feat(message): added meta attribute to waku message

waku/v2/protocol/waku_message/codec.nim

@@ -21,6 +21,7 @@ proc encode*(message: WakuMessage): ProtoBuffer =
   buf.write3(2, message.contentTopic)
   buf.write3(3, message.version)
   buf.write3(10, zint64(message.timestamp))
+  buf.write3(11, message.meta)
   when defined(rln):
     buf.write3(21, message.proof)
   buf.write3(31, message.ephemeral)
@@ -62,6 +63,16 @@ proc decode*(T: type WakuMessage, buffer: seq[byte]): ProtobufResult[T] =
     msg.timestamp = Timestamp(timestamp)
 
 
+  var meta: seq[byte]
+  if not ?pb.getField(11, meta):
+    msg.meta = @[]
+  else:
+    if meta.len > MaxMetaAttrLength:
+      return err(ProtobufError.invalidLengthField("meta"))
+
+    msg.meta = meta
+
+
   # Experimental: this is part of https://rfc.vac.dev/spec/17/ spec
   when defined(rln):
     var proof: seq[byte]

waku/v2/protocol/waku_message/message.nim

@@ -13,6 +13,8 @@ import
   ../../utils/time
 
 const
+  MaxMetaAttrLength* = 32 # 32 bytes
+
   MaxWakuMessageSize* = 1024 * 1024 # 1 Mibytes. Corresponds to PubSub default
 
 
@@ -30,6 +32,8 @@ type WakuMessage* = object
     payload*: seq[byte]
     # String identifier that can be used for content-based filtering.
     contentTopic*: ContentTopic
+    # Application specific metadata.
+    meta*: seq[byte]
     # Number to discriminate different types of payload encryption.
     # Compatibility with Whisper/WakuV1.
     version*: uint32