
-    enr: Record, contentKey: string, contentValue: string
+    enr: Record, contentItems: seq[ContentItem]
   ) -> string:
-    let
-      node = toNodeWithAddress(enr)
-      key = hexToSeqByte(contentKey)
-      content = hexToSeqByte(contentValue)
-      contentKV = ContentKV(contentKey: ContentKeyByteList.init(key), content: content)
-      res = await p.offer(node, @[contentKV])
+    let node = toNodeWithAddress(enr)
 
-    if res.isOk():
-      return SSZ.encode(res.get()).to0xHex()
-    else:
-      raise newException(ValueError, $res.error)
+    var contentItemsToOffer: seq[ContentKV]
+    for contentItem in contentItems:
+      let
+        contentKey = hexToSeqByte(contentItem[0])
+        contentValue = hexToSeqByte(contentItem[1])
+        contentKV = ContentKV(
+          contentKey: ContentKeyByteList.init(contentKey), content: contentValue
+        )
+      contentItemsToOffer.add(contentKV)
+
+    let offerResult = (await p.offer(node, contentItemsToOffer)).valueOr:
+      raise newException(ValueError, $error)
+
+    SSZ.encode(offerResult).to0xHex()
 
   rpcServer.rpc("portal_" & network & "RecursiveFindNodes") do(
     nodeId: NodeId

fluffy/rpc/rpc_types.nim

@@ -31,6 +31,8 @@ type
     content*: string
     utpTransfer*: bool
 
+  ContentItem* = array[2, string]
+
 NodeInfo.useDefaultSerializationIn JrpcConv
 RoutingTableInfo.useDefaultSerializationIn JrpcConv
 (string, string).useDefaultSerializationIn JrpcConv
@@ -125,3 +127,22 @@ proc readValue*(
         discard
   except ValueError as exc:
     r.raiseUnexpectedValue("PingResult parser error: " & exc.msg)
+
+# Note:
+# This is a similar readValue as the default one in nim-json-serialization but
+# with an added exact length check. The default one will successfully parse when
+# a JSON array with less than size n items is provided. And default objects
+# (in this case empty string) will be applied for the missing items.
+proc readValue*(
+    r: var JsonReader[JrpcConv], value: var ContentItem
+) {.gcsafe, raises: [IOError, SerializationError].} =
+  type IDX = typeof low(value)
+  var count = 0
+  r.parseArray(idx):
+    let i = IDX(idx + low(value).int)
+    if i <= high(value):
+      readValue(r, value[i])
+      count.inc
+
+  if count != value.len():
+    r.raiseUnexpectedValue("Array length mismatch")